Sunday, July 17, 2016

Solar System Wiring, Bigger is Better!

Is bigger wire gauge better? For low voltage DC, Yes! Get every watt you can from your system by simply using bigger wires.

The Test:
I wanted to find out if bigger gauge wires really made a difference with the amount of amps delivered to the batteries.

My System as First Set-Up:
Is a simple 200 watt system, two 100 watt panels, similar to what is being used by van-dwellers and RV’s. My controller is 12 feet from the panels and by most wire size charts available allow the use of #10 wire from the panels to the controller. The wire used from the controller to the batteries was #8.

My System Re-Wire:
I kept the length of wires the same but used #4 welding cable from the panels to the controller and #4 wire from the controller to the batteries. #4 cable was used to keep the voltage loss to a minimum. All connections are made with typical ‘crimp style connectors’.
Most hardware and big box stores have a good selection of connectors for #4 wire. The use of ‘welding cable’ is not necessary, but it’s far more flexible and easy to work with than household stranded wire at only a few cents more per foot.

The Results are Stunning:
I actually ‘Doubled’ the amps to my batteries just by using the larger gauge wire! I now have 68 amps of useable power everyday to run fans, lights, radio, TV, recharge my ‘AA’ Batteries and even a 12v refrigerator. For test comparison accuracy I used a 750 watt electric heater for a few minutes at a time to maintain a 12.2 volt battery state of discharge between the hours of logging the results.

The chart below shows the amps to the battery readings on clear sunny Florida days. The chart shows the hour of day and the delivered amps using #10 wire compared with using #4 wire and the amps delivered at the same hour of day:

Time          #10ga  #4ga
7:00am         0.0       0.0                 
8:00am         0.2       1.1
9:00am         0.3       1.9
10:00am       2.1       4.2
11:00am       4.0       8.8
12:00pm       5.0       9.7
1:00pm         5.6      12.0
2:00pm         5.1      10.2
3:00pm         4.2      8.1
4:00pm         1.7      6.0
5:00pm         1.5      4.1
6:00pm         0.3      2.0
7:00pm         0.0      0.0

Results:       30.0  vs  68.1   Total amps delivered for the day.


Large wire sizing and solid connections are critical to get every watt from your solar panels and may save you from buying unnecessary panels to deliver more amps.


  1. Considering they are fixed and in partial shade 68 is not bad. If my math is right that's around 1000 watts. That's a big increase. With your 1 battery down to 70% your recharged 100% way before noon. You need a 2nd battery.

    1. Gary,
      I did have two batteries until a lightening strike next door fried my controller and my pure sign wave inverter. I thought I cold save the controller but found out the charge set point failed and over charged the batteries then boiled out all the water. Since that happened they would never hold a charge. So I went to a single battery to save some money. I looks like I now could use a second battery.

      I regret throwing out the old #10 wire without checking the ohms resistance. I now suspect that the China made wire was made with inferior copper and could never carry the amps it was supposed to. Another lesson learned about critical components and China.

  2. Mike,

    Great information to know. I'm sure my husband will be testing out solar on the trailer when things slow down here.

    1. If you want to read some excellent information about RV Solar read
      He lives in an RV and uses solar only without a generator. Smart man (Electrical Engineer) with a lot of detailed information and not much nice to say about RV dealer installed solar. He corrects a lot of them.

  3. Mike, you could probably make a living up here installing and maintaining those systems. I see them everywhere, including huge commercial banks of solar cells on the road to Chattanooga and also in a small town in the next county. When I installed my system in 1999, solar cells were largely unheard of up here. The people who built my system came from Spartanburg, South Carolina and I had to pay for their travel time and to put them up in a motel for three days. And then the damn thing didn't work because I had no area on my property that got enough sunlight to keep the batteries charged, it's too steep and too thickly wooded. We put the solar panel next to a parking pad, but in winter it only got about four hours of direct sunlight a day. The generator was activated by the inverter when the batteries got low, and it was on almost all the time if I tried to use the system instead of the grid.

    1. As soon as the wife agrees I want to move the extreme Northeast corner of Georgia. I have friends living there an always liked that area when visiting.

      I really don’t want a job anymore, too old, but have no issues with helping people fix a bad install. In the early days of solar like yourself, setting up a new system was mostly by luck an the lack of skill or even caring was common and forget about an hourly printout of the performance and a solid seasonal projection of amps to be expected. Today it’s better because of experience and competition.

      It’s interesting to me that here in Jacksonville we have a utility owned 100 acre solar farm. The green weenies pushed hard for it now we hear nothing about its operation and money savings to we grid people. I do smell a rat there.

  4. Mike I meant to send this to you a while back. Its a cheap pointer for solar panels. the site is one I scan weekly for ne tips.


Your thoughts are welcome!