Page 1 of 1

Cell fuse with battery pack fuse

Posted: Nov 01 2020 10:52pm
by chronosgarage
I’m using 20S9P battery with 45A from recycled laptop 18650 cell. It work well during testing until my controller was dead short.
When the controller is dead short, it doesn’t trip the 100A main circuit breaker, but it killed my 45A bms along with burned 3 of the cell fuse. I’m replacing the bms and also replace the cell fuse. My question is; do I need to add a fuse from the main battery (before the contactor)? I’m thinking about using a dc 60amp glass fuse. My plan is also to add another 20S12P with separate bms. Can the fuse protect the bms?

Thank you for your help.

Re: Cell fuse with battery pack fuse

Posted: Nov 02 2020 12:03am
by john61ct
link to the cell fuse please

Re: Cell fuse with battery pack fuse

Posted: Nov 02 2020 4:53am
by kdog
Usually not. Fuses take a definite period of time to blow and that is usually a lot longer than the time it takes the bms to die. Just get a bigger bms. Don't know why you have a 100amp CB on a 45a bms, that won't protect bms. If you have a CB rated at the peak load of the bms then maybe it would but that might cause you issues of it inadvertent tripping, right when you crank the throttle to nip in front of a truck :shock: Also when a switch/fuse suddenly pops open the voltage spine alone can kill the bms. I'd get a bms that can handle well above the controllers rating and if you want it protected, an adequate cb. Bear in mind they all have different ways of tripping.

Re: Cell fuse with battery pack fuse

Posted: Nov 02 2020 5:15am
by chronosgarage
kdog wrote:
Nov 02 2020 4:53am
Usually not. Fuses take a definite period of time to blow and that is usually a lot longer than the time it takes the bms to die. Just get a bigger bms. Don't know why you have a 100amp CB on a 45a bms, that won't protect bms. If you have a CB rated at the peak load of the bms then maybe it would but that might cause you issues of it inadvertent tripping, right when you crank the throttle to nip in front of a truck :shock: Also when a switch/fuse suddenly pops open the voltage spine alone can kill the bms. I'd get a bms that can handle well above the controllers rating and if you want it protected, an adequate cb. Bear in mind they all have different ways of tripping.
Thank you for your reply. The reason I choose 45a bms is because my 20S9P battery is build from recycled laptop battery. So I think the max amp drain of the battery is about 36A.

I’m replace the mosfets of the bms so that it use 2 mosfet in parallel in the same position
9AE1A26A-F424-4FF3-9668-B6D334414C96.jpeg
Bms mosfet
9AE1A26A-F424-4FF3-9668-B6D334414C96.jpeg (118.75 KiB) Viewed 221 times
740A9347-AC00-467B-B16F-89D0FEFF7510.jpeg
Bms mosfet
740A9347-AC00-467B-B16F-89D0FEFF7510.jpeg (104.87 KiB) Viewed 221 times

Re: Cell fuse with battery pack fuse

Posted: Nov 02 2020 5:17am
by chronosgarage
john61ct wrote:
Nov 02 2020 12:03am
link to the cell fuse please
I’m using 1/8 watt resistor legs as a fuse wire.
CBBD4D44-2973-4F03-847E-80E0B356E9A9.jpeg
Cell fuse
CBBD4D44-2973-4F03-847E-80E0B356E9A9.jpeg (205.69 KiB) Viewed 218 times

Re: Cell fuse with battery pack fuse

Posted: Mar 03 2021 12:49am
by amberwolf
chronosgarage wrote:
Nov 02 2020 5:17am

I’m using 1/8 watt resistor legs as a fuse wire.
CBBD4D44-2973-4F03-847E-80E0B356E9A9.jpeg
A thread with relevant discussion to this
https://www.eevblog.com/forum/beginners ... tor-leads/

One of the most important points
resistors use tin plated steel
(for leads)
meaning they aren't good fuses, since they aren't likely to just melt like a fuse wire (made of low-melting point materials), but instead just generate a lot of heat (and perhaps even glow).

There could be a possibility that they'll make enough heat to melt the solder holding them in place, if they aren't mechanically attached as well as soldered, and then fall off to short stuff out in the pack.