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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Northy on January 15, 2022, 04:58:08 pm

Title: Advice on calibrating an RC lipo testing thingy I've put together?
Post by: Northy on January 15, 2022, 04:58:08 pm
Hi,

I've built a testing set-up to test RC lipos to try and get an idea of how they are holding up to the abuse they get while being used.

By connecting an external resistor bank to my charger I can discharge them at up to 20A, this is done by connecting the battery under test to the input of the charger and the resistor bank to the charging port. I've got this bit working fine.

While the battery is discharging I monitor it with a Picologger.
The batteries are 2S, so have a centre 'balancing' terminal. So with the Picologger I am using two channels to log the centre tap point and the +ve terminal - both with respect to the -ve terminal.

In the Picologger software I log the overall pack voltage, the centre tap voltage and then subtract the centre tap voltage from the overall voltage to log the second individual cell voltage.

I'm getting a small discrepancy between the two individual cell voltages, that I'd like to calibrate out as much as possible in the software logging. I'm not looking for absolute, traceable calibration here, just good enough to see if I've got a bad battery or not.

All I've got to hand is a variable bench power supply and a few hand-held meters. None of them calibrated themselves. I don't have access to any calibrated equipment either.

What's the best way to try and get my set-up as good as I can, with the equipment I've got?

Thanks,

G

Title: Re: Advice on calibrating an RC lipo testing thingy I've put together?
Post by: IanB on January 15, 2022, 05:06:32 pm
It is intended that you can trust the readings on the hand-held meters. You don't need a calibration certificate except for specific traceability requirements. Therefore, just use a meter to measure the voltages and adjust accordingly.

What I typically do if I have a few hand-held meters is to measure the same voltage on all of them and compare readings. Any meters that are deviating significantly from true will typically be revealed by giving outlying readings.

Title: Re: Advice on calibrating an RC lipo testing thingy I've put together?
Post by: Northy on January 18, 2022, 10:46:50 pm
Hmmm, yeah, maybe I was thinking too much about it  |O

Thanks,

G