Charging 8.4V Li-Ion packs for front lights

[Joerg]

Folks,

Probably most of you know these kinds of lights:

http://www.amazon.com/Masione-Waterproof-1000-Lumen-Headlamp-Battery/dp/B005WPFVPC/ref=pd_sim_sbs_sg_1/192-3438671-9442951?ie=UTF8&refRID=1HG3MNSFBQ2EJ3NXQB12

The Li-Ion battery packs are a bit wimpy and only provide 1-2h of juice
but there are bigger ones:

http://www.amazon.com/WindFire%C2%AE-11000mAh-Rechargeable-Replacement-Flashlight/dp/B00J4EC326/ref=pd_sbs_sg_6?ie=UTF8&refRID=19CGQWDKC5RNZVQKDKY7

Here is my question. Li-Ion is very picky about charging. Go above 4.3V
and there may be a need for the fire department to come out. These 8.4V
packs contain two battery sets in series. Yet AFAICT there are only two
wires in the cable. So how does the charging process get balanced? If
they only rely on internal protection electronics which isn't 100%
kosher then over time one side will get less and less charge because the
other turns off earlier and allows no more current through the stack.

Does anyone know? Can anyone share experiences about lifetime? Or about
better and more sturdy mounting option for hard MTB use?

I'd also like to tie in the rear light somehow plus possibly provide a
homebrew voltage readout so I know how much juice is left for the
remainder of a ride (most lights have no warning, for whatever reason).
I guess that's only possible via a hack and splice.

Please, no discussions about dynamo lights if you can help it. Those are
simply too weak for my riding.

--
Regards, Joerg

http://www.analogconsultants.com/

[sms]

It's not perfectly balanced but it doesn't matter. They will use cells
from the same lot which are pretty close.

For most multi-cell Li-Ion batteries, cells are charged in series. There
are some larger packs where there is a series/parallel arrangement i.e.
multiple parallel sets of multiple series-connected batteries.

[Joerg]

Then maybe I should just try these out. If it works I'd have to figure
out a more sturdy seat post mount, possibly inside a bottle holder that
could at the same time carry the rear light.

[somebody]

On Sat, 01 Nov 2014 11:39:11 -0700, Joerg <ne...@analogconsultants.com>
wrote:

I have one that's about 4 years old. Works OK. The charger is 8.4
volts and the pack has some type of circuit that must balance the
cells when charging. Otherwise it would have exploded. There is a
board in there, just couldn't read the SMD IC's well enough to see
what they were.

You can get a USB-to-8.4 converter from dx.com and charge it using a
normal 5 volt supply. I have one and it cost < $3.

Slightly off topic: Many of the newer Chinese lights run from 4.2
volts. I have one that uses 4 18650's in parallel. Much cheaper to
build and simpler charging.

Hub dyno! Hub dyno! Hub dyno!

[Joerg]

Thanks, that is encouraging.

> You can get a USB-to-8.4 converter from dx.com and charge it using a
> normal 5 volt supply. I have one and it cost < $3.
>

I don't need USB because the bikes stay in the garage. Well, at least
since I am married they do :-)

> Slightly off topic: Many of the newer Chinese lights run from 4.2
> volts. I have one that uses 4 18650's in parallel. Much cheaper to
> build and simpler charging.
>

Newer ones? I looked at some 4.2V solutions but it seems they are going
out of style. It sure would be simpler and I could easier splice in a
Portland 1/2W rear light that normally takes two AAs. The downside is
that when the Li-Ion is down to 3.5V or so the converter in the light
would need to draw around 3.5 amps to get it to run at full brightness.
That's a bit much for the cable and causes voltage drop.

Amazon doesn't seem to have many 4.2V lights anymore.

> Hub dyno! Hub dyno! Hub dyno!

:-)

It would be nice to have something that can put at least a little charge
back into a Li-Ion and a hub dynamo at a good speed could deliver 5W.
For example by switching to a very low power mode or strobe when the
charge level becomes iffy. But neither my road bike nor my MTB has that.
A roller dynamo would be nice because it can (sometimes) be retrofitted
without a major wheel rebuild.

[Jeff Liebermann]

On Sat, 01 Nov 2014 17:34:05 -0700, Joerg <ne...@analogconsultants.com>
wrote:

>Amazon doesn't seem to have many 4.2V lights anymore.

Search Amazon, eBay, and DX.com for "18650 bicycle light". You should
find plenty. Amazon shows 2,629 hits of which 615 are bicycle
headlight specific.

You need one of these. 4200 lumens:
<http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>



--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jeff Liebermann]

On Sat, 01 Nov 2014 20:51:34 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>You need one of these. 4200 lumens:
><http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>

More power:
<http://www.amazon.com/Angelbubbles-Aluminum-Waterproof-HeadLight-HeadLamp/dp/B00ILOE8IM/>
8000 lumens using six 18650 cells in parallel.
Looking at the Cree XML data sheet:
<http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20Binning/XLampXML.pdf>
each LED at 2A might put out 692 lumens. With 7 LED's:
7 * 692 = 4800 lumens
Not exactly 8000 lumens, but probably accurate if I used an abacus. Of
course, that means:
2A * 3.7V = 7.4 watts per LED
or:
7 * 7.4 watts = 51.8 watts
total power consumption. Well, if you used 10 bottle dynamos, it
might work. Of course:
7 * 2A = 14A
through the thin pack battery cables isn't going to work very well and
might get hot or melt. Too bad LiIon cells have short circuit
protection PCB's or you could use the battery pack for emergency
welding.

One problem... Do you really want "AngelBubbles" inscribed on your
headlight?

[John B. Slocomb]

On Sat, 01 Nov 2014 11:39:11 -0700, Joerg <ne...@analogconsultants.com>
wrote:

>Folks,
>
>Probably most of you know these kinds of lights:
>
>http://www.amazon.com/Masione-Waterproof-1000-Lumen-Headlamp-Battery/dp/B005WPFVPC/ref=pd_sim_sbs_sg_1/192-3438671-9442951?ie=UTF8&refRID=1HG3MNSFBQ2EJ3NXQB12
>
>The Li-Ion battery packs are a bit wimpy and only provide 1-2h of juice
>but there are bigger ones:
>
>http://www.amazon.com/WindFire%C2%AE-11000mAh-Rechargeable-Replacement-Flashlight/dp/B00J4EC326/ref=pd_sbs_sg_6?ie=UTF8&refRID=19CGQWDKC5RNZVQKDKY7
>
>Here is my question. Li-Ion is very picky about charging. Go above 4.3V
>and there may be a need for the fire department to come out. These 8.4V
>packs contain two battery sets in series. Yet AFAICT there are only two
>wires in the cable. So how does the charging process get balanced? If
>they only rely on internal protection electronics which isn't 100%
>kosher then over time one side will get less and less charge because the
>other turns off earlier and allows no more current through the stack.
>

Any battery with a voltage higher than the value of a single cell
battery, of the same type, is, by necessity, a number of one cell
batteries in series. Your 4.3V batteries are, internally, three 1.4V
cells. If charging one 3 cell battery causes no problems then it is
likely that charging them 2 at a time should present very few
additional problems.

>Does anyone know? Can anyone share experiences about lifetime? Or about
>better and more sturdy mounting option for hard MTB use?
>
>I'd also like to tie in the rear light somehow plus possibly provide a
>homebrew voltage readout so I know how much juice is left for the
>remainder of a ride (most lights have no warning, for whatever reason).
>I guess that's only possible via a hack and splice.
>
>Please, no discussions about dynamo lights if you can help it. Those are
>simply too weak for my riding.
--

Cheers,

John B.

[somebody]

On Sat, 01 Nov 2014 17:34:05 -0700, Joerg <ne...@analogconsultants.com>
wrote:

>> You can get a USB-to-8.4 converter from dx.com and charge it using a
>> normal 5 volt supply. I have one and it cost < $3.
>>
>
>I don't need USB because the bikes stay in the garage. Well, at least
>since I am married they do :-)

I bring the pack into the cube at work to top off the charge. Just
because I can.

>
>
>> Slightly off topic: Many of the newer Chinese lights run from 4.2
>> volts. I have one that uses 4 18650's in parallel. Much cheaper to
>> build and simpler charging.
>>
>
>Newer ones? I looked at some 4.2V solutions but it seems they are going
>out of style. It sure would be simpler and I could easier splice in a
>Portland 1/2W rear light that normally takes two AAs. The downside is
>that when the Li-Ion is down to 3.5V or so the converter in the light
>would need to draw around 3.5 amps to get it to run at full brightness.
>That's a bit much for the cable and causes voltage drop.
>
>Amazon doesn't seem to have many 4.2V lights anymore.

Both lights came from dx.com. I avoided the really cheap and really
expensive ones. Both worked out OK. The 8.4 volt pack runs a tail
light now.

>
>It would be nice to have something that can put at least a little charge
>back into a Li-Ion and a hub dynamo at a good speed could deliver 5W.
>For example by switching to a very low power mode or strobe when the
>charge level becomes iffy. But neither my road bike nor my MTB has that.
>A roller dynamo would be nice because it can (sometimes) be retrofitted
>without a major wheel rebuild.

It would be nice to try a hub dyno just to see it in action. Think of
it as a bucket list item.

