Some LiFePO4 Battery Testing Results Manual and Automated

On Wednesday, April 17, 2019 at 6:58:40 PM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
Every year I test my two LiFePO4 batteries to gauge how long they will last during a flight. I decided to open the field a bit and also tested some soaring friend's batteries.

You can read about my simple cheap manual process (later automated - see below) here http://aviation.derosaweb.net/#batterytest which was also detailed in Soaring (Feb 2012). Yeah, I know there are automated testers on the market but I want to create something cheap that everyone can make.

My battery go/no-go is how long it will take for the battery to drop to 12.0Vdc with a continuous 12Ω (~1A) resistive load. Here is what I found;

2013 Bioenno Model BLF-1209T- 6.5H
2015 Stark Model SP-12V9-EF - 5.5h
2015 Bioenno Model HN12V9AHF- 7.0H
2017 Bioenno model BLF-1209WS - 9.0H

Full details of my results can be found here http://aviation.derosaweb.net/batter...s_04.08.19.pdf

Anyone else tested their batteries in this same way? What are your results?

Automation - Manually gathering data every 10 minutes for 6-9 hours on four different batteries is tedious at best. I watched a lot of movies. So I decided to automate the process with an cheap $10 Arduino Duo. The Arduino software takes a reading at different points of time based on the current voltage. Every one minute at the beginning and end of the test, and every 10 minutes in the middle.

It still takes 6-9 hours to run the test but recording the voltages is fully automated so running the test is a start-then-walk-away-and-come-back-later-for-the-findings kind of deal. Luckily with the LiFePO4 batteries when they get below ~11.0Vdc the BMS basically shuts the battery off. The program detects any voltage drop below 8Vdc and terminates itself.

If anyone is interested in duplicating my Arduino test rig, drop me a line and I will share the details. My Arduino code can be found at http://aviation.derosaweb.net/batterytest/arduino.

John OHM Ω

Well done John - very impressive, and a fun project.

I'm some combination of too busy and too lazy, so I spent $179 on one of these. I still watch movies, but maybe not under duress. ;-)

https://www.dxengineering.com/parts/...COCcQAvD_ BwE

Andy

My battery analyzer is based on this cheap chinese coulometer:

https://www.ebay.com/itm/DC8-80V-50A...-/252470874308

I use small car light bulb (10-20W) as a load.

I connect the thing between charger and batter or load and battery. That way I can measure capacity both ways. It is also super easy to discharge battery to optimum state for winter storage.

I like it so much I seriously thought about putting it my glider panel. If it only would support 2 or 3 batteries.

Checkout (Google) "ZB2L3" or "Battery Capacity Meter Discharge Tester
Analyzer". (Less than $10, 15 volts max, doesn't provide a log, just
shows capacity)

I used an old micro-USB phone charger to power the tester. (Low-power
is OK as it is not doing any charging).

For the load I used a couple of 7 Watt car taillight bulbs in parallel.
(The
resistors supplied with the tester are not suitable as they get too hot at

12 volts)
I mounted everything in an old metal toolbox.

Easy to use, cuts out at the voltage you choose, shows capacity in amp-
hours.

I've been using 6 of these for years, haven't had any problems.

I get much more repeatable results if I only test batteries that have
been left on charge for a few days after the 'full' light illuminates.
I suspect that lithium chargers may indicate 'full' a bit early while there

is still ~5% to go before they actually shut off.
I know that Gellcell / NiMh / Lead Acid chargers indicate 'Fully charged'
when the battery is around 85 - 95% full.

Lots of good info on general glider wiring practices at
http://aviation.derosaweb.net/presentations/#wiring

Particularly like the bit about fusing light current wiring so that it
doesn't
go up in flames. After a bumpy landing I once had an undercarriage-
warning wire let out some smoke. It was connected to a 10 amp fused
bus. The fuse didn't blow due to the resistance of the thin wire but it
still
got very hot! Luckily it was Tefzel wire and didn't melt.