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.
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.
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.
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.
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?