DIY Battery Fuse?

[PeterH]

I have built four 12VDC batteries built from 130 Ah CALB Lithium Iron Phosphate cells. Each battery has an Overkill Solar BMS. I will place the batteries in parallel to build a battery bank supplying power to my inverter. Question: Is it necessary to add a fuse to each battery to protect the system? Seems it might be redundant given the BMS has its own ability to prevent overcurrent. Of course, the line from the battery bank to the inverter will have a 400 Amp fuse in the circuit and each of the other circuits will have their own fuse as overcurrent protection.

Thanks for sharing any thoughts you have on this!

 

[sunshine_eggo]

I have built four 12VDC batteries built from 130 Ah CALB Lithium Iron Phosphate cells. Each battery has an Overkill Solar BMS. I will place the batteries in parallel to build a battery bank supplying power to my inverter. Question: Is it necessary to add a fuse to each battery to protect the system? Seems it might be redundant given the BMS has its own ability to prevent overcurrent. Of course, the line from the battery bank to the inverter will have a 400 Amp fuse in the circuit and each of the other circuits will have their own fuse as overcurrent protection.

Thanks for sharing any thoughts you have on this!

You're protecting the conductors between batteries with fuses and effectively protecting the batteries from each other. Imagine if one of your batteries completely shorts out and the parallel batteries can dump all their charge at very high current.

FET based BMS have been known to fail closed.

All components are cheap Chinese hardware.

You establish your level of trust.

 

[Dzl]

The role of a BMS and the role of a fuse are not the same. While the BMS has overcurrent protection, its not really a safe replacement for a fuse. At least that is my understanding. Not sure my view is 100% accurate but I think of BMS overcurrent protection as the BMS protecting itself from an overcurrent situation, and useful as OCP in some scenarios but not catastrophic protection. And I just wouldn't trust a cheap chinese BMS as a main OCP device, even if it were designed to be. A fuse from a reputable brand is nice peace of mind.

 

[PeterH]

Thank you for your input. I just wanted to be sure what I was doing was necessary, before I ordered parts for the other 3 batteries. I am going with a terminal post fuse from West Marine. I've finished the first battery shown here.

I've been capacity testing each cell before re-assembling the battery. These 130 Ah cells are purchased in Feb of 2011 making them over 10 years old. They are still showing around 120 Ah of capacity at a 10 amp load. I can't test at a higher load because of the tester I am using.