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Pass through power bank
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Gordon Levi
Jan 24, 2015, 9:07:41 AM1/24/15
to
I want to use a power bank as battery back up for a Raspberry Pi. The
power bank has to have pass through charging so that I can leave the
power bank connected to the mains while the Pi is powered from the
output. I gather not all power banks can be used that way.
Does anybody have any general or specific advice about how to choose
the power bank?
power bank has to have pass through charging so that I can leave the
power bank connected to the mains while the Pi is powered from the
output. I gather not all power banks can be used that way.
Does anybody have any general or specific advice about how to choose
the power bank?
David Taylor
Jan 24, 2015, 2:40:42 PM1/24/15
to
Someone recommended this to me:
http://uk.rs-online.com/web/p/product/7757508
and there is a 10 Ah one as well. Also a smaller 2Ah unit.
--
Cheers,
David
Web: http://www.satsignal.eu
Don McKenzie
Jan 24, 2015, 4:36:38 PM1/24/15
to
What I found was if there is power being put into the unit, then no power comes out, so it won't work as a UPS type of
supply, which basically is what you want, correct?
Mine is a 20000mAh. Sure it has 2.1A and 1A outputs, but nothing comes out unless you either pull out the input plug, or
switch off the source of input power.
http://www.dx.com/p/bp-l2k-1-0-lcd-20000mah-dual-usb-mobile-power-source-w-led-for-iphone-samsung-silver-white-328011#.VMQQGy6WXKA
May pay to check the unit before you purchase.
BTW
I got mine for phone backup, not as a micro UPS.
Cheers Don...
--
Don McKenzie
http://www.dontronics-shop.com
All Olimex products now 60% to 95% off normal Olimex Prices.
http://www.dontronics-shop.com/olimex-ltd.html
Many other items discounted up to 95% off.
Also discounts on FTDI modules, Sparkfun, CCS, SimmStick, etc.
Gordon Levi
Jan 25, 2015, 9:42:22 AM1/25/15
to
learned that not all power banks have pass through charging. I should
have acknowledged those posts and explained I am in Australia. The
10Ah RS product costs three times as much as an eBay sourced one
<http://www.ebay.com.au/itm/XIAOMI-10400mAh-Portable-Power-Bank-Li-ion-Battery-Charger-5V-2-1A-iPad-iPhone-/261478644375#ret>.
I was hoping that someone had bought something similar and could
assure me it had pass through charging or had a general method for
determining if a unit has pass through charging.
Gordon Levi
Jan 25, 2015, 9:45:47 AM1/25/15
to
Don McKenzie <5...@2.5A> wrote:
>On 25/01/2015 6:40 AM, David Taylor wrote:
>> On 24/01/2015 14:07, Gordon Levi wrote:
>>> I want to use a power bank as battery back up for a Raspberry Pi. The
>>> power bank has to have pass through charging so that I can leave the
>>> power bank connected to the mains while the Pi is powered from the
>>> output. I gather not all power banks can be used that way.
>>>
>>> Does anybody have any general or specific advice about how to choose
>>> the power bank?
>>
>> You haven't been reading the group messages, have you?
>>
>> Someone recommended this to me:
>>
>> http://uk.rs-online.com/web/p/product/7757508
>>
>> and there is a 10 Ah one as well. Also a smaller 2Ah unit.
>
>I just got a similar unit from dx.com
>
>What I found was if there is power being put into the unit, then no power comes out, so it won't work as a UPS type of
>supply, which basically is what you want, correct?
>
>Mine is a 20000mAh. Sure it has 2.1A and 1A outputs, but nothing comes out unless you either pull out the input plug, or
>switch off the source of input power.
>http://www.dx.com/p/bp-l2k-1-0-lcd-20000mah-dual-usb-mobile-power-source-w-led-for-iphone-samsung-silver-white-328011#.VMQQGy6WXKA
>
>May pay to check the unit before you purchase.
My post was intended to check the unit before I purchased! Thanks for
>On 25/01/2015 6:40 AM, David Taylor wrote:
>> On 24/01/2015 14:07, Gordon Levi wrote:
>>> I want to use a power bank as battery back up for a Raspberry Pi. The
>>> power bank has to have pass through charging so that I can leave the
>>> power bank connected to the mains while the Pi is powered from the
>>> output. I gather not all power banks can be used that way.
>>>
>>> Does anybody have any general or specific advice about how to choose
>>> the power bank?
>>
>> You haven't been reading the group messages, have you?
>>
>> Someone recommended this to me:
>>
>> http://uk.rs-online.com/web/p/product/7757508
>>
>> and there is a 10 Ah one as well. Also a smaller 2Ah unit.
>
>I just got a similar unit from dx.com
>
>What I found was if there is power being put into the unit, then no power comes out, so it won't work as a UPS type of
>supply, which basically is what you want, correct?
>
>Mine is a 20000mAh. Sure it has 2.1A and 1A outputs, but nothing comes out unless you either pull out the input plug, or
>switch off the source of input power.
>http://www.dx.com/p/bp-l2k-1-0-lcd-20000mah-dual-usb-mobile-power-source-w-led-for-iphone-samsung-silver-white-328011#.VMQQGy6WXKA
>
>May pay to check the unit before you purchase.
eliminating the DX one.
David Taylor
Jan 25, 2015, 10:21:13 AM1/25/15
to
On 24/01/2015 21:36, Don McKenzie wrote:
[]
Anyway, I can confirm that RS 10 Ah unit /does/ work as a UPS. I have
one of my Raspberry Pi PCs working on it right now. Unplugged the main,
and the RPi carried on working. Replugged the mains and the device
continues to supply power to the RPi.
[]
> I just got a similar unit from dx.com
>
> What I found was if there is power being put into the unit, then no
> power comes out, so it won't work as a UPS type of supply, which
> basically is what you want, correct?
>
> Mine is a 20000mAh. Sure it has 2.1A and 1A outputs, but nothing comes
> out unless you either pull out the input plug, or switch off the source
> of input power.
> http://www.dx.com/p/bp-l2k-1-0-lcd-20000mah-dual-usb-mobile-power-source-w-led-for-iphone-samsung-silver-white-328011#.VMQQGy6WXKA
>
>
> May pay to check the unit before you purchase.
> BTW
> I got mine for phone backup, not as a micro UPS.
>
> Cheers Don...
Yes, that's the problem. I guess you could always ask before purchase.
>
> What I found was if there is power being put into the unit, then no
> power comes out, so it won't work as a UPS type of supply, which
> basically is what you want, correct?
>
> Mine is a 20000mAh. Sure it has 2.1A and 1A outputs, but nothing comes
> out unless you either pull out the input plug, or switch off the source
> of input power.
> http://www.dx.com/p/bp-l2k-1-0-lcd-20000mah-dual-usb-mobile-power-source-w-led-for-iphone-samsung-silver-white-328011#.VMQQGy6WXKA
>
>
> May pay to check the unit before you purchase.
> BTW
> I got mine for phone backup, not as a micro UPS.
>
> Cheers Don...
Anyway, I can confirm that RS 10 Ah unit /does/ work as a UPS. I have
one of my Raspberry Pi PCs working on it right now. Unplugged the main,
and the RPi carried on working. Replugged the mains and the device
continues to supply power to the RPi.
David Taylor
Jan 25, 2015, 10:22:53 AM1/25/15
to
On 25/01/2015 14:42, Gordon Levi wrote:
[]
to Don, you could always ask before purchase. I also saw the cheap
units and was very tempted.
[]
> Honest Mister, I have been paying attention. In fact that is how I
> learned that not all power banks have pass through charging. I should
> have acknowledged those posts and explained I am in Australia. The
> 10Ah RS product costs three times as much as an eBay sourced one
> <http://www.ebay.com.au/itm/XIAOMI-10400mAh-Portable-Power-Bank-Li-ion-Battery-Charger-5V-2-1A-iPad-iPhone-/261478644375#ret>.
> I was hoping that someone had bought something similar and could
> assure me it had pass through charging or had a general method for
> determining if a unit has pass through charging.
Good point, Gordon, you /had/ indeed been paying attention. As I said
> learned that not all power banks have pass through charging. I should
> have acknowledged those posts and explained I am in Australia. The
> 10Ah RS product costs three times as much as an eBay sourced one
> <http://www.ebay.com.au/itm/XIAOMI-10400mAh-Portable-Power-Bank-Li-ion-Battery-Charger-5V-2-1A-iPad-iPhone-/261478644375#ret>.
> I was hoping that someone had bought something similar and could
> assure me it had pass through charging or had a general method for
> determining if a unit has pass through charging.
to Don, you could always ask before purchase. I also saw the cheap
units and was very tempted.
Don McKenzie
Jan 25, 2015, 4:08:46 PM1/25/15
to
One of the sad points about attempting to buy from dx.com and similar, is you will never get an answer out of them to
any technical question. Almost like trying to get an answer out of Paypal on anything, unless things have changed since
I last tried asking them.
And ebay sellers, you may be lucky to get a sensible answer out of most of them too David. I am in Australia also, so I
understand your problem.
Keep asking for suitable types. :-)
Perhaps the EEVblog forum, whirlpool, or similar Aussie forums may help.
Don McKenzie
Jan 25, 2015, 4:13:37 PM1/25/15
to
> And ebay sellers, you may be lucky to get a sensible answer out of most of them too David. I am in Australia also, so I
> understand your problem.
rickman
Jan 25, 2015, 4:21:09 PM1/25/15
to
I'm not sure if that limits the input current to 500 mA or if it is
saying 500 mA is required from the power source. If the unit won't draw
more than 500 mA it won't power the rPi at max current draw without
draining the battery, no?
--
Rick
Martin Gregorie
Jan 25, 2015, 8:51:20 PM1/25/15
to
https://www.modmypi.com/pi-modules-upis-advanced-stacking
is currently the best bet at GBP 48.99? This charges at 350 mA, but then
again it is a UPS and can run off mains, batteries or solar cells and
seems to accept supply voltages from 5v - 18v.