[Joerg]

John B. Slocomb wrote:
> On Sat, 01 Nov 2014 11:39:11 -0700, Joerg <ne...@analogconsultants.com>
> wrote:
>
>> Folks,
>>
>> Probably most of you know these kinds of lights:
>>
>> http://www.amazon.com/Masione-Waterproof-1000-Lumen-Headlamp-Battery/dp/B005WPFVPC/ref=pd_sim_sbs_sg_1/192-3438671-9442951?ie=UTF8&refRID=1HG3MNSFBQ2EJ3NXQB12
>>
>> The Li-Ion battery packs are a bit wimpy and only provide 1-2h of juice
>> but there are bigger ones:
>>
>> http://www.amazon.com/WindFire%C2%AE-11000mAh-Rechargeable-Replacement-Flashlight/dp/B00J4EC326/ref=pd_sbs_sg_6?ie=UTF8&refRID=19CGQWDKC5RNZVQKDKY7
>>
>> Here is my question. Li-Ion is very picky about charging. Go above 4.3V
>> and there may be a need for the fire department to come out. These 8.4V
>> packs contain two battery sets in series. Yet AFAICT there are only two
>> wires in the cable. So how does the charging process get balanced? If
>> they only rely on internal protection electronics which isn't 100%
>> kosher then over time one side will get less and less charge because the
>> other turns off earlier and allows no more current through the stack.
>>
>
> Any battery with a voltage higher than the value of a single cell
> battery, of the same type, is, by necessity, a number of one cell
> batteries in series. Your 4.3V batteries are, internally, three 1.4V
> cells. If charging one 3 cell battery causes no problems then it is
> likely that charging them 2 at a time should present very few
> additional problems.
>

Not quite. A single Li-Ion cell has a full-charge voltage of 4.2V. Those
8.4V batteries are a series combination of either two single Li-Ion
cells or of two bundles of two or more each.

This ain't you grandpa's NiCd stuff no more :-)

[...]

[Joerg]

Jeff Liebermann wrote:
> On Sat, 01 Nov 2014 17:34:05 -0700, Joerg <ne...@analogconsultants.com>
> wrote:
>
>> Amazon doesn't seem to have many 4.2V lights anymore.
>
> Search Amazon, eBay, and DX.com for "18650 bicycle light". You should
> find plenty. Amazon shows 2,629 hits of which 615 are bicycle
> headlight specific.
>

Sure, but generally that's 8.4V lights these days AFAICS.

> You need one of these. 4200 lumens:
> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>

Amazing! I didn't want to illuminate a stadium though and this could
leave a major gash when turfing the MTB,

[Joerg]

somebody wrote:
> On Sat, 01 Nov 2014 17:34:05 -0700, Joerg <ne...@analogconsultants.com>
> wrote:
>
>
>>> You can get a USB-to-8.4 converter from dx.com and charge it using a
>>> normal 5 volt supply. I have one and it cost < $3.
>>>
>> I don't need USB because the bikes stay in the garage. Well, at least
>> since I am married they do :-)
>
> I bring the pack into the cube at work to top off the charge. Just
> because I can.
>
>>
>>> Slightly off topic: Many of the newer Chinese lights run from 4.2
>>> volts. I have one that uses 4 18650's in parallel. Much cheaper to
>>> build and simpler charging.
>>>
>> Newer ones? I looked at some 4.2V solutions but it seems they are going
>> out of style. It sure would be simpler and I could easier splice in a
>> Portland 1/2W rear light that normally takes two AAs. The downside is
>> that when the Li-Ion is down to 3.5V or so the converter in the light
>> would need to draw around 3.5 amps to get it to run at full brightness.
>> That's a bit much for the cable and causes voltage drop.
>>
>> Amazon doesn't seem to have many 4.2V lights anymore.
>
> Both lights came from dx.com. I avoided the really cheap and really
> expensive ones. Both worked out OK. The 8.4 volt pack runs a tail
> light now.
>

If those are around 1000 lumesn or more, which ones at dx.com? Prices
for head lights seem to be higher there than Amazon.

>
>> It would be nice to have something that can put at least a little charge
>> back into a Li-Ion and a hub dynamo at a good speed could deliver 5W.
>> For example by switching to a very low power mode or strobe when the
>> charge level becomes iffy. But neither my road bike nor my MTB has that.
>> A roller dynamo would be nice because it can (sometimes) be retrofitted
>> without a major wheel rebuild.
>
> It would be nice to try a hub dyno just to see it in action. Think of
> it as a bucket list item.

Not really. A hub dynamo is a major change on a bike. It has to have
disc brake mounts which puts it into the >$100 category. Then new
spokes, wheel asembly. The latter I don't want to really do myself
anymore so that's going to cost as well.

[Frank Krygowski]

On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>
> You need one of these. 4200 lumens:
> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>

Is that all?



--
- Frank Krygowski

[Ralph Barone]

Joerg, I'm running rim brakes with my hub Dynamo.

[Joerg]

Ralph Barone wrote:
> Joerg <ne...@analogconsultants.com> wrote:
>> somebody wrote:
>>> On Sat, 01 Nov 2014 17:34:05 -0700, Joerg <ne...@analogconsultants.com>
>>> wrote:

[..]

>>>> It would be nice to have something that can put at least a little charge
>>>> back into a Li-Ion and a hub dynamo at a good speed could deliver 5W.
>>>> For example by switching to a very low power mode or strobe when the
>>>> charge level becomes iffy. But neither my road bike nor my MTB has that.
>>>> A roller dynamo would be nice because it can (sometimes) be retrofitted
>>>> without a major wheel rebuild.
>>> It would be nice to try a hub dyno just to see it in action. Think of
>>> it as a bucket list item.
>>
>> Not really. A hub dynamo is a major change on a bike. It has to have
>> disc brake mounts which puts it into the >$100 category. Then new
>> spokes, wheel asembly. The latter I don't want to really do myself
>> anymore so that's going to cost as well.
>
>
> Joerg, I'm running rim brakes with my hub Dynamo.

That would get you into serious "Oh dang!" situations out here. My old
MTB has rim brakes and I quickly learned that I don't want those. Plus
the rims wear down really fast.

Even 6" discs up front are marginal, has to be at least 7" for even some
of the local trails.

[Ralph Barone]

Just saying that Hub dynos and disk brakes don't always have to go
together. Luckily, Hub dynos come in both flavours.

[Joerg]

Yes, but the disc flavor commands a three digit investment. A bit much.
Batteries are more economical.

[sms]

On 11/2/2014 7:03 AM, Joerg wrote:

> Not really. A hub dynamo is a major change on a bike. It has to have
> disc brake mounts which puts it into the >$100 category. Then new
> spokes, wheel asembly. The latter I don't want to really do myself
> anymore so that's going to cost as well.

A dynamo makes little sense on a mountain bike no matter the price.

As I pointed out, suitable dynamo wheels for commute bicycles are
available for a pretty reasonable price. Decent rims and a decent hub
dyno, though probably not for randonneuring where you'd want high-end stuff.

[Joerg]

sms wrote:
> On 11/2/2014 7:03 AM, Joerg wrote:
>
>> Not really. A hub dynamo is a major change on a bike. It has to have
>> disc brake mounts which puts it into the >$100 category. Then new
>> spokes, wheel asembly. The latter I don't want to really do myself
>> anymore so that's going to cost as well.
>
> A dynamo makes little sense on a mountain bike no matter the price.
>

It does if you use the MTB for longer trips. Except for errands and
commutes which are around an hour mine are mostly 3-5h, much of it in
the dark or where I prefer to ride with lights. That's something a
battery cannot stomach without at least some recharging.

[...]

[Jeff Liebermann]

9600 lumens and climbing:
<http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
There are flashlights with more lumens, but this is the highest rating
claimed for a bicycle head light.

I was a somewhat off on my previous power consumption estimate. I
would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
for this head light. At 5 watts per bottle dynamo, it would take at
least 8 bottle dynamos to power it.

[sms]

On 11/2/2014 10:21 AM, Jeff Liebermann wrote:
> On Sun, 02 Nov 2014 10:13:47 -0500, Frank Krygowski
> <frkr...@sbcglobal.net> wrote:
>
>> On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>>>
>>> You need one of these. 4200 lumens:
>>> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>>
>> Is that all?
>
> 9600 lumens and climbing:
> <http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
> There are flashlights with more lumens, but this is the highest rating
> claimed for a bicycle head light.
>
> I was a somewhat off on my previous power consumption estimate. I
> would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
> for this head light. At 5 watts per bottle dynamo, it would take at
> least 8 bottle dynamos to power it.

Love this part of the specs: "Modes: Week, Strong and Strobe"

[Jeff Liebermann]

On Sun, 02 Nov 2014 06:49:39 -0800, Joerg <ne...@analogconsultants.com>
wrote:

>Not quite. A single Li-Ion cell has a full-charge voltage of 4.2V. Those
>8.4V batteries are a series combination of either two single Li-Ion
>cells or of two bundles of two or more each.

While the maximum terminal voltage of a LiIon battery is about 4.2V,
it rapidly drops to 3.9v under load. See graph at:
<http://802.11junk.com/jeffl/LiPo/Ultrafire%20LiPo%203000%20ma-hr%2018650.jpg>
I use 3.7v average voltage for calculations.

8.4v is certainly two LiIon batteries in series.
11.1V (3 cells) is easier to work with as 12v components are common
and copper losses are less.

>This ain't you grandpa's NiCd stuff no more :-)

Using NiCd's can have "memory effect" problems. I have the problem
and am trying to forget everything I know about NiCd's.

[James]

On 03/11/14 02:44, Joerg wrote:

> Ralph Barone wrote:

>>
>> Joerg, I'm running rim brakes with my hub Dynamo.
>
>
> That would get you into serious "Oh dang!" situations out here. My old
> MTB has rim brakes and I quickly learned that I don't want those. Plus
> the rims wear down really fast.
>
> Even 6" discs up front are marginal, has to be at least 7" for even some
> of the local trails.
>

Amazing that we are still alive today, having ridden all those lonely
mountainous goat tracks away from "cell" coverage and with only rim
brakes to stop us!

--
JS

[James]

On 03/11/14 04:00, Joerg wrote:
> Ralph Barone wrote:

>>

>> Just saying that Hub dynos and disk brakes don't always have to go
>> together. Luckily, Hub dynos come in both flavours.
>
>
> Yes, but the disc flavor commands a three digit investment. A bit much.
> Batteries are more economical.
>

So what is the price and MTBF of each battery?

