Amp-hour meter?

[Newshound]

I have several 12V lead acid batteries of different sizes with various
uses. It would be handy to be able to check their capacity, and to know
when they are fully charged. Most of the commercial meters seem to be
aimed at boats or solar panel systems, and therefore attract premium
prices. The cheapest seem to be made for the ham radio or RC model
community, but are still around 60 dollars. Does anyone know of anything
a bit cheaper (or even that price, but from a UK source?). I'm happy to
build one, but I don't really want to have to make the PCB.

[Dave Plowman (News)]

In article <9n6j0p...@mid.individual.net>,

I have an ACT which cost a lot more than 60 dollars. They're quite a
complicated piece of kit.

--
*I have plenty of talent and vision. I just don't care.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Colin Stamp]

One cheap, dirty way is to use an analogue clock. Use the battery under
test to power the clock through a simple potential divider. Set the
clock to 12 o'clock, add a fixed load and then do something else for a
few hours until the clock stops.

It's all a bit crap of course. It can't really be calibrated and it's
hard on the batteries, but it would allow you to compare one battery
with another.

Well, you did want cheap...

Cheers,

Colin.

[Theo Markettos]

There are various chips from the likes of Maxim, Analog Devices, TI, Linear
Tech, etc etc that will do it: 'battery monitor', 'gas gauge', 'watt
counter' etc. Look in Farnell. The chips are a few quid, but the cost
saving is probably outweighed by the faff in interfacing to them (unless you
have an Arduino or something lying around). The 'gas gauge' ones are
designed to drive LEDs etc so might be simpler.

Theo

[harry]

It's not possible to test the charge/deterioraton on a lead acid
battery by simply measuring the voltage.
The only way is to measure the voltage when it's under heavy load/
discharge conditions.
There is a tool to do this that consists of a massive resistor and
voltmeter.
Even with this there is an element of uncertainty as to whether the
battery is discharged or knackered. (Heavy duty battery tester)
http://www.amazon.com/3181-Heavy-Duty-Battery-Load-Tester/dp/B000O3U2UQ

Also you need to test the cells if possible with a hydrometer.
http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_530647_langId_-1_categoryId_255205

There are no little electronic gizmos that do the job properly.

[Dave Liquorice]

On Wed, 11 Jan 2012 23:07:05 +0000, Newshound wrote:

> I have several 12V lead acid batteries of different sizes with various
> uses. It would be handy to be able to check their capacity, and to know
> when they are fully charged.

Hydrometer.

--
Cheers
Dave.

[Dave Plowman (News)]

In article
<24feca79-22fe-4677...@k8g2000yqk.googlegroups.com>,

harry <harol...@aol.com> wrote:
> It's not possible to test the charge/deterioraton on a lead acid
> battery by simply measuring the voltage.
> The only way is to measure the voltage when it's under heavy load/
> discharge conditions.
> There is a tool to do this that consists of a massive resistor and
> voltmeter.
> Even with this there is an element of uncertainty as to whether the
> battery is discharged or knackered. (Heavy duty battery tester)
> http://www.amazon.com/3181-Heavy-Duty-Battery-Load-Tester/dp/B000O3U2UQ

> Also you need to test the cells if possible with a hydrometer.
> http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_530647_langId_-1_categoryId_255205

> There are no little electronic gizmos that do the job properly.

Yes there are. My ACT unit does all that - in a device little bigger than
a DVM. It measures the battery voltage, ambient temperature, then puts a
very heavy load across it for a short defined time. Then calculates the
actual amp.hr capacity. But it is not cheap.

--
*Nothing is foolproof to a sufficiently talented fool*

[harry]

On Jan 12, 10:18 am, "Dave Plowman (News)" <d...@davenoise.co.uk>
wrote:
> In article
> <24feca79-22fe-4677-bac6-190f589f5...@k8g2000yqk.googlegroups.com>,

>    harry <haroldhr...@aol.com> wrote:
>
> > It's not possible to test the charge/deterioraton on a lead acid
> > battery by simply measuring the voltage.
> > The only way is to measure the voltage when it's under heavy load/
> > discharge conditions.
> > There is a tool to do this that consists of a massive resistor and
> > voltmeter.
> > Even with this there is an element of uncertainty as to whether the
> > battery is discharged or knackered.  (Heavy duty battery tester)
> >http://www.amazon.com/3181-Heavy-Duty-Battery-Load-Tester/dp/B000O3U2UQ
> > Also you need to test the cells if possible with a hydrometer.

> >http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_100...

> > There are no little electronic gizmos that do the job properly.
>
> Yes there are. My ACT unit does all that - in a device little bigger than
> a DVM. It measures the battery voltage, ambient temperature, then puts a
> very heavy load across it for a short defined time. Then calculates the
> actual amp.hr capacity. But it is not cheap.
>
> --
> *Nothing is foolproof to a sufficiently talented fool*
>

>     Dave Plowman        d...@davenoise.co.uk           London SW

>                   To e-mail, change noise into sound.