This looks a bit more reasonable when you know that Amazon flogs 2500 mAh
'phone chargers, i.e. a pocketable 2500 mAh hard-cased Li-poly battery
for anywhere between GBP 9 - GBP 25 and only the more expensive ones have
chargers and a micro-USB output connector.
--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |
David Taylor
Jan 26, 2015, 6:01:58 AM1/26/15
to
On 25/01/2015 21:21, rickman wrote:
[]
1A or more the unit will draw 1A otherwise it draws 0.5A. Not sure how
it determines that. Mine has been running an RPi B with Wi-Fi and a GPS
attached for 20 hours now, and as soon as I started it the "charge
greater than 80% LED" was flashing, and it still is. When running, that
RPi takes 0.4A. My USB ammeter is only USB-A connectors, so I can't
easily measure the current into the unit, or know how it determines
whether to draw 0.5A or 1A.
[]
> The spec says, "Input power source rating: 500mA @ +5V"
>
> I'm not sure if that limits the input current to 500 mA or if it is
> saying 500 mA is required from the power source. If the unit won't draw
> more than 500 mA it won't power the rPi at max current draw without
> draining the battery, no?
The instructions are along the lines of: if the input source can supply
>
> I'm not sure if that limits the input current to 500 mA or if it is
> saying 500 mA is required from the power source. If the unit won't draw
> more than 500 mA it won't power the rPi at max current draw without
> draining the battery, no?
1A or more the unit will draw 1A otherwise it draws 0.5A. Not sure how
it determines that. Mine has been running an RPi B with Wi-Fi and a GPS
attached for 20 hours now, and as soon as I started it the "charge
greater than 80% LED" was flashing, and it still is. When running, that
RPi takes 0.4A. My USB ammeter is only USB-A connectors, so I can't
easily measure the current into the unit, or know how it determines
whether to draw 0.5A or 1A.
David Taylor
Jan 26, 2015, 6:05:35 AM1/26/15
to
On 26/01/2015 01:50, Martin Gregorie wrote:
[]
experimenting, I preferred the more versatile in-the-power-line unit,
although it's not a true UPS.
[]
> Does that mean that this:
> https://www.modmypi.com/pi-modules-upis-advanced-stacking
>
> is currently the best bet at GBP 48.99? This charges at 350 mA, but then
> again it is a UPS and can run off mains, batteries or solar cells and
> seems to accept supply voltages from 5v - 18v.
>
> This looks a bit more reasonable when you know that Amazon flogs 2500 mAh
> 'phone chargers, i.e. a pocketable 2500 mAh hard-cased Li-poly battery
> for anywhere between GBP 9 - GBP 25 and only the more expensive ones have
> chargers and a micro-USB output connector.
It's only a quarter of the capacity, though. In any case, as I am only
> https://www.modmypi.com/pi-modules-upis-advanced-stacking
>
> is currently the best bet at GBP 48.99? This charges at 350 mA, but then
> again it is a UPS and can run off mains, batteries or solar cells and
> seems to accept supply voltages from 5v - 18v.
>
> This looks a bit more reasonable when you know that Amazon flogs 2500 mAh
> 'phone chargers, i.e. a pocketable 2500 mAh hard-cased Li-poly battery
> for anywhere between GBP 9 - GBP 25 and only the more expensive ones have
> chargers and a micro-USB output connector.
experimenting, I preferred the more versatile in-the-power-line unit,
although it's not a true UPS.
Rob Morley
Jan 26, 2015, 7:56:08 AM1/26/15
to
On Mon, 26 Jan 2015 11:01:57 +0000
David Taylor <david-...@blueyonder.co.uk.invalid> wrote:
> The instructions are along the lines of: if the input source can
> supply 1A or more the unit will draw 1A otherwise it draws 0.5A. Not
> sure how it determines that. Mine has been running an RPi B with
> Wi-Fi and a GPS attached for 20 hours now, and as soon as I started
> it the "charge greater than 80% LED" was flashing, and it still is.
> When running, that RPi takes 0.4A. My USB ammeter is only USB-A
> connectors, so I can't easily measure the current into the unit, or
> know how it determines whether to draw 0.5A or 1A.
>
USB devices negotiate current draw with the host when connected.
David Taylor <david-...@blueyonder.co.uk.invalid> wrote:
> The instructions are along the lines of: if the input source can
> supply 1A or more the unit will draw 1A otherwise it draws 0.5A. Not
> sure how it determines that. Mine has been running an RPi B with
> Wi-Fi and a GPS attached for 20 hours now, and as soon as I started
> it the "charge greater than 80% LED" was flashing, and it still is.
> When running, that RPi takes 0.4A. My USB ammeter is only USB-A
> connectors, so I can't easily measure the current into the unit, or
> know how it determines whether to draw 0.5A or 1A.
>
Default is 100/150mA (USB2/3) maximum 500/900mA. If the data pins are
shorted the device knows it's a dumb charger and can draw 500-1500mA.
ISTR there's a recent extension (USB3.1?) to this that provides 2A at 5V
but I don't recall the details, and of course Apple chargers/devices
have their own method.
Andrew Gabriel
Jan 26, 2015, 9:11:51 AM1/26/15
to
In article <20150126125...@ntlworld.com>,
it's a dedicated charging port. Shorting (usually done with a 200 ohm
resistor) is one way. Another is 2.0V on one and 2.7V on the other data
line to indicate 10W output (2.1A), or 5W output if the voltages on the
two data lines are are swapped. Another is 1.2V on the DP line.
There are USB PSU chips which detect which method the USB device is
trying to use, and adapt the effective resistance and voltages on the
data lines to match it (such as Texas Instruments TPS2511).
However, the mess with USB charging standards (the Chinese standard, EU
standard, Apple, and USB Consortium standard) mean many devices nowadays
work out the current available by steadily increasing the draw whilst
monitoring the voltage drop, and back off a bit when the voltage drops
below some device specific threshold (such as 4.75V), or if the supply
cuts out. This can mean that a low spec charging cable can severely limit
the ability to draw max current from a supply even when both the device
and the supply are capable of high current use.
> ISTR there's a recent extension (USB3.1?) to this that provides 2A at 5V
> but I don't recall the details, and of course Apple chargers/devices
> have their own method.
10W (2.1A) can be available from USB chargers to Chinese and EU standards.
The USB consortium standards allow for up to 1.5A on USB2 dedicated
charging port I think, but they also have standards for up to 90W or 100W
for laptops but using different connectors and higher voltages. I've never
seen these in use anywhere, possibly because you have to pay a license
fee to implement their standards, which I don't think is the case if you
use the Chinese or EU dedicated charging port standards.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Rob Morley <nos...@ntlworld.com> writes:
> On Mon, 26 Jan 2015 11:01:57 +0000
> David Taylor <david-...@blueyonder.co.uk.invalid> wrote:
>
>> The instructions are along the lines of: if the input source can
>> supply 1A or more the unit will draw 1A otherwise it draws 0.5A. Not
>> sure how it determines that. Mine has been running an RPi B with
>> Wi-Fi and a GPS attached for 20 hours now, and as soon as I started
>> it the "charge greater than 80% LED" was flashing, and it still is.
>> When running, that RPi takes 0.4A. My USB ammeter is only USB-A
>> connectors, so I can't easily measure the current into the unit, or
>> know how it determines whether to draw 0.5A or 1A.
>>
> USB devices negotiate current draw with the host when connected.
> Default is 100/150mA (USB2/3) maximum 500/900mA. If the data pins are
> shorted the device knows it's a dumb charger and can draw 500-1500mA.
There are (at least) 3 different schemes for the data lines to indicate
> On Mon, 26 Jan 2015 11:01:57 +0000
> David Taylor <david-...@blueyonder.co.uk.invalid> wrote:
>
>> The instructions are along the lines of: if the input source can
>> supply 1A or more the unit will draw 1A otherwise it draws 0.5A. Not
>> sure how it determines that. Mine has been running an RPi B with
>> Wi-Fi and a GPS attached for 20 hours now, and as soon as I started
>> it the "charge greater than 80% LED" was flashing, and it still is.
>> When running, that RPi takes 0.4A. My USB ammeter is only USB-A
>> connectors, so I can't easily measure the current into the unit, or
>> know how it determines whether to draw 0.5A or 1A.
>>
> USB devices negotiate current draw with the host when connected.
> Default is 100/150mA (USB2/3) maximum 500/900mA. If the data pins are
> shorted the device knows it's a dumb charger and can draw 500-1500mA.
it's a dedicated charging port. Shorting (usually done with a 200 ohm
resistor) is one way. Another is 2.0V on one and 2.7V on the other data
line to indicate 10W output (2.1A), or 5W output if the voltages on the
two data lines are are swapped. Another is 1.2V on the DP line.
There are USB PSU chips which detect which method the USB device is
trying to use, and adapt the effective resistance and voltages on the
data lines to match it (such as Texas Instruments TPS2511).
However, the mess with USB charging standards (the Chinese standard, EU
standard, Apple, and USB Consortium standard) mean many devices nowadays
work out the current available by steadily increasing the draw whilst
monitoring the voltage drop, and back off a bit when the voltage drops
below some device specific threshold (such as 4.75V), or if the supply
cuts out. This can mean that a low spec charging cable can severely limit
the ability to draw max current from a supply even when both the device
and the supply are capable of high current use.
> ISTR there's a recent extension (USB3.1?) to this that provides 2A at 5V
> but I don't recall the details, and of course Apple chargers/devices
> have their own method.
The USB consortium standards allow for up to 1.5A on USB2 dedicated
charging port I think, but they also have standards for up to 90W or 100W
for laptops but using different connectors and higher voltages. I've never
seen these in use anywhere, possibly because you have to pay a license
fee to implement their standards, which I don't think is the case if you
use the Chinese or EU dedicated charging port standards.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Oscar
Feb 3, 2015, 11:52:31 AM2/3/15
to
In article <ma31k9$1jg$1...@dont-email.me>,
camera I ordered via ebay) that exibits this behaviour. I was more or
less happy until I found out it did not recharge the battery when
something is connected to the output.
