10s6p cell level fusing.... Ideas?

I’m warming up more and more to this idea. One question I have is are you doing anything to adhere glassfibre sheet to the P group? Or are you just relying on the nickel tabs to take care of that? Do you feel like it is secure enough if that is the case?

The nickel strips themselves basically just hold the fibreglass sheets in place. Before I fold the nickel strips over the edges of fibreglass, I also apply a thin strip of hot glue along each long edge of fibreglass which you can kinda see in the last photo.

This means that when you fold the nickel strips over, the bending angle of the strips isn’t quite as sharp which should ideally create a little less stress in the bend but it also means when you solder the fuse wires to the strips, the glue underneath melts and helps to secure the strips in place.

Keep in mind that this battery build took a lot longer than I was expecting. Reproducing it now would take a lot less time due to the fact that I did a fair bit of prototyping with similar ideas and testing etc.

To speed up the process even more though, I wouldn’t worry about fuse wires on the negative terminals. Instead you could possibly just create a bus bar out of a bunch of nickel strips welded on top of each other and then spot weld each negative terminal directly to it.

Also could be worth playing around with the idea of using flat copper braid instead of the 10AWG wire that I’ve used for the wire that runs up the side of the cells, should be easier to work with in regards to bending to the angles and will be a bit flatter/cleaner looking :slight_smile:

The fuses open a circuit when a single cell in the p group shorts but when would a single cell short to begin with? I’m wondering is this solely a safety feature for cells that are poorly manufactured and somehow have some conductive contaminant in a cell that surprises you later by shorting or are there other ways a shorting cell could happen?

It’s too late once a cell hits runaway, probably for the entire pack, but would a runaway cell be internally shorting or open?

The only circumstance I can see a cell shorting is against another cell.

A runaway cell, i guess can be open and/or closed throughout the runaway?

Yea that’s hella common I bet. Done that. No fire just sound of vents opening and I ran it outside.

I find the CID to be an adequate protection device, the only issue is not being able to visually tell if a cell in p group had it’s CID triggered without taking the p group apart, or doing a capacity test on each P group

But if the CID is triggered I imagine with the now decreased capacity of the p group the voltage will go higher than the rest when charging and lower when discharging than the other p groups and could be spotted

Yeah that would be the effect Though there could circumstances when that doesn’t show, like if youre not draining the whole battery below the capacity of the affected p group.

I gotta look back at all that tests I did when starting my PowerWall, 10000 mixed cells working in harmony :smiley:

One easy to way to spot if you’ve got a broken fuse wire when using a BMS is you’ll find that the BMS will cut the charge to the pack before you can charge the battery to 100%

Another guess would be for when over time as cell resistances increase, if some cell resistances increase at greater rates than others, you’ll end up with different current levels going through different cells. You could potentially get to the point where a significantly larger current, potentially greater than what the cell is designed to handle, is being drawn from a single lower resistance cell in a P pack.

Either way, there’s obviously a reason why Tesla does it :stuck_out_tongue:

As for Tesla, last I can recall their cells don’t have a CID, that mightve changed in newer models though, haven’t looked in a while

@michaelcpg or @scepterr I picked up this non-flamable industrial glue. I’m considering it to hold down the bussbar. Any reason I shouldn’t or should I stick with the battle tested hot glue?

The description is deceiving, not sure what about is “industrial” lol. Pretty sure it’ll burn off when soldering,

I would use a high temp safe epoxy or just some kapton to hold it down when soldering

Neutral cure silicone is another good option which handles vibrations really well although it takes a while to set

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Did you get anywhere with this :slight_smile:

edit - looked at the fusion file. Looks very promising

abandoned. too complex and ultimately unnecessary.

To to 10s6p fused just use two 3p backer PCB’s and set them up for fusing. Use braid between the 3p busses to get to 6p. That’s my plan anyway.

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Ok. I just liked the travel pack part of it the most

I think I have to to use those pcbs too but this is my first pack and can’t seem to find many packs that use those pcbs you made. I am making a 10s3p 30q pack now

I have already welded the cells together with 1 layer 8*0.15mm nickel. I was hoping I could get some good advice on what I could do next.

I was planning on using 12awg or 10awg to solder onto the nickel that’s welded to the batteries. Then solder the other side to the pcb, probably two connections on both the positive and negative side of the pack.like this image: image

Then for balance wires I have no clue where to start😥