Test results LiFePO4 glider batteries after 6 years

What's a decimal among friends?

On Thursday, February 23, 2017 at 6:49:13 PM UTC+3, Papa3 wrote:
What's a decimal among friends?

Do you have some issue with my calculations?

On 02/23/2017 09:00 AM, Bruce Hoult wrote:
On Thursday, February 23, 2017 at 6:49:13 PM UTC+3, Papa3 wrote:
What's a decimal among friends?

Do you have some issue with my calculations?


He said 1C, meant to say .1C

I suppose battery mfgs use whatever discharge rating makes the numbers
look the best.

On Thursday, February 23, 2017 at 7:09:26 PM UTC+3, kinsell wrote:
On 02/23/2017 09:00 AM, Bruce Hoult wrote:
On Thursday, February 23, 2017 at 6:49:13 PM UTC+3, Papa3 wrote:
What's a decimal among friends?

Do you have some issue with my calculations?


He said 1C, meant to say .1C

I suppose battery mfgs use whatever discharge rating makes the numbers
look the best.

Oh, referring to his own dodgy calculations earlier .. fair enough.

Generic Panasonic batteries last about 400 cycles of 1C charge/discharge before falling to 70% capacity. The actual ones built for Tesla are though to be good for up to 1000 cycles of that treatment. You can charge a Tesla at 1C, but you're not going to discharge it anywhere near that rate unless you're on a racetrack. With the actual typical owner's normal daily use of using maybe 10% - 20% of the battery capacity and keeping the charge between 50% and 80% they'll do the equivalent of maybe somewhere between 2000 and 5000 full cycles.

At 400 - 500 km range per full cycle, that's 800k to 2.5M km.

Should be enough for most owners.

Yes, if you do road trips every day and use the whole capacity every time and then fast charge them multiple times a day then you might only get 200k - 500k km out of a battery pack. You could even potentially kill a battery pack in a year. Even less if you use multiple drivers 24/7. If you're doing that I assume it's for a business venture, and you'd better just factor in $20k - $30k [1] each for new battery packs as part of your cost of doing business. If you call it 10c/km you're probably reasonably safe.

[1] Tesla have promised replacements 80 kWh packs for $12k, but only eight years after vehicle purchase. The cost to make them will drop a lot between now and then. Roadster owners have been charged $30k for an upgrade to a modern battery pack.

On 02/23/2017 09:08 AM, kinsell wrote:
On 02/23/2017 09:00 AM, Bruce Hoult wrote:
On Thursday, February 23, 2017 at 6:49:13 PM UTC+3, Papa3 wrote:
What's a decimal among friends?

Do you have some issue with my calculations?


He said 1C, meant to say .1C

I suppose battery mfgs use whatever discharge rating makes the numbers
look the best.

And if they still don't look good enough, then they invent some
preposterous AH rating based on cranking amps, like some of the lithium
battery mfgs do.

The tests I'm running at approx 2.5A are being run with two batteries in parallel. I'm still deep discharging and recharging the old K2's trying to bring them back to life. I'll report back when I'm finished.

Updating on my results from deep discharging/prolonged recharging.

My 2 season old K2 LiFePO4 battery was showing a drop to 60.5% (5.8 Ah)when tested using a West Mountain Radio CBA III with 1.5A constant discharge current and test cut off of 11.0V.

After 2 cycles of discharge and 10 day recharge, the battery is back to 93.2% (8.95 Ah) of original. Pretty good results.

On Monday, February 27, 2017 at 6:12:49 PM UTC-8, wrote:
Updating on my results from deep discharging/prolonged recharging.

My 2 season old K2 LiFePO4 battery was showing a drop to 60.5% (5.8 Ah)when tested using a West Mountain Radio CBA III with 1.5A constant discharge current and test cut off of 11.0V.

After 2 cycles of discharge and 10 day recharge, the battery is back to 93.2% (8.95 Ah) of original. Pretty good results.

Keep in mind that it is the act of recharging that causes the cell balancing, once the battery is charged fully or near fully the cell balancing stops (in most of these cheap schemes). No cell balancing takes place (typically) on discharge as doing so wastes energy. The best strategy may be to do several discharge/charge cycles to 40 - 50% or so in succession. Slow charging may be best if you can arrange it - the bypass shunts are very limited in capacity and would be more effective with lower charging currents.

I recently consulted one of the K2 Battery representatives he told me the following...

I would suggest getting one of our chargers and charging the battery with it every few months to let the battery float and balance. It starts balancing at approximately 14.4V to 14.6V, and our charger is a 14.6V charger.

So it appears that balancing doesn't really start to occur until it reaches the 14.4 volts, and letting it float there for a while will help re-balance the cells.

Brian

On Thursday, February 23, 2017 at 8:36:41 AM UTC-5, wrote:
On Wednesday, February 22, 2017 at 10:20:46 PM UTC-5, Papa3 wrote:
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'm testing at very close to 1 amp using six 2 ohm resistors that actually measure 13 ohms total and plan on using 12 volts as end point. I doesn't seem like there is much useful capacity past that point. I'll report my data back.
UH

Update after testing four batteries. All charged and allowed to balance over night
#1- K2: run 1 was 6AH, run 2 was 6AH
#2- K2: run 1 was 7.75 AH, run 2 was 8.33AH
#3- K2: run 1 was 6.50 AH, run 2 was 8.75 AH
#4- Stark: run 1 was 7.2 AH, run 2 was 8.50

I'm going to do another cycle to see if any improve.
FWIW
UH