--
JS

[James]

On 03/11/14 05:21, Jeff Liebermann wrote:
> On Sun, 02 Nov 2014 10:13:47 -0500, Frank Krygowski
> <frkr...@sbcglobal.net> wrote:
>
>> On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>>>
>>> You need one of these. 4200 lumens:
>>> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>>
>> Is that all?
>
> 9600 lumens and climbing:
> <http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
> There are flashlights with more lumens, but this is the highest rating
> claimed for a bicycle head light.
>
> I was a somewhat off on my previous power consumption estimate. I
> would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
> for this head light. At 5 watts per bottle dynamo, it would take at
> least 8 bottle dynamos to power it.
>
>

... @ something like 25 km/h.

http://www.myra-simon.com/bike/dynotest.html

"It's worth noting that dynamo lighting is optimised for the mass of
ordinary utility riders and made to pass German standards - which demand
that a generator reaches 95% of its rated output by 15km/h (a mere 9mph)."

40W @ 0.5A requires 20V. That's about three and a half times minimum
rating for one dynamo, so one dynamo could provide that power at about
three and a half times minimum operating speed for 3W - or 52.5km/h.

I'd say between 55km/h and 60km/h. Doable at downhill speeds!

--
JS

[Ralph Barone]

Jeff Liebermann <je...@cruzio.com> wrote:
> On Sun, 02 Nov 2014 10:13:47 -0500, Frank Krygowski
> <frkr...@sbcglobal.net> wrote:
>
>> On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>>>
>>> You need one of these. 4200 lumens:
>>> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>>
>> Is that all?
>
> 9600 lumens and climbing:
> <http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
> There are flashlights with more lumens, but this is the highest rating
> claimed for a bicycle head light.
>
> I was a somewhat off on my previous power consumption estimate. I
> would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
> for this head light. At 5 watts per bottle dynamo, it would take at
> least 8 bottle dynamos to power it.
>

Somewhat OT, but the business end of that light would work great with a
dynamo. Rewire the LEDs as four series groups of two anti parallel LEDs,
then add a minimum amount of electronics to selectively short more pairs as
the dynamo frequency drops (or unshort them as the frequency rises...). If
you can them fudge the reflector assembly to get tighter focus on the LEDs
that are enabled at higher speeds, even better.

[Jeff Liebermann]

On Mon, 03 Nov 2014 08:31:17 +1100, James <james.e...@gmail.com>
wrote:

>On 03/11/14 05:21, Jeff Liebermann wrote:
>> On Sun, 02 Nov 2014 10:13:47 -0500, Frank Krygowski
>> <frkr...@sbcglobal.net> wrote:
>>
>>> On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>>>>
>>>> You need one of these. 4200 lumens:
>>>> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>>>
>>> Is that all?
>>
>> 9600 lumens and climbing:
>> <http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
>> There are flashlights with more lumens, but this is the highest rating
>> claimed for a bicycle head light.
>>
>> I was a somewhat off on my previous power consumption estimate. I
>> would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
>> for this head light. At 5 watts per bottle dynamo, it would take at
>> least 8 bottle dynamos to power it.

>... @ something like 25 km/h.
>http://www.myra-simon.com/bike/dynotest.html

The highest output on the power graph shows 4.5 watts at 40 km/hr. The
5 watts required ignores losses in the current source that drives the
LED's. Assuming 90% efficiency, the power requirement would be:
5w / 0.90 = 5.56 watts

I'll randomly decide that the best operating point is near the "knee"
of the dynamo curves in the aforementioned URL or about 20 km/hr. At
that speed, the average output seems to be about 3.3w. Therefore, to
power this lamp, it would require:
5.56w * 8 LEDs / 3.3w = 13.4 -> 14 dynamos.

Maybe power it with one of these?
<http://www.wired.com/2011/06/tiny-rotary-engines-could-power-gadgets-with-gasoline/>

>"It's worth noting that dynamo lighting is optimised for the mass of
>ordinary utility riders and made to pass German standards - which demand
>that a generator reaches 95% of its rated output by 15km/h (a mere 9mph)."

Thanks. That explains how the "knee" on the curve was specified. If
the curve didn't level off at 100% of output (thanks to core
saturation), and the curve just kept increasing linearly, the dynamo
could easily produce hazardous voltages (i.e. over 50v) and require
enough input pedal power to make it feel like riding an exercise
machine.

>40W @ 0.5A requires 20V. That's about three and a half times minimum
>rating for one dynamo, so one dynamo could provide that power at about
>three and a half times minimum operating speed for 3W - or 52.5km/h.
>
>I'd say between 55km/h and 60km/h. Doable at downhill speeds!

Ok, but I have a minor objection. These days, the voltage or current
doesn't really count. DC to DC converters and boost/buck switching
regulators make the actual input voltage somewhat irrelevant since
these converters can produce whatever output is necessary. For LED
lighting, the output is a constant current source at whatever number
of amps is needed. What is important are the number of watts needed
to light the LEDs, switcher efficiency, and the number of watts of
input power available. According to Wikipedia and "Bicycling Science
3rd Edition", the average rider will need to deliver around 200 watts.
The 3 to 5 watts to run a conventional dynamo would probably never be
notices. The 45 watts to run this light probably will be a drag (pun
intended).

Of course, with multiple LED's it is possible to run each LED
individually. So, visualize a headlight that sets the number of LEDs
that are lit by the speed. At a crawl, only one LED is on. When
going downhill at suicidal speeds, all 8 LEDs are on. Yet another
feature for a TUBA (The Ultimate Bicycle Accessory).

[Frank Krygowski]

On 11/2/2014 12:38 PM, sms wrote:
>
> A dynamo makes little sense on a mountain bike no matter the price.

Just a few years ago, SMS was saying the same thing about all bikes -
that one couldn't be safe with a dynamo light, at least in America,
where things were so very different from Amsterdam.

Then he began telling us about the dynamos he'd installed on his
family's bikes. In America.

--
- Frank Krygowski

[John B. Slocomb]

On Sun, 02 Nov 2014 06:49:39 -0800, Joerg <ne...@analogconsultants.com>
wrote:

Ok. But the point remains that you are charging a battery that is
composed of more than one cell, regardless of whether it is two,
three, four, or ten.

If, as I said, charging one multi cell battery causes no problems then

it is likely that charging them 2 at a time should present very few
additional problems.

--
Cheers,

John B.

[James]

On 03/11/14 11:21, Jeff Liebermann wrote:
> On Mon, 03 Nov 2014 08:31:17 +1100, James <james.e...@gmail.com>
> wrote:
>
>> On 03/11/14 05:21, Jeff Liebermann wrote:
>>> On Sun, 02 Nov 2014 10:13:47 -0500, Frank Krygowski
>>> <frkr...@sbcglobal.net> wrote:
>>>
>>>> On 11/1/2014 11:51 PM, Jeff Liebermann wrote:
>>>>>
>>>>> You need one of these. 4200 lumens:
>>>>> <http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>>>>
>>>> Is that all?
>>>
>>> 9600 lumens and climbing:
>>> <http://www.amazon.com/Totoab-Bicycle-9600lumen-9600mAh-Battery/dp/B00ORO72U6/>
>>> There are flashlights with more lumens, but this is the highest rating
>>> claimed for a bicycle head light.
>>>
>>> I was a somewhat off on my previous power consumption estimate. I
>>> would guess(tm) about 5 watts per LED. With 8 LED's, that is 40 watts
>>> for this head light. At 5 watts per bottle dynamo, it would take at
>>> least 8 bottle dynamos to power it.
>
>> ... @ something like 25 km/h.
>> http://www.myra-simon.com/bike/dynotest.html
>
> The highest output on the power graph shows 4.5 watts at 40 km/hr.

http://www.jim-easterbrook.me.uk/cycling/dynamo_limiter.html

"It has been suggested that you can get more power from a dynamo by
using 12V 6W bulbs instead of 6V 3W. This gives a load resistance of
24Ω. Full power will be reached at 17mph, at 30mph the power will be
7.7W (28% overload)."

By doubling the load resistance (effectively more LEDs in series) , the
dynamo can produce double the power quite easily.

--
JS

[James]

On 03/11/14 11:35, Phil W Lee wrote:
> James <james.e...@gmail.com> considered Mon, 03 Nov 2014 08:31:17

> I think you may want to check those figures.
> 40 watts @ 0.5 amps needs 80 volts.
>
> If you could even get that out of a single dynamo, you might have to
> be a bit careful with insulation.
>

From my old and inefficient roller dynamo, I quite easily got over
50VAC with an open circuit.

With a 40ohm load and a lot less speed I got 20VAC, which is 10W.

I suspect that with a well designed dynamo, it would be possible - but
you're right, 80V is getting a bit much without good insulation. Well
above the low voltage directive.

Dynamo's are dangerous! DANGER! DANGER!

--
JS

[klaus.m...@googlemail.com]

Sat, 01 Nov 2014 20:51:34 -0700, Jeff Liebermann:

>You need one of these. 4200 lumens:
><http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>

Why would someone buy from a company which is obviously lying? They claim to use a battery with 8.4V and 7800mAh resulting in 65.5 Wh. They claim 4 hours run time which results in impressive 16.4 Watt electrcal power. If the electronics is 100% efficient this will mean 255 lm/W. This is twice as much what might be possible with the most expensive parts...

[sms]

The four hour claim did not indicate which power level.

The battery pack is probably about 55WH (2500mAH/cell * 3.7V * 6 cells).
They really should not claim and 8.4V battery. That's the voltage at end
of charge but the actual voltage is 3.7V.

