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I am attempting to change the temperature that a 3.7v rechargeable LiPo Battery is discharged in and am seeing how this affects the capacity and discharge rate of the battery. My setup currently uses an Ammeter and Voltmeter to log the data over time. However, from my research, I have found that I must use a constant Power load or a constant current load for this setup. Since I do not have access to these, is there no way that I can find a discharge rate with what I have?

If not, what can I find out/compare at different temperatures with the data provided?

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  • \$\begingroup\$ Presumably you are using a resistive load. Doing so will mean that the discharge current varies as a function of voltage, but the variation over the useful discharge voltages is not so extreme as to create an invalid experiment. It simply means that you must base you calculations on the actual voltage and current at a given point in time, not a set point current. You will, however, need some sort of cut-off to stop the discharge before you damage the cell. \$\endgroup\$ – Chris Stratton Sep 24 '20 at 15:27
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    \$\begingroup\$ Maybe you have a buck (or boost) convertor spare. If you feed its output into a resistor, it will act as a constant power load for as long as the convertor can keep the output voltage constant. Don't discharge the LiPo cell too far. Maybe add a fan to cool the resistor and convertor. \$\endgroup\$ – Andrew Morton Sep 24 '20 at 16:07
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What you need is a "constant current sink". It's a fairly straightforward circuit to build out of a transistor, an op-amp, and a couple of resistors:

https://circuitdigest.com/electronic-circuits/voltage-controlled-current-source-circuit-using-op-amp

https://circuitdigest.com/electronic-circuits/design-a-simple-constant-current-sink-circuit-using-op-amp

Good luck.

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