Well you need several hundred amperes.

[Dave Plowman (News)]

In article
<9a0235dc-ef6c-481a...@h12g2000yqg.googlegroups.com>,

harry <harol...@aol.com> wrote:
> > > There are no little electronic gizmos that do the job properly.
> >
> > Yes there are. My ACT unit does all that - in a device little bigger
> > than a DVM. It measures the battery voltage, ambient temperature, then
> > puts a very heavy load across it for a short defined time. Then
> > calculates the actual amp.hr capacity. But it is not cheap.

> Well you need several hundred amperes.

Not to measure the amp.hr, you don't. That is done at the 20 hour rate.
However, if it passes this test it will also deliver its peak current
capability. The two are interdependent.

--
*Some people are only alive because it is illegal to kill.

Dave Plowman da...@davenoise.co.uk London SW

[Alan Deane]

On 12/01/2012 10:18, Dave Plowman (News) wrote:
> In article
> <24feca79-22fe-4677...@k8g2000yqk.googlegroups.com>,
> harry<harol...@aol.com> wrote:
>> It's not possible to test the charge/deterioraton on a lead acid
>> battery by simply measuring the voltage.
>> The only way is to measure the voltage when it's under heavy load/
>> discharge conditions.
>> There is a tool to do this that consists of a massive resistor and
>> voltmeter.
>> Even with this there is an element of uncertainty as to whether the
>> battery is discharged or knackered. (Heavy duty battery tester)
>> http://www.amazon.com/3181-Heavy-Duty-Battery-Load-Tester/dp/B000O3U2UQ
>
>> Also you need to test the cells if possible with a hydrometer.
>> http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_530647_langId_-1_categoryId_255205
>
>> There are no little electronic gizmos that do the job properly.
>
> Yes there are. My ACT unit does all that - in a device little bigger than
> a DVM. It measures the battery voltage, ambient temperature, then puts a
> very heavy load across it for a short defined time. Then calculates the
> actual amp.hr capacity. But it is not cheap.
>

I also have an ACT battery tester - very good, but way above the OP's
budget I suspect.
There are a few on ebay, item 280804981670 for example.

[Newshound]

Not a lot of good on gel batteries though

[Newshound]

Thanks, I'll think about one of them. But this is a bit more than I
wanted. For a car battery with a big cranking current, internal
resistance makes a lot of difference and you need to test at high
current to get an accurate reading. Either with an ACT or the "old
fashioned" sparky sort where you put an electric fire element across it
and measure the volts. But most applications are not like this.

I have a couple of leisure batteries which are used to run an inverter
for lighting and sometimes a pump at a stables with no mains, some old
car batteries which I use for electric fencers, another gel battery
which drives a clippers. If I had an amp-hour meter then I could check
the capacity of these when charging them from flat, it would help me
know how long I will get at different loads, and also recognise when
batteries are losing capacity. Also it would help me make sure I go to
full charge without leaving them longer than necessary. I know that
voltage gives an indication of charge, but you have to leave it a little
while after you disconnect.

But thanks to all who responded

Steve

[cynic]

On Jan 11, 11:07 pm, Newshound <newsho...@fairadsl.co.uk> wrote:

ebay HIGH CURRENT CAR BIKE BATTERY TESTER vehicle auto 6 12v £19.99

[Dave Plowman (News)]

In article <9n92mm...@mid.individual.net>,

Newshound <news...@fairadsl.co.uk> wrote:
> > I also have an ACT battery tester - very good, but way above the OP's
> > budget I suspect.
> > There are a few on ebay, item 280804981670 for example.

> Thanks, I'll think about one of them. But this is a bit more than I
> wanted.

Indeed. But to do what you want and quickly, it's the only way.

> For a car battery with a big cranking current, internal
> resistance makes a lot of difference and you need to test at high
> current to get an accurate reading. Either with an ACT or the "old
> fashioned" sparky sort where you put an electric fire element across it
> and measure the volts. But most applications are not like this.

The high load tester doesn't really tell you much about the battery
capacity, though. I recently replaced a car battery which would start the
car ok when fully charged, but was well down on capacity. The other way
round, I'm told, can't exist.

> I have a couple of leisure batteries which are used to run an inverter
> for lighting and sometimes a pump at a stables with no mains, some old
> car batteries which I use for electric fencers, another gel battery
> which drives a clippers. If I had an amp-hour meter then I could check
> the capacity of these when charging them from flat, it would help me
> know how long I will get at different loads, and also recognise when
> batteries are losing capacity. Also it would help me make sure I go to
> full charge without leaving them longer than necessary. I know that
> voltage gives an indication of charge, but you have to leave it a little
> while after you disconnect.

Given the cost of replacing all these, a decent tester would seem like a
bargain. However, as regards charging a smart charger won't hurt them
regardless of how long left on.

> But thanks to all who responded

--
*How many roads must a man travel down before he admits he is lost? *

[Newshound]

Thanks, but this is basically testing for bad cells on a battery which
has to run a starter motor. My applications are all at currents of no
more than a few amps.

