Test results LiFePO4 glider batteries after 6 years

Thank you for the West Mountain Radio battery tester recommendation Richard. It's a cracker of a little unit.

Casey

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.

On Tuesday, March 7, 2017 at 2:08:55 PM UTC-5, SF wrote:
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.

Make batteries great again!
LOL
UH

Its a useful discussion, if only to show the confusion about the LiFePO4 batteries. I've just got a Bienno 20AH battery to replace my old 20AH lead-acid battery (that really didn't give me a useful 20AH, as neither did the same lead-acid battery before that). 20AH is a large size for a glider, but I need a heavy nose battery for my motorglider anyway. The Bienno is a featherweight compared to the lead-acid, so I may need to add some weight in the nose now. I decided on a 20AH capacity because 1) it was the exact same size as my old lead-acid 20AH battery, so the battery holder didn't need to be altered 2) I distrust the manufacturer's claims of capacity, so only expect to get maybe 15AH 3) my impression (data is hard to find) is that battery lifetime (number of charge-discharge cycles) gets much shorter if a battery is routinely discharged more than 50%. So I'm planning on using 50% discharge (7.5AH) on my flights. Although the 20AH size is more expensive, I hope the lower % discharge will give me a compensating increase in battery lifetime. At my draw of 1.8A, 7.5AH is a 4hr flight. So I should typically land with the battery still strong.

So after all this, the question remains, are they worth it? I'm ready to replace my 14volt lead acids, the advantage is that the Lifepo4 will give me enough voltage with out building 14volt packs of lead acid. So again are they worth the extra hassle/money?

On Tuesday, March 7, 2017 at 6:26:07 PM UTC-6, wrote:
So after all this, the question remains, are they worth it? I'm ready to replace my 14volt lead acids, the advantage is that the Lifepo4 will give me enough voltage with out building 14volt packs of lead acid. So again are they worth the extra hassle/money?

The answer is clear as can be Cliff: No hassle and well worth the money. Take the plunge.. Lead-acid is so quaint.. keep up with the Jones'es.

wrote on 3/7/2017 4:25 PM:
3) my impression (data is hard to find) is that battery lifetime (number of charge-discharge cycles) gets much shorter if a battery is routinely discharged more than 50%

LiFe batteries "lifetime" is generally not affected by discharges as low as 80%.
The 50% number you mention is just a rule-of-thumb for deep cycle lead acid
batteries, and lead acid "lifetime" is substantially reduced if it's routinely
discharged to 80%.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

Yes worth it. Higher voltage will be appreciated by the radio. More capacity.
Lighter weight, longer life.
Not really a hassle with the right charger, just a little different.

SF wrote on 3/9/2017 6:16 PM:
Yes worth it. Higher voltage will be appreciated by the radio.

The radio will show it's appreciation by using less current; otherwise, a "modern"
radio won't care. "Modern" radios use power regulators that provide the correct
wattage to the radio, within a wide range of input voltages.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

My Dittle FSG60M, (May it RIP after it's death three weeks ago) Was the first thing in the airplane that suffered from the effects of low voltage. It seemed to receive just fine, but it made me sound like a Wookie when trying to transmit. That is the source material for my radio comment.

I've hated sailplane batteries ever since one died on a gold distance badge flight, I was 10 miles out at 6,000 FT. My argument that the landing witness should suffice for the missing final 10 miles of the .igc file, wasn't persuasive enough, so I had to do it again, with a different battery.