Battery capacity checker

[Roger Druce]

Perhaps someone out in r.a.s land may be able to point me in the direction
of a commercial piece of equipment which would perform the following task.

I would like to be able to charge up a 12 volt (nominal) gell cell battery
and then plug it into a piece of equipment to check its total AmpHour
capacity during discharge at some constant rate current (say the "10 hour"
rate or the "20 hour" rate). All this towards assessing whether the battery
has proven useful capacity and life left in it, or has it reached its
discard date?

The equipment would show the delivered amp-hours up to the point at which
the voltage has fallen to a nominated end voltage.

I realise that you can do it in a way with a light globe to discharge the
battery and then time the length the light holds up glowing brightly. This
is all too primative for this day and age, and there ought to be some piece
of equipment available for the task.

Or some circuit from an electronics hobby magazine??

Thanks in antcipation.
Roger Druce

[Peter Nyffeler]

In article >, "Roger Druce" > wrote:
>Perhaps someone out in r.a.s land may be able to point me in the direction
>of a commercial piece of equipment which would perform the following task.
>
>I would like to be able to charge up a 12 volt (nominal) gell cell battery
>and then plug it into a piece of equipment to check its total AmpHour
>capacity during discharge at some constant rate current (say the "10 hour"
>rate or the "20 hour" rate). All this towards assessing whether the battery
>has proven useful capacity and life left in it, or has it reached its
>discard date?
>
>The equipment would show the delivered amp-hours up to the point at which
>the voltage has fallen to a nominated end voltage.
>
>I realise that you can do it in a way with a light globe to discharge the
>battery and then time the length the light holds up glowing brightly. This
>is all too primative for this day and age, and there ought to be some piece
>of equipment available for the task.
>
>Or some circuit from an electronics hobby magazine??
>
>Thanks in antcipation.
>Roger Druce

I built one myself.
You find the schematic at http://www.ppc.ethz.ch/~peny/sf/ah_test.html

Peter Nyffeler
Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21

[John Morgan]

"Roger Druce" > wrote in message
u...
> Perhaps someone out in r.a.s land may be able to point me in the direction
> of a commercial piece of equipment which would perform the following task.
>
> I would like to be able to charge up a 12 volt (nominal) gell cell battery
> and then plug it into a piece of equipment to check its total AmpHour
> capacity during discharge at some constant rate current (say the "10 hour"
> rate or the "20 hour" rate). All this towards assessing whether the
battery
> has proven useful capacity and life left in it, or has it reached its
> discard date?


Check

http://www.laaudiofile.com/elkbltv2.html

for a quick review and then search Google for <ELK battery tester>.

My company uses these to test batteries in the field. While the ELK tester
won't do all the things you asked, it tests batteries quickly and gives, in
my experience, an accurate assessment of the battery's remaining life. And
at just over $100 USD, it's not that expensive.
--
bumper - ZZ >
"Dare to be different . . . circle in sink."
to reply, the last half is right to left




---
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[John Giddy]

Hi Peter,
Good circuit !
However I have a couple of questions:


1.
I presume the FET (Q2) will need a heatsink, as it will
dissipate approximately 12W when discharging at 1 Amp ?

2.
R9 should be 470 ohm, not 470 K

Cheers, John G.

"Peter Nyffeler" > wrote in
message ...
| In article
>, "Roger
Druce" > wrote:
| >Perhaps someone out in r.a.s land may be able to point me
in the direction
| >of a commercial piece of equipment which would perform
the following task.
| >
| >I would like to be able to charge up a 12 volt (nominal)
gell cell battery
| >and then plug it into a piece of equipment to check its
total AmpHour
| >capacity during discharge at some constant rate current
(say the "10 hour"
| >rate or the "20 hour" rate). All this towards assessing
whether the battery
| >has proven useful capacity and life left in it, or has it
reached its
| >discard date?
| >
| >The equipment would show the delivered amp-hours up to
the point at which
| >the voltage has fallen to a nominated end voltage.
| >
| >I realise that you can do it in a way with a light globe
to discharge the
| >battery and then time the length the light holds up
glowing brightly. This
| >is all too primative for this day and age, and there
ought to be some piece
| >of equipment available for the task.
| >
| >Or some circuit from an electronics hobby magazine??
| >
| >Thanks in antcipation.
| >Roger Druce
|
| I built one myself.
| You find the schematic at
http://www.ppc.ethz.ch/~peny/sf/ah_test.html
|
| Peter Nyffeler
| Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21

