Lipo experiences. Please post your personal findings!

[liveforphysics]

You never want them to puff, and if they do, you want to get that gas out and re-seal them (ideally replacing the solvent that is missing before resealing, but that is difficult to aquire).

Pressure does help prevent puffing, not because any amount of pressure can prevent off-gassing from occurring, but because it helps minimize the circumstances that enable puffing to happen. But it will have no effect on puffing from over-discharge or over-charge.

LiPo virtually can't explode (like round cells or lead-acid), but it can vent a large amount of flame very quickly. In this situation, Doc isn't in any danger from his box blowing up or shrapnel, but it would direct a lot of flame out of the open end of the box, and likely melt parts of the box. IMHO, this is an acceptable risk.

I personally like to use electrical tape to put the pressure on my cells. 3-4lbs of stretch tension on the tape as I wrap it, and I try to make about 15-20 passes of tape (generally uses a roll per tape band). That makes each tape band have around 50lbs of clamping force on it, and I use 4 bands of tape, for around 200lbs of clamping force total on the cells. This enables the clamping load to flex and move with the change in thickness of the cells due to thermal expansion and SOC etc.

 

[kfong]

Luke, that seems a more reasonable approach. Having no outlet of expansion may put more stress on the packs this way. The flames from my 1000ma pack was quite amazing. The flames from such big packs in ebikes and the chance of one pack causing a chain reaction with others when ignited would to me be a very enormous fire ball. I know this is unlikely if cells stay within a charge and discharge window, but best plan where that fire flows when it does happen. Sitting onto of the opening could be a bad wakeup call.

 

[John in CR]

Doc does have the top of that potential flame thrower pointed right at the family jewels, not what I would consider an acceptable risk. Aim that fire cannon either forward or backward, not directly at yourself.

It seems worth finding out what the failure events are like with compression. It seems there's potential for a faster release, but the flip side is that it sounds like compression reduces the chance of a catastrophic failure event.

 

[sn0wchyld]

linked the wrong video a moment ago.. i made a video but have not loaded to YT yet.

pictues will do :

View attachment 1

and :


Wood clamps to compress the packs, and secure them with filament tape that will not strech keeping the cells tight.

what materials did you use to build the pack? love to see those vids!

is anyone willing to test this 'compression = less puff = less chance of pack go boom boom' idea? Ill be upfront and state that i dont have either the know-how yet, nor the finances... yet. so props and thanks go to anyone who is willing. and bee safe!

 

[Doctorbass]

Just think about that... The gas will ignite due to spark or melting metal in these pouch.

What cause metal to melt or making spark: pouches deformations

Wanna avoid that or deduce the risk ?.. maintain their original shape by the best way you can...

The electrical tape that Luke use is good but i think that it will force the cells to adopt a circular shape and not the square shape and will make the surrounding cell to round near the edges... and that's deformation.. Plus, the electrical tape have not the same tensil strengh when the cell will heat up.. the tape usually become soft.. so the 50 lbs of force will decrease :wink:

From John in CR: potential flame thrower pointed right at the family jewels,

Btw.. John, Thanks for thinking about my jewels :lol:.. But i dont show it on the picture but i use 1/8 thick rubber with flame retardant blanket on the top of the box...

My aluminum box make each of the 6s packs to keep their square original shape on any pressure they have.

Doc

 

[mud2005]

I just got started with lipo and have no intentions of going back to ping batteries.

I'm running 12s2p nano tech and the batteries are new. my CA reads 1 cycle

the only thing I've noticed that isn't perfect is when I'm charging one of the packs there is one cell that takes longer to charge so that pack always takes a bit longer to charge. I'm new to lipo, but I suspect that wil be the first cell to go. maybe after a few cycles it will be "broken in"

best part of lipo -> these ichargers. freakin awesome. I can balance charge and watch the individual cells voltage. with a ping charger you're just hoping it's doing it's job. I realize a ping charger is much cheaper and simpler than an icharger, but thats what I was using before.

other best part -> size (duh)

party on lipo :wink:

 

[neptronix]

doctorbass/liveforphysics

Hmm.. i don't know about all this. Packs seem to expand and shrink naturally, from the factory! I'd want to give them the room to do that, and be able to see if a pack is starting to puff... then i can take it out of my pack!

If everything was sealed tight, things would be going on inside the cell that i wouldn't be able to detect visually and that worries me.

Cells should not puff very much normally.. i think it's a good idea to catch them before they do though. I want to know if i have damaged goods in the pack..

Sorry if i sound stubborn but i am just paranoid.. actually it would be nice to see what you read so i can see the science behind it.



and mud; it seems like you could have a bad cell in one of your packs, occasionally you do get a bad pack from HK! Give it another balance charge and cycle though. Try a discharge on the iCharger and graph the voltages with logview, It will give you an idea if you have a weak cell in there.

 

[Ypedal]

if you have a runt cell in a pack it's aparent by the operating votlage compared to it's neighbors.. packed tightly just helps in keeping the mass solid and not bounding around while riding rough on the bike and getting mushed in bad ways..

some packs can have varying voltage cells and still work perfectly fine.. my 100v pack on the Chaos gets bulk charged with 2 meanwells and a 3rd ps in series and at 99.7v i get cell voltages from 4.14 to 4.18 .. i can individually ballance charge each pack and the very next cycle all these cells will go back to their 4.14 to 4.18v but they don't drift from there .. that's just how they want to be.

a " perfect " pack with all cells exactly the same voltge would be ideal but i've yet to find such an animal. closest thing i had was my PSI pack on the chopper but after 2 years of abuse they are drifting slightly however still charge perfectly well without a BMS and no cell is going over yet.

 

[MitchJi]

Hi Doc,

What cause metal to melt or making spark: pouches deformations

Wanna avoid that or reduce the risk ?.. maintain their original shape by the best way you can...

My aluminum box make each of the 6s packs to keep their square original shape on any pressure they have.

Doc

It seems to me that your box will keep the cells from deforming due to a swelling increase in thickness.

But if the cells expand in width your box will cause distortion.

 

[neptronix]

some packs can have varying voltage cells and still work perfectly fine.. my 100v pack on the Chaos gets bulk charged with 2 meanwells and a 3rd ps in series and at 99.7v i get cell voltages from 4.14 to 4.18 .. i can individually ballance charge each pack and the very next cycle all these cells will go back to their 4.14 to 4.18v but they don't drift from there .. that's just how they want to be.

a " perfect " pack with all cells exactly the same voltge would be ideal but i've yet to find such an animal. closest thing i had was my PSI pack on the chopper but after 2 years of abuse they are drifting slightly however still charge perfectly well without a BMS and no cell is going over yet.

I totally agree with your naturopathic view of handling Lithium batteries

As long as things are within a certain threshold, don't mess with them. If you constantly balance a pack that is operating just fine, you're essentially just wasting energy ( bleed-off style of balancing ) and wearing the cells that are out of balance unevenly.

Bleeding off the voltage to balance cells just puts more wear on them over time. Going BMSless is not for everyone, but i think it is the superior way.