I am trying to measure capacity of a Li-ion battery(APR18650M1). For this goal, I am using a DAQ, a Mosfet key, a high power resistance with Matlab software. With all of these components and with creating PWM to on/off the Mosfet key, I discharged a full charged battery to completely full discharged with constant current.
Meanwhile, the number I am finding for battery's capacity is about .65 Ah while it's nominal capacity is about 1.1 Ah(cells are new and I bought them from an official retailer for A123 systems company).
For instance Once I discharged one of those cells with 1.04 A current,number of times that PWM worked was 2321(and each one took 1 sec), so according to these numbers capacity is about 2424 mAh, however whole time to run the program was about 3821.41 seconds which if I multiply it to 1.04A, the result is about 3927mAh.
The second number is close to battery's nominal capacity, but I think it is not acceptable since the time that I had current in the circuit was about 2321 seconds.
What do you think? if you have any suggestion.
Thanks in advance for your help and attention.