Cell Level Fusing: Discussion

There is a lot of info on builders regarding this and I feel that it deserves it’s own topic away from the battery building thread.

I’m about to start building a couple of batteries and would like to incorporate cell level fusing. I have some ideas of how I would like to do it, but it would be great to see some examples and explanations in here.

There is a good write up by @akhlut but I can’t seem to find it to link.

EDIT: not my photo so don’t grill me about soldering to cells :rofl:


Here is the writeup by akhult, I’ve built 2 batterys this way and it seems to work perfect.


Soldering on the positive doesn’t bother me, but the negative side makes me nervous.


You dont solder the negative side, you just use nickle strip.

If you read threw the thing it explains alot.

1 Like

Oh I know that. Just saying soldering on the neg makes me nervous. But I’ve also done it lots of times and nothing’s gone wrong.

Edit* Yet…


Cell level fusing is a good thing, hands down.

There’s a reason Tesla’s have a fuse on EVERY cell.

Also, if it’s an option for any of you, heatsink your packs people! A simple aluminum bar with heatpads on every cell will do wonders for fire mitigation. Preventing the first cell from entering thermal runaway is 100% of the battle because it’s only downhill from there.


or dont be a wacko and push your packs above the safe rated current

Why do I have a feeling that everyone on here just tries to complicate things :face_with_raised_eyebrow:


I’ll always advocate for that. Don’t exceed the spec.

Heatsinking will prevent fires, though.

If a cell begins to vent, it USUALLY has already reached the temp required for ignition.

If you heatsink all your cells together, and one begins to vent (for any reason), it will dissipate the heat among the cells around it and decrease the venting cells temperature. Usually enough to prevent ignition in the first place.

The last thing you want is the pack to go up in flames like a string of firecrackers.

1 Like

There is a reasons why BMS has that temperature sensor that almost on one uses
When the temp of one cell gets to idk 80c/whatever it was programmed it cuts off the power

Also cells have heatshrink on which lowers the thermal conductivity a LOT 30q have the thin one, but cells like VTC5 seem to have a quite thicker one
Yes a heatsink would be a better solution but its quite hard to realize it, plus it will take a lot of very limited space


Oh, yeah. Those a great and everybody should use them.

BUT they’re really only good for monitoring the average temperature of the pack. If you want true temperature protection in the case of shorts or physical damage you need an array of thermistors on at least every other P group.

In the line of defense for runaway, it typically goes like this:

  • vesc settings (current limit)
  • BMS current limit
  • BMS thermistor (too much current)
  • cell level fusing (physical short)
  • heatsinking (venting cell)

While these all help, some of them are useless on their own. I strongly advocate for points 4, 1, 2, 5, and 3 in order of priority. But realistically a pack should have ALL of these at a minimum.

I really wish I could share the solution to this now but it’ll have to wait till later in development.

1 Like

I have never seen a cell short itself out on the forums, all of the flames were from lack of insulation between the p groups/cells themselves

Cells will be max 1-2 Celsius different from each p pack, so you put it the temp sensor on one p group and program it to be in the safe zone (5-10)less than runaway temp you will be safe

Also pushing things to the max of their capabilities always leads to unreliability and shorten life span and no one wants that

Anyways I feel like this has derailed and wont comment more on this

Cell level fusing also protects from a short from one P group to the next. All the fuses in one of the groups will blow.

I love the idea of cell level fusing but I can’t really get my head around one thing.

I understand that 24AWG copper wire has a fusing current of around 30A. However, i think it also has a recommended current rating of about 3.5A.

If for example you are asking for 15-20A from a cell, wouldn’t you be going 5 times over the recommended current?

1 Like

How well does cell lvl fusing work with a bms? Let’s say you ride 40km/h and for whatever reson a P group blows. Battery saved but bms is shot off and you don’t have any brakes… Is this the outcome with having cell level fusing and a bms for charge/discharge?

Talking about heat sink not heat shrink

If a cell vents it will not melt anything. If it ignites it will. They vent for a reason. The heatsink idea is to dissipate the heat away from the other cells to prevent thermal runway.

Hey bro are you building a 13s10p?

1 Like

He’s talking about a aluminium plate for a heat sink… Not heat shrink. You are correct heat shrink will melt.

Ahh gotcha.

no comment…

it would be done by now but psychotiller hasn’t responded… :sob:

1 Like

Gone a bit dark on me too. Never mind he will come through he always does.

yeah approaching the 3 month mark.

1 Like

ooh. Don’t like the sound of that for my trucks arriving anytime soon. Its a back burner build so not too bothered.