[Steve Bralla]

"Roger Druce" > writes:
>
>I would like to be able to charge up a 12 volt (nominal) gell cell battery
>and then plug it into a piece of equipment to check its total AmpHour
>capacity during discharge at some constant rate current (say the "10 hour"
>rate or the "20 hour" rate). All this towards assessing whether the battery
>has proven useful capacity and life left in it, or has it reached its
>discard date?
>
>The equipment would show the delivered amp-hours up to the point at which
>the voltage has fallen to a nominated end voltage.

At the research lab I work at, we use a power resistor (for the load) and a
strip chart recorder (Vout/time).
Steve

[Peter Nyffeler]

In article >, "John Giddy" > wrote:
>Hi Peter,
>Good circuit !
>However I have a couple of questions:
>1.
>I presume the FET (Q2) will need a heatsink, as it will
>dissipate approximately 12W when discharging at 1 Amp ?
>2.
>R9 should be 470 ohm, not 470 K
>
>Cheers, John G.

John you are right.

The FET needs a heatsink, as it works as a variable power resistor to provide
a constant discharge current
And R9 should have 470 ohm to turn on the monitor LED.

Thanks
Peter

Peter Nyffeler
Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21

[Chris]

Looks like a good project, what should the value of R7 be ?

Chris Runeckles
Western Australia


"Roger Druce" > wrote in message
u...
> Perhaps someone out in r.a.s land may be able to point me in the direction
> of a commercial piece of equipment which would perform the following task.
>
> I would like to be able to charge up a 12 volt (nominal) gell cell battery
> and then plug it into a piece of equipment to check its total AmpHour
> capacity during discharge at some constant rate current (say the "10 hour"
> rate or the "20 hour" rate). All this towards assessing whether the
battery
> has proven useful capacity and life left in it, or has it reached its
> discard date?
>
> The equipment would show the delivered amp-hours up to the point at which
> the voltage has fallen to a nominated end voltage.
>
> I realise that you can do it in a way with a light globe to discharge the
> battery and then time the length the light holds up glowing brightly.
This
> is all too primative for this day and age, and there ought to be some
piece
> of equipment available for the task.
>
> Or some circuit from an electronics hobby magazine??
>
> Thanks in antcipation.
> Roger Druce
>
>

[JTH]

>
> "Roger Druce" > wrote in message
> u...
> > Perhaps someone out in r.a.s land may be able to point me in the
direction
> > of a commercial piece of equipment which would perform the following
task.
> >
> > I would like to be able to charge up a 12 volt (nominal) gell cell
battery
> > and then plug it into a piece of equipment to check its total AmpHour
> > capacity during discharge at some constant rate current (say the "10
hour"
> > rate or the "20 hour" rate). All this towards assessing whether the
> battery
> > has proven useful capacity and life left in it, or has it reached its
> > discard date?
> >
> > The equipment would show the delivered amp-hours up to the point at
which
> > the voltage has fallen to a nominated end voltage.
> >
> > I realise that you can do it in a way with a light globe to discharge
the
> > battery and then time the length the light holds up glowing brightly.
> This
> > is all too primative for this day and age, and there ought to be some
> piece
> > of equipment available for the task.
> >
> > Or some circuit from an electronics hobby magazine??
> >
> > Thanks in antcipation.
> > Roger Druce
> >
> >
If cost is no problem, then look at the modern chargers that the RC flyers
use. The better chargers measure the discharge and charge capacity of
batteries/accus. Look for brand names like Schulze, Orbit and Graupner.
Price level 100 - 300 eur depending about the charger model.
regs, Jyrki

[John Giddy]