Another one for the checklist: does it recharge when power comes back?
--
[J|O|R] <- .signature.gz
David Taylor <david-...@blueyonder.co.uk> wrote:
> Anyway, I can confirm that RS 10 Ah unit /does/ work as a UPS. I have
>one of my Raspberry Pi PCs working on it right now. Unplugged the main,
>and the RPi carried on working. Replugged the mains and the device
>continues to supply power to the RPi.
I once got a pack somewhere (I think it was included with an old HD 808
> Anyway, I can confirm that RS 10 Ah unit /does/ work as a UPS. I have
>one of my Raspberry Pi PCs working on it right now. Unplugged the main,
>and the RPi carried on working. Replugged the mains and the device
>continues to supply power to the RPi.
camera I ordered via ebay) that exibits this behaviour. I was more or
less happy until I found out it did not recharge the battery when
something is connected to the output.
Another one for the checklist: does it recharge when power comes back?
--
[J|O|R] <- .signature.gz
Gordon Henderson
Feb 3, 2015, 12:10:47 PM2/3/15
to
In article <ksl6catkkg0n06kue...@4ax.com>,
FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I powered
a Pi from it last week - noticed the following morning it was down to 1
dot, so plugged it in to charge - and it started charging. However it's
taken 3 days to charge fully - while powering in the Pi.
That, I suspect is the biggest issue with these units - the ability to
take 2x the output capacity to enable charging in a sensible time span...
I suspect it would go off an stay off when it ran out of juice though.
Gordon
a Pi from it last week - noticed the following morning it was down to 1
dot, so plugged it in to charge - and it started charging. However it's
taken 3 days to charge fully - while powering in the Pi.
That, I suspect is the biggest issue with these units - the ability to
take 2x the output capacity to enable charging in a sensible time span...
I suspect it would go off an stay off when it ran out of juice though.
Gordon
Martin Gregorie
Feb 3, 2015, 12:42:29 PM2/3/15
to
On Tue, 03 Feb 2015 17:10:12 +0000, Gordon Henderson wrote:
> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I powered
> a Pi from it last week - noticed the following morning it was down to 1
> dot, so plugged it in to charge - and it started charging. However it's
> taken 3 days to charge fully - while powering in the Pi.
>
> That, I suspect is the biggest issue with these units - the ability to
> take 2x the output capacity to enable charging in a sensible time
> span...
>
Might this have something to do with limitations in the mains PSU you
> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I powered
> a Pi from it last week - noticed the following morning it was down to 1
> dot, so plugged it in to charge - and it started charging. However it's
> taken 3 days to charge fully - while powering in the Pi.
>
> That, I suspect is the biggest issue with these units - the ability to
> take 2x the output capacity to enable charging in a sensible time
> span...
>
were using to charge it? I assume that's a USB charger, so what's its
maximum current capability?
> I suspect it would go off an stay off when it ran out of juice though.
>
Gordon Henderson
Feb 3, 2015, 1:33:01 PM2/3/15
to
In article <mar191$7hp$2...@dont-email.me>,
However who knows if the battery device actually senses the input voltage
or what. USB power is notoriously rubbish.
>> I suspect it would go off an stay off when it ran out of juice though.
>>
>Might be worth testing that.
One day maybe!
Gordon
Martin Gregorie <mar...@address-in-sig.invalid> wrote:
>On Tue, 03 Feb 2015 17:10:12 +0000, Gordon Henderson wrote:
>
>> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I powered
>> a Pi from it last week - noticed the following morning it was down to 1
>> dot, so plugged it in to charge - and it started charging. However it's
>> taken 3 days to charge fully - while powering in the Pi.
>>
>> That, I suspect is the biggest issue with these units - the ability to
>> take 2x the output capacity to enable charging in a sensible time
>> span...
>>
>Might this have something to do with limitations in the mains PSU you
>were using to charge it? I assume that's a USB charger, so what's its
>maximum current capability?
2 amps.
>On Tue, 03 Feb 2015 17:10:12 +0000, Gordon Henderson wrote:
>
>> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I powered
>> a Pi from it last week - noticed the following morning it was down to 1
>> dot, so plugged it in to charge - and it started charging. However it's
>> taken 3 days to charge fully - while powering in the Pi.
>>
>> That, I suspect is the biggest issue with these units - the ability to
>> take 2x the output capacity to enable charging in a sensible time
>> span...
>>
>Might this have something to do with limitations in the mains PSU you
>were using to charge it? I assume that's a USB charger, so what's its
>maximum current capability?
However who knows if the battery device actually senses the input voltage
or what. USB power is notoriously rubbish.
>> I suspect it would go off an stay off when it ran out of juice though.
>>
>Might be worth testing that.
Gordon
David Taylor
Feb 3, 2015, 2:51:55 PM2/3/15
to
On 03/02/2015 16:51, Oscar wrote:
[]
the charging light resumes as you would expect.
[]
> I once got a pack somewhere (I think it was included with an old HD 808
> camera I ordered via ebay) that exibits this behaviour. I was more or
> less happy until I found out it did not recharge the battery when
> something is connected to the output.
>
> Another one for the checklist: does it recharge when power comes back?
Yes, it does. You can unplug it from the mains, plug it back in, and
> camera I ordered via ebay) that exibits this behaviour. I was more or
> less happy until I found out it did not recharge the battery when
> something is connected to the output.
>
> Another one for the checklist: does it recharge when power comes back?
the charging light resumes as you would expect.
news13
Feb 3, 2015, 9:46:45 PM2/3/15
to
what ever duration blackout/relocation period you want and then mate it
to the appropriately battery charger and USB power supply.
rickman
Feb 3, 2015, 11:29:31 PM2/3/15
to
charging, but they warn you that it "may" reduce the battery life in the
Anker unit. I found in the manual for one of the smaller Anker units
they tell you not to do it because of harm to the battery life.
--
Rick
David Taylor
Feb 4, 2015, 4:31:14 AM2/4/15
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On 04/02/2015 02:46, news13 wrote:
[]
[]
> My 2c is to choose the appropriate sla/wet/agm/lipoly/???? to provide for
> what ever duration blackout/relocation period you want and then mate it
> to the appropriately battery charger and USB power supply.
Which is just what the pre-made units I've been mentioning do.
> what ever duration blackout/relocation period you want and then mate it
> to the appropriately battery charger and USB power supply.
Martin Gregorie
Feb 4, 2015, 7:45:52 AM2/4/15
to
On Tue, 03 Feb 2015 18:32:26 +0000, Gordon Henderson wrote:
> In article <mar191$7hp$2...@dont-email.me>,
> Martin Gregorie <mar...@address-in-sig.invalid> wrote:
>>On Tue, 03 Feb 2015 17:10:12 +0000, Gordon Henderson wrote:
>>
>>> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I
>>> powered a Pi from it last week - noticed the following morning it was
>>> down to 1 dot, so plugged it in to charge - and it started charging.
>>> However it's taken 3 days to charge fully - while powering in the Pi.
>>>
>>> That, I suspect is the biggest issue with these units - the ability to
>>> take 2x the output capacity to enable charging in a sensible time
>>> span...
>>>
>>Might this have something to do with limitations in the mains PSU you
>>were using to charge it? I assume that's a USB charger, so what's its
>>maximum current capability?
>
> 2 amps.
>
As a 72 hour charge for that battery should (in theory) need just 208mA,
> In article <mar191$7hp$2...@dont-email.me>,
> Martin Gregorie <mar...@address-in-sig.invalid> wrote:
>>On Tue, 03 Feb 2015 17:10:12 +0000, Gordon Henderson wrote:
>>
>>> FWIW: I have an Anker 15,000 mAh unit (bought from amazon) and I
>>> powered a Pi from it last week - noticed the following morning it was
>>> down to 1 dot, so plugged it in to charge - and it started charging.
>>> However it's taken 3 days to charge fully - while powering in the Pi.
>>>
>>> That, I suspect is the biggest issue with these units - the ability to
>>> take 2x the output capacity to enable charging in a sensible time
>>> span...
>>>
>>Might this have something to do with limitations in the mains PSU you
>>were using to charge it? I assume that's a USB charger, so what's its
>>maximum current capability?
>
> 2 amps.
>
a 2 amp PSU should have plenty of capacity for running both.
Charging a LiPO or Li-ion battery is fairly complex: a good charger
provides constant current at a 1C rate (a 1000mA cell is charged at 1
amp) until the full pack voltage is reached and then constant voltage
until the current falls to an arbitrary small value, when the charger
reports fully charged and turns off.
My guess is that the built-in charger was designed on the assumption that
there is no load on the pack when its being charged, so the running RPi
is simply eating some of the 1C current, meaning that the battery is
being changed at a rather lower rate than expected. That shouldn't hurt
the battery as the charging circuit will just dimly sit and wait until
the battery gets to the end of the constant current phase. After a power
outage I imagine that the charger restarts in constant current mode.
rickman
Feb 4, 2015, 1:05:30 PM2/4/15
to
to constant voltage charging may reach a point where the battery is
being discharged. I assume if the voltage starts to droop the charger
will revert to constant current mode, etc. switching back and forth,
charging and discharging the internal battery. Such light charge cycles
will eventually wear out the battery sooner than if it were managed more
like a "proper" USP. That would imply that there is a charging circuit
for the battery and a separate supply for the output which does not draw
from (and disrupt) the operation of the charging circuit.
The documents on the Anker web site support this. The lighter 10,000
mAHr unit says it will be damaged if used this way and the larger unit
mentioned here says it "may" be damaged.
--
Rick
Martin Gregorie
Feb 4, 2015, 1:42:07 PM2/4/15
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On Wed, 04 Feb 2015 13:05:21 -0500, rickman wrote:
> I think the issue is that once the battery is fully charged the switch
> to constant voltage charging may reach a point where the battery is
> being discharged. I assume if the voltage starts to droop the charger
> will revert to constant current mode, etc. switching back and forth,
> charging and discharging the internal battery. Such light charge cycles
> will eventually wear out the battery sooner than if it were managed more
> like a "proper" USP. That would imply that there is a charging circuit
> for the battery and a separate supply for the output which does not draw
> from (and disrupt) the operation of the charging circuit.
