Have You Built Battery Pack WITHOUT BMS?

[Kimchi]

Let me clarify what I was thinking. For someone who unfortunately experienced by accidently shorted part of the battery during the built. My 24 AWG wire would just break quickly vs a thicker wire or nickel strip might be still heating up during the short.

Just a thought:

You're accepting worse performance all the time (power loss as heat in the smaller wire) for the sake of a preventing potential problem during building the battery?

It is not about during the build but after the build. If battery were to have a very bad crash will less likely result in fire. I would imagine copper wire breaking during any shorts.
But you did brought out a good point about performance loss cause by heat. Wire had break do to heat from high current, but that was from bad wiring design. This current build was done 3 months ago. I been using it at least once a week. Wires haven't break. But on my next build if I were to double my wiring or triple it, would I see a big significant in performance? Worth looking into.

FWIW, it sounds like you need to individually test each of your cells, based at least on the original cell manufacturer data, to eliminate any that are already damaged, and characterize the rest to eliminate any that can't handle the loads you're putting on them (or replace them all with cells that can handle it, if these aren't designed to).

I had mentioned that these are modem backup batteries, just like laptop batteries. I know they weren't design for motor application. Replaced one of my drill batteries with these, the torque is much weaker than the original. They are new batteries.

If you have cells low enough to become reversed, your pack already has serious enough problems to require replacement of those cells (groups), even before they reverse.

This was the choice I had to choose before. I know my battery was low when suddenly the speed drop or momentarily stop working, but still had to push at very low speed to get home.

So you know, I no longer bother charging pack with bad group of cell. (I would just replace that bad group first). It would not charge, even if charged it no longer can handle the loads, and it is not safe.

I want to emphasize the failure of the pack was mainly the bad wiring designs of the pack which create heat build up at certain point.

Pics of the failure points.


So far after I haven't seen any burnt marking over taped battery. It also help that I pedal during step section to lighten the load on the battery and motor.
If battery were to fail again all cells should be similarly low voltages on well build pack.

 

[whatever]

I've used packs I've built myself without bms without issues for a very long time.
But you have to keep an eye on the pack, usually when I go to charge is when you will notice if there are any
problems. I split a 48v pack into two 24v packs and charge them separately. If one pack is showing lower voltage or any irregularity in charging then I will check the voltage of the cells using cell log or similar.
You usually get some clue and some lead time when a problem is occuring.
I also keep the cells exposed so I can put my hand on them and feel is any heat being produced, that is a really good indicator of a failing cell. I do have to occasionally replace a cell, and its usually just keeping an eye on things and some clue will arise that there is an issue to look into.
Having two identical packs charing at same time, if there is no issue then they both charge up at same rate also. Voltage and temperature are really all that is needed to monitor a pack, many will disagree but I have had no major issues.