PWDickerson
Senior Member
- Location
- Clinton, WA
- Occupation
- Solar Contractor
With L-ion and LFP batteries becoming more popular, I have been thinking about the need to provide fusing for individual battery strings similar to how PV string combiners are fused at a DC combiner box. One manufacturer of a 3.4 kWh, 48V LFP battery states that you can place as many of their batteries in parallel as you need, and that no other OCPD would be required other than the breaker built into each battery unit. I just watched a video where an employee of the product manufacturer stated that many paralleled batteries can be combined together at a DC bus without fusing at the bus, I have talked with tech support at the same company and was told this is generally how it is done in the field.
I know that lots of folks think that paralleling multiple battery strings is a bad idea even for LFP chemistries, but I want to avoid that argument here. I am primarily interested in finding out how others have installed this type of equipment and why you do or do not think individual parallel battery strings should be fused at the DC bus.
I think fusing the strings at the bus should be necessary for the same reason that PV string fusing is required at the DC combiner. A short to ground in a battery cable will have current driven to it by the non-shorted batteries, and the short may not conduct enough current to trip the breakers on board the dozen or so non-shorted batteries in the system. A fuse at the bus side of the shorted cable would trip immediately.
I know that lots of folks think that paralleling multiple battery strings is a bad idea even for LFP chemistries, but I want to avoid that argument here. I am primarily interested in finding out how others have installed this type of equipment and why you do or do not think individual parallel battery strings should be fused at the DC bus.
I think fusing the strings at the bus should be necessary for the same reason that PV string fusing is required at the DC combiner. A short to ground in a battery cable will have current driven to it by the non-shorted batteries, and the short may not conduct enough current to trip the breakers on board the dozen or so non-shorted batteries in the system. A fuse at the bus side of the shorted cable would trip immediately.