AviationBanter - View Single Post - Some LiFePO4 Battery Testing Results Manual and Automated

2G · October 17th 19, 03:56 AM posted to rec.aviation.soaring

On Wednesday, October 16, 2019 at 3:05:58 AM UTC-7, krasw wrote:
On Wednesday, 16 October 2019 05:44:35 UTC+3, 2G wrote:
On Thursday, May 2, 2019 at 2:11:13 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Some updates;

- I was lent a Bioenno BLF-1209WS purchased in Jan 2019. Tested and ran for 8.8h.
- Updated my Arduino automated tester by adding an "LCD Keypad Shield" display to allow monitoring of the testing. The updated code has been uploaded.
- Created a new XLS spreadsheet to parse the automated testing results and create a graph from them
- Added pictures of my test rig.

Find all this, and more, at http://aviation.derosaweb.net/batterytest..

John OHM Ω

Congratulations on building a battery tester (I wouldn't bother, myself).

But here are the shortcomings of your tester:
1. It has no discharge cutoff. It keeps discharging the battery until totally discharged. This can damage the battery, and is certainly not good for it. I would not test a battery w/o this.

2. It does not discharge at a constant current. The current decreases as the voltage drops. Modern battery testers will do this.

3. It does not discharge at a constant wattage. This is a more typical scenario where avionics will increase current as the voltage drops.

That said, it is better than sitting down for 6 to 10 hours and recording meter readings. I have switched my avionics battery from a Pb to a LiFePO4 partly because I don't want to buy a new battery every 2 years.

Tom

1. BMS does the cutoff inside battery anyway
2. Voltage does not drop much with LFP
3. How is this relevant, most just want to know if their battery capacity is 10Ah or 7 Ah, not 9.998 Ah.

1. No, the BMS will not cutoff discharge - I know.
2. Relevant when comparing different battery chemistry's.
3. It's relevant when comparing lithium batteries to lead-acid.

As a former electrical engineer, I strove to minimize error sources as much as feasible because until you know the answer, you don't know which error is going to bite you in the butt. Nothing worse than having your glass panel go dark in the middle of nowhere because you under-estimated.

Tom