Chris,
Depends a bit on what current is drawn by the relay coil.
A typical small PCB mounted relay would draw about 13 mA, so
to ensure that Q1 is in saturation, its base current should
be about 1.3 mA (1/10 of the collector current is a good
rule of thumb for saturated switching transistors) this
gives R7 = 12/ 1.3 kilohms approximately.
i.e. R7 = 9.2 K Probably use R7 = 10 K, as an easily
obtainable value, (or 8.2 K if you are nervous !).
(The relay I based the above on is a Fujitsu type FBR46 with
12v coil, available from Radio Parts here in Victoria,
Australia)

Would Peter Nyffeler care to comment ?

Cheers, John G.

"Chris" > wrote in message
. au...
| Looks like a good project, what should the value of R7 be
?
|
| Chris Runeckles
| Western Australia
|
|
| "Roger Druce" > wrote in message
| u...
| > Perhaps someone out in r.a.s land may be able to point
me in the direction
| > of a commercial piece of equipment which would perform
the following task.
| >
| > I would like to be able to charge up a 12 volt (nominal)
gell cell battery
| > and then plug it into a piece of equipment to check its
total AmpHour
| > capacity during discharge at some constant rate current
(say the "10 hour"
| > rate or the "20 hour" rate). All this towards assessing
whether the
| battery
| > has proven useful capacity and life left in it, or has
it reached its
| > discard date?
| >
| > The equipment would show the delivered amp-hours up to
the point at which
| > the voltage has fallen to a nominated end voltage.
| >
| > I realise that you can do it in a way with a light globe
to discharge the
| > battery and then time the length the light holds up
glowing brightly.
| This
| > is all too primative for this day and age, and there
ought to be some
| piece
| > of equipment available for the task.
| >
| > Or some circuit from an electronics hobby magazine??
| >
| > Thanks in antcipation.
| > Roger Druce
| >
| >
|
|

[Martin Gregorie]

On Tue, 21 Oct 2003 11:23:28 GMT, "JTH"
> wrote:

>>
>> "Roger Druce" > wrote in message
>> u...
>> > Perhaps someone out in r.a.s land may be able to point me in the
>direction
>> > of a commercial piece of equipment which would perform the following
>task.
>> >
>> > I would like to be able to charge up a 12 volt (nominal) gell cell
>battery
>> > and then plug it into a piece of equipment to check its total AmpHour
>> > capacity during discharge at some constant rate current (say the "10
>hour"
>> > rate or the "20 hour" rate). All this towards assessing whether the
>> battery
>> > has proven useful capacity and life left in it, or has it reached its
>> > discard date?
>> >
>> > The equipment would show the delivered amp-hours up to the point at
>which
>> > the voltage has fallen to a nominated end voltage.
>> >
>> > I realise that you can do it in a way with a light globe to discharge
>the
>> > battery and then time the length the light holds up glowing brightly.
>> This
>> > is all too primative for this day and age, and there ought to be some
>> piece
>> > of equipment available for the task.
>> >
>> > Or some circuit from an electronics hobby magazine??
>> >
>> > Thanks in antcipation.
>> > Roger Druce
>> >
>> >
>If cost is no problem, then look at the modern chargers that the RC flyers
>use. The better chargers measure the discharge and charge capacity of
>batteries/accus. Look for brand names like Schulze, Orbit and Graupner.
>Price level 100 - 300 eur depending about the charger model.
>regs, Jyrki
>

Better yet, check any RC electric flight magazine (Quiet Flight for
instance) and take a look at the charger/cyclers they're using for the
electric power systems.

The rapid charge facility probably isn't necessary for us, but the
batteries these chargers are dealing with are nearer our battery sizes
than the ones used for standard RC transmitters and receivers.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Tom Seim]

Get a 10 ohm power resistor (25W) and a digital voltmeter. If you
don't have a digital voltmeter - BUY ONE; they are a must have tool!
Connect the resistor across the battery and start recording the
battery voltage. The discharge current is V/R (Ohm's law), and is
about 1.2 amp. Your typical battery is 6 A-hr, so your test will be
over in about 5 hours (less if your battery is tired). In any case
stop the test when the battery voltage drops below 11V. Your
incremental value per reading is:
(Time interval [min] / 60) * (Voltage / Resistance)
Add these incremental values together to get the A-Hr capacity of the
battery.