At 100 lumens per watt it would run for around two hours at low power.
At 200 lumens per watt it would run for about four hours at low power.

I doubt if a sub-$100 light is using the latest 200 lm/watt LEDs.

[Jeff Liebermann]

On Mon, 3 Nov 2014 08:24:27 -0800 (PST), klaus.m...@googlemail.com
wrote:

>Sat, 01 Nov 2014 20:51:34 -0700, Jeff Liebermann:
>
>>You need one of these. 4200 lumens:
>><http://www.amazon.com/SecurityIng%C2%AE-Waterproof-Temperature-Headlight-Rechargeable/dp/B00K7SRZ4Y>
>
>Why would someone buy from a company which is obviously lying?

Price. Buying a similar product from an honest company, that can
demonstrate their testing methodology and test results, is often many
times as expensive.

>They claim to use a battery with 8.4V and 7800mAh resulting in 65.5 Wh.
>They claim 4 hours run time which results in impressive 16.4 Watt
>electrcal power. If the electronics is 100% efficient this will mean
>255 lm/W. This is twice as much what might be possible with the most
>expensive parts...

Yep. Typically, such lights lie about the total light output (lumens)
and battery capacity (ma-hrs). In self defense, buyers might be
expected to make some sanity check calculations, as you have done. Few
will do it, but the option exists.

For example, the common 18650 LiIon battery is usually rated at 0.2C
discharge rate, which results in large ma-hr capacity values. However,
that's not where the headlight operates. When tested at the current
drain of a typical LED light, the numbers are not so impressive. For
example, I ran a discharge test on an Ultrafire 3000 ma-hr battery at
1.3A:
<http://802.11junk.com/jeffl/LiPo/Ultrafire%20LiPo%203000%20ma-hr%2018650%20test.jpg>
Instead of 3000 ma-hr, I got about 800 ma-hr. Assuming the
Securitylng from Amazon head light used a similar cell, the 7800 ma-hr
battery pack becomes a 2080 ma-hr battery pack.

Note that the average battery voltage on my graph is more like 3.7v
than 4.2v making it a:
3.7v * 2cells * 2.08A-hr = 15.4 watt-hrs
battery pack instead of 65.5 watt-hrs.

Lumens is another inflated claim, mostly because few people have the
integrating sphere and photometry equipment needed to accurately
measure lumens[1]. I contrived a crude scheme using a lux meter, tape
measure, and ruler to measure the spot diameter, which gets the lumens
numbers in the ballpark, but nobody in this newsgroups seemed
interested in pursuing it. I can't seem to find my test results right
now, but as I recall, the few name brand flashlights and bicycle
headlights I tried were fairly close but the 500 lumen Amazon
flashlight was overstated by a factor of three.

I'm not sure what can be done to fix this problem. Government "truth
in bicycle headlight labeling" rules will probably become a
bureaucratic mess and only increase costs. What I was thinking is
selling a fairly simple wall hanging, with a built in lux meter. Set
the bicycle headlight at a known distance from the lux meter and
measure the spot diameter and brightness. Then, calculate the lumens.
This won't produce an accurate value, but will probably produce
numbers no worse than a +/-50% range which will help reduce the +300%
claims. (Yet another project.)



[1] Do it thyself integrating sphere:
<http://budgetlightforum.com/node/1763>
<http://sites.biology.duke.edu/johnsenlab/pdfs/tech/improvintegspheredesign.pdf>
<http://www.candlepowerforums.com/vb/showthread.php?200334-Building-an-Integrating-Sphere>
<http://www.edmundoptics.com/testing-targets/spectrometers/general-purpose-integrating-spheres/2697>

[sms]

It's six cells, not two cells for that light on Amazon. But I questions
the actual capacity of the cells that they are including.

Despite the inconsistencies in the specs, there are some positives about
that light. Rather than cram all the LEDs into one lamp housing, with
all the thermal issues that causes, they are spreading the heat out.

Their exaggerations of lumens and run time is probably no worse than
most other vendors.

[Joerg]

Around $15. If you don't torture the battery it can deliver several
hundred charge-discharge cycles. So an average ride would get several
years. Also, it is not that it suddenly fails completely but the
capacity starts to sag. If you select a battery with a lot of margin
that will typically tack on useful lifetime for your application.

Example: I have a Li-Ion battery in a netbook that is now over five
years old and I still get around 8h of operation out of it.

But as I said the main thing for me is that a hub dynamo cannot drive a
10W LED plus 1-2W rear light. It would only be useful for recharging
purposes.

[Joerg]

Have you ever done really serious mountain biking with nasty long
downhill sections?

Why do you think disc brakes (finally!) made it into the world of
cycling? Why do you think they were introduced much earlier on cars and
motorcycles?

[Joerg]

Well, that was my question and the whole reason for this thread. The
4.2V packs are single cell paralleled so they cannot have a chrge
distribution issue. 8.4V is not single cell and normally would need
charge balancing just like 3,4,5 ... cells in sries would need.

[Jeff Liebermann]

On Mon, 03 Nov 2014 11:16:43 -0800, sms <scharf...@geemail.com>
wrote:

>> Note that the average battery voltage on my graph is more like 3.7v
>> than 4.2v making it a:
>> 3.7v * 2cells * 2.08A-hr = 15.4 watt-hrs
>> battery pack instead of 65.5 watt-hrs.

>It's six cells, not two cells for that light on Amazon. But I questions
>the actual capacity of the cells that they are including.

Oops and thanks. Last minute math before running out the door without
double checking. That should be:
3.7v * 6cells * 2.08A-hr = 46.2 watt-hrs
that's still not 65.5 watt-hrs, but is getting closer.

>Despite the inconsistencies in the specs, there are some positives about
>that light. Rather than cram all the LEDs into one lamp housing, with
>all the thermal issues that causes, they are spreading the heat out.

Yep. Someone here also mentioned that distributing the light over a
larger source area tends to reduce glare when looking directly at the
light. I tried it with very large reflector from a hand held "10
million candlepower" lantern
<http://media.midwayusa.com/productimages/880x660/Primary/818/818559.jpg>
and it seemed to work. The total light output (lumens) is the same,
but the glare was much less.

>Their exaggerations of lumens and run time is probably no worse than
>most other vendors.

Everyone lies, but that's ok because nobody listens. How many retail
bicycle headlight buyers walk into a LBS with a light meter, lux
meter, integrating globe, or even a reference pocket flashlight? I
don't know the number, but suspect it would be approximately zero.
Trust, but verify.


Divertimento: I bought a multi color remote controlled LED to test
how my lux meter responds to different color LED's:
<http://www.ebay.com/itm/350973170093>
I expected the IR remote control to have a separate sensor that would
not be affected by the light from the LEDs. Nope. It uses the LED's
as detectors for the IR remote control using the same method that I
proposed to sense oncoming auto headlights. Turn off the light output
for a few msec a few times per second, and test for remote IR data
during those off intervals. Nice.

[Jeff Liebermann]

On Mon, 03 Nov 2014 12:05:31 +1100, James <james.e...@gmail.com>
wrote:

>http://www.jim-easterbrook.me.uk/cycling/dynamo_limiter.html
>
>"It has been suggested that you can get more power from a dynamo by
>using 12V 6W bulbs instead of 6V 3W. This gives a load resistance of

>24?. Full power will be reached at 17mph, at 30mph the power will be
>7.7W (28% overload)."

Quite true. What limits the dynamo output is the *CURRENT* through
the windings saturating the core and not producing any more output.
The increase in inductive reactance at higher rotation frequencies
also plays a part, but not in this discussion. By cutting the current
in half, the dynamo is now operating below core saturation, and
therefore allowed to produce more voltage.

>By doubling the load resistance (effectively more LEDs in series) , the
>dynamo can produce double the power quite easily.

Almost, but not quite. If you ignore the effects of the series
inductive reactance, that would probably be true. However, to produce
those higher voltages, one must spin the dynamo faster, which produces
higher frequencies, which results in higher inductive reactances,
which in this series AC circuit, will result in lower current. Exactly
how much less is going to take some more math, or a SPICE model of the
dynamo and load.

A few months ago I found a SPICE model of a bicycle dynamo:
<http://www.electronics-related.com/sci.electronics.design/thread/304923/bicycle-hub-dynamo-subcircuit.php>
<http://www.candlepowerforums.com/vb/showthread.php?355392-Spice-code-for-dynamo-output>
My problem is that I can't seem to work out the fairly simple
transmogrification of the PSPICE model to LTSPICE. Asking for
assistance is beneath my rapidly eroding dignity. Howver, if and
LTSPCIE dynamo model should magically appear, I should be able to see
exactly what happens with different loads, including non-linear LED
loads. It would also be of interest to see how closely the model
matches the various dynamo bench tests.

Sigh. Yet another project.

[Joe Riel]

I've created a model of a hub generator using Modelica. It's mainly
theoretical, it models the various magnetic components. The handling of
the magnetic commutating is interesting but I have doubts as to how
realistic it is. While I have a good understanding of how the device
works, I lack details (i.e. magnetic materials, gaps, turns in coil,
etc). As such, the model is of less use than it could be.

--
Joe Riel

[Jeff Liebermann]

On Mon, 03 Nov 2014 17:04:08 -0800, Joe Riel <jo...@san.rr.com> wrote:

>I've created a model of a hub generator using Modelica. It's mainly
>theoretical, it models the various magnetic components. The handling of
>the magnetic commutating is interesting but I have doubts as to how
>realistic it is. While I have a good understanding of how the device
>works, I lack details (i.e. magnetic materials, gaps, turns in coil,
>etc). As such, the model is of less use than it could be.

<https://openmodelica.org>
Modelica looks like it would be very useful for designing a new dynamo
or optimizing the performance of existing dynamos. My ambition level
is limited to the electrical characteristics.