>
> The documents on the Anker web site support this. The lighter 10,000
> mAHr unit says it will be damaged if used this way and the larger unit
> mentioned here says it "may" be damaged.
That seems quite likely. There's certainly some missing information.
> I think the issue is that once the battery is fully charged the switch
> to constant voltage charging may reach a point where the battery is
> being discharged. I assume if the voltage starts to droop the charger
> will revert to constant current mode, etc. switching back and forth,
> charging and discharging the internal battery. Such light charge cycles
> will eventually wear out the battery sooner than if it were managed more
> like a "proper" USP. That would imply that there is a charging circuit
> for the battery and a separate supply for the output which does not draw
> from (and disrupt) the operation of the charging circuit.
>
> The documents on the Anker web site support this. The lighter 10,000
> mAHr unit says it will be damaged if used this way and the larger unit
> mentioned here says it "may" be damaged.
There's nothing specific on the Amazon site advertising the 15000 mAh
battery. About all I could see is that both USB sockets have the same
label alongside them and IIRC there's a comment about charging two
devices at once.
Methinks this could be a case where an SLA may be the better solution
simply because you can use a much simpler charger. Building one that
switched between 'fast charge' and 'float' (or even ON and OFF) on
voltage should be simple enough. I notice that COTS UPSes don't seem to
be in a hurry to switch from SLA to to LiPO chemistry.
rickman
Feb 4, 2015, 1:49:38 PM2/4/15
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connection is flaky and needs to be reset, I cycle the UPS that powers
my entire bench! lol I want the pi to not go down when I do that just
like my laptop. I might be able to do this with a super cap on the 5
volt line...
--
Rick
Martin Gregorie
Feb 4, 2015, 4:18:47 PM2/4/15
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the end of a LM358 plus transistor constant current source set to feed
them 1% of capacity + RPi current draw and, if I was feeling keen, a 7805
or equivalent to drive the RPi. The point being that NiMH last forever if
trickle charged at 1% of the rated capacity, i.e. 10mA into a 1000mAh
NiMH.
Yeah, I know you prolly think I'm a heather, but I've used this sort of
rig for long-term NiCd and NiMH maintenance over the last couple of
decades and never had a problem with any of them.
rickman
Feb 4, 2015, 7:53:25 PM2/4/15
to
--
Rick
Mel Wilson
Feb 4, 2015, 9:33:46 PM2/4/15
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Rube Goldberg?
Mel.
Tony van der Hoff
Feb 5, 2015, 4:25:34 AM2/5/15
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Martin Gregorie
Feb 5, 2015, 7:39:44 AM2/5/15
to
On Wed, 04 Feb 2015 19:53:17 -0500, rickman wrote:
>> Yeah, I know you prolly think I'm a heather, but I've used this sort of
>> rig for long-term NiCd and NiMH maintenance over the last couple of
>> decades and never had a problem with any of them.
>
> What's a heather?
For 'heather' read 'heathen'.
>> rig for long-term NiCd and NiMH maintenance over the last couple of
>> decades and never had a problem with any of them.
>
> What's a heather?
Martin Gregorie
Feb 5, 2015, 7:42:00 AM2/5/15
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A. Dumas
Feb 5, 2015, 7:57:12 AM2/5/15
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Andrew Gabriel
Feb 5, 2015, 8:55:02 AM2/5/15
to
In article <mau2aj$ljj$1...@dont-email.me>,
(easily available in the form of cigarette light socket mobile chargers).
Lithium batteries have special properties making them ideal for portable
use, but that doesn't apply here. They are much more complex to charge,
and absolutely mustn't be continuously trickle or float charged. That
makes them unsuitable for use in a UPS of the type discussed here,
unless there was more complex circuitry designed in to the UPS to take
them out of the circuit once charged. It seems the products people have
identified are not designed this way, which is probably why the
manufacturers don't support simulteneous charge and use.
The easiest way to build one would be a 12V SLA battery and charger
designed to float at 13.8V, and a DC-DC converter to supply 5V for the
Pi. (These are available at 2.1A nowadays, and even 2 x 2.1A.)
You could add some circuitry to turn off the load if voltage drops to
10V (to protect the SLA battery), and if you expect the battery to be
run down to this level, use a deep discharge battery, which is capable
of deep draining without seriously shortening its life. Battery capacity
will typically decline linearly to nothing over about 5 years in float
charging at 13.8V - use that to decide how often to replace the battery.
Sizing the battery and charge current capacity depends on the load and
the min hold-up time you need after a power outage. Another factor is
how long you are prepared to wait for the battery to fully recharge
after power restoration before you have enough energy stored to
satisfy your min hold-up requirement again - you have an at-risk time
when the UPS will not yet be able to meet your hold-up requirement.
With batteries which need constant current charging (or controlled
current charging) such as NiCd/NiHM/LiPo, you need a different
approach.
Martin Gregorie <mar...@address-in-sig.invalid> writes:
> For that sort of job, I'd probably use 4 AA size NiMH or hybrid cells on
> the end of a LM358 plus transistor constant current source set to feed
> them 1% of capacity + RPi current draw and, if I was feeling keen, a 7805
> or equivalent to drive the RPi. The point being that NiMH last forever if
> trickle charged at 1% of the rated capacity, i.e. 10mA into a 1000mAh
> NiMH.
>
> Yeah, I know you prolly think I'm a heather, but I've used this sort of
> rig for long-term NiCd and NiMH maintenance over the last couple of
> decades and never had a problem with any of them.
Agree, or even a sealed lead acid battery with a DC-DC converter to 5v
> For that sort of job, I'd probably use 4 AA size NiMH or hybrid cells on
> the end of a LM358 plus transistor constant current source set to feed
> them 1% of capacity + RPi current draw and, if I was feeling keen, a 7805
> or equivalent to drive the RPi. The point being that NiMH last forever if
> trickle charged at 1% of the rated capacity, i.e. 10mA into a 1000mAh
> NiMH.
>
> Yeah, I know you prolly think I'm a heather, but I've used this sort of
> rig for long-term NiCd and NiMH maintenance over the last couple of
> decades and never had a problem with any of them.
(easily available in the form of cigarette light socket mobile chargers).
Lithium batteries have special properties making them ideal for portable
use, but that doesn't apply here. They are much more complex to charge,
and absolutely mustn't be continuously trickle or float charged. That
makes them unsuitable for use in a UPS of the type discussed here,
unless there was more complex circuitry designed in to the UPS to take
them out of the circuit once charged. It seems the products people have
identified are not designed this way, which is probably why the
manufacturers don't support simulteneous charge and use.
The easiest way to build one would be a 12V SLA battery and charger
designed to float at 13.8V, and a DC-DC converter to supply 5V for the
Pi. (These are available at 2.1A nowadays, and even 2 x 2.1A.)
You could add some circuitry to turn off the load if voltage drops to
10V (to protect the SLA battery), and if you expect the battery to be
run down to this level, use a deep discharge battery, which is capable
of deep draining without seriously shortening its life. Battery capacity
will typically decline linearly to nothing over about 5 years in float
charging at 13.8V - use that to decide how often to replace the battery.
Sizing the battery and charge current capacity depends on the load and
the min hold-up time you need after a power outage. Another factor is
how long you are prepared to wait for the battery to fully recharge
after power restoration before you have enough energy stored to
satisfy your min hold-up requirement again - you have an at-risk time
when the UPS will not yet be able to meet your hold-up requirement.
With batteries which need constant current charging (or controlled
current charging) such as NiCd/NiHM/LiPo, you need a different
approach.
Martin Gregorie
Feb 5, 2015, 9:02:11 AM2/5/15
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Martin Gregorie
Feb 5, 2015, 10:09:55 AM2/5/15
to
On Thu, 05 Feb 2015 13:54:26 +0000, Andrew Gabriel wrote:
> Agree, or even a sealed lead acid battery with a DC-DC converter to 5v
> (easily available in the form of cigarette light socket mobile
> chargers).
>
I thought about suggesting that, but its fairly hard to find 6 or 12v
> Agree, or even a sealed lead acid battery with a DC-DC converter to 5v
> (easily available in the form of cigarette light socket mobile
> chargers).
>
SLAs of under, say, 2.5AH and anything bigger is likely to be overkill
for running an RPi, Also, looking through the Sunpower catalogue, I
didn't find any multistage chargers for 6v SLAs. However, if you use,
say, a 7.2Ah 12v SLA I agree its dead easy: connect a 2-stage charger to
one side and use a cigarette socket 2v->5v converter to provide the 5v.
Again, I've done this for some years. I use a pair of 12v 7.2AH SLAs to
run the instruments in a glider and have a pair of Sunpower 2-stage
chargers to keep them topped up at home. Most glider instruments want
12v, but the PNA I use for navigation wants 5v via a mini-USB socket, so
I use a cannibalised cigarette socket 12v->5v converter to power it. Yes,
the PNA has an internal battery, but that's only good for 2-2.5 hours and
a good cross country flight is 4 hours plus. 'Cannibalised' because you
get more reliable connections by removing the converter's plastic case,
installing the PCB in a small Maplins metal box and soldering the 12v
inputs to it. Stuffing the unmodified converter into a Maplins/Farnell/RS
car lighter socket is a recipe for bad connections: all those lighter
sockets are just rubbish for anything except heating a lighter. For home
use, mounting the converter in a plastic box would probably be OK, but
these (tiny, dirt cheap) converters are switch-mode devices that put out
a lot of RF hash: not good to have anywhere near an airband radio set.
> The easiest way to build one would be a 12V SLA battery and charger
> designed to float at 13.8V, and a DC-DC converter to supply 5V for the
> Pi. (These are available at 2.1A nowadays, and even 2 x 2.1A.)
>
is rated at 1.4 amps.
> You could add some circuitry to turn off the load if voltage drops to
>
Nice touch - a job for one of the 8 pin PICAXEs?
