Do cells on final connection before controller work harder ?

[johnrobholmes]

I would guess that the majority of the users here do not have hard cases around their pouch cells. Maybe heat shrink at most which offers almost zero compression on the outer cells except at the corners.


Any thoughts regarding switching ripple and how it is distributed among cells?

 

[John in CR]

....I will leave them alone for about 4 weeks just using and balance charging and then when I know they balance and work I will open them and put them back together with pegboard sides and filament tape. They may last a while and not ignite. I have my old grill out on the porch ready for charging them. Does this sound reasonable?
otherDoc

I'd balance them perfectly before the first use, and then bulk charge with a conservative cutoff voltage and check for balance. The goal of the test use is to identify problem cells to exclude them from the pack you put significant effort into building. By "pegboard" I hope you don't mean the kind with holes, because you want a flat surface, not one that makes the surface of the end cells like inside out golf balls. No filament tape either. Electrical tape is the way to go because it is somewhat elastic. On the first wrap go light on the stretch as it's harder to make the pressure even. Let it sit for a few minutes to expose uneven pressure easily visible as non-parallel end plates. Then you can adjust on the second pass. If it looks more compressed at one end after the second pass, just roll the tape backward onto the roll and do it again (another good thing about electrical tape is that you can pull it off and redo it with the same tape). I try to use a single continuous piece of tape, and don't cut it until it all looks good. After the compression wrap, then I add a 2-3 turns of very low pressure, because electrical tape comes loose if the end it stretched. I put a layer of cardboard between the compressed series strings when I use duct tape to join them side by side with same polarity at each end.

 

[dnmun]

for the end plates, i use 1/8" hardboard i got for free and wrap the pack with long zip ties one end to the other and cinch them up tight while the pack is compressed by the wood clamp. but that is then compressed inside a wooden frame around the perimeter with blocks inserted at the ends as shims to keep the pouches under compression inside the hardboard end plates.

 

[docnjoj]

I also use wood clamps and hardboard (no holes!) but used filament tape on my A123 packs about 1.5 years ago. Still going strong with a balance charge every ride. I think I will wait for Agnius to do his kits for 18650 and scrounge for new Konions and pay through the nose for them. Gotta be safer than hobby lipo.
otherDoc

 

[dnmun]

I also use wood clamps and hardboard (no holes!) but used filament tape on my A123 packs about 1.5 years ago. Still going strong with a balance charge every ride. I think I will wait for Agnius to do his kits for 18650 and scrounge for new Konions and pay through the nose for them. Gotta be safer than hobby lipo.
otherDoc

you should not have to worry that the HK lipoly is so dangerous. the risk is charging with no protection from overcharging and that is eliminated by using the balancing chargers or a BMS.

as always, the biggest risk of fires is from shorts. chroot's headway pack fire was a short and the german guy with that cargo bike that burned on the side of the road was built from Vpower cells that shorted.

john had a pouch short internally and smoked that pouch but did not catch the entire pack on fire.

 

[fechter]

for the end plates, i use 1/8" hardboard i got for free and wrap the pack with long zip ties one end to the other and cinch them up tight while the pack is compressed by the wood clamp. but that is then compressed inside a wooden frame around the perimeter with blocks inserted at the ends as shims to keep the pouches under compression inside the hardboard end plates.

Do you have a picture of this? I have some used packs I got for free, but one already puffed a cell. I'd like to come up with a simple but effective way to compress them and keep the edges from getting dented.

 

[\/ampa]

I also use wood clamps and hardboard (no holes!) but used filament tape on my A123 packs about 1.5 years ago. Still going strong with a balance charge every ride. I think I will wait for Agnius to do his kits for 18650 and scrounge for new Konions and pay through the nose for them. Gotta be safer than hobby lipo.
otherDoc

you should not have to worry that the HK lipoly is so dangerous. the risk is charging with no protection from overcharging and that is eliminated by using the balancing chargers or a BMS.

as always, the biggest risk of fires is from shorts. chroot's headway pack fire was a short and the german guy with that cargo bike that burned on the side of the road was built from Vpower cells that shorted.

john had a pouch short internally and smoked that pouch but did not catch the entire pack on fire.

But they told me its hazardous and that over 100Wh the battery can self ignite and explode even the ultra safe lifepo4 and safer 18659 have to be in the Hazard Class 9

 

[dnmun]

this requires 3 looong zip ties in series

 

[fechter]

OK, thanks for the picture.

My packs are 1P, so all the cells are in a single row. This should make it a bit easier. I see the end plates should be something pretty stiff. I might try aluminum, insulated by a layer of Nomex paper or plastic.
Somewhere I have some old fiberglass PCB material that might work well too.