Battery testing, part 1

This is a follow – up to my post in late February, “A battery project”. I was curious about the actual amp-hour capacity of the battery, compared to the nominal capacity printed on the label, and generally interested to learn a bit more about a key element of portable radio operating.

The setup:

Checking the accuracy of the voltage reading; all of the meters agree within 0.01 – 0.02 volt, good enough to go forward with. I didn’t check the accuracy of the current measurement, I probably should do that sometime soon.

The equipment:

The test load is a (tr)uSDX transceiver drawing about 60 mA on receive.
RC Electronics Watt’s Up (rev. 2.1) DC multimeter, used to measure voltage, ampere-hours, and watt-hours.
QRPguys SWR / power meter, mostly there as a dummy load to protect the PA transistors if I happen to transmit.
The Fluke DMMs are used only to check calibration.

I’m using a couple of CR2032 batteries to provide external power to the Watt’s Up meter so the amp-hour data will be preserved when the pack shuts down.

I have been through 3 full charge – discharge cycles now, and still don’t have a data set without gaps, interruptions, and loss of data. There seems to be an intermittent fault in the battery pack itself which triggers a shutdown which is only cleared by disconnecting and reconnecting the load; I think this points to the BMS board. Short circuit / overcurrent? Not sure; I am going to take the pack apart and examine it carefully, for a start. There may be other intermittent problems, too; it seemed like the external power failed on one occasion. In any case I have paused this project for the moment, subject to verifying the equipment and setup.

A few extracts from my patchy and incomplete data:

Capacity of the pack seems to be about 2.8 Ah
Voltage under load starts at 12.23, the BMS shuts it down at 9.41
About 50 hours run time for the (tr)uSDX receiver, volume set at 11

It seems like the run-time has increased over the course of the 3 trials, implying an increase in amp-hour capacity, but it’s hard to put a number on it.

And incidental data from the (tr)uSDX: Transmitting on 20 meters into 50 ohm dummy load @ 11.12 volts, 0.73 amps (8.1 watts) input (measured by the Watt’s Up) gives 5.29 watts out on as measured by the (tr)uSDX itself; or 5.19 watts out measured by the QRPguys meter.

Watch for a Part 2 post when I (hopefully) have better data to present.

Thanks for visiting driftlessqrp!

The setup:

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