Mersen Disconnect

Hi all, does anyone protect their pylontech with a mersen disconnect fuse
i am using 80 amp fuse to protect my 2 pylontech us3000c wired in parallel, i was worried that this was too high and have now found some 63a mersen fuses, which one would you use? , my solar is mainly to power a home office and small kitchen appliances, i have a 48/3000 multiplus, when i upgrade to 4 us3000c ( wired in 2 sets of 2 ) i will be getting a 48/5000 multiplus.

Fuses are there to protect the cable. Pylontech batteries of this size typically ship with cabling that is 25mm^2, which if i recall is good for 125A. So rather than make the fuses smaller, I would rather make them larger. I would go with 100A or 125A fuses.

A 3kVA can run at 120% for quite a few minutes, which is around 72A already. I would definitely not go lower than 80A. Remember also that fuses tend to suffer a kind of fatigue over time. If they constantly run close to their capacity, you can get nuisance-blowing.

hi, would you stick with the 80a when i upgrade to the 48/5000

and 2 more us3000c, biggest thing we will be running will be an air fryer at about 3000w

Look in the Victron manual for recommended fuse sizes. 125A is recommended for the 3kVA, and 200A for the 5kVA.

Still, the rule is that the fuse protects the cable. If you upgrade to a 5kVA, a 100A fuse already feels a bit small to me. These batteries can safely push 200A for 15 seconds, per module, so there is ample capacity to blow a larger fuse under a fault condition.

Again, I want to emphasise, the cable dictates the fuse size, not your loads. Well, if I’m a tad more pedantic, the “thinnest” part of the circuit determines the fuse size, so the cable, or what the inverter manual tells you, whichever is lower. For your setup, that should be 125A.

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hi, i am going to have 4 batteries, in 2 sets of 2, so 2 batteries in parallel on each pair of cables, between the inverter ( 48/5000) and the victron distributor i will have a 200 amp T class fuse,