If you don't want to spend $100 on the ELK battery tester (or have 6V
batteries like I do) buy a 2nd resistor. Attach the first resistor and
measure the battery voltage. Do the same thing for the second
resistor. You will have to compute the following:

I1 = V1/R1, I2 = V2/R2

deltaI = I2 - I1
deltaV = V2 - V1

mhos = deltaI / deltaV

Mhos are the inverse of ohms, so more is better as far as a battery is
concerned (more than 100). Check a new battery for a base-line value.
The resistors should load the battery close to its operating point.
The resistors could be a single power FET with a variable voltage
control. Suggested resistor values: 10 and 20 ohm (10W min):

http://www.digikey.com/scripts/us/dksus.dll?Detail?Ref=89534&Row=282775
http://www.digikey.com/scripts/us/dksus.dll?Detail?Ref=93090&Row=279318

You can also parallel 10 100 ohm 1W resistors to get a 10 ohm 10W
resistor.

Tom

[John Giddy]

Another question on Peter Nyffeler's circuit:

I think the part number for the dual operational amplifier
is wrong. It should read "LM358" NOT "LM385". This last
item is a precision voltage reference, not an amplifier.

Cheers, John G.

"John Giddy" > wrote in message
...
| Hi Peter,
| Good circuit !
| However I have a couple of questions:
|
|
| 1.
| I presume the FET (Q2) will need a heatsink, as it will
| dissipate approximately 12W when discharging at 1 Amp ?
|
| 2.
| R9 should be 470 ohm, not 470 K
|
| Cheers, John G.
|
| "Peter Nyffeler" > wrote in
| message ...
| | In article
| >, "Roger
| Druce" > wrote:
| | >Perhaps someone out in r.a.s land may be able to point
me
| in the direction
| | >of a commercial piece of equipment which would perform
| the following task.
| | >
| | >I would like to be able to charge up a 12 volt
(nominal)
| gell cell battery
| | >and then plug it into a piece of equipment to check its
| total AmpHour
| | >capacity during discharge at some constant rate current
| (say the "10 hour"
| | >rate or the "20 hour" rate). All this towards
assessing
| whether the battery
| | >has proven useful capacity and life left in it, or has
it
| reached its
| | >discard date?
| | >
| | >The equipment would show the delivered amp-hours up to
| the point at which
| | >the voltage has fallen to a nominated end voltage.
| | >
| | >I realise that you can do it in a way with a light
globe
| to discharge the
| | >battery and then time the length the light holds up
| glowing brightly. This
| | >is all too primative for this day and age, and there
| ought to be some piece
| | >of equipment available for the task.
| | >
| | >Or some circuit from an electronics hobby magazine??
| | >
| | >Thanks in antcipation.
| | >Roger Druce
| |
| | I built one myself.
| | You find the schematic at
| http://www.ppc.ethz.ch/~peny/sf/ah_test.html
| |
| | Peter Nyffeler
| | Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10
21
|

[Peter Nyffeler]

In article >, "Chris" > wrote:
>Looks like a good project, what should the value of R7 be ?

Sorry I for the missing value
R7 = 10 k ohm
R9 should be 470 ohm
and don't forget a heatsink with more than 5 Kelvin/Watt
Unfortunately I don't have access to the webpages at the moment to replace the
schematic diagram.

Let me warn you to be carful with Chargers for RC modelers.
Most of them are not well designed to charge lead acid batteries.

A good reference for charging characteristics of lead acid batteries can be
found at
http://www.panasonic.com/industrial/battery/oem/chem/seal/index.html
in the pdf document "VRLA Charge Methods - 508KB".

I use a charger with current limited "two-step constant voltage charge control
method" and temperature coefficient compensation, published some years ago in
Elektor.

Peter Nyffeler
Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21