Test results LiFePO4 glider batteries after 6 years

On Sunday, February 19, 2017 at 3:22:29 PM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
Sounds like this chemistry has a memory...

No. This is about cell balancing.

If they have a built in balance board, how is this balancing?

On Sunday, February 19, 2017 at 12:50:04 PM UTC-5, SF wrote:
I'm game, I'll repeat the charge discharge process a few times and report back.

SF

What cut off voltage are you using in your tests?
Also what discharge rate.
Thx
UH

On Wednesday, February 22, 2017 at 7:01:10 AM UTC-8, wrote:
On Sunday, February 19, 2017 at 12:50:04 PM UTC-5, SF wrote:
I'm game, I'll repeat the charge discharge process a few times and report back.

SF

What cut off voltage are you using in your tests?
Also what discharge rate.
Thx
UH

With the West Mountain Radio CBA IV I use:

1 or 2 aH and 10 volts for the cutoff on the CBA IV. If you set the cutoff at 8 volts you will see if the battery BMS works.

You can use up to 100 watt about 6 aH with this device after that you go above 100 watts and need an amplifier.


Richard
www.craggyaero.com

I used 2.5 amp as the discharge rate, was about 45 watts, and used a cutoff of 10 volts. Also using a CBA IV.

David

Are LiFePo4 batteries not rated using a standard 1C discharge rate like SLA batteries? So, for a 10ah battery the rated capacity would be achieved at a discharge rate of 1a. 2.5a seems on the high side for a glider, even one with a fair number of electronic goodies. My ship draws not too much over 1a with FSG71, Trig, Clearnav, Flarm, and CNv. No?

P3

I was using 11.5 volts as the voltage to stop testing at. After 11.5 v not much left, and didn't want to over discharge for a test. Don't completely trust the bms board.

Sf

On Sunday, January 29, 2017 at 1:41:07 PM UTC-6, SF wrote:
I started using K2 LiFeP04 batteries in my glider in 2010. I have had excellent results with these batteries. The electronics, especially the radio, enjoy staying above 12V, and I've never run out of power inflight with them.

This winter after taking some of the instruments out to have them calibrated & upgraded, I took one of these batteries with me to the shop to power everything up to see if all the magic smoke remained in the equipment after it was reinstalled. Imagine my surprise when nothing came on, and I found the battery at 10.5 volts.

This battery was charged after its last usage 1-1/2 months ago and left in a cabinet. Since these batteries are not supposed to self discharge that fast I decided to charge, and test them using two batteries in parallel on a 2.04A load. My six year old 9.6AH K2's were down to 5.4 Ah each, 10.8 Ah total.

I purchased two new Stark Power SP-12V9-EP LiFeP04 batteries and wired them in parallel on the same 2.04A load, and got 8.67 Ah each, 17.34 Ah total..

The tests were run until the voltage under load dropped to 11.5 V, not the 10.5V level where the battery management board turns off the output. There are probably some additional Ah's left in there after 11.5 V but not much, these batteries drop off pretty fast after 12.5V. The stark batteries are listed at 9Ah each.

The LiFePO4 batteries are advertised as having a cycle life of 2,000 cycles. Over the six years they were in use, I probably put less than 400 cycles on these. So obviously they also degrade with age and not just the number of charge/discharge cycles.

I still recommend these over the old sealed lead acid batteries. I also advocate annual testing to see if they still have the capacity you need, rather than waiting until they surprise you in flight.

SF

Richard just checked my 15 Amp and 12 Amp LifePo4 batteries purchased in 2013 from Bioenno, both are at 13.30 Volts waiting for the season to start. See you in Nephi

On Monday, February 20, 2017 at 6:32:36 AM UTC-8, glidergreg wrote:
On Sunday, January 29, 2017 at 1:41:07 PM UTC-6, SF wrote:
I started using K2 LiFeP04 batteries in my glider in 2010. I have had excellent results with these batteries. The electronics, especially the radio, enjoy staying above 12V, and I've never run out of power inflight with them.

This winter after taking some of the instruments out to have them calibrated & upgraded, I took one of these batteries with me to the shop to power everything up to see if all the magic smoke remained in the equipment after it was reinstalled. Imagine my surprise when nothing came on, and I found the battery at 10.5 volts.

This battery was charged after its last usage 1-1/2 months ago and left in a cabinet. Since these batteries are not supposed to self discharge that fast I decided to charge, and test them using two batteries in parallel on a 2.04A load. My six year old 9.6AH K2's were down to 5.4 Ah each, 10.8 Ah total.

I purchased two new Stark Power SP-12V9-EP LiFeP04 batteries and wired them in parallel on the same 2.04A load, and got 8.67 Ah each, 17.34 Ah total.

The tests were run until the voltage under load dropped to 11.5 V, not the 10.5V level where the battery management board turns off the output. There are probably some additional Ah's left in there after 11.5 V but not much, these batteries drop off pretty fast after 12.5V. The stark batteries are listed at 9Ah each.

The LiFePO4 batteries are advertised as having a cycle life of 2,000 cycles. Over the six years they were in use, I probably put less than 400 cycles on these. So obviously they also degrade with age and not just the number of charge/discharge cycles.

I still recommend these over the old sealed lead acid batteries. I also advocate annual testing to see if they still have the capacity you need, rather than waiting until they surprise you in flight.

SF

Richard just checked my 15 Amp and 12 Amp LifePo4 batteries purchased in 2013 from Bioenno, both are at 13.30 Volts waiting for the season to start. See you in Nephi

You have to check the fine print on their web page "battery allows for extraction of 90% of the rated capacity"

Richard

My oldest K2 battery (6 years old), has obviously lost one or more cells. During an unloaded voltage check it appears to be fine. Put a load on it, and the voltages plummets to a little over 12V, then starts a gradual decline. With about 2AH left out of 9AH, only available at a voltage lower than desired, it's going to the recycler.

The newer (5 year old) K2 responded pretty well to the discharge - charge - leave it on float for a few days - repeat process. it came back to about 80% of it's original capacity while discharging down to 11.5V.

The take away from this is if you think you may have a LiFePo4 battery issue, a test under load, after a few times through the discharge - charge - leave it on float for a few days - repeat process. will confirm it or fix it.. The old myth that one battery will charge the other battery if you run them in parallel has also been successfully debunked. So go ahead put both batteries on the 12V bus, and you have one less switch to flip in flight,.

SF

We may have set a new record with this topic for actually staying on track. Don't know who is keeping up with this, someone somewhere probably has a graph or two to document what the average number of posts it takes to start arguing about the rules or Flarm stealth mode on a post about a canopy cover.