Disagree. At the very least, the pvc wrap acts as a sacrificial barrier between your battery and your chosen method of sticking the battery into the enclosure. It’s 100% necessary IMO.
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Shrink wrap isn’t worth a damn when it comes to vibratory abrasion. That why even cheap chinese battery packs come enclosed in fiber plastic board. Either secure it properly or encase it with plastic, shrink wrap is more used for ensuring a forced closure between all cells/groups and an additional layer of safety.
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Ya, you’d need about the same for either the copper sandwich or 0.3mm nickel. Really up to you. I haven’t tried weldning either as yet so can’t give you much in the way of what would be more robust long term.
One thing that wasn’t mentioned in that video is that after a PTC/polyswitch has tripped once, its resistance never goes all the way back down to what it was when new.
That might not seem like much, but that would increase the power dissipation in the polyswitch, which would make it even more sensitive in the future, and cause it to trip at lower currents.
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Why the charge line? I’ve heard of them being used as an antispark.
Hello there
I had a old mboards battery pack laying around, thought I would open it up and peek inside for some scares.
Unfortunately I cant really get to the bms side of the pack because it was held together with generous amounts of glue.
I made some pics, what do u guys think these white and black discolorations could be on both the cell wrapping and the poles? Defenetly not glue, I can remove some of the white stuff with my fingernails.
I wanted to make a powerbank out of the usable cells, altho that might not happen.
Because I never fuse my discharge, but I always put a fuse on my charge ports, as I thought was the norm in esk8 and makes sense to me (why would I want my brakes cut).
Idfk how you think these can be used as an antispark, the highest rated one I’ve seen only handles 30A before tripping.
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Ok yea on the charge port makes sense. Duu.
I thought these were essentially a resistor that increases resistance with heat and would be good for an antispark. Maybe got it confused
well yeah but the resistance goes up a lot right? so it’s like disconnecting the circuit until it reaches it’s stable state again
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I think these use them.
Nope, those are just SMD resistors just like the XT90-S.
What you are thinking of are NTC resistors that have a resistance which drops as they heat up, commonly used for inrush current limiting on many electronics. The higher initial resistance would suppress the inrush (and spark), then the current draw of the device would heat up the NTC and cause its resistance to drop, lowering the electrical losses while the device is operating.
Our application is probably a bit too extreme for them unfortunately. Even a few dozen milliohms added to a circuit with dozens of amps flowing is going to result in a pretty significant heating effect and voltage drop.
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You wouldn’t happen to have a FLIR camera, would you? One of those FLIR USB modules for smartphones or access to one? That might be able to tell you where the current is going.
Would a PTC resistor (increases resistance when heated) be good for the initial connection? With Xt90s’ initial connection blowing up from too much current and ultimately heat…and the PTC increasing resistance as it’s heated it seems possibly indestructible.
No, because you need resistance immediately, not once the thing heats up. Heat takes time.
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I was going to use 3 pieces of nickel (30mm and 50mm) to avoid having to waste 20mm of material on the 100mm wide full sheets. saving the 100mm for the main and positive leads of the pack only. For the combined pieces, how many welds is sufficient to connect the pieces together?
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Is there any sweet chemical smell in the pack? I opened a pack with white discoloration like that and it had a busted cell
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There is a little, could be from the glue maybe. Altho it’s not very strong so I really had to sniff around haha
Were there any other signs? If I check the resistance of the groups it would be obvious, right?
Ouch… Did you find the issue?
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