Do I need to add a fuse to my parallel DIY batteries?

[caesarv]

I have a Gobel 48v DIY battery (~305Ah) and will soon be adding an additional identical one in parallel. Both already have a beefy 250A circuit breaker and a 200A Pace BMS, but no fuses. Typical maximum draw will be 100A (both in and out.) Do I really need to add two class T fuses to this system, and if so, what rating should the fuse be? I am assuming this would only blow under some catastrophic condition.

 

[HRTKD]

Yes, each battery should have a dedicated Class T fuse. If something bad happens, the circuit breaker is likely not rated for the amount of fault current that a Class T fuse can handle. Compare the AIC ratings.

In reality, most systems use a single Class T fuse after the batteries come together. But that leaves one battery susceptible to a very large current that could get generated should the other battery have a catastrophic failure.

 

[ericfx1984]

Class t fuse, of appropriate size for the wire gauge you are using, placed between the BMS and the buss, for each battery

Then a single appropriately sized breaker, of good quality for each device placed after the buss bar (any device being powered)

 

[tghowe]

In case of an internal battery failure, should each battery in a bank have a terminal block MRBF fuse attached to prevent current-runaway?

 

[SparkyJJO]

Take A pic of the breaker and post it.
My guess is it is a MCB with a rated AIC of around 6kA. In the event of a dead short that won't cut it.

 

[caesarv]

Thanks. I don't want to open my current battery box now to look up the circuit breaker. My new box has arrived from China and is in Long Beach awaiting customs. It should be shipped to me soon. I will then see if I can get any technical specs on it once it arrives.
Regarding the fuse rating: The BMS is rated for 200A, but I doubt I would ever go over 125-150A. Should I fuse it at 175, 200, 225, 250, or ???

 

[HRTKD]

Regarding the fuse rating: The BMS is rated for 200A, but I doubt I would ever go over 125-150A. Should I fuse it at 175, 200, 225, 250, or ???

I had originally fused at 175 amps, because none of my combined loads would have exceeded more than about 140 amps. 175 amps wasn't enough for when the inverter capacitors were initially charged. I had to implement a pre-charge circuit and I decided to go with a Class T fuse of 225 amps, which just barely covers the 200 amp BMS.

 

[caesarv]

I believe the 250A circuit breakers used in the Gobel DIY box are rated at 20k AIC, but cannot guarantee it. In any case, I did add a 225A Class T fuse in series with the breaker. This was pretty easy as there is plenty of room. I probably should have used a lower rating of around 175A, but oh well. The second battery was installed today and seems to be working well. I also added a similar class T fuse to my older box.

 

[Brucey]

Looks like a full size breaker and not the common underrated trash. A lot of catching up to be done by many of the diy box builders imo.