> Battery capacity
> will typically decline linearly to nothing over about 5 years in float
> charging at 13.8V - use that to decide how often to replace the battery.
>
charge after a day's flying and never left on charge for more than 12
hours. My panel draws less than 1A at worst case (measured with
everything on and the radio on receive at 400mA). I cycle the batteries
once a year to check capacity and notice that even good quality Yuasa
batteries only hold full capacity for the first three years and then
decline quite steeply (>20% a year) after that. I've seen 500 cycles
quoted but don't think its that much in real life.
Johny B Good
Feb 5, 2015, 11:03:45 AM2/5/15
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On Thu, 05 Feb 2015 09:25:31 +0000, Tony van der Hoff
--
J B Good
Johny B Good
Feb 5, 2015, 11:06:02 AM2/5/15
to
On Thu, 05 Feb 2015 13:57:11 +0100, "A. Dumas"
...confirming that he meant "heathen". :-)
--
J B Good
rickman
Feb 5, 2015, 2:48:09 PM2/5/15
to
rather different from the lead acid battery used in automotive apps
where they can last much longer. I worked for the railroad once and saw
batteries that were 20 years old still working fine. They were backup
for crossing signals and were on trickle charge 99.9% of the time.
--
Rick
Martin Gregorie
Feb 5, 2015, 8:33:44 PM2/5/15
to
On Thu, 05 Feb 2015 14:48:00 -0500, rickman wrote:
> I'm surprised that SLA batteries die so quickly.
>
Yes, surprised me too. My pnly consoation is that other brands I tried
> I'm surprised that SLA batteries die so quickly.
>
(uniRoss, Maplins one brand) were on their way down after two years.
> rather different from the lead acid battery used in automotive apps
> where they can last much longer.
>
don't know if that makes a difference to their lifetimes. It makes a big
difference to usability: the glider's battery box was designed round a
single wide, flat 12v battery of unknown capacity that's hard/expensive
to find now, but i can get two 12v 7.2 AH batteries into the same space
if I stand them on end and raised the lid 50mm. Obviously this is only
possible because they are sealed types. And, in any case they spend at
least 80% of their time the right way up being charged or waiting for
flying weather.
Johny B Good
Feb 5, 2015, 9:01:47 PM2/5/15
to
the case for UPSes and _anything_ that acts as a UPS, is avoiding
excess float voltage across any one cell in the string (6 cells in the
case of 12v lead acid batteries - or 24 cells in total for the battery
pack used by my venerable SmartUPS2000, currently bypassed until I can
get hold of a suitable set of batteries at a seriouly low price).
Getting the float charge voltage per cell on each and every cell in
the string can be nigh on impossible, especially when using multiples
of 12v batteries to provide the higher voltages (24, 36 and 48 volts).
The 2.3v per cell float charging voltage is a compromise between
sulphation and corrosion. Too low and you risk sulphation. Too high
and you increase the rate of corrosion (excessive voltage also
increases the risk of water loss).
To further complicate the 'ideal voltage' level, this is also
effected by temperature which, according wikipedia, requires a
-0.0235v adjustment for each deg C increase above the 20 deg C
reference standard for a 6 cell (12v) battery.
You might think that the typical 5 year service life of an SLA
battery pack in UPS service is unimpressive but, if you care to
substitute the UPS SLAs with car batteries, you'll swiftly change your
mind (usually after a mere six months of continous float charge and a
small fortune in de-ionised water).
I know this only too well from experience, three experiments in
total! The first 'experiment' was keeping a single 12v car battery
charged from a 13.8v CB powerpack to allow not only battery backup but
also to serve the high current demands of a "Burner". I didn't realise
this actually was an experiment at the time. It took the 20/20 vision
of hindsight to reach this conclusion over 20 years later. At the
time, I simply put this down to the 'bad luck' of using a defective
battery.
When I got my hands on the SmartUPS2000 at a radioham rally about a
decade back, it didn't have the seperate clip on battery box so I had
to use an external battery pack. I think I used a pack of four 7AH
12v SLAs to begin with. Since the orginals specified 17AH SLAs, I
investigated a cheaper option in the form of a set of 36AH car
batteries for a mere 60 quid from a local automotive dealer.
Initial testing results with these bad boys wired in parallel with
the SLAs were very encouraging indeed but the batteries gradually got
more and more 'thirsty' over the following months before developing
low voltage cells due to excessive self discharge effects which,
effectively, rendered the whole battery pack useless after only 6
months or so.
By then, I'd managed to accumulate a complete set of 24AH SLAs to go
with the 7AH ones. I didn't rush back out to my friendly automotive
dealer straight away for yet another battery bargain, that second
experiment didn't happen until maybe 6 to 12 months later (the penny
_still_ hadn't dropped that I had run 'The Experiment' for a second
time). Extremely annoyingly, the 'new' set of car batteries suffered
exactly the same fate 6 months or so later.
Only then did it occur to me that in spite of the more 'benign
charging regime', a total lack of vibration and extreme variations of
temperature such batteries seemed well able to cope with, there was a
fundamental problem in using such batteries as UPS backup power.
It was only then that, like Milton's frisbee, it struck me! I finally
realised that I had experienced exactly the same problem more than two
decades ago with that aforementioned battery and CB 'charger/PSU'
setup. Only then did I shy away from "The Cheap Car Battery Solution".
I strongly suspect the main problem was the sustained float charging
voltage that was causing corrosion in the paste filled plates and I am
tempted to experiment again, only this time reduce the 13.8v per 12v
battery down to 13.5v. I'd need to find another set of car batteries
at a bargain price yet again before investing in a fourth experiment
though.
Another alternative would be to try a set of deep cycle
leisure/marine batteries (again, only if I can find a trader prepared
to sell me them at a bargain price) since these are designed for
similar service only with more frequent deep discharge cycles in mind.
In this case, a Raspberry Pi with a low power demand, the ideal
battery voltage is 2.3v (float) i.e a single lead acid cell. A
constant volt charger can guarantee that all the cells are getting the
right voltage (there's only the one cell to worry about and any
additional cells wired in parallel will also enjoy this benefit).
You do need a high efficiency low input voltage converter to generate
the required 5 volt supply in this setup but if it avoids the
conditions that would otherwise accelerate corrosion due to cell
voltage imbalance issues common to 6 and 12 volt lead acid batteries,
it will simplify battery care (only the one cell to check voltage (and
keep topped up if it's an open cell type)).
What you lose in voltage, you simply make up in ampere hours to get
the same watt hour capacity. One bonus of packing all your watt hour
requirements into a single cell is that it will either occupy slightly
less space than the equivilent in a 6 or 12 volt battery or allow you
to gain a larger watt hour rating out of the same volume (but slightly
heavier) battery with this gain being greater over the 12 volt battery
than over the 6 volt battery options.
In this case, it's worth giving the single cell SLA option serious
consideration, after all, you're going to need a 5v switching
converter in the mix anyway so why not make it an up converter?
The only remaining problem lies with obtaining a high efficiency
single cell mains charger. The standard shotcky rectifier diodes used
on 5 volt supplies represent a 10% loss of efficiency all on their own
from their typical 450 to 500mV forward volt drops when used in the
classic bi-phase fullwave rectifier mode at full rated output current.
The only way to eliminate such losses in a 2.3v charging supply would
be the use of power FETs in an active rectifier circuit. In theory,
reducing the volt drop to 100mV or less, depending on output current
and the choice of and number of FETs used. Such extra complication
will no doubt increase manufacturing costs and hence price _and_
availability. I've no doubt that the benefit of large scale
manufacturing will reduce the premium to just a few percent but that
pre-supposes a high market demand.
More realistically, a compromise on this 'ideal' would be to choose a
14AH 6v SLA over a 7A 12v SLA. They should both cost about the same
(same materials and manufacturing costs in either case, ignoring
disparities in market demand between these two options). Fewer
permutations by which cell voltage imbalance can start the cascade of
overcharging each cell in turn assuming you don't employ them as part
of a higher voltage string.
Perhaps a better version of the 6 volt SLA, where portability is not
a concern, would be to make up the 6 volt battery using seperate
cells. This neatly solves both the inexpensive high efficiency charger
and voltage converter issues and allows monitoring of the individual
cell voltages or, better yet, provision of a voltage sensitive shunt
module across each cell to save healthy cells from the effect of
being overvolted by other less considerate cells dropping in voltage
to due a slightly higher self discharge effect.
Such voltage shunt modules will, naturally include an indicator to
show excessive shunt current demand so you can deal with the real
culprit in a more timely fashion.
HTH
--
J B Good
Martin Gregorie
Feb 5, 2015, 9:53:45 PM2/5/15
to
On Fri, 06 Feb 2015 02:01:45 +0000, Johny B Good wrote:
> Such voltage shunt modules will, naturally include an indicator to
> show excessive shunt current demand so you can deal with the real
> culprit in a more timely fashion.
>
Thanks for that!
> Such voltage shunt modules will, naturally include an indicator to
> show excessive shunt current demand so you can deal with the real
> culprit in a more timely fashion.
>
Stupidly, it had never occurred to me that multicell SLA's could from thje
same need for a balancing charger that all multicell LIPOs require.
Presumably one could design a 2/3 stage SLA charger that uses a LiPO
charger's cell balancing circuitry to work with a set of single cell SLAs?
rickman
Feb 5, 2015, 10:36:53 PM2/5/15
to
but wouldn't Li-ion be a lot lighter for the same capacity? I think
that is the main reason why they use them in autos. I take it this is a
fairly sizable glider? What's the wing span? Are you talking about one
that carries people? I was picturing a drone type aircraft.
--
Rick
Ahem A Rivet's Shot
Feb 6, 2015, 1:30:02 AM2/6/15
to
On Fri, 06 Feb 2015 02:01:45 +0000
Johny B Good <johnny...@invalid.ntlworld.com> wrote:
> In this case, it's worth giving the single cell SLA option serious
> consideration, after all, you're going to need a 5v switching
> converter in the mix anyway so why not make it an up converter?
