Wire size?

[Clemmo]

I bought a 150W. solar kit.

I got it out today to see what I have and plan the install.
The solar panel is pre-wired with 5m of wire and connectors. This wire is a good size and I know goes to my controller.
The fused loom provided to link the controller to the batteries is a fraction of the size...maybe 25% of the panel wire.?
is this correct?

all advice /guidance appreciated ?

Cheers
Clemmo

 

[Charlie9038]

What is the 150w kit, solar panel or invertor?

 

[Clemmo]

150W Solar panel

 

[pappajohn]

4mmsq should be adequate from controller to battery if the length is only 2 or 3 mtrs.
After 3 mtrs 6mmsq will be better.
The pre-wired wiring from the panel will be standard 4mmsq but with thick insulation.

 

[Clemmo]

Controller to battery will be less than 1m .... the wire provided is similar to car audio wire? ( not sure of sq mm)

solar panel to controller is 4mm sq. ( it’s printed on the wire)

clemmo

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[autorouter]

the wire provided is similar to car audio wire? ( not sure of sq mm)

It's sometimes stamped into the wire instead of being printed, and shining a torch at a very shallow angle along the wire shows it up better.

 

[Stealaway]

The biggest connection in the solar controller will probably be for 6mm cable.

 

[Johnny Johnson]

Your charging not drawing so 2.5mm upwards is fine

 

[tonyidle]

Your charging not drawing so 2.5mm upwards is fine

Amps are Amps no matter the direction. Cable size as a minimum must be heavy enough to carry the anticipated current. That isn't the whole story though especially when dealing with low voltage: the cable must be larger than the minimum safe size so that the cable itself doesn't offer any meaningful resistance. The resistance of the cable is what causes voltage drop which is not what you want. So ........ the size you need in any circumstances must be the minimum safe size plus thicker as determined by the length of the cable run. If in this case the controller is close to the battery the size provided will be fine. You will need to consider using thicker cable if the run from the controller to the battery is more than, say, 4 or 5 feet.

 

[Two on Tour]

Here are a couple of links to information Clemmo that will give you a better understanding of cable sizing.

https://www.12voltplanet.co.uk/cable-sizing-selection.html

Wire Size Calculator

www.wirebarn.com

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[autorouter]

With a 150W panel, the solar controller output current is unlikely to exceed 80% of 150/12 = 10amps. The maximum recommended voltage drop of 3% is 0.36V.

If it was my motorhome, I'd be thinking of 1% rather than 3%.

Use Two on Tour's 12voltplanet calculator, enter the current (amps) and length of cable run. Try different sizes (areas) until you find one that gives a voltage drop below the limit you choose.

So from the table if the controller to battery is 1m, even 1mm2 meets the 3% standard, and 2.5mm2 almost meets the 1% standard.

If the controller to battery is 2m, 2.5mm2 meets the 3% standard, and 6mm2 meets the 1% standard.

Whatever you choose, that's how you work it out, and you balance cost and benefit to suit you and your pocket.

 

[Off da Grid]

I went for the largest that my controller advised would fit in the terminals but the controller is less than 0.5m from the battery.

 

[Lenny HB]

was my motorhome, I'd be thinking of 1% rather than 3%.

I would agree for general wiring on the van but for solar I'm quite happy to accept a 5% loss.
My reasoning behind this is that in summer with maximum output for long hours & lower usage and your panel is producing 10 amps a loss of 0.5 amps is acceptable.
In winter if the panel is producing say 2 amps (it will often be less) a loss of 100 ma is so small it's not going to worry you.

 

[autorouter]

I would agree for general wiring on the van but for solar I'm quite happy to accept a 5% loss.
My reasoning behind this is that in summer with maximum output for long hours & lower usage and your panel is producing 10 amps a loss of 0.5 amps is acceptable.
In winter if the panel is producing say 2 amps (it will often be less) a loss of 100 ma is so small it's not going to worry you

Even that is a bit pessimistic. 2 amps is 1/5 of the current so the losses will be only 1%, not 5%.

 

[9526]

There’s a whole article on this subject in Jim’s latest mag

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