# Need help with wire calculation regarding 120mm2

Hi all,

Im designing the electrical of my campervan, and im having trouble with the wire going from the busbar (positive and negative) to the battery. According to calculations the cable should be 120mm2. But that seems so bulky for me.. Could anyone help out? Thanks.

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use 2 x 75mm^2 in parallel, or move to a higher voltage system. if you run your storage batteries in series, then a 24V 2kW inverter will need ~90A, and you can use thinner cables. you then need dc/dc converter for dc charging and the loads which will benefit from a regulated supply.

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I didn't think of this option yet.. :)

14129
In that case, go for 48V (if you did not purchased anything yet).

Cable sizes seem very large. How did you get to 120mm?

Agree with the 24V suggestion. Did mine that way. Just added a basic Orion to handle the 12V DC loads.

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166 Amps from the multiplus, 25A from the solar charge controller, 20A DC-Dc charger and 32A from 12v appliances for a total of 242A.. over a length of 2 meters.. I see now that I can use 90mm2 from busbar to battery. but still bulky..
Are you going to use all that together?

Probably worth looking at expected use.

And check the current paths. So for instance solar will flow to the busbars and offset battery load. And solar + multiplus charge is only going just over 100A at best. You won't be using multiplus and alternator charging together, I'd guess.

Unless you bought the multiplus already, well worth considering a 24V setup.

kevgermany ♦♦
No im not expecting it to use all together, thanks for your answer.

Should be easy enough. Keep cable lengths to a minimum. Do you really need 1m each end of the shunt?

My 500A SmartShunt has terminals with 150mm² cable on both ends. One side leads to our combined house/starter 12V 300Ah LiFePO4 battery and is about 300mm long. The other is a similar length to the busbar and also to the starter motor (c3m) of the 3.9l TD engine. I have measured a peak current of 747A!

Often multiple starts daily for the last 7 years. No smoke yet.

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Probably I don't need 1 meter no. 747 peak current.. Damn haha.