>
> The only remaining problem lies with obtaining a high efficiency
> single cell mains charger. The standard shotcky rectifier diodes used
> on 5 volt supplies represent a 10% loss of efficiency all on their own
> from their typical 450 to 500mV forward volt drops when used in the
> classic bi-phase fullwave rectifier mode at full rated output current.
Why not start with a high efficiency 5V PSU (like the one that
> In this case, it's worth giving the single cell SLA option serious
> consideration, after all, you're going to need a 5v switching
> converter in the mix anyway so why not make it an up converter?
>
> The only remaining problem lies with obtaining a high efficiency
> single cell mains charger. The standard shotcky rectifier diodes used
> on 5 volt supplies represent a 10% loss of efficiency all on their own
> from their typical 450 to 500mV forward volt drops when used in the
> classic bi-phase fullwave rectifier mode at full rated output current.
currently poweers the Pi or perhaps a higher current one) feeding a 2.3V
switching converter feeding the cell feeding a 5V switching converter
feeding the Pi ?
--
Steve O'Hara-Smith | Directable Mirror Arrays
C:>WIN | A better way to focus the sun
The computer obeys and wins. | licences available see
You lose and Bill collects. | http://www.sohara.org/
Gordon Levi
Feb 6, 2015, 8:49:46 AM2/6/15
to
Gordon Levi <gor...@address.invalid> wrote:
>I want to use a power bank as battery back up for a Raspberry Pi. The
>power bank has to have pass through charging so that I can leave the
>power bank connected to the mains while the Pi is powered from the
>output. I gather not all power banks can be used that way.
>
>Does anybody have any general or specific advice about how to choose
>the power bank?
Here's the one I chose <http://www.mi.com/en/mipowerbank10400/>. They
>I want to use a power bank as battery back up for a Raspberry Pi. The
>power bank has to have pass through charging so that I can leave the
>power bank connected to the mains while the Pi is powered from the
>output. I gather not all power banks can be used that way.
>
>Does anybody have any general or specific advice about how to choose
>the power bank?
don't actually specify pass through charging but some of the rave
reviews do
<http://gadgetadda.com/2014/11/24/xiaomi-10400mah-mi-power-bank-review-bang-for-the-buck/>.
I'm in Australia and chose this seller on eBay
<http://www.ebay.com.au/itm/XIAOMI-10400mAh-Portable-Power-Bank-Li-ion-Battery-Charger-5V-2-1A-iPad-iPhone-/261478644375#ret>.
I was a little worried before it arrived that it might be a fake
<http://en.miui.com/thread-19104-1-1.html>. I'm fairly sure it is not
but I haven't taken it apart to check. Looking on the bright side, if
they are worth faking they must be good!
The instructions are only in Chinese but the LEDS are informative and
easy to interpret. The "Power button" is more mysterious. It seems to
be a momentary switch that will reset the power bank circuitry and
turn off the output power only while it is pressed. Looking on the
bright side again, that makes it an ideal reset switch for the Pi.
I have followed with interest the discussion on the possible
variations of pass through charging but have not yet observed how mine
behaves. I'll post again if I find out.
Martin Gregorie
Feb 6, 2015, 9:38:03 AM2/6/15
to
On Thu, 05 Feb 2015 22:36:50 -0500, rickman wrote:
> I don't know what the reason for using SLA batteries in your glider is,
> but wouldn't Li-ion be a lot lighter for the same capacity?
>
The weight difference isn't significant: a factor of two at the most. My
> I don't know what the reason for using SLA batteries in your glider is,
> but wouldn't Li-ion be a lot lighter for the same capacity?
>
glider is a Standard Libelle. It is a single seat type, 15m span, weighs
206kg ready to fly less pilot. More details and pics here in case you're
interested:
http://www.gregorie.org/gliding/libelle/index.html
> I was picturing a drone type aircraft.
>
batteries since a lot of us are or have been model flyers and are well
aware of their reputation for catching fire while being charged and in
crashes. The Boeing 787 fun and games hasn't helped their rep. either.
They were using SAFT Li-ion batteries.
I don't need the extra capacity these chemistries offer since even one of
my pair of 7.2Ah SLAs can run my panel for 14 hours plus. Besides, a new
7.2AH SLA currently sells for GBP 16.80 as against GBP 86.56 for a
Lithium iron phosphate drop-in replacement. This price does include the
charger but its still only a 7AH battery. The alternative US sourced K2
12 LFP 7, another 12v 7AH SLA drop-in replacement, is $US 140 without the
charger, so that looks like a lot more money for very little benefit.
Admittedly the LiFePO4 chemistry is *much* safer than the SAFT cells that
Boeing was using but I still don't need something behind my seat that can
spew toxic smoke after a bad accident: in a glider the pilot is the nose
weight that puts the balance point, known as the CG (centre of gravity)
where it needs to be for safe flight: in this case about 30-35 cm behind
the seat back. Heavy, removable items such as batteries tend to be fitted
as close to the CG as possible. Yes, we do need to know what we weigh and
the acceptable weight is always written on a placard in the cockpit - and
checked by weighing and recalculating it every 7 years.
-----
The only glider type that does get serious benefit from lithium battery
chemistry is something like the Antares 20E, an electric self-launching
motor glider. It is a single seat 20m span beast with wings full of
batteries. It carries enough power to take off and climb 10,000 ft or to
motor 150-200km if the weather turns bad. Its an excellent, very fast and
efficient glider too. One has flown 1500km in Scottish wave. The pilot
had declared a 750 km triangle for his day's flight, but got round it so
fast he decided it would be rude to stop so early and went round a second
time before heading home.
http://www.lange-flugzeugbau.de/htm/english/products/antares_20e/
antares_20E.html
rickman
Feb 6, 2015, 7:45:22 PM2/6/15
to
On 2/6/2015 9:37 AM, Martin Gregorie wrote:
> On Thu, 05 Feb 2015 22:36:50 -0500, rickman wrote:
>
>> I don't know what the reason for using SLA batteries in your glider is,
>> but wouldn't Li-ion be a lot lighter for the same capacity?
>>
> The weight difference isn't significant: a factor of two at the most. My
> glider is a Standard Libelle. It is a single seat type, 15m span, weighs
> 206kg ready to fly less pilot. More details and pics here in case you're
> interested:
> http://www.gregorie.org/gliding/libelle/index.html
I guess the batteries are a small part of the weight of the aircraft so
> On Thu, 05 Feb 2015 22:36:50 -0500, rickman wrote:
>
>> I don't know what the reason for using SLA batteries in your glider is,
>> but wouldn't Li-ion be a lot lighter for the same capacity?
>>
> The weight difference isn't significant: a factor of two at the most. My
> glider is a Standard Libelle. It is a single seat type, 15m span, weighs
> 206kg ready to fly less pilot. More details and pics here in case you're
> interested:
> http://www.gregorie.org/gliding/libelle/index.html
not so important. I worked on a radio design for a drone (powered, not
a glider) which was probably about the same size as your glider but with
a smaller wingspan. The radio unit (an aluminum box) had a stud for a
ground cable. In the design review they spend some 20 minutes
discussing (arguing) over whether the stud should be shortened a half
inch to save weight. lol
So I'm thinking weight is important in any aircraft and especially so in
a glider.
>> I was picturing a drone type aircraft.
>>
> Understood. We, the gliding community, have always been wary of Li-ion
> batteries since a lot of us are or have been model flyers and are well
> aware of their reputation for catching fire while being charged and in
> crashes. The Boeing 787 fun and games hasn't helped their rep. either.
> They were using SAFT Li-ion batteries.
batteries are not allowed on commercial passenger flights as cargo.
Sort of like the oxygen generators on that flight that crashed some
years back because of the fire.
I have thought of getting into flying, but I have many, many other
things in the way at the moment. I am very into kayaking, but need a
hip replacement before I make any plans.
--
Rick
Martin Gregorie
Feb 7, 2015, 9:16:28 AM2/7/15
to
On Fri, 06 Feb 2015 19:45:14 -0500, rickman wrote:
> I guess the batteries are a small part of the weight of the aircraft so
> not so important.
>
Yes. Yuasa NP12-7 batteries are 2.65Kg, so the pair of them are less than
> I guess the batteries are a small part of the weight of the aircraft so
> not so important.
>
2% of the flying weight.
> So I'm thinking weight is important in any aircraft and especially so in
> a glider.
>
model and full size. In any aircraft in steady flight, lift from the wing
exactly equals the flying weight and lift varies as the square of the
speed, so doubling the weight of a glider only makes it fly 40% faster,
though the sink speed will rise by more than 40% because drag will also
increase. It can be useful to increase a competition glider's weight
because that increases its cruise speed, but you'd only do that on a day
with strong lift because its rate of climb in thermals. Consequently, all
modern racing gliders are set up with water tanks or bladders in their
wings so they can carry water ballast on strong days.
Gliders are faster than you might expect too: I never fly mine, a 45 year
old design, at less than 42 kts (48 mph) when climbing carefully in a
very weak thermal) and its interthermal speed will be somewhere between
53 and 85 kts (60-98 mph) depending on the air mass I'm flying through
and hence what speed to fly the glide computer is suggesting. The redline
is 118 kts (136 mph). Modern gliders are considerably faster than mine: I
know that in 2012 at the Woprd Champs in Texas the better Open Class
gliders, e.g. the Antares 23, were cruising at over 100 kts between
thermals.
By contrast a powered aircraft is much more weight sensitive, since
increasing the weight increases the flying speed and so maintaining level
flight requires more power as a direct result. This has a direct effect
on the length of the take-off run, take-off speed and on climb rate after
take-off. This has a bearing on the steady trickle of light aircraft take-
off crashes which turn out to be carrying four heavy people plus their
golf clubs or hunting/fishing gear and where the pilot didn't weigh
people and stuff and check the take-off weight.
