Wiring my solar panels, charge controler, batteries, etc

[Rick & Patsey]

I need someone to look over my shoulder and make sure I’m figuring my wire gauge sizes correctly. I’m installing four 100W panels on my RV. 12 volts at 5.29 amps. I plan and bringing two panels together and running a two set of wires down to the charge controller. about 20 feet away.  So a total of 10.6 amps per set of wires. At 2% loss the tables tell me to use 6 gauge. Is this correct? Also the wire isn’t cheep. What do you think about using booster cable wires. I can buy 25ft cables in 6 gauge for $24. That works out to 48 cents a foot. It’s 500 amp wire and already in red and black pairs. I can’t even come close to that price for 6 gauge on line and my local hardware store sells it for 96 cents per foot.

Rick

[Ray]

I think you should be fine. Most of the 200-watt solar starter kits on the market are shipping with 10GA 20 foot cables so you’re way ahead of that. 🙂

[J J]

Hi Rick,

There are many ways to approach this however I can tell you from experience that the major cause of solar system underperformance is cuting corners during instalation. I would check to ensure those battery booster cables are not copper coated aluminum. A good solution to lower the current from the panels and thus the losses associated with that is to run a system of series parrellel, higher voltage and lower current to the controller. I try to run the highest voltage my controller will accept, in my case it’s 50V..

 

Good luck with your install.

J

 

[Stephen C Keller]

While I am not advising to use this but in my adventures at looking at many installations of solar panels there seems to be a lot of people using 10 gauge copper extension cords for the run from panels to controller. Since it is copper strand it seems to work great for them. I am not saying to use this but maybe something to look at if all else fails. The claim is the amps being produced is high enough that the loss is minimal. I know many claim the best is welding cable mas it is all copper which is like good jumper cables. I know from personal experience that I made a set of 30 foot jumper cables with welding lead replacement cable and there was not any loss.

[Richard Machida]

I also installed 4×100 watt panels and estimated the run to be about 15′. I found 15′ of 4awg arc welding cable on Amazon to be cheaper ($34 for a pair) than 2 runs of 6awg. I wanted to plan for up to 4 additional panels in the future and sized everything appropriately. And like JJ mentioned, don’t skimp just to save a few bucks. You may not be satisfied with the results. And it is worth spending the time and effort to find the shortest path from the roof. I made my combiner box on the roof from a box store waterproof junction box.

Good luck with your project.

• This reply was modified 6 years, 3 months ago by Richard Machida.

[Kent V. W.]

Your calculations look good if you want to limit to 2%. What’s the battery bank consist of?

.96 a foot for #6? Good Grief! I bought some #1 from a supply house a couple of months ago for .97/ft.

I wouldn’t think twice about using the jumper cables if they are CU. The “500A” is misleading for continuous loads but no matter if they are #6.

One additional thought if the cable is “fine stranded”. Depending on what type or class it is it may need to have crimp type terminations rather than a screw/lug type terminations.

I’ll add as well that I am using a #10 drop on 290A worth of panels charging 220Ah of batteries. On sunny days (Even partially cloudy days) the system provides more available power than the batteries need to recharge.

• This reply was modified 6 years, 3 months ago by Kent V. W..
• This reply was modified 6 years, 3 months ago by Kent V. W..

[Rick & Patsey]

Thanks to all the replied. It was a great help. Just to answer a couple questions you had. I’m installing 4 100W panels, with 4 T-105 batteries. Trimetric TM-2030-RV with SC-2030 12/24 Volts Solar Charge Controller. 1000W inverter. All of the parts are ordered. Should be installing next week. I’m retiring Dec. 1 and on Jan. 2 my wife and I are heading south. If this doesn’t post correctly it’s because I just haven’t figured this out yet.

[Kent V. W.]

Sounds much like Ray’s system.. (System that was my first preference/choice but didn’t have the option at the time and went MPPT..) Why? Less to go wrong on a PWM controller.

If it were “my” system I would do just what Ray did and run down (2) 12-2 “tray cable” cables  – (Two panels per down-lead pair.)  Why? Because if I have a failure for some reason on one panel I still have the other pair still pumping out power to the controller. It would be “easier” to isolate a pair at the controller rather than the roof But? Not a biggy really.

http://www.solarpanelstore.com/solar-power/wire/tray_cable/12-2-tc.html?_vsrefdom=adwords&gclid=CjwKCAjwxJnNBRAMEiwA8X_-QeSyr0gOUAY3te0sZWHMDe3FvEHNZPjST3yGbFs7B-W-7Mkf0z6ghRoCoNMQAvD_BwE

Second option would be a single pair of say, #6 like you mentioned.

The cost would be about the same if you bought the #6 at wholesale pricing and ran down one pair for all four panels (Not taking into account the shipping charges.) (What you might look in to is try buying from a local wholesaler rather than a hardware store.) (Many if not most will sell to the public if you know Exactly what you want.)

https://www.wireandcableyourway.com/6-awg-thhn-building-wire.html?utm_source=google&utm_medium=adwords&utm_campaign=thhn&utm_term=6%2520awg%2520thhn%2520wire&gclid=CjwKEAjwxJnNBRCMqNXM6vKAq1wSJADxf_5BXaKUpN7lguoI_pTdfgQGYUPGMBdjQo6OMTHN2hzCdBoCEJjw_wcB

Also… Yes, it looks like you can wire a pair of panels in series and run down 24volts.. But keep in mind that if you get shading on one panel it will drop the output on both panels.. (Drop off from even the slightest shading is huge..) If wired in parallel (12v output) and one panel is shaded you still have the other panel putting out 100% of available solar power..

 

Sounds like a great system. Look forward to hearing about how it works out for you.

 

• This reply was modified 6 years, 3 months ago by Kent V. W..

[J J]

Hey, congrats on your impending retirement. . Best of luck on your system install.  Maybe our paths will cross down south somewhere.

 

J

[Flyingppg]

Hi, the problem in your system, and from what I read in most of the starter kits on the market, is your charge controller. You are using a PWM charge controller which is very inefficient. You may be throwing away 20-30% of your power with that charge controller, almost a whole panel, and making them run hotter too which increases the losses further. You also, as you figured out, need thicker wires if you are going to be dragging the voltage down to 13-15v with pwm charge controller to charge your batteries. Given your longish cable run, connect your 18v panels in series (72v) run it (still at 5 amps) into an MPPT charge controller like the Epever tracer ($100 on eBay), the 3210AN is right for your 400w of panels. A single set of 4mm cables will be OK although obviously the thicker the better and with a 6m run I’d use 6mm. Put the charge controller as close to your batteries as you can on short big thick cables, 10mm or so. Running higher voltages from your panels is how to minimise your cable losses.

I’m generally baffled as to why all you Americans with your enormous RV’s are still using 18v panels on PWM charge controllers. You get a lot more bang for your buck with the big 60 element 36v panels but of course then you absolutely must use an MPPT charge controller.

Kind regards. Richard

[Author]

Posts