On Wed, 17 Apr 2019 18:58:38 -0700, 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/batterytest/
Battery_Testing_Results_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.

I do much the same each winter, but I use an old Pro-Peak Prodigy II
battery charger/cycler mainly because I already had one, bought for model
flying. This does lead-acid, NiCd, NiMH and Li and discharges at 400 mA -
a bit low (my panel draws 480 mA excluding the radio, which is on a
second battery along with the T&B) but it does measure capacity
automatically: connect a battery, hit start and go do something else
until its finished.

You can find similar charger/cyclers on Ebay for GBP 22 ($30).

I used to run my Prodigy II off another SLA, but at some point weakened
and bought a cheapish 12 volt supply for it.


--
Martin | martin at
Gregorie | gregorie dot org