Fortunately, the electrical model is quite simple. It's just a series
circuit consisting of a variable frequency and variable amplitude AC
voltage source, a constant series resistance, and a non-linear series
inductance. I don't believe that LTSPICE will do anything for
modeling input power (or energy) and will probably require tweaking
the components to fit the test data and graphs. I'll eventually get
it done, but only after a few other projects are finished.

[James]

On 04/11/14 07:12, Joerg wrote:
> James wrote:
>> On 03/11/14 02:44, Joerg wrote:
>>> Ralph Barone wrote:
>>
>>>>
>>>> Joerg, I'm running rim brakes with my hub Dynamo.
>>>
>>>
>>> That would get you into serious "Oh dang!" situations out here. My old
>>> MTB has rim brakes and I quickly learned that I don't want those. Plus
>>> the rims wear down really fast.
>>>
>>> Even 6" discs up front are marginal, has to be at least 7" for even some
>>> of the local trails.
>>>
>>
>>
>> Amazing that we are still alive today, having ridden all those lonely
>> mountainous goat tracks away from "cell" coverage and with only rim
>> brakes to stop us!
>>
>
> Have you ever done really serious mountain biking with nasty long
> downhill sections?
>

How long is long, and how serious is serious?

> Why do you think disc brakes (finally!) made it into the world of
> cycling?

Better control/modulation, and no wear on the rim.

> Why do you think they were introduced much earlier on cars and
> motorcycles?
>

Weight.

Rim brakes work fine for most people. I only recently bought a MTB with
disc brakes and suspension forks. It works too.

--
JS

[James]

The model in the link I provided is most adequate.

--
JS

[Andre Jute]

On Monday, November 3, 2014 12:37:59 AM UTC, Frank Krygowski wrote:
> On 11/2/2014 12:38 PM, sms wrote:

> Just a few years ago, SMS was saying the same thing about all bikes -
> that one couldn't be safe with a dynamo light, at least in America,
> where things were so very different from Amsterdam.

You really have a railroad mind, Franki-boy, and now you're applying willfully selective memory loss to Scharfie as well. Scharfie was right *when he said that* because the available dynamo lamps were crappy halogens that came on late and glimmered low. Unlike you, I remember it distinctly. You and George Clive and that mercenary clown Andreas Oehler abused my for saying that the SON/BUMM setup on my bike, then the best available, was utter, dangerous crap. It was only when the IQ series (Fly/Cyo) became available that matters improved from lethal to barely acceptable.

You growing senile if you cannot remember what happened a handful of years ago.

> Then he began telling us about the dynamos he'd installed on his
> family's bikes. In America.

Sure. Scharfie moved with the times, fitted the better available equipment when it became available at a price he wanted to pay. You didn't. You, Frank Krygowski, got stuck in your "danger, danger" obsession and started sounding like old shellac record stuck in a groove under a bad needle.

Scharfie may be a careless asshole, as some think, but that doesn't make him automatically wrong whatever he says, as that idiot Krygowski tries to pretend. Far too much of RBT is about personalities rather than principles, and it makes the tech content unreliable.

Andre Jute

[Andre Jute]

On Sunday, November 2, 2014 5:48:25 PM UTC, Joerg wrote:
> sms wrote:
> > On 11/2/2014 7:03 AM, Joerg wrote:
> >
> >> Not really. A hub dynamo is a major change on a bike. It has to have
> >> disc brake mounts which puts it into the >$100 category. Then new
> >> spokes, wheel asembly. The latter I don't want to really do myself
> >> anymore so that's going to cost as well.

> >
> > A dynamo makes little sense on a mountain bike no matter the price.
> >
>

> It does if you use the MTB for longer trips. Except for errands and
> commutes which are around an hour mine are mostly 3-5h, much of it in
> the dark or where I prefer to ride with lights. That's something a
> battery cannot stomach without at least some recharging.
>
> [...]

>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/

I don't think you'll get enough of a charge out of a hub dynamo to run the lamps long enough to consider the weight and the cost worthwhile. The guys who have the most experience of these hub-dynamo-USB-(buffer)-battery charge schemes are the long-range tourers for their comms, and their early enthusiasm appears to be tempering down to cautious hope. But it seems to me that even if the losses in the chain are overnight reduced to more reasonable proportions (and how likely could that be, considerting the engineering and research attention lavished on electrics for so long now?), a 3W charging device will have to work a very long time on the level to charge a satisfactory downhill lamp. Effectively you're waiting for another quantum jump in low-consumption high-out LEDs.

Andre Jute

[Rolf Mantel]

Am 04.11.2014 09:32, schrieb James:
> On 04/11/14 07:12, Joerg wrote:

>> Why do you think they were introduced much earlier on cars and
>> motorcycles?
>
> Weight.

Heat dissipation. The old hub brakes were unable to dissipate the heat
of repeated braking from high speed and prevent brake fading (that's why
cars before the advent of disc brakes needed to go downhill in low
gear). Disc brakes make it easier to increase the surface size
necessary (just apply double discs and increase the disc size).

[somebody]

On Mon, 3 Nov 2014 08:24:27 -0800 (PST), klaus.m...@googlemail.com
wrote:

They all lie. Look up "Chinese lumens" sometime...

The big thing to watch for is outright fraud - recycled used laptop
batteries and small batteries padded out to a larger size. For normal
packs I expect mediocre 18650's with capacity exaggerated by 20-50%.
They still work OK.

For more info head to:
http://www.candlepowerforums.com/vb/forumdisplay.php?9-Flashlight-Electronics-Batteries-Included

[klaus.m...@googlemail.com]

Joerg:

> Example: I have a Li-Ion battery in a netbook that is now over five
> years old and I still get around 8h of operation out of it.

If you find a supplier with a serious guarrantee for the battery of your new bicycle headlamp - go for it.

> But as I said the main thing for me is that a hub dynamo cannot drive a
> 10W LED plus 1-2W rear light. It would only be useful for recharging
> purposes.

What kind of "Watt" are you talking about: The estimated power from the creative numbers of chinese manufactures? A European steady rear lamp (battery or dynamo powered) with around 0.2 Watt measured power uptake is already blinding bright - a flasher should even consume less power. A setup combining a 3 Watt LED with oval beam shape and a helmet lamp with a tight focus from a 2 Watt LED should be more than sufficient - if you are willing to build it yourself.

And - 6 Watt are easy to get from a hub dynamo.

[Joerg]

James wrote:
> On 04/11/14 07:12, Joerg wrote:
>> James wrote:
>>> On 03/11/14 02:44, Joerg wrote:
>>>> Ralph Barone wrote:
>>>
>>>>>
>>>>> Joerg, I'm running rim brakes with my hub Dynamo.
>>>>
>>>>
>>>> That would get you into serious "Oh dang!" situations out here. My old
>>>> MTB has rim brakes and I quickly learned that I don't want those. Plus
>>>> the rims wear down really fast.
>>>>
>>>> Even 6" discs up front are marginal, has to be at least 7" for even
>>>> some
>>>> of the local trails.
>>>>
>>>
>>>
>>> Amazing that we are still alive today, having ridden all those lonely
>>> mountainous goat tracks away from "cell" coverage and with only rim
>>> brakes to stop us!
>>>
>>
>> Have you ever done really serious mountain biking with nasty long
>> downhill sections?
>>
>
> How long is long, and how serious is serious?
>

1/2 mile or more, with large rocks strewn around and switchbacks.

>> Why do you think disc brakes (finally!) made it into the world of
>> cycling?
>
> Better control/modulation, and no wear on the rim.
>

Exactamente. One rider in our family had a rim blow-out
(disintegration). Luckily it was the rear wheel, else the consequences
would have been nasty.

It's also about heat. When you have to lean into the brakes for a longer
time the rim and then the tire will heat up more and more ... *KAPOOF*

>> Why do you think they were introduced much earlier on cars and
>> motorcycles?
>>
>
> Weight.
>

Nope. Mainly for performance.

> Rim brakes work fine for most people. I only recently bought a MTB with
> disc brakes and suspension forks. It works too.
>

An example out here is the American River South Fork Trail. It connects
Coloma and Lotus (California) with Folsom. If you head west there is a
long gnarly downhill parts before Salmon Falls Bridge. Going down there
with rim brakes at a serious clip would be close to a suicide mission.
But at least that area has cell service so the next rider could call the
rescue helicopter if you go over the cliff and miraculously survive.

[Joerg]

All I'd need is a roller dynamo to give me enough juice for a "limp
home" in case the battery prematurely exhausts. In flash mode a 10W Cree
can drop to less than 2W, that still allows safe passage at reduced
speeds on the roads.

[Joerg]

klaus.m...@googlemail.com wrote:
> Joerg:
>> Example: I have a Li-Ion battery in a netbook that is now over five
>> years old and I still get around 8h of operation out of it.
>
> If you find a supplier with a serious guarrantee for the battery of
> your new bicycle headlamp - go for it.
>

You can only try. It's all from China these days but most will swap out
an early-failure battery for free. Longterm I want to build my own battery.

>> But as I said the main thing for me is that a hub dynamo cannot
>> drive a 10W LED plus 1-2W rear light. It would only be useful for
>> recharging purposes.
>
> What kind of "Watt" are you talking about: The estimated power from
> the creative numbers of chinese manufactures? A European steady rear
> lamp (battery or dynamo powered) with around 0.2 Watt measured power
> uptake is already blinding bright - a flasher should even consume
> less power.

I have German rear lights on my road bike. Nothing "blindingly bright"
about that. I also rode a bike early September north of Frankfurt. The
light on the various bicycle didn't impress me much.


> ... A setup combining a 3 Watt LED with oval beam shape and a

> helmet lamp with a tight focus from a 2 Watt LED should be more than
> sufficient - if you are willing to build it yourself.
>

I will not mount anything on the helmet. That would be suicide on most
of the trails I use because branches will then snag you head. At
15-20mph that can break the neck.

