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Topic: Reading Battery Voltage using ADC (Read 1 time) previous topic - next topic

alainagius

Ok I'll give that a go! Thanks a lot all!

retrolefty

Well 1k ohm is just a 1.5ma load and 12k is just a .000125 ma load, neither of which is really 'load testing' a 2500ma cell. I would think C/10 (250ma) would be the minimum size load you would want for a decent 'voltage under load' measurement, or 250ma = 6 ohm 1 watt resistor.

alainagius

OK so first off, just tried the setup as James C4S instructed me to with a 5V reference and it worked, a put a 1kOhm resistor and the resolution seemed to play around so I put a 12kOhm resistor (trial and error) and the resolution stabilised. The Arduino Mega has a built in 2.56V and 1.1V reference so I applied the 2.56V range and so I managed to use a larger percentage of the resolution available.

It seems to be ok with a 12kOhm resistor but if you can suggest any math that I should look into to determine an ideal resistance value I would be very grateful. The 1.5V cells have 2500mAh

retrolefty

Let me ask you this before deciding if you need to do anything with the Aref or not. You are measuring 1.5vdc DC batteries for some kind of fail/pass test procedure. What value is your decision point value if the battery is to be accepted or rejected? I suspect that the standard 0-5vdc range will be more then good enough resolution for such a test/pass procedure. Also the mah rating of your 1.5v cells should be looked at for the proper sizing of a load resistor. What cell size are you testing?

Lefty

AWOL

You could put a 2:1 divider onto Aref, which would give you 2.5V FSD, so giving you just under 2.5mV resolution.

Yes, you should (briefly) put the battery under load.
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