Guy Farebrother wrote:
> 
> Pardon me for asking what may be a simple question.
> 
> If you discharge the 7.5 V nicads into 47R (160mA) for 10 seconds what
> would you expect to see in a good / marginal / bad battery for voltage?
Take the difference as a percentage of the first voltage.
Fully charged batteries will be > 90%
Marginally charged batteries will be > 80%
This will indicate the charge level only. If you want to determine the
state of the battery (good, bad, or ugly), you'll have to charge them
fully before discharging. This will give you an indication of remaining
capacity.

VERY IMPORTANT : Make it impossible for the battery to discharge for
longer than 10s. If your software goes haywire, the resistor will
unsolder itself with disasterous effect (fire & brimstone) !!

> Does the manufacturers data indicate these values?
No - unfortunately not. I think it is for safety reasons (see the
warning above)

> If I had a 12 volt
> lead-acid battery at 1AH and I discharged it at X mA would I discharge a 10
> AH 12 V lead acid cell at 10X for the same indication of battery condition.
> Could I use the PWM O/P (set at 10% or 100%) of a PIC to control the load
> via a FET for both of these tests or would I require two separate loads?
This test will not work for Pb batteries. The internal resistance is a
very poor indication for a Pb cell. The voltage drop vs capacity,
however,
is a lot 'better' than a NiCd for capacity measurement.

Very important : Never let a Pb battery discharge completely - it will
cost you a fortune in replacements. If you absolutely have to, the ONLY
Pb battery in the world that can handle it, is at http://hepi.com

> 
> Thanks in advance for any assistance.
No problem

-- 
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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