> And - 6 Watt are easy to get from a hub dynamo.
>

Only at high speed and it is not enough for the light I want to use. Ok
for recharging though in case I run out of battery juice. But a bottle
dynamo cannot readily be affixed on a full suspension mountain bike.
Well, maybe I'll kludge something, the rear struts look suitable but are
rectangular.

[James]

And that, though drum brakes, for the same diameter, usually provide
more braking effort for the same pedal force, IIRC - which is a reason
trucks usually have drum brakes I believe.

But we were discussing rim brakes and disc brakes.

Rim brakes are disc brakes. The disc is the rim. Great cooling and due
to the diameter, little input force for excellent braking force.

--
JS

[James]

On 05/11/14 03:10, Joerg wrote:
> James wrote:
>> On 04/11/14 07:12, Joerg wrote:
>>> James wrote:
>>>> On 03/11/14 02:44, Joerg wrote:
>>>>> Ralph Barone wrote:
>>>>
>>>>>>
>>>>>> Joerg, I'm running rim brakes with my hub Dynamo.
>>>>>
>>>>>
>>>>> That would get you into serious "Oh dang!" situations out here. My old
>>>>> MTB has rim brakes and I quickly learned that I don't want those. Plus
>>>>> the rims wear down really fast.
>>>>>
>>>>> Even 6" discs up front are marginal, has to be at least 7" for even
>>>>> some
>>>>> of the local trails.
>>>>>
>>>>
>>>>
>>>> Amazing that we are still alive today, having ridden all those lonely
>>>> mountainous goat tracks away from "cell" coverage and with only rim
>>>> brakes to stop us!
>>>>
>>>
>>> Have you ever done really serious mountain biking with nasty long
>>> downhill sections?
>>>
>>
>> How long is long, and how serious is serious?
>>
>
> 1/2 mile or more, with large rocks strewn around and switchbacks.
>

That doesn't sound very serious. I just looked on Google maps at a
track I used to ride frequently with some high school mates. Over
1.3km, gravel, rock, roots and washouts, and some sections >30% gradient.

>
>>> Why do you think disc brakes (finally!) made it into the world of
>>> cycling?
>>
>> Better control/modulation, and no wear on the rim.
>>
>
> Exactamente. One rider in our family had a rim blow-out
> (disintegration). Luckily it was the rear wheel, else the consequences
> would have been nasty.
>
> It's also about heat. When you have to lean into the brakes for a longer
> time the rim and then the tire will heat up more and more ... *KAPOOF*
>
>

Rarely ever a problem. One rider in our family was Australian MTB cross
country champion several times. Punctures are normally pinch flats or
penetration from a sharp stick. The initial pressures are not normally
high enough to blow a tyre off the rim due to the rim heating the air
inside.

>>> Why do you think they were introduced much earlier on cars and
>>> motorcycles?
>>>
>>
>> Weight.
>>
>
> Nope. Mainly for performance.
>
>

No, disc brakes were not made a regular item on bicycles until recently
because they added weight and rim brakes performed well enough in most
circumstances.

>> Rim brakes work fine for most people. I only recently bought a MTB with
>> disc brakes and suspension forks. It works too.
>>
>
> An example out here is the American River South Fork Trail. It connects
> Coloma and Lotus (California) with Folsom. If you head west there is a
> long gnarly downhill parts before Salmon Falls Bridge. Going down there
> with rim brakes at a serious clip would be close to a suicide mission.
> But at least that area has cell service so the next rider could call the
> rescue helicopter if you go over the cliff and miraculously survive.
>

Easy. Don't out ride your equipment capabilities.

--
JS

[Lou Holtman]

Now disc brakes become available for roadbikes and fading and overheated
and warped disc are an issue TOUR magazine did a test on steep Alpes
descents similating hard and long braking with a heavy rider or some kind
of loaded bike and they came to the conclusion thar for now your best and
safest option are still good quality rimbrakes for that kind of situations.
--
Lou

[James]

Obviously more serious than Joerg's serious mountain bike routes!

--
JS

[Frank Krygowski]

On 11/4/2014 1:28 PM, Joerg wrote:
>
>
> I will not mount anything on the helmet. That would be suicide on most
> of the trails I use because branches will then snag you head. At
> 15-20mph that can break the neck.

:-)


--
- Frank Krygowski

[Frank Krygowski]

On 11/4/2014 11:10 AM, Joerg wrote:
> Going down there
> with rim brakes at a serious clip would be close to a suicide mission.
> But at least that area has cell service so the next rider could call the
> rescue helicopter if you go over the cliff and miraculously survive.

[James]

Yes riding at a serious clip through busy city streets with your hands
tied behind your back would be close to a suicide mission...

--
JS

[Frank Krygowski]

On 11/4/2014 4:56 PM, Lou Holtman wrote:
>
>
>
> Now disc brakes become available for roadbikes and fading and overheated
> and warped disc are an issue TOUR magazine did a test on steep Alpes
> descents similating hard and long braking with a heavy rider or some kind
> of loaded bike and they came to the conclusion thar for now your best and
> safest option are still good quality rimbrakes for that kind of situations.

Interesting. The only times I've really worried about braking has been
descending very long hills when loaded with camping gear.

I recall descending Lolo Pass in Idaho. The beginning is pretty
extreme, and and I consciously decided to go much faster than my wife
and daughter, so that air resistance would dissipate more of my bike's
energy. Their bikes carried much less load, and they were more cautious
than I was.

They had no problems using their brakes more heavily, although I have
seen a rider suffer a blowout just after descending a hill. It's been
pointed out that many riders limit their speed to about 30 mph (50 kph),
which happens to deliver roughly the maximum heat wattage to the rims.

Back when Jobst was contributing, we had some extensive discussions
about blowouts from braking heat.

--
- Frank Krygowski

[James]

Recently a mate inflated his road bike tyre with a CO2 canister in the
cool of morning, in a hurry to leave home after discovering a flat, only
to have it blow off the rim a couple of hours later while the bike was
leaning against a wall at a bakery.

--
JS

[Frank Krygowski]

On 11/4/2014 7:07 PM, James wrote:
>
>
> Recently a mate inflated his road bike tyre with a CO2 canister in the
> cool of morning, in a hurry to leave home after discovering a flat, only
> to have it blow off the rim a couple of hours later while the bike was
> leaning against a wall at a bakery.

I may have mentioned this, but a few weeks ago, I used the trailer frame
from my Bike Friday to knock together a kid trailer for my grandson. We
were going to visit for a couple days, so I took about an hour to fit up
some wood pieces to mount a child seat to the frame.

It worked well. But as I was doing other work up on the roof at their
house, I heard a loud BANG. One of the trailer tires, sitting in the
sun, had blown off the 12" plastic rim. Later, examining things in the
bright sunlight, I could see that the trailer tires called for 35 psi.
When I'd pumped them up in much dimmer light, I thought it said 85 psi.

--
- Frank Krygowski

[Joerg]

Had one today on the way home ... *THWOCK* ... the sun was blinding me
suddenly by reflecting in the sunglasses. Happens. With a camera it
might have snagged me. Without a helmet there would have been some blood.

[Joerg]

We've got those as well, for example near Folsom Lake (California). A
friend had a front brake fade out there despite a massive 8" disc up
front. That was a close call.

>>
>>>> Why do you think disc brakes (finally!) made it into the world of
>>>> cycling?
>>>
>>> Better control/modulation, and no wear on the rim.
>>>
>>
>> Exactamente. One rider in our family had a rim blow-out
>> (disintegration). Luckily it was the rear wheel, else the consequences
>> would have been nasty.
>>
>> It's also about heat. When you have to lean into the brakes for a longer
>> time the rim and then the tire will heat up more and more ... *KAPOOF*
>>
>>
>
> Rarely ever a problem.

A friend had it happen.


> ... One rider in our family was Australian MTB cross

> country champion several times. Punctures are normally pinch flats or
> penetration from a sharp stick. The initial pressures are not normally
> high enough to blow a tyre off the rim due to the rim heating the air
> inside.
>

I mostly ride 45psi. The limit for the tires is 55psi. But the rim wear
is the worst enemy. The front rim on my old MTB is about 50% worn down
after less than 1000 miles. Because we have decomposed granite out here
that tends to embed itself in the brake rubber pads during winter rides.

>>>> Why do you think they were introduced much earlier on cars and
>>>> motorcycles?
>>>>
>>>
>>> Weight.
>>>
>>
>> Nope. Mainly for performance.
>>
>>
>
> No, disc brakes were not made a regular item on bicycles until recently
> because they added weight and rim brakes performed well enough in most
> circumstances.
>

Sorry, not true. If you splash through a mud puddle and then there is a
steep switchback section right after that it can go seriously wrong. All
you hear initially is a horrid grinding noise, no braking, and it can
take 2-3 revolutions until the brake grabs. Discs work instantly (with a
freight train noise though).

>>> Rim brakes work fine for most people. I only recently bought a MTB with
>>> disc brakes and suspension forks. It works too.
>>>
>>
>> An example out here is the American River South Fork Trail. It connects
>> Coloma and Lotus (California) with Folsom. If you head west there is a
>> long gnarly downhill parts before Salmon Falls Bridge. Going down there
>> with rim brakes at a serious clip would be close to a suicide mission.
>> But at least that area has cell service so the next rider could call the
>> rescue helicopter if you go over the cliff and miraculously survive.
>>
>
> Easy. Don't out ride your equipment capabilities.
>

And that's exactly why I bought a new MTB with disc brakes. Because
there'd be too many trails I could not safely ride otherwise.

[Joe Riel]

At one point I had computed, and posted here, a computation of the
descending speed that would generate the maximum wheel temperature (in
addition to braking power, it considered the velocity-dependent
convection cooling of the rim). Jobst was working with someone to build
a device that mounted inside the tire and would record air temperature.


