Wire sizing for a 100W panel, 5m run (1 Viewer)

Apr 28, 2021
78
133
Aberdeen, UK
Funster No
80,763
MH
Compass Drifter 410
Hi All,

I've yet to install it, but I have a 100W panel which I'm going to mount on the roof of the Drifter to keep the (single) hab battery topped up. The current battery wiring back to the switchboard leaves much to be desired, and looks to be around 10 AWG/6mm2 - the run is about 5m from the MPPT to the battery (as it's underslung in the nearside rear, and the controller will be mid hab on the other side).

I've been toying with the idea of just tapping into that cable for the output of the charge controller, but do I need to up the wiring thickness to 8 AWG or even 6?

According to most calculators, for a 5m run over 6mm2 cable, I'll lose about 1.96%. The panel should put out 8.3A max, so that would be under the 50A cable rating, and even if I add another panel, I should be well within the cable's capability (although the voltage drop would increase to 3.78%).

What size of cable are people using between the MPPT controller and battery/batteries?

Any tips?

Cheers,
S.
 

Kannon Fodda

LIFE MEMBER
Feb 26, 2019
2,666
8,202
Seek and Ye May Find
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58,768
MH
Autotrail V-line 540
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I Make Schoolboy Errors!
I believe rule of thumb is that up to 3% loss is acceptable so on that basis your 6mm cable is fine for the 100W panel. If you do think you are likely to add another panel then a larger cable now would save pain of the reinstall for later, but do check the size of terminals into any connectors or controllers.
 
Mar 23, 2012
9,621
32,436
sleights
Funster No
20,245
MH
c class
Exp
1
I think the controller would be better as near the battery as possible as the voltage will be a bit higher along that part of the cable run and the power loss lower especially if you add an extra panel later.
 
Dec 2, 2019
3,659
7,907
Amersham
Funster No
67,145
MH
van conversion
Exp
Since 2019
Hi All,

I've yet to install it, but I have a 100W panel which I'm going to mount on the roof of the Drifter to keep the (single) hab battery topped up. The current battery wiring back to the switchboard leaves much to be desired, and looks to be around 10 AWG/6mm2 - the run is about 5m from the MPPT to the battery (as it's underslung in the nearside rear, and the controller will be mid hab on the other side).

I've been toying with the idea of just tapping into that cable for the output of the charge controller, but do I need to up the wiring thickness to 8 AWG or even 6?

According to most calculators, for a 5m run over 6mm2 cable, I'll lose about 1.96%. The panel should put out 8.3A max, so that would be under the 50A cable rating, and even if I add another panel, I should be well within the cable's capability (although the voltage drop would increase to 3.78%).

What size of cable are people using between the MPPT controller and battery/batteries?

Any tips?

Cheers,
S.
Best tip I can give you, move the controller near the battery.
At 5m with 6mm2 at full load 100w, you will have a 2,8% loss and 0.3v drop;to much. Bring the controller near the battery, and you will be in better position for future upgrades to. It’s ok to have some loss from panel to controller, but not from controller to battery, unless you have some voltage sense on battery communicating with the controller.

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OP
OP
Slopey
Apr 28, 2021
78
133
Aberdeen, UK
Funster No
80,763
MH
Compass Drifter 410
Thanks for the feedback all. Moving the battery closer is going to be problematic purely because of the layout. It's a U shaped lounge, and on that side I've already got the water tank/pump/accumulator and the new Malaga 5E.

At 5m with 6mm2 at full load 100w, you will have a 2,8% loss and 0.3v drop;to much.

I was getting less for the current - 100w at 12v would be a max of 8.3 amps no? (under ideal conditions). From the calculator above I would maybe get away with a 2.2% loss?

I might be able to either extend the run from the panels to the MPPT by a couple of meters to shorten the MPPT - battery distance, or I could look at bringing the battery inside under the other side of the lounge, but I'd probably have to go down and out, and run the feed under the hab area then back up and in again which isn't as ideal. If I get it down to 3m that gives me 1.3% drop.

Or I might rewire with 10mm2 cables round to the battery compartment anyway, and chop out the 6mm2 cables.

Decisions decisions....
 
Mar 23, 2012
9,621
32,436
sleights
Funster No
20,245
MH
c class
Exp
1
Thanks for the feedback all. Moving the battery closer is going to be problematic purely because of the layout. It's a U shaped lounge, and on that side I've already got the water tank/pump/accumulator and the new Malaga 5E.



I was getting less for the current - 100w at 12v would be a max of 8.3 amps no? (under ideal conditions). From the calculator above I would maybe get away with a 2.2% loss?

I might be able to either extend the run from the panels to the MPPT by a couple of meters to shorten the MPPT - battery distance, or I could look at bringing the battery inside under the other side of the lounge, but I'd probably have to go down and out, and run the feed under the hab area then back up and in again which isn't as ideal. If I get it down to 3m that gives me 1.3% drop.

Or I might rewire with 10mm2 cables round to the battery compartment anyway, and chop out the 6mm2 cables.

Decisions decisions....
I think we both said move the controller near the battery probably a lot easier than moving the battery!. What's the maximum voltage for your solar panel? Try working out the loss at that voltage I bet the sums look better thats the reason for moving the controller as near the battery as possible if you add an extra panel it will make even more sense.
 

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