Some LiFePO4 Battery Testing Results Manual and Automated

On 10/16/19 4:05 AM, 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

Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.