--
Joe Riel

[Joe Riel]

Joerg <ne...@analogconsultants.com> writes:

>> Easy. Don't out ride your equipment capabilities.
>>
>
> And that's exactly why I bought a new MTB with disc brakes. Because
> there'd be too many trails I could not safely ride otherwise.

What you really mean, I think, is that you could not ride them at the
speed you'd like. It's called risk compensation. I doubt that these
trails were unridden before disk brakes became common.

--
Joe Riel

[Joerg]

Joe Riel wrote:
> Joerg <ne...@analogconsultants.com> writes:
>
>>> Easy. Don't out ride your equipment capabilities.
>>>
>> And that's exactly why I bought a new MTB with disc brakes. Because
>> there'd be too many trails I could not safely ride otherwise.
>
> What you really mean, I think, is that you could not ride them at the

> speed you'd like. It's called risk compensation. ...


Almost true. I had sections where the bike would simply not hold during
wet weather. Meaning it accelerated with me pulling both brakes real
hard. That leaves an iffy feeling in the stomach.


> ... I doubt that these

> trails were unridden before disk brakes became common.
>

On the gnarliest trail here in town I have never seen any other mountain
bikers. No even hikers. Unless I take friends up there I am all alone
except for wildlife. Coyotes, foxes, the occasional rattlesnake and
hopefully never a mountain lion (but got to be careful).

[James]

They were ridden before disc brakes... Look at the bones!

--
JS

[Frank Krygowski]

On 11/4/2014 8:18 PM, Joerg wrote:

> James wrote:
>>
>>
>> No, disc brakes were not made a regular item on bicycles until recently
>> because they added weight and rim brakes performed well enough in most
>> circumstances.
>>
>
> Sorry, not true. If you splash through a mud puddle and then there is a
> steep switchback section right after that it can go seriously wrong.

Joerg, you (and certain others) frequently use "it _can_ happen" as a
rebuttal to "it almost never happens." We see that above. But James
did not say "rim brakes _always_ perform well enough." Therefore your
hypothetical and rare example is not really a rebuttal to his statement.

Instead, you're saying "I can imagine one situation where risk might be
elevated, so we must be fearful enough to spend money on yet more exotic
equipment."

It's another version of "Danger! Danger!"

--
- Frank Krygowski

[Frank Krygowski]

On 11/4/2014 8:33 PM, Joe Riel wrote:

> Frank Krygowski writes:
>
>>
>> Back when Jobst was contributing, we had some extensive discussions
>> about blowouts from braking heat.
>
> At one point I had computed, and posted here, a computation of the
> descending speed that would generate the maximum wheel temperature (in
> addition to braking power, it considered the velocity-dependent
> convection cooling of the rim). Jobst was working with someone to build
> a device that mounted inside the tire and would record air temperature.

Yep. And back then, I was saying that I believed it was not just air
pressure that was the problem. I think the hot rim transferred heat to
the tire material at and near the bead, and softened, weakened and
perhaps expanded tire components.

--
- Frank Krygowski

[Frank Krygowski]

On 11/4/2014 8:56 PM, Joerg wrote:
>
> On the gnarliest trail here in town I have never seen any other mountain
> bikers. No even hikers. Unless I take friends up there I am all alone
> except for wildlife.

If that's true, it seems inaccurate to describe it as a "trail."


--
- Frank Krygowski

[Clive George]

On 04/11/2014 08:32, James wrote:

>> Why do you think disc brakes (finally!) made it into the world of
>> cycling?
>
> Better control/modulation, and no wear on the rim.

Rim wear was a biggie for MTB wasn't it? Certainly round here - wet mud
ate rims.

[avag...@gmail.com]

AE6KS

?


https://www.google.com/#tbm=shop&q=CATEYE+BICYCLE+LIGHT+1000+CANDLEPOWER

[John B. Slocomb]

Did the discussions ever come to any conclusions? I remember reading
something by Jobst about going to the mountains to test the effect of
braking on wheels but I don't remember that any data was obtained by
the "test".
--
Cheers,

John B.

[John B. Slocomb]

On Wed, 05 Nov 2014 11:07:31 +1100, James <james.e...@gmail.com>
wrote:

I've seen a table somewhere that listed tire size, CO2 cartridge size
and the resulting pressure.

--
Cheers,

John B.

[Sir Ridesalot]

Rim heating from extended braking must have some effect on the tire pressure due to internal heating of the air. After all, extended braking was kmnow to cause glued on tubular tires to loosen and sometimes even roll off the rim.

It'd be interesting tomeasure the air pressure and temperature of a cold tire and then on some machine have the tire spun up to speed and then have brakes applied for a whiler and then measure pressure and temperature again.

Hmm, I wonder, would an increase in pressure and temperature have more effect on a wire beaded tire or a Kevlar beaded tire?

Cheers

[avag...@gmail.com]

BBBBBBBBBBBBBBBBB


https://www.google.com/#q=coefficient+materials+tables&spell=1

[jbeattie]

On Sunday, November 2, 2014 1:19:10 PM UTC-8, James wrote:
> On 03/11/14 02:44, Joerg wrote:
> > Ralph Barone wrote:
>
> >>
> >> Joerg, I'm running rim brakes with my hub Dynamo.
> >
> >
> > That would get you into serious "Oh dang!" situations out here. My old
> > MTB has rim brakes and I quickly learned that I don't want those. Plus
> > the rims wear down really fast.
> >
> > Even 6" discs up front are marginal, has to be at least 7" for even some
> > of the local trails.
> >
>
>
> Amazing that we are still alive today, having ridden all those lonely
> mountainous goat tracks away from "cell" coverage and with only rim
> brakes to stop us!

I am kind of curious about why Joerg's trails are so dangerous. Maybe he could post some pictures.

-- Jay Beattie.

[avag...@gmail.com]

and why buy an off the wall light unit off Amazon when Cateye apparently sells developed units at twice the power for half the cost ?

is the question larger batteries for longer run times ?

are Cateye units pluggable to larger batts ?

is there a structured approach for Cateye to aux batts ?

[AMuzi]

I was not there, but more likely had an anomaly (bead not
evenly seated, valve base or tube caught under tire edge,
etc) than a simple overinflation.

In my experience, bicycle tires can run extreme pressures,
like 1.5x normal, uneventfully. You may not like the harsh
ride, and Heine's data indicates rolling resistance goes
_up_ with extreme pressures, but tires can do that if evenly
mounted.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[Frank Krygowski]

On 11/5/2014 6:41 AM, Sir Ridesalot wrote:
> On Wednesday, November 5, 2014 6:19:53 AM UTC-5, John B. Slocomb wrote:
>>
>>
>> Did the discussions ever come to any conclusions? I remember reading
>> something by Jobst about going to the mountains to test the effect of
>> braking on wheels but I don't remember that any data was obtained by
>> the "test".

I guess someone should do a search on the discussions. I don't recall
any hard data. There was talk of using temperature detecting stickers
like this: http://www.omega.com/pptst/TL-10.html on rims. And IIRC
Jobst was talking about using telemetry to digitally record temperatures
and air pressures.

> Rim heating from extended braking must have some effect on the tire pressure
due to internal heating of the air.

Yes, that's well known. But as Andrew noted above, someone had pumped
tires to insanely high pressures and seen no blowoff when the tires were
at room temperature and stationary. That led to the idea that perhaps
heat softening of the tire material was a factor. Also, possibly, the
force applied to the tire by the road surface might distort the casing
and tend to peel the tire from the rim.

But all this is dim memory.

>After all, extended braking was kmnow to cause glued on tubular tires
to loosen and sometimes even roll off the rim.
>
> It'd be interesting tomeasure the air pressure and temperature of a cold
tire and then on some machine have the tire spun up to speed and then have
brakes applied for a whiler and then measure pressure and temperature again.
>
> Hmm, I wonder, would an increase in pressure and temperature have more
effect on a wire beaded tire or a Kevlar beaded tire?

My original guess was that Kevlar beads would suffer more, because most
plastics have thermal expansion coefficients that are way higher than
those of metals. But since, I've learned that Kevlar is different. It
actually shrinks very slightly when heated. So my current guess is "I
don't know."

I can recall blowing off bike tires just twice. Both were on our
ancient tandem, with the old non-hook-bead Weinmann A-124 rims, with
wire bead tires. The first incident was the day we brought the tandem
home and I first installed tubes and tires. We hadn't even ridden the
bike; it was leaning against the wall in the back bedroom, but a couple
hours after I pumped the tires up, one of them blew off. Many years
later (same rims, wire bead tire) we blew a back tire on a very short
but super-steep downhill. Aside from that, I've seen a guys kevlar bead
front tire blow after he braked to a stop at the bottom of a long steep
hill.


--
- Frank Krygowski

[jbeattie]

Same here, but only once on a tandem up front. It was a Scott SE rim brake, Sun Chinook 48H rim on a steep, four mile decent. The tire was a 25mm or 28mm Conti, probably 100psi. A good reason for a drag brake.

-- Jay Beattie.

[Frank Krygowski]

On 11/5/2014 1:20 PM, jbeattie wrote:
>
>
> Same here, but only once on a tandem up front. It was a Scott SE rim brake,
Sun Chinook 48H rim on a steep, four mile decent. The tire was a 25mm or
28mm
Conti, probably 100psi. A good reason for a drag brake.

When Jim Bradford (then of Georgia) built our tandem for us, I asked for
a double-threaded Phil rear hub so I could add a drag brake once I could
afford it. Bradford instead installed a single threaded hub - one of
the many things he got wrong on the bike.

He did claim, however, that we wouldn't need it, saying that he and his
girlfriend had toured the Alps on one of his tandems using just
cantilever rim brakes. I don't know whether to believe him or not.