Altitude also doesn't affect gliders much: again they just fly faster to
compensate for the thinner air, but it had a double wammy for powered
planes. Thinner air requires the plane to fly faster, so more power is
needed for level flight, BUT the thinner air also adversely affects the
engine, reducing available power, and propeller efficiency, reducing the
thrust it produces. This is generally not a problem in the UK, but is a
regular cause of accidents in the USA, where the combination of high
mountain airfields and high temperature (which also reduces air density)
can be lethal.
>>> I was picturing a drone type aircraft.
>>>
why there was such extreme concentration on weight reduction. The other
aircraft that is famous for the concentration on weight is the U-2
reconnaissance plane. Despite its size and speed it had no power assisted
controls and a single wheel undercarriage - both, among other features,
were entirely for weight reduction.
> But I understand the concern for safety. I believe that many Li
> batteries are not allowed on commercial passenger flights as cargo.
>
> I have thought of getting into flying, but I have many, many other
> things in the way at the moment. I am very into kayaking, but need a
> hip replacement before I make any plans.
>
see what its like. Who knows, you may get hooked. I've done both. Last
summer I finally got round to having a flight in a Tiger Moth biplane,
which was nice but I realised that, apart from an infinitely better all-
round view, the other thing I really like about gliding is the continual
awareness you must maintain to find your next climb if you want to stay
airborne. Besides, every winch launch is a real blast: 35 seconds from
standstill to releasing at 1200 ft or more above the winch can't be all
bad.
Sooner or later you'll have to stop kayacking and glider pilots can fly
into their 80s if they remain reasonably fit and alert. In the UK (and, I
think, Europe) its very much cheaper than power flying, especially if you
enjoy winch launching. I've also flown in the USA and, talking to pilots
there, it seems gliding is still cheaper, but only about 80% cheaper. But
then again, almost all gliding over there is off aero-tows, so there is
the cost of tug operation to cover.
Message has been deleted
Johny B Good
Feb 7, 2015, 3:19:04 PM2/7/15
to
On Fri, 6 Feb 2015 06:13:28 +0000, Ahem A Rivet's Shot
<ste...@eircom.net> wrote:
>On Fri, 06 Feb 2015 02:01:45 +0000
>Johny B Good <johnny...@invalid.ntlworld.com> wrote:
>
>> In this case, it's worth giving the single cell SLA option serious
>> consideration, after all, you're going to need a 5v switching
>> converter in the mix anyway so why not make it an up converter?
>>
>> The only remaining problem lies with obtaining a high efficiency
>> single cell mains charger. The standard shotcky rectifier diodes used
>> on 5 volt supplies represent a 10% loss of efficiency all on their own
>> from their typical 450 to 500mV forward volt drops when used in the
>> classic bi-phase fullwave rectifier mode at full rated output current.
>
> Why not start with a high efficiency 5V PSU (like the one that
>currently poweers the Pi or perhaps a higher current one) feeding a 2.3V
>switching converter feeding the cell feeding a 5V switching converter
>feeding the Pi ?
That's a good question. Indeed, since we're not _too_ concerned with
<ste...@eircom.net> wrote:
>On Fri, 06 Feb 2015 02:01:45 +0000
>Johny B Good <johnny...@invalid.ntlworld.com> wrote:
>
>> In this case, it's worth giving the single cell SLA option serious
>> consideration, after all, you're going to need a 5v switching
>> converter in the mix anyway so why not make it an up converter?
>>
>> The only remaining problem lies with obtaining a high efficiency
>> single cell mains charger. The standard shotcky rectifier diodes used
>> on 5 volt supplies represent a 10% loss of efficiency all on their own
>> from their typical 450 to 500mV forward volt drops when used in the
>> classic bi-phase fullwave rectifier mode at full rated output current.
>
> Why not start with a high efficiency 5V PSU (like the one that
>currently poweers the Pi or perhaps a higher current one) feeding a 2.3V
>switching converter feeding the cell feeding a 5V switching converter
>feeding the Pi ?
the mains charger efficiency at sub KW power levels (circa 10 to
25W?), that sort of pragmatic approach will do the trick without
adding too much to a Raspberry-Pi owner's electricity bill. Besides,
if it ever became a more important consideration, you still have the
option to upgrade the single cell charger at a later date.
Using a high efficiency laptop charger to feed a switcing converter
to float the single cell at the 2.3v mark will probably represent the
next best solution to highest efficiency short of buying an expensive
dedicated high efficiency single cell charger.
The additional losses in the extra switching converters in this case,
are simply the price you pay for a more reliable energy storage system
based on the electrochemistry of a single cell which doesn't have to
be restricted to lead acid technology.
All other issues aside, a 3.7v lithium cell would be a better choice
but it takes a lot to beat the charm of the simplicity of lead acid
battery technology which has been around even longer than CRT
technolgy (both now over a hundred years old).
One thing to watch out for regarding the charging circuit is the
possible need for an extra blocking diode to stop reverse current flow
from the battery into the output terminals of a home made charger
(one, perhaps based on a 12v mains PSU driving a 2.3v output switching
regulator). A dedicated high efficiency 2.3v mains charger, if they
exist at all, should have the need for such a blocking diode designed
out. Careful selection of your chosen 10v to 24v input, 2.3v output
switching regulator may eliminate the need of a blocking diode
altogether.
A typical homebrewed single cell UPS solution would most probably
involve a cheap, but high efficiency laptop charging brick (which has
the charm of accepting mains voltage inputs over the range 90v to 265v
rms ac - you could, in the case of nominal 230v ac mains supplies, use
an autotransformer to step the mains voltage down to 150v rms to
protect against overvolting faults in the mains supply (up to a max
voltage of 406v and a cut out voltage of 138v rms).
Your laptop charging brick (with or without the optional step down
transformer) would then feed a 2.3v output switching regulator,
preferably one that doesn't need a seperate blocking diode, to float
charge the battery _and_ supply current to the 2.3v to 5v 1 or 2 amp
converter(s). You could choose to use a 3.7v lithium cell if you're
feeling adventurous but I suspect the power management circuitry would
be significantly more complex than the charmingly simple constant
voltage requirements of a single SLA cell.
It's the relative simplicity of constant voltage charging of SLAs
that contributes to the ongoing popularity of lead acid battery
technology despite the advent of more exotic battery types. Also,
since pretty well all batteries are "Consumable" items, their relative
cheapness also works in favour of SLAs.
The biggest downside in any multicell battery is the issue of
maintaining charge state equilibrium between the cells. Such
imbalances can be corrected in the case of open wet lead acid
batteries by using a "Gassing Charge" once every few months. However,
this technique can't be used for the AGM and Gel SLAs since it will
produce hydrogen/oxygen bubbles trapped in the Gel or the glass fibres
of such cells. There's a lot of merit in opting for a 'single cell
solution' where relatively low power requirements make this a viable
and reasonably efficient option.
--
J B Good
rickman
Feb 7, 2015, 10:09:13 PM2/7/15
to
On 2/7/2015 9:15 AM, Martin Gregorie wrote:
>
> Sooner or later you'll have to stop kayacking and glider pilots can fly
> into their 80s if they remain reasonably fit and alert. In the UK (and, I
> think, Europe) its very much cheaper than power flying, especially if you
> enjoy winch launching. I've also flown in the USA and, talking to pilots
> there, it seems gliding is still cheaper, but only about 80% cheaper. But
> then again, almost all gliding over there is off aero-tows, so there is
> the cost of tug operation to cover.
I'm not so sure of that. I bought my 17 foot boat from a 70+ guy who
>
> Sooner or later you'll have to stop kayacking and glider pilots can fly
> into their 80s if they remain reasonably fit and alert. In the UK (and, I
> think, Europe) its very much cheaper than power flying, especially if you
> enjoy winch launching. I've also flown in the USA and, talking to pilots
> there, it seems gliding is still cheaper, but only about 80% cheaper. But
> then again, almost all gliding over there is off aero-tows, so there is
> the cost of tug operation to cover.
had cancer. He was still kayaking until he got sick. Plus it is such
great exercise. You may *need* to be fit to fly, but you will *become*
fit by kayaking. It fixed my lower back trouble by strengthening my
torso (core muscles). In fact, kayaking is a great social activity with
most participants in their later years. Flat water kayaking is a bit
tame for the 20 year old crowd I guess.
--
Rick
Rob Doyle
Feb 8, 2015, 1:40:26 AM2/8/15
to
On 2/7/2015 12:06 PM, Dennis Lee Bieber wrote:
> On Sat, 7 Feb 2015 14:15:52 +0000 (UTC), Martin Gregorie
> <mar...@address-in-sig.invalid> declaimed the following:
> between stalling from going too slow, and ripping the wings off from going
> supersonic, was around 20 knots. The pilot had to concentrate on airspeed
> control.
The "Coffin Corner". See:
http://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%29
Rob.
> On Sat, 7 Feb 2015 14:15:52 +0000 (UTC), Martin Gregorie
> <mar...@address-in-sig.invalid> declaimed the following:
>
>
>> Was the drone you worked on a high altitude type? If so I can understand
>> why there was such extreme concentration on weight reduction. The other
>> aircraft that is famous for the concentration on weight is the U-2
>> reconnaissance plane. Despite its size and speed it had no power assisted
>> controls and a single wheel undercarriage - both, among other features,
>> were entirely for weight reduction.
>>
>
> It also has the minor problem that, at cruise altitude, the difference
>
>> Was the drone you worked on a high altitude type? If so I can understand
>> why there was such extreme concentration on weight reduction. The other
>> aircraft that is famous for the concentration on weight is the U-2
>> reconnaissance plane. Despite its size and speed it had no power assisted
>> controls and a single wheel undercarriage - both, among other features,
>> were entirely for weight reduction.
>>
>
> between stalling from going too slow, and ripping the wings off from going
> supersonic, was around 20 knots. The pilot had to concentrate on airspeed
> control.
The "Coffin Corner". See:
http://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%29
Rob.
Martin Gregorie
Feb 8, 2015, 7:01:45 AM2/8/15
to
On Sat, 07 Feb 2015 14:06:17 -0500, Dennis Lee Bieber wrote:
> It also has the minor problem that, at cruise altitude, the
difference
> between stalling from going too slow, and ripping the wings off from
> going supersonic, was around 20 knots. The pilot had to concentrate on
> airspeed control.
