# Re: [NTLK] Testing Battery Capacity on MP2x00

From: Johannes Wolf (mp2100_at_mail-gw.estec.esa.nl)
Date: Mon Jun 10 2002 - 03:27:32 EDT

I fully agree with you, Frank, but as far as I understood the original post,
the issue was a more professional method for the treatment/test of a big
number of battery packs.
And of course you can treat the complete pack only, but this is the case as
with more than one cell in series is a widely used practice for instance for
R/C racing car battery packs.
You Formula for calculating the capacity is only an estimation because
according to Ohms law the current through the resistors will vary with
voltage. For this method it would be much more precise simply to compare the
time until the 4V are reached

> -----Original Message-----
> From: newtontalk-bounce_at_newtontalk.net
> [mailto:newtontalk-bounce_at_newtontalk.net]On Behalf Of Frank Gruendel
> Sent: Saturday, June 08, 2002 10:56 PM
> To: newtontalk_at_newtontalk.net
> Subject: [NTLK] Testing Battery Capacity on MP2x00
>
>
>
> > there are a lot of "intelligent" charge processors on the market.
> > This would be the best way to determine the battery capacity
> and to apply
> > several treatments like normal charge, fast charge and controlled
> discharge
> > to the batteries.
>
> This would only make sense if it was done to the cells seperately. Which
> you can do on a 110/120/130, but not on an OMP/100/2x00/eMate.
>
> > The only problem is to interface the Newt battery pack to the charger.
> > But this is solveable I think.
>
> If all you want is the capacity, there's an easier way (assuming the four
> cells are in pretty much the same condition. If they aren't, forget it).
>
> 1) Get yourself four 10 ohms resistors and a voltmeter.
>
> 2) Connect the resistors like that:
>
> A o---XXX---XXX---XXX---XXX---o B
>
> 2) Fully charge the pack in the Newton.
>
> 3) Remove the pack.
>
> 4) Connect A to the round contact (-) and B to the
> rectangular contact at the side where only one
> rectangular contact is. Write down the start
> time.
>
> 5) Monitor the voltage across A and B until it
> reaches 4.0 volts.
> This will take about 10 hours for a new original pack
> or about 14 hours for one I refurbished.
>
> 6) Remove the resistors.
>
> 7) Write down the elapsed time.
>
> The formula to calculate the capacity is
>
> Capacity = 120 mA * elapsed time (in hours)
>
> Caution: It is mandatory that you stop the discharge as soon as the
> pack's voltage reaches 4.0 volts. If you forget this, the pack will be
> deep-discharged which is for a couple of reasons not a good thing
> (I know some of you disagree here, but I'm not going to change
> my mind).
>
> Note: If you manage to get a 1 Watt 40 ohms resistor, you needn't
> get the four I described above. But those are kind of hard to come
> by. 10 Ohms can be obtained pretty much everywhere, moreover,
> if you do it that way you could use a 0.25 Watt type which is quite
> cheap.
>
> Frank
>
> Newton hardware and software at http://www.pda-soft.de
>
>
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