We've never done mountain touring on the tandem, but except for that one
anomalous incident, we've done fine with its two cantilever brakes.
That includes many smaller downhills with my wife plus my daughter in a
kid seat on the back.

--
- Frank Krygowski

[Clive George]

On 05/11/2014 19:58, Frank Krygowski wrote:

> He did claim, however, that we wouldn't need it, saying that he and his
> girlfriend had toured the Alps on one of his tandems using just
> cantilever rim brakes. I don't know whether to believe him or not.

The Alps are pretty easy on tandem brakes, though we did get them a bit
hot this summer on a series of hairpins with just enough space between
them to build up speed but not cool down rims.

The drag brake comes into its own when descending with a load though -
keeps the speed sane and the rims cool ready for using the rim brakes at
the hairpins. Hills here are also a lot less easy than alps - what they
lack in length they make up in steepness. It's amusing stopping at the
bottom of a 1:4 hill and squirting water on it - very big clouds of steam.

I've had flats from overheating at least twice when the drum wasn't on
(or the other bike). Both times were patches coming away. I think both
were on the back wheel - I'd tend to drag that more than the front,
preferring to keep the front ready for actual stops.

[James]

Most people inflate a bike high pressure road tyre until they think it
feels hard enough. The gas temperature in the tyre will be less than
ambient because the gas was allowed to expand in to the tyre/tube. As
the gas then warms to ambient, the pressure increases further.

So it may be over pressure to begin with. (Harder is better, right? ;-)

With the additional pressure due to the gas warming, the chances of a
blow out are increased.

--
JS

[James]

On 06/11/14 03:27, Frank Krygowski wrote:
> On 11/5/2014 6:41 AM, Sir Ridesalot wrote:
>> On Wednesday, November 5, 2014 6:19:53 AM UTC-5, John B. Slocomb wrote:
>>>
>>>
>>> Did the discussions ever come to any conclusions? I remember reading
>>> something by Jobst about going to the mountains to test the effect of
>>> braking on wheels but I don't remember that any data was obtained by
>>> the "test".
>
> I guess someone should do a search on the discussions. I don't recall
> any hard data. There was talk of using temperature detecting stickers
> like this: http://www.omega.com/pptst/TL-10.html on rims. And IIRC
> Jobst was talking about using telemetry to digitally record temperatures
> and air pressures.

After a few kms of 8% descent a couple of weeks back, where several slow
cars kept us on the brakes, when we got to a set of traffic lights at
the bottom, I put my fingers on the rim. My calibrated finger tips
measured pretty close to 50 degrees C. Maybe as high as 60 degrees C.

I couldn't leave my fingers on the rim for many seconds.

--
JS

[James]

That's possible too.

> In my experience, bicycle tires can run extreme pressures, like 1.5x
> normal, uneventfully. You may not like the harsh ride, and Heine's data
> indicates rolling resistance goes _up_ with extreme pressures, but tires
> can do that if evenly mounted.
>

It would be interesting to measure the pressure they get directly after
inflation with a CO2 canister, and again a couple of hours later.

*IF* there is enough heat transfer to the air in the tyre from a hot rim
to cause the pressure to rise significantly, tyre manufacturers have to
be conservative on the inflation pressure I suppose.

I guess normally a bicycle pump will heat the air going in to the tyre,
so the initial pressure may drop a couple of hours later when the air
temperature returns to ambient, where as with a CO2 canister it may rise.

--
JS

[jbeattie]

When I lived in California, I would frequently heat my rims to the point of softening tubular cement -- rolling a tire was a real worry. But I never had problems blowing a clincher off a rim on a single bike. Tandems are different because the braking forces are so high.

Carbon tubulars have their own high heat cement. http://www.racycles.com/product/continental-rim-cement-carbon

Per seller:

"Be safe! It's important to get a cement designed for carbon for your carbon rims, or the unfavorable heat dissipation can soften conventional cement, particularly during long descents, which could lead to the tire detaching from the rim."

Oh my Gawd! Danger, danger! Next they'll be telling us to get special brake shoes, too!

-- Jay Beattie.

[Clive George]

On 05/11/2014 21:58, James wrote:

> After a few kms of 8% descent a couple of weeks back, where several slow
> cars kept us on the brakes, when we got to a set of traffic lights at
> the bottom, I put my fingers on the rim. My calibrated finger tips
> measured pretty close to 50 degrees C. Maybe as high as 60 degrees C.
>
> I couldn't leave my fingers on the rim for many seconds.

That's not really very warm :-)

I've mentioned squirting water onto a drum brake - I've also had it boil
instantly on rims.

[James]

At what temperature does the cement soften?

>
> Oh my Gawd! Danger, danger! Next they'll be telling us to get special brake shoes, too!
>

Most CF rim manufacturers demand the use of special brake shoes.

--
JS

[James]

On 06/11/14 10:59, Clive George wrote:
> On 05/11/2014 21:58, James wrote:
>
>> After a few kms of 8% descent a couple of weeks back, where several slow
>> cars kept us on the brakes, when we got to a set of traffic lights at
>> the bottom, I put my fingers on the rim. My calibrated finger tips
>> measured pretty close to 50 degrees C. Maybe as high as 60 degrees C.
>>
>> I couldn't leave my fingers on the rim for many seconds.
>
> That's not really very warm :-)

I agree. I've often touched the front rim after braking hard to a stop,
and found it's only warm.

>
> I've mentioned squirting water onto a drum brake - I've also had it boil
> instantly on rims.
>

I've had water sizzle on the front disc on my MTB.

http://www.johnforester.com/Articles/BicycleEng/safe_brakes_that_burn_up.htm

No hotter than 200F, or approx 93C.

With added load and steepness I'm sure rims could exceed 100C and boil
water.

That doesn't mean the air in the tyre is at the same temperature of
course. Heat conduction through the rubber will be limited and there is
air rushing over the outside of the tyre.

--
JS

[John B. Slocomb]

On Thu, 06 Nov 2014 08:52:56 +1100, James <james.e...@gmail.com>

Exactly. This is why it is good to know what pressure a full CO2
cartridge will charge the tire to. One assumes that they are talking
about what pressure the CO2 filled tire will be when the gas reaches
ambient temperature.

Example: from the chart a 12 gm. cartridge into a 700-23C tire results
in a tire pressure of ~90psi, a 16 gm. cartridge would give 130 psi.
the 12 gm cartridge into a 700-28C would give 62 psi and the 16 gm
cartridge = 88 psi.

see
http://bicycles.stackexchange.com/questions/9583/not-sure-about-using-a-co2-cartridge

Another point about CO2, it is said to leak through the inner tube so
the tire should be bled and refilled with air as soon as practical.
--
Cheers,

John B.

[jbeattie]

Mine was a Cannondale (recently sold due to wife's incapacity and son's exit to college). Two cantis. New models are awesome. http://www.cannondale.com/nam_en/2015/bikes/fitness-urban/fitness/tandem-29/road-tandem-1

180/203mm discs.

I've never done any touring on a tandem. My tandem saw its heyday when my wife and I were both racing. She was an incredible climber, and we would drag race friends up hill. On one climb (in fact, it was Rocky Point -- I posted that motorcycle video with the van), we were racing a friend and dropped him on a 20+% section that is about 50 yards long but still about a mile or more from the top. I had no idea how much I was punishing my wife, and about a quarter mile from the top, she just stopped pedaling. Crap man! Where's my cattle prod! She went on strike, and it was like I was pulling a trailer full of bricks. I about blew a lung trying not to get passed (which I did). She threatened to quit riding with me if I did that again. That's why they call them divorcycles.

When my son was born, we hooked on the Burley trailer and then the Piccolo. We would all commute to work together over Terwilliger. http://www.flickr.com/photos/the_chirs/1685186052/ It was like the circus had come to town.

Yes, it was much like when my father and mother rode me to kindergarten on their tandem (not). Actually, my first six months of kindergarten were in the Santa Cruz mountains. http://www.losgatosca.gov/ImageRepository/Document?documentID=10916 My parents would have gotten an awesome workout -- between drags on their cigarettes. Even more O.T., I made a clay ashtray for my mother in kindergarten. She had it until she died of lung cancer. Shame on the public school system!

-- Jay Beattie.

[James]

Agree. I have no idea what size canister my friends use to inflate
their 23mm tyres. They might not know either!

I continue to use a pump.

--
JS

[Clive George]

On 06/11/2014 00:54, jbeattie wrote:

> Mine was a Cannondale (recently sold due to wife's incapacity and son's exit to college). Two cantis.

Upgrade to Magura and they work well.

> New models are awesome. http://www.cannondale.com/nam_en/2015/bikes/fitness-urban/fitness/tandem-29/road-tandem-1
>
> 180/203mm discs.

Needs 203/203. Wonder why they cocked that up?

[sms]

I would like to sell my Trek tandem. I have a second back wheel for it,
with an Arai drum brake. Never did mountain touring on that bike though.
That bike also has the Burley Kid Back which I think is long since
discontinued so it might appeal to someone with small children. But the
spousal unit wants to keep the tandem. The longest ride I took on it was
an 800km ride in Russia which was quite an adventure.

[jbeattie]

I know. That was a joke. I'm pathologically opposed to emoticons.

As for heat, this paper assumes 60C (140F) http://www.engr.ku.edu/~kuktl/bicycle/Part6.pdf

I mentioned California because apart from heat from breaking, the ambient air and asphalt were hot -- which probably describes your neck of he woods as well. We don't get that kind of heat in Oregon, and you have to go out of your way to get a descent more than five miles, which is not the case in Santa Clara Valley. http://media-cache-ec0.pinimg.com/736x/66/04/aa/6604aabab8df5000df7ac7c2e563811b.jpg

-- Jay Beattie.