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Geoff

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Posts: 76
Reply with quote  #1 
I'm about to arrange a permanent mounting point for my solar panel and I need to know what wire gauge to use from the panel to the batteries. The cable length will be 30ft.

As regulars like Rick, Willie and Gordy will know, I started out real small powering only the house lighting with a little 20W panel. Gradually the setup is expanding (solar is addictive) Currently I'm running a 30W panel with plans to double that in the near future, but there it will end for the time being.

stmbtwle

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Posts: 2,702
Reply with quote  #2 
There are dozens of charts ou there, google "wire gauge chart" and find one you like. I like this one: https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
At the bottom of the page is a metric conversion.

Bear in mind that for the length of wire you use the ROUND TRIP length, in your case 60 ft. You also use the maximum amperage, for a solar panel that would be the Isc rating. For panels in parallel you would add the Isc of all the panels, for panels in series you don't. If in doubt use the next size larger wire. For 1.5 amps and 60' I could use 16 ga wire, if I were planning expansion I'd use larger wire. For 3 amps I'd use 14 ga (2 mm2) or maybe the next size larger.

60w is about 5 amps, and would call for #10 ga, or about 5 mm2.
I use the 3% chart, if you're willing to accept a 10% loss you can use the 10% chart, which will specify a smaller wire.

Hunt around I'm sure you can find a metric chart that will suit you better.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Gordy

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Posts: 137
Reply with quote  #3 
Geoff,

How far do you think this addiction will take you? ;-)  If your going to dig a trench for the wire, Get bigger wire for future expansion, only draw back will be $$$ spent now.  Or install 4" PVC in the trench as a conduit so you could change the wire as needed later. I haven't kept up on the new tech, but there are MPPT (Maximum Power Point Tracking) charge controllers that allow you to hook your panels in series to get high voltage. Then the controller knocks the high voltage down at the batteries. With the high voltage you can use smaller wire. I seem to recall seeing MPPT with up to 600 volt input. So there are options you may want to check into, once you determine how far this addiction will take you. ;-)

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Gordy,
Minnesota
Rick H Parker

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Posts: 727
Reply with quote  #4 
There are three wire guage standards. Standard Wire Gauge (SWG), American Wire Gauge
(AWG) and ISO Metric sizes.

Within a given wire gauge/size the current carrying capacity varies with the number of strands of wire.

The more strains:
1. The greater the flexablity without breaking.
2. lower the current carrying capacity,
3. The higher the cost,


That is why they use lower cost solid wire in the walls of your house where the wires will not be moving around and subject to breakage. Expensive multistrand wires on your arc weilder where the leads get moved around an flexed a lot.

There are different wire insulations. The higher voltage insulations cost more then the lower voltage insulations.

Your first task is to figure out how much peak current and voltage you will be subjecting thw wire to. The current carrying capacity of the wire needs to be higher then your peak current and the breakdown voltage of the wire insulation needs to be higher then your operating voltage.

It would be helpful if you decide on a charge controller first. We can then look at the specs of the charge controller and panels, then determine if you should add more panels in parallel ( More current ) or in series ( more voltage) .



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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
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