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Students Click Here

measure available charge

measure available charge

measure available charge

(OP)
Is there any reliable way to measure/calculate the
available charge in rechargeable batteries of different types ?

May measure and use current and/or voltage history
during previous charges and discharges or measure
internal resistance and temperature.


Plesae read FAQ240-1032
My WEB: <http://geocities.com/nbucska/>

RE: measure available charge

To some level of granularity, yes:
http://www.duracell.com/oem/rechargeable/Nickel/discharge.asp

The discharge curves show that for a given battery type, temperature and discharge current, you could hypothetically predict the amount of available charge.  

You might also want to look at how laptop power management software/hardware make their prognistications as to when your laptop runs out of juice.

While the predictions appear repeatable, I'm not sure how accurate they are.

TTFN



RE: measure available charge

With a lead-acid battery, a voltage reading does the job properly.  Not for the other chemistries.  There was a company called Benchmarq who pionnered the so-called gas-gauge chips for batteries.  They are now part of Texas Instruments.  The parts prefixed bq are the ones.  The applications notes and schematics will teach you a lot about the subject.  Do these chips also take into account the theoretical degradation of the batteries as a function of its use?

RE: measure available charge

Hi nbucska,

The only way to figure out the remaining charge is to discharge the battery and measure these amphours.

This will give different results depending on the discharge current used. And that's one of the problems you face when trying to estimate the remaining charge.

If the discharge current is known and constant then an estimation is possible if you know the battery discharge history and the amount of capacity already used and the current rate. If the temperature is changing a lot and the discharge-time is long then the whole thing won't work properly, especially if the battery is a big one (forklift truck battery).

What application are you thinking of?

:)  roman

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