S

[Newshound]

On 12/01/2012 23:27, Dave Plowman (News) wrote:
> In article<9n92mm...@mid.individual.net>,
> Newshound<news...@fairadsl.co.uk> wrote:
>>> I also have an ACT battery tester - very good, but way above the OP's
>>> budget I suspect.
>>> There are a few on ebay, item 280804981670 for example.
>
>> Thanks, I'll think about one of them. But this is a bit more than I
>> wanted.
>
> Indeed. But to do what you want and quickly, it's the only way.

Except that it has that extra functionality, the short duration high
current test which doesn't bother me too much.

Superficially, it seems to me that if you put a modest limit on the
current handling capacity (say, a few amps) then it shouldn't require
all that much electronics, given modern chips, to count amp-hours. It's
basically an ammeter, a timer/sampler, a bit of memory, and a display.
Only a little more "stuff" than in a basic DVM, and you can get quite a
reasonable one for a tenner.

Whereas the "high current" test is a bit like an earth loop impedance
tester, and you need protection to stop stuff from blowing up if the
microprocessor hangs.

>
>> For a car battery with a big cranking current, internal
>> resistance makes a lot of difference and you need to test at high
>> current to get an accurate reading. Either with an ACT or the "old
>> fashioned" sparky sort where you put an electric fire element across it
>> and measure the volts. But most applications are not like this.
>
> The high load tester doesn't really tell you much about the battery
> capacity, though. I recently replaced a car battery which would start the
> car ok when fully charged, but was well down on capacity. The other way
> round, I'm told, can't exist.
>
>> I have a couple of leisure batteries which are used to run an inverter
>> for lighting and sometimes a pump at a stables with no mains, some old
>> car batteries which I use for electric fencers, another gel battery
>> which drives a clippers. If I had an amp-hour meter then I could check
>> the capacity of these when charging them from flat, it would help me
>> know how long I will get at different loads, and also recognise when
>> batteries are losing capacity. Also it would help me make sure I go to
>> full charge without leaving them longer than necessary. I know that
>> voltage gives an indication of charge, but you have to leave it a little
>> while after you disconnect.
>
> Given the cost of replacing all these, a decent tester would seem like a
> bargain. However, as regards charging a smart charger won't hurt them
> regardless of how long left on.

Point taken. I think most of my chargers are OK

[harry]

You probably need to do some research into deep discharge batteries.
http://en.wikipedia.org/wiki/Deep_discharge
http://en.wikipedia.org/wiki/Deep_cycle_battery

[harry]

.
>
> Except that it has that extra functionality, the short duration high
> current test which doesn't bother me too much.
>
> Superficially, it seems to me that if you put a modest limit on the
> current handling capacity (say, a few amps) then it shouldn't require
> all that much electronics, given modern chips, to count amp-hours. It's
> basically an ammeter, a timer/sampler, a bit of memory, and a display.
> Only a little more "stuff" than in a basic DVM, and you can get quite a
> reasonable one for a tenner.
>
> Whereas the "high current" test is a bit like an earth loop impedance
> tester, and you need protection to stop stuff from blowing up if the
> microprocessor hangs.

Absolutely wrong from begining to end.

[Dave Plowman (News)]

In article <9n9bs8...@mid.individual.net>,

Newshound <news...@fairadsl.co.uk> wrote:
> > Indeed. But to do what you want and quickly, it's the only way.

> Except that it has that extra functionality, the short duration high
> current test which doesn't bother me too much.

It's not an ultra high current test. The leads aren't thick enough for
that. Just high in DVM terms.

> Superficially, it seems to me that if you put a modest limit on the
> current handling capacity (say, a few amps) then it shouldn't require
> all that much electronics, given modern chips, to count amp-hours. It's
> basically an ammeter, a timer/sampler, a bit of memory, and a display.
> Only a little more "stuff" than in a basic DVM, and you can get quite a
> reasonable one for a tenner.

Of course it could be a lot cheaper if made in vast quantities. But it's
not. I dunno if the Chinese do a cheaper copy - but it is quite well
protected by patents. Which, of course, also cost.

> Whereas the "high current" test is a bit like an earth loop impedance
> tester, and you need protection to stop stuff from blowing up if the
> microprocessor hangs.

--
*If at first you don't succeed, destroy all evidence that you tried *

[Theo Markettos]

Newshound <news...@fairadsl.co.uk> wrote:
> Superficially, it seems to me that if you put a modest limit on the
> current handling capacity (say, a few amps) then it shouldn't require
> all that much electronics, given modern chips, to count amp-hours. It's
> basically an ammeter, a timer/sampler, a bit of memory, and a display.
> Only a little more "stuff" than in a basic DVM, and you can get quite a
> reasonable one for a tenner.

Chips to do this (voltmeter, ammeter, A-D, integrator, I2C output) are about
3 quid, just add a series resistor for the current measurement and a pile of
capacitors to keep it stable. Then a microcontroller and a little LCD, and
some software, job done.

Theo