I’m building a battery setup for an RV. It’ll be two batteries in parallel, each made up of 24V MB31 314Ah cells.
Each battery has a 200A BMS, but I’ll limit it to 150A via software. I’m also planning to put a 175A MRBF fuse on each positive terminal.
For short circuit protection, I’m thinking about using Adler EF3 fuses - they’re cheaper and have a higher AIC than Class T fuses. They’ll go in MEGA fuse holders, which should fit fine. I’m looking at 200–300A EF3 fuses. Higher-rated fuses mean lower losses at low currents, but I’m not sure I want to go too high since my max load won’t exceed 150A.
For wiring, I’m planning 70 mm² cables. Maybe 50 mm² would be enough - would oversizing be better?
Any opinions on the schematic and what EF3 fuse rating makes the most sense (200A, 250A, or 300A).
If you worried about a fuse using power at low loads ( new one for me, please link data for this), why does each battery have two fuses!!!
How would you disconect individual batterys, as no isolator / breaker shown.
I am also wondering why you have two fuses on each battery. Why isn’t the MRBF sufficient for circuit protection by itself? The next step in circuit protection would be for individual loads and chargers. That would be based on their conductor size and individual needs.
The answer to your wire gauge will also depend on the size of your loads and charges. In a 24V system you could likely use the 50mm2 and be fine. Generally I use 2/0(70mm2) for most things. The exception would be for longer distances and inverters over 2500VA. 70mm2 will cover just about all your needs and not be undersized. The cost difference is minimal and not worth debating over in my opinion. Use a voltage calculator to get more specific if you need too.
Any fuse has some resistance. Usually the higher fuse amperage is, the lower resistance, so the less power loss.
I used MRBF solely for over-current protection if BMS fails.
EF3 fuse is solely for short-circuit protection since it has higher AIC rating (50 kA). MRBF might not be enough as it has only 5 kA rating at 24V. In case of a short, MRBF might successfully open the circuit or gets welded due to very high amperage, so that’s when EF3 fuse comes into play. At least that’s what I’m thinking.
I was thinking of using Class T fuse but it is way more expensive in Europe. EF3 fuse is around 4 times cheaper. Also, you would need Class T fuse holders like Lynx Class-T Power In which is also an additional cost. Also, there is not much space in my installation so that’s why I’m thinking of using individual fuse holders
Not saying you are wrong but I have never seen anyone do that. Maybe overthinking it.
