pau-farreny avatar image
pau-farreny asked

Fuse rate and cable sizing


I have very little knowledge of electronics but these diagram has been very helpful to represent it in a simpler way.

I hope that somebody could give me a recommendation on my design, fuse rate and wire size. I’m open to any recommendations and adjustments.

Thanks to everyone

Wire Location

Max Length (meters)

Wire, mm2

Fuse/Breaker Rating (Amp)

Solar Panels to MPPT


10 - 16 ???


MPPT to (+) Bus Bar




(+) Bus Bar to Second Battery




(+) Bus Bar to DC Fuse Box




(+) Bus Bar to Alternator




(+) Bus Bar to Orion DC-DC


10 ?

45 ?

Orion to main car Battery


35 ?


(+) Bus Bar to Inverter




Inverter to loads 220




Components Used:

  • 1 x 370 W, 24 v, Mono Solar Panels by Jinko ( Link )

  • Smart Solar 100|30 MPPT by Victron ( link )

  • Orion tr DC-DC 30A Isolated by Victron ( link )

  • 4 x REPT 3.2 280 AH Lifepo4 Battery cells ( link )

  • Smart BMS 4S cells 12V 120A (link)

  • 300 A Shunt by Mictuning ( link + link shunt )

  • 1000 W, 12V, Pure Sine Inverter ( link )

  • Main switch 300A ( link )

  • Auto midi Fuses (50A to 100A) (Link)

I am living in Europe and I am using this table to guide me in the current withstand in amperes of the cables


1- I am going to use the Inverter to power 2 laptops and a 50L fridge (which opens three times a day). Is it necessary to increase the 25mm2 cables and the 100A fuses?

2- In the MPPT Smart Solar manual, it indicates that it is optional to connect the ground (chassis), is it recommended?

3- Can I connect the negatives (-) of both batteries through the chassis ? Instead of two negative cables from the Orion DC-DC to each battery.

4- Do the negatives (-) have to be connected to the chassis in a lifepo4 system?

5- Should I fuse the positive (+) cable of the main battery to Orion tr?

Diagram attached in PDF
Planol imitacio angles..pdf

Diagram in Imagur

PS: i got the diagram from

Lithium Batteryfuses
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2 Answers
greendovefarms avatar image
greendovefarms answered ·

Have you downloaded the victron toolkit as it has a great cable calculator in there that will be able to help you with your cable sizing

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Vance Mitchell avatar image
Vance Mitchell answered ·

A few things stand out immediately.

1. The Orion 12/12-30 can only accept 16mm cable so that is what I would use for both sides of it.

2. The solar panels only have 4mm cable attached, 4mm would be suitable to connect it to the MPPT but upgrading to 6mm wouldn’t be a bad idea.

3. I would make All the cables between the battery and the busbar at least 35mm and you might as well change the inverter cable to 35mm while you are at it.

4. I would reconsider the inverter, Once you are converting into dangerous voltages, a good brand with a known reputation and warranty is worth it for your safety. If need be a smaller inverter might handle your loads (depending on the starting current of your fridge).

5. Definitely add a fuse as close to the main battery as possible.

I hope this helps a bit.

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pau-farreny avatar image pau-farreny commented ·

Thank you, it helped alot

1- Thank you for telling, I didn't knew that.

2- 4mm2 or 6mm2 wold be enought if didn't take in consideration the lenght betwen PV and MPPT. 5 meters

3- would you alse increase the fuse ?

thanks for your time !

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pau-farreny avatar image pau-farreny commented ·

I forgot last one,

5- what fuse wolud you use there ? 50 or 100 ? My alternator is 110 or 140. and my batery 100Ah

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Vance Mitchell avatar image Vance Mitchell pau-farreny commented ·

2. 6mm will still be fine even up to twice that distance, At that distance it will still be less than 2% loss in the cabling and can safely carry more than twice the current that the solar panel will output.

3. With 35mm cable you could upgrade to 150A. For the battery fuse I would upgrade to 150A, the Inverter I would also use 150A unless the inverter manual recommends smaller.

5. The Orion manual recommends a 60A fuse which is within the safe range for 16mm cable.

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