Filament Taped Compression of Aged Zippy 8AH Packs

[icecube57]

Ok im getting my chops busted for doing this. Apparently its hog wash but I have some 6s 8AH Zippys that are little over a year old. Varying states of abuse. Some I ran at 3s 1p for a while with a 65A Lyen 3077 Mosfet controller and when I got my bike setup I ran 3s 3P in a Falcon EV Frame bag. About 100+ or so cycles and varying DOD but roughly probably 25 discharges at 100% 75% 50% and 25%.

I recently did discharge tests on my packs to get a feel on how they were aging and check capacity.I had 4 packs that were giving around 7AH and the others were 7400-7500mah. When they were fresh they were all about 7800-7900 at .5C 4A discharge. Ive never been able to get full AH out of these packs at 1C nor at .5C they came close. They only delivered at .25C or lower so IR i think is a factor with these batteries.

So I have a few that are a little fluffy not OMG throw it away bloated. Guess which ones.. the ones that were the lowest capacity. When I discharged them I didnt charge them back up. When packs are discharge the shrink and get squishy a bit. However these packs still are a little bit swollen. I put the packs in the fridge and the felt a bit more solid and they had gone down in size. I went to the store and got some filament tape and took the packs out of the fridge. Waited for them to return to room temp and start putting rows of tap around the pack very tightly. I went length and width wise. I put the pack back on the charger.

I have an Icharger 406 Duo by the way. Its hard for me to mess this up.

The pack originally gave 6915AH on the first discharge. 4A Discharge
After wrapping I put back 7414AH into the pack (8A Charge Slow Balance)
One the second discharge test I got 7218AH out of the pack. 4A Discharge
On the charge up I put back 7519AH.(8A Charge Slow Balance)

I will do one more discharge to see if there is any improvement or if it stays the same.

Im also going to check the pack that didnt have any physical deformities. This was one of the better packs that delivered 7445AH on first discharge. I wrapped it the same way as the swollen pack and will charge it back up and discharge it again to see if there is any gain if any.

The packs do seem much harder and not due to the tape.

Your thoughts

 

[Punx0r]

Luke (liveforphysics) has confirmed before that appropriate compression of the pack will extend life, reduce gassing and increase capacity.

However,

Waited for them to return to room temp and start putting rows of tap around the pack very tightly. I went length and width wise.

I imagine you crushed the edges of the pack doing this, and that is bad news.

 

[icecube57]

Wouldnt they be crushing themselves already with the heat shrink to some extent.The heatshrink gives a little but there still a significant amount of containment vs filament tape which has no give at all. So if the packs are expanding and contracting with discharge compression would help with IR wouldn't it. In short from what I see any form of compression helps. In the long term what it does to the cell is unknown. With the pack Im testing now Im seeing minor improvements 100-150mah at a time as I cycle the packs. And the problem pack does feel alot firmer.I think what you think i should do is has some end caps for a more consistent and even compression over the entire cell. This would require something like those plastic butch boards cut to size and put in some C clamps and then strapped.

 

[dnmun]

i use 1/8" hardboard i got for free. cut to the size of the pouches, but i also remove all the shrink wrap and the big band of tape that circles over the top and bottom.

then i clamp it tight in a wood clamp and wrap with duck tape.

the idea of compression goes all the way back to the time when gel cell SLA batteries, VRLA batteries, were developed.

it turns out that the gel type VRLA packs will have extended cycle life if the electrodes are stacked horizontally like pancakes. this was discovered back in the 30-40's when the VRLA batteries were developed.

my understanding is that the plates do not suffer as much of the slight fracturing of the electrode, lead, surface as the cell is charged and discharged because the weight keeps the two electrode plates in tight contact with the gel as the gas formation at the surface during charging tries to push the plates apart so the surfaces do not move and cause spalling off of the lead on the surface.

for the cathodic material in the lipo packs it may be a similar type of behavior that allows more of the charge to reach the cathodic matrix by maintaining good contact under compression.

i have now mounted the big 100Ah gel VRLA batteries in my ZENN car vertically on end so that the plates are pushed together inside the casing by the force of gravity and i expect the batteries to last a long time now. maybe another 1000 cycles.

it is hard to get uniform compression. i had some nanotech 8,000mAh lipos that had swelled without reason. never overcharged or over discharged, just sitting at relative discharge around 3.6-3.8V and they puffed up on the ends of the 6S packs. i put the 6S packs between two boards and clamped them with the wood clamp and after about a week or two the swelling had gone, enuff that i had no problem building the 21S pack with them.

 

[icecube57]

3 inch molding cut to size comes to mind comes to mind

 

[dogman dan]

It's too bad there isn't a piece of very stiff plastic or something like that under the shrink wrap. Tape or shrink, It's trying to make the pack round.

I think the hobby industry is not too worried about it, because drone owners just cycle packs to death so fast it matters little to them.

We bike riders, we put 1000 wh of it in a pile, and hope to get more than a year, or even two. So our needs are more extending calendar lifespan.

 

[icecube57]

Well I actually took this a step further and pricked and resealed the gas in the packs while under compression. Wrapped with filament tape an made huge improvements. Packs are as hard as a rock. I had 1 pack that tested out to 7013mah before and retested it to 7750 and another pack that gave 6985mah and afterwards it gave 7762mah. There is is 1 more pack to "refurbish" These will definitely be charged and used with caution. but the performance including IR is great. Cells that were the runt cells on the first discharge are performing very well and no longer are the runt cells.

 

[dawrench]

What did you use to reseal the pouches? I have some puffed NanoTech bricks that have lost capacity.

 

[dnmun]

i use nail polish, i have several bottles and i use the hardener stuff too, it is stronger and it seals better than the nail polish i think.

 

[liveforphysics]

Well I actually took this a step further and pricked and resealed the gas in the packs while under compression. Wrapped with filament tape an made huge improvements. Packs are as hard as a rock. I had 1 pack that tested out to 7013mah before and retested it to 7750 and another pack that gave 6985mah and afterwards it gave 7762mah. There is is 1 more pack to "refurbish" These will definitely be charged and used with caution. but the performance including IR is great. Cells that were the runt cells on the first discharge are performing very well and no longer are the runt cells.

Not uncommon levels of improvement. Anywhere you have bubbles, micro or macro, you aren't able to use that portion of the cell.