Hi,
I am using a Multiplus 24/3000/70-16 in my motorhome and I'd like to carry some spare fuses for every fuse build in. So before starting to disassamble the device and find out myself, could you tell me what is a complete set of spare fuses needed.
Thanks,
Henning
The one is the 3000 and the other the 5000 model
Although there may be electronic internal protection for various error states I don't believe there are any internal fuses.
As per manual you / the installer should be adding a ~300A fuse into the positive power cable during installation.
PS. There are also many different types of fuses available in a 300A rating, so you will need to check the type of fuse holder used.
The manual recommends a 300A fuse, but only a 50mm wire (in between 1 and 1/0 AWG for us North Americans) which isn't rated for 300A current.
Why the discrepancy
I'm looking at the manual for the "Multiplus 3K 120V" found here:
Link to manual:
https://www.victronenergy.com/upload/documents/Manual-MultiPlus-3k-120V-(firmware-xxxx4xx)-EN.pdf
Link to product page:
https://www.victronenergy.com/inverters-chargers/multiplus-12v-24v-48v-800va-3kva#manuals
1/0 wire is rated for 285A, and is a little over 53mm2 actually. True 50mm2 wire therefore should actually have a slightly lower limit.
The peak draw of the Multiplus (6000W) should only be around a 250A draw, and the Multiplus won’t sustain that for very long before shutting down - nominal current draw will only be up to 100A.
So I think in general it should work okay, as the Multiplus should always be below the current limit of the fuse and wire. But, if something shorts out on the inverter side, the amp draw will jump to the maximum output capacity of the battery bank minus whatever the resistance in the cables and any other components between are. In this case, the fuse should blow quickly. The 1/0 wire is close enough that it may heat up more than it ought to first, but the fuse should blow before there’s any risk of fire.
I agree with you though that fuses should never exceed the rating of the wire, and I personally use 4/0 wire, which is rated up to 440A. I went with 4/0 rather than 2/0 because I intend to swap out my Multiplus 3000 with a Quattro 5000 in the future, and don’t want to replace the wire then. 4/0 wire should be adequate for both. I don’t think it’s a likely scenario to occur, but should something short out in the Multiplus and it were to draw something like 295A for a while, the wire would fail before the fuse, potentially starting a fire in the process.
Interestingly, a 400A fuse is recommended for the Quattro 5K, although its peak current would draw around 417A - this is close enough that I am fine with the fuse imposing a slightly lower limit though. More strangely, a 500A fuse is recommended for the Quattro 8K, though its peak current would draw 667A, so the recommended fuse imposes a limit that’s 4000W less than the inverter can handle. It recommends wire that can handle 650A as well. I would think that for an 8K, a 700-750A fuse would be better (along with thicker wires that could handle the fuse amperage).