>
Ah, the so-called coffin corner, where stalling speed and the IAS at that
> It also has the minor problem that, at cruise altitude, the
difference
> between stalling from going too slow, and ripping the wings off from
> going supersonic, was around 20 knots. The pilot had to concentrate on
> airspeed control.
>
altitude (actually the TAS (True Air Speed) coincide. Get fractionally
fast and the you're beyond airframe limits: fractionally slow and stall/
spin is the likely result. I believe U2 pilots know it well.
That is what happens when the required cruising altitude is "as high as
she'll go".
Martin Gregorie
Feb 8, 2015, 7:10:46 AM2/8/15
to
On Sat, 07 Feb 2015 22:09:10 -0500, rickman wrote:
> I'm not so sure of that. I bought my 17 foot boat from a 70+ guy who
> had cancer. He was still kayaking until he got sick. Plus it is such
> great exercise. You may *need* to be fit to fly, but you will *become*
> fit by kayaking. It fixed my lower back trouble by strengthening my
> torso (core muscles). In fact, kayaking is a great social activity with
> most participants in their later years. Flat water kayaking is a bit
> tame for the 20 year old crowd I guess.
>
Yeah, I assumed you meant white water or ocean kayacking. I'd forgotten
> I'm not so sure of that. I bought my 17 foot boat from a 70+ guy who
> had cancer. He was still kayaking until he got sick. Plus it is such
> great exercise. You may *need* to be fit to fly, but you will *become*
> fit by kayaking. It fixed my lower back trouble by strengthening my
> torso (core muscles). In fact, kayaking is a great social activity with
> most participants in their later years. Flat water kayaking is a bit
> tame for the 20 year old crowd I guess.
>
how popular flat-water kayacking is in the US and Canada and know very
little about it.
Good point about the social aspect. I think those who don't take part in
what are inherently group sports don't understand that side of the game.
Its the main difference between gliding and GA flying: since you need at
least three people to launch a glider (tug pilot/winch driver, wing
runner and glider pilot) almost by definition its a group game, unlike
GA, where you can wander onto the field, do the walk round, climb in,
start up and fly.
Christian Brunschen
Feb 8, 2015, 7:27:15 AM2/8/15
to
In article <mb7jn0$8lb$3...@dont-email.me>,
Being at the launch point and helping is part of the fun! (At least it
was for me when I was actively gliding.)
And there's also a lot of waiting around the launchpoint for suitable
weather - perhaps depending on where you are in the world!
// Christian
was for me when I was actively gliding.)
And there's also a lot of waiting around the launchpoint for suitable
weather - perhaps depending on where you are in the world!
// Christian
Graham.
Feb 8, 2015, 3:12:01 PM2/8/15
to
On Wed, 04 Feb 2015 19:53:17 -0500, rickman <gnu...@gmail.com> wrote:
>On 2/4/2015 4:18 PM, Martin Gregorie wrote:
>> On Wed, 04 Feb 2015 13:49:30 -0500, rickman wrote:
>>
>>> On 2/4/2015 1:41 PM, Martin Gregorie wrote:
>>>> On Wed, 04 Feb 2015 13:05:21 -0500, rickman wrote:
>>>>
>>>>> I think the issue is that once the battery is fully charged the switch
>>>>> to constant voltage charging may reach a point where the battery is
>>>>> being discharged. I assume if the voltage starts to droop the charger
>>>>> will revert to constant current mode, etc. switching back and forth,
>>>>> charging and discharging the internal battery. Such light charge
>>>>> cycles will eventually wear out the battery sooner than if it were
>>>>> managed more like a "proper" USP. That would imply that there is a
>>>>> charging circuit for the battery and a separate supply for the output
>>>>> which does not draw from (and disrupt) the operation of the charging
>>>>> circuit.
>>>>>
>>>>> The documents on the Anker web site support this. The lighter 10,000
>>>>> mAHr unit says it will be damaged if used this way and the larger unit
>>>>> mentioned here says it "may" be damaged.
>>>>
>>>> That seems quite likely. There's certainly some missing information.
>>>> There's nothing specific on the Amazon site advertising the 15000 mAh
>>>> battery. About all I could see is that both USB sockets have the same
>>>> label alongside them and IIRC there's a comment about charging two
>>>> devices at once.
>>>>
>>>> Methinks this could be a case where an SLA may be the better solution
>>>> simply because you can use a much simpler charger. Building one that
>>>> switched between 'fast charge' and 'float' (or even ON and OFF) on
>>>> voltage should be simple enough. I notice that COTS UPSes don't seem to
>>>> be in a hurry to switch from SLA to to LiPO chemistry.
>>>
>>> Funny, my need for a UPS for my pi is because when the Internet
>>> connection is flaky and needs to be reset, I cycle the UPS that powers
>>> my entire bench! lol I want the pi to not go down when I do that just
>>> like my laptop. I might be able to do this with a super cap on the 5
>>> volt line...
--
Graham.
%Profound_observation%
>On 2/4/2015 4:18 PM, Martin Gregorie wrote:
>> On Wed, 04 Feb 2015 13:49:30 -0500, rickman wrote:
>>
>>> On 2/4/2015 1:41 PM, Martin Gregorie wrote:
>>>> On Wed, 04 Feb 2015 13:05:21 -0500, rickman wrote:
>>>>
>>>>> I think the issue is that once the battery is fully charged the switch
>>>>> to constant voltage charging may reach a point where the battery is
>>>>> being discharged. I assume if the voltage starts to droop the charger
>>>>> will revert to constant current mode, etc. switching back and forth,
>>>>> charging and discharging the internal battery. Such light charge
>>>>> cycles will eventually wear out the battery sooner than if it were
>>>>> managed more like a "proper" USP. That would imply that there is a
>>>>> charging circuit for the battery and a separate supply for the output
>>>>> which does not draw from (and disrupt) the operation of the charging
>>>>> circuit.
>>>>>
>>>>> The documents on the Anker web site support this. The lighter 10,000
>>>>> mAHr unit says it will be damaged if used this way and the larger unit
>>>>> mentioned here says it "may" be damaged.
>>>>
>>>> That seems quite likely. There's certainly some missing information.
>>>> There's nothing specific on the Amazon site advertising the 15000 mAh
>>>> battery. About all I could see is that both USB sockets have the same
>>>> label alongside them and IIRC there's a comment about charging two
>>>> devices at once.
>>>>
>>>> Methinks this could be a case where an SLA may be the better solution
>>>> simply because you can use a much simpler charger. Building one that
>>>> switched between 'fast charge' and 'float' (or even ON and OFF) on
>>>> voltage should be simple enough. I notice that COTS UPSes don't seem to
>>>> be in a hurry to switch from SLA to to LiPO chemistry.
>>>
>>> Funny, my need for a UPS for my pi is because when the Internet
>>> connection is flaky and needs to be reset, I cycle the UPS that powers
>>> my entire bench! lol I want the pi to not go down when I do that just
>>> like my laptop. I might be able to do this with a super cap on the 5
>>> volt line...
>>
>> For that sort of job, I'd probably use 4 AA size NiMH or hybrid cells on
>> the end of a LM358 plus transistor constant current source set to feed
>> them 1% of capacity + RPi current draw and, if I was feeling keen, a 7805
>> or equivalent to drive the RPi. The point being that NiMH last forever if
>> trickle charged at 1% of the rated capacity, i.e. 10mA into a 1000mAh
>> NiMH.
>>
>> For that sort of job, I'd probably use 4 AA size NiMH or hybrid cells on
>> the end of a LM358 plus transistor constant current source set to feed
>> them 1% of capacity + RPi current draw and, if I was feeling keen, a 7805
>> or equivalent to drive the RPi. The point being that NiMH last forever if
>> trickle charged at 1% of the rated capacity, i.e. 10mA into a 1000mAh
>> NiMH.
>>
>> Yeah, I know you prolly think I'm a heather, but I've used this sort of
>> rig for long-term NiCd and NiMH maintenance over the last couple of
>> decades and never had a problem with any of them.
>
>What's a heather?
https://www.youtube.com/watch?v=JnUOPsjC2qk#t=84
>> rig for long-term NiCd and NiMH maintenance over the last couple of
>> decades and never had a problem with any of them.
>
>What's a heather?
--
Graham.
%Profound_observation%
rickman
Feb 8, 2015, 3:57:25 PM2/8/15
to
--
Rick
Martin Gregorie
Feb 8, 2015, 5:28:37 PM2/8/15
to
Martin Gregorie
Feb 8, 2015, 5:40:50 PM2/8/15
to
includes the point that it will tend to collect a group of like-minded
individuals which means that its a nice place to hang out. Many (all?)
pilots tend to have a fairly black sense of humour, so its nice to know
that the associated jokes and viewpoints aren't likely to be appreciated.
For instance, I like Sir Charles Kingston-Smiths comment that "The only
time you can have too much petrol in board is when the plane is on fire".
Look him up if you don't recognise the name.
> And there's also a lot of waiting around the launchpoint for suitable
> weather - perhaps depending on where you are in the world!
>
RASP (respectively US/American terms for the same software or XCWeather.
There's also a growing network of ground-based FLARM receivers in the UK
and Europe, so you can see if your friends are flying and where they're
going. All this stuff is available on the 'Net and many of the tracking
sites the use radar feeds are now taking FLARM feeds as well.
Alex Potter
Feb 11, 2015, 7:06:43 AM2/11/15
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On Sun, 08 Feb 2015 12:26:39 +0000, Christian Brunschen wrote:
> Being at the launch point and helping is part of the fun! (At least it
> was for me when I was actively gliding.)
>
> And there's also a lot of waiting around the launchpoint for suitable
> weather - perhaps depending on where you are in the world!
Ditto.
> was for me when I was actively gliding.)
>
> And there's also a lot of waiting around the launchpoint for suitable
> weather - perhaps depending on where you are in the world!
--
Alex
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