My head is battered! Am I using the correct solar cable?

[CamperJack]

I have used a 6mm2 solar extension cable with a 70A rating to attach my 2 x 170w panels to my controller.

The cable run is 7.5M. The amps are 9.93A per panel so in parallel that's about 20A. The Voltage per panel is 22.8V, in parallel the total remains 22.8V.

Putting this into the calculator below says a wire of 6awg should be used. 6awg is equivalent to 16mm2, which seems HUGE and examples online have a rating of 110A. However the calculator also says that 6awg should have an amp rating of 75A, which is closer to the 70A rating of cable I used.

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So is my 6mm2 70A cable correct, or not? I'm getting to the point where my head is totally battered, and the more I look into it the more conflicting info I find, so advice would be much appreciated.

Thanks in advance.

 

[Silver-Fox]

I was told the biggest cable you can get into a controller is 6mm.

I run 2 x 150 panels linked on the roof to one 6mm twin cable to the controller.

H T H

 

[Reallyretired]

Mine uses 16mm sq welding cable. 4 panels in parallel, though would probably be better as 2 pairs in series with the benefit of hindsight

 

[Silver-Fox]

Mine uses 16mm sq welding cable. 4 panels in parallel, though would probably be better as 2 pairs in series with the benefit of hindsight

How do you fit that into the controller out of interest

 

[Reallyretired]

How do you fit that into the controller out of interest

It fits, perhaps my controller just has big connectors.

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[Robert Clark]

6mm solar cable is fine, though my controller suggested using 10mm from the controller to the battery

 

[Clipgate]

wire-sizing-calculator

This may assist

 

[eddie]

On my camper I used 6mm Sq for each of the panels to their regulators, the shortest run through the roof, and each regulator is connected via 25mmSq on binding posts to the Batteries

 

[Geo]

It fits, perhaps my controller just has big connectors.

I would love a pic of your controller.
I'm no expert but of the dozens I've worked 6 mm have been a struggle.
Your not confusing solar controller with an inverter are you? They take welding size cables in the bigger versions.

 

[The Wino]

I'm no expert but if you wire in series won't the voltage be higher and the cable size matter less?

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[Raul]

I would love a pic of your controller.
I'm no expert but of the dozens I've worked 6 mm have been a struggle.
Your not confusing solar controller with an inverter are you? They take welding size cables in the bigger versions.

There are controllers that take 35mm on the panel side, the 250/100; 250/85; 150/100 and 100/150 victron, all take 35mm2 for the panel side, as well as the battery side.
A controller with 6mm2 limitation is due to their small amp output. For the voltage drop, you need to get creative. If needed, you run a short 6mm2 to a buss bar, then you up the size needed. Usually from panel to controller the voltage is higher, hence less loss compared to controller battery; where the voltage has been brought down to the bank voltage.

 

[Raul]

I have used a 6mm2 solar extension cable with a 70A rating to attach my 2 x 170w panels to my controller.

The cable run is 7.5M. The amps are 9.93A per panel so in parallel that's about 20A. The Voltage per panel is 22.8V, in parallel the total remains 22.8V.

Putting this into the calculator below says a wire of 6awg should be used. 6awg is equivalent to 16mm2, which seems HUGE and examples online have a rating of 110A. However the calculator also says that 6awg should have an amp rating of 75A, which is closer to the 70A rating of cable I used.

solar powered calculators, solar panel calculator | Renogy

Renogy's Solar Power Calculator Tool can quickly help to estimate your solar power requirements, calculate the size and cost of an off-grid solar system needed.

www.renogy.com

So is my 6mm2 70A cable correct, or not? I'm getting to the point where my head is totally battered, and the more I look into it the more conflicting info I find, so advice would be much appreciated.

Thanks in advance.

You will be fine with the 6mm2 cable. At worst, on full power 340w if your panels kick out 18v, your controller will see 17v. A max 5,5% drop on the panel side, no problem. Keep the drop to under 3% from controller to battery, this is more important.

 

[eddie]

I'm no expert but if you wire in series won't the voltage be higher and the cable size matter less?

But you increase the problem with shading

On a house, all the panels point the same way, the elevation the same and little chance of shading

On a motorhome if you wire them in series and one panel is shaded it will impact on the other panels.

Wire them in parallel or even better independently and if one panel is in the shade, the others will not be affected at all

 

[The Wino]

But you increase the problem with shading

On a house, all the panels point the same way, the elevation the same and little chance of shading

On a motorhome if you wire them in series and one panel is shaded it will impact on the other panels.

Wire them in parallel or even better independently and if one panel is in the shade, the others will not be affected at all

Yes I can see that but why is wiring independently better than in parallel for shading unless you have several controllers?
I really meant series was better just in terms of cable sizing.

 

[eddie]

Yes I can see that but why is wiring independently better than in parallel for shading unless you have several controllers?
I really meant series was better just in terms of cable sizing.

I personally prefer separate regulators.

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[Lenny HB]

6mm cable is more than adequate, you need to remember the highest losses are when the panels are producing maximum output in mid summer when a small loss won't worry you. In winter when the panels are producing sod all the loss will be so small it won't worry you.

 

[Geo]

Right that's it then Cables out and upgrade due
Know anyone who can bend Railway Lines

My opinion of course but when you start talking welding cables to charge a 12v Battery or two
I think youv'e lost the plot just a tad I think the 6mm are a pain in the arse
Anyone for damp string

 

[CamperJack]

6mm cable is more than adequate, you need to remember the highest losses are when the panels are producing maximum output in mid summer when a small loss won't worry you. In winter when the panels are producing sod all the loss will be so small it won't worry you.

Thanks for the reassurance, Lenny. I was reading about voltage drops and fires online. Scary stuff and it got me worried.

 

[CamperJack]

This is what I am getting this morning, so I'm getting something coming in. Does this look normal for a cloudy day? I'm surprised to see the voltage so close to the given open circuit voltage (VOC) with total cloud cover, or is that to be expected?

Broken Link Removed

Tis table shows that the maximum wire size from the solar panels is 16mm2.

 

[chaser]

Right that's it then Cables out and upgrade due
Know anyone who can bend Railway Lines

My opinion of course but when you start talking welding cables to charge a 12v Battery or two
I think youv'e lost the plot just a tad I think the 6mm are a pain in the arse
Anyone for damp string

Thanks for that, I couldn't really believe the others, have a look at the cables on your alternator, or your mains battery charger, more like 2.5 than 25.

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[Richard n Ann]

Our 150w panel came with 5 metres of 4mm cable. And the little cable off to the cab battery is 0.5mm

 

[chaser]

Our 150w panel came with 5 metres of 4mm cable. And the little cable off to the cab battery is 0.5mm

As did mine, but I used the same 4 mm all through for convenience.

 

[olley]

Frank on facts who was solar guru said you only buy cables once but voltage drop is for life.
I fitted 16mm but I did have a 10metre run from panels on the roof to the controller under the step.

 

[Geo]

Shoulda used Train lines ian it's how scalextric do it.
If you ever scrap yer winnie weigh it in as copper you,l get your money back inc import duties