Testing capacity of a battery..

[Barrymung]

All,

I have been approached by someone who wants to "test the capacity" of a particular lipo battery pack.

What they'd like to do is draw a certain constant current from the battery and record the voltage (manually) using a volt meter every so many minutes and draw a graph. This would then be repeated at different current loads. Current could be up to 11 amps at 4.2 volts, worst case.

I have suggested some sort of adjustable load, that they can manually adjust while monitoring the current with an ammeter.

What other cheap and cheerful ways would there be to do this? Can anyone suggest a cheap variable load that would accomplish this?

(Yes, I have stressed that a lipo should not be taken beyond it's maximum load under any circumstances..)

 

[Alec_t]

It probably won't be a 'cheap and cheerful' solution. It will need an adjustable constant-current source able to dissipate ~44W, hence a high-power-handling FET on a BIG heatsink, plus current-monitoring and control circuitry and, importantly, voltage monitoring circuitry to provide automatic switch-off when the battery reaches its safe discharge threshold.
A reputable LiPo battery manufacturer should be able to supply the required data.