I have an off-grid solar system up and running well so far. However, as far as understand there is one essential part is missing in the setup which is the DC disconnector between the inverter and the batteries. I need an advice on what kind of DC disconnector/breaker and battery fuses I should use. I often see many notes advices on NH00 but wanted to make sure what I am doing is appropriate for my particular setup. The links to ebay or amazon would be lovely.

My current setup:


  • 50A PWM - Sorotec Solar Hybrid Inverter SSP3118C 3K
  • 24V


  • 2 x 12V 100Ah - Vision AGM GEL CG12-100XA (Wired in series to get 24V)


  • 4mm diameter copper cable has been used
  • \$\begingroup\$ Battery charge and discharge rate are calculated using a C factor. 1 C in your case equals to a current of 100A. Depending on the battery chemistry, there will be an ideal charge profile. The fuse should be rated for slightly less than the max charge current of your battery. Here is a quick example to look at for a lead-acid battery: batteryuniversity.com/learn/article/… Your disconnector should be rated much higher than the fuse. \$\endgroup\$ Commented May 10, 2018 at 21:45
  • \$\begingroup\$ Usually we use cross section area for conductors [mm^2], D=4mm would give approx 12mm^2 which doesn't exist. 4,6,10,16,25,35,....mm^2 are standard cross section. \$\endgroup\$ Commented May 10, 2018 at 21:45
  • \$\begingroup\$ @MarkoBuršič I wonder if they mean 4mm diameter including insulation? \$\endgroup\$
    – Hearth
    Commented May 10, 2018 at 21:47
  • \$\begingroup\$ I've just added the brands above for the inverter and the batteries if it helps. The cable is 13.30mm^2 \$\endgroup\$
    – BentCoder
    Commented May 10, 2018 at 22:15
  • \$\begingroup\$ IMO that's too small. Search an online automotive ampacity calculator. Choose the fuse as suggested by the manufacturer, then calculate the wire cross section. IMO: 35mm^2, fuse 100A. \$\endgroup\$ Commented May 10, 2018 at 22:31

1 Answer 1


Since inverter discharges batteries, you should check your batteries' specifications for their maximum discharge current. Double the value if you connect two of them in parallel or leave it as is in series connection. For a disconnector I recommend a DC MCB(miniature circuit breaker) since you can also use it safely as a switch. Fuse blow out every time the inverter rated above your battery bank overloads them. And these solar fuses together with their DIN-rail holders cost around half the price of their counterpart DC MCB. There's also the auto reset DC circuit breakers that will save you the hassle of having to manually reset them after an overload that might happen during your absence. A search for "auto reset dc circuit breaker" will yield variety of them to choose the one suitable for your DC application.


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