Wire gauge rooftop solar to battery compartment
Hi all. I have 200w of solar from a Renogy starter kit on my 42' toy hauler. I'm currently running 22 feet of 10 gauge from the panels, which are at the front of the RV mounted behind the cap. The cables run to the sink vent, down through that bathroom and then to the battery compartment. I have a Morningstar TS45 controller feeding the batteries with 2 AWG cables that are 12" long. I have four 6v Trojan T105 batteries.
I am preparing to add two more panels, likely Renogy 160w panels to give a total of 520w. I suspect that the 22' run of 10 gauge is resulting in significant loss. I'm thinking I should add a combiner box on the roof and then run 4 gauge welding cable down to the battery compartment and solar controller. The two new panels will be closer to the vent due to placement of the two AC units.
Has anyone done 4 gauge wire from the roof to the battery compartment? I've seen the flexible 4 gauge car audio wire. Would it be the same as welding cable? I'm interested in combiner boxes, as well. Would anyone have any suggestions about ones acceptable for this project? Help is much appreciated. I'll post pics and a schematic as I upgrade and install.
Thanks to everyone here for sharing. I have learned a ton and saved thousands on RV service calls. Not only that - I have gained the confidence to take on projects I might have hired someone to do!
I started with the 200W Renogy kit and the 10 gauge and then added another Renogy Kit with more 10ga paralleled for an effective gauge of 7. When I added 2 more for 600W I removed the wires running down and added a 4 gauge run.
I just used a cheap 4 gauge off the roll at Home Depot, it was quite stiff but I didn't have many sharp bends to deal with.
Every time my systems have worked great so losses in wiring have never been a problem. Cheers, Ray
Another option is to wire the panels in searies if your controller can handle the higher voltage. I know there are pros and cons to this but the 10 gauge wire could handle this and save the cost of 4 gauge
In my humble opinion one of the first tools to acquire for solar work is a DC clamp meter like the UNI-T
UT210E. This $50 meter (simple to use) takes all the guesswork out of what is lost from the panels to the batteries. I run 900 watts total, split into 2 fuse blocks, which feeds two trimetric controllers (slaved)
That means I have a max of 450 watts available to each controller in the Arizona sun. The total length of cable for each controller is about 30 feet and the largest gauge in the system is 8 if I remember right, no larger than 6 for sure. I took a reading of how many amps were produced directly behind each panel
and then just before the controllers. There was NO measurable loss in the 30 feet. My trimetric battery monitor confirmed my readings. I forgot to say this system is 12V (parallel) . This $50 meter and any good battery monitor will take all the guesswork out of most situations.
On one of my runs on my 5th wheel it is over 22' so I bought a pair of 2 Gauge battery cables At 25'
You can check around we have princess auto you guys have harbour freight you can get a pretty good deal.
Dan and Joyce Karau
Here is a great reference with charts...
Dan and Joyce Karau
If you find battery cables at a low price be sure to check they are not COPPER COATED ALUMINUM
For all my cable sizing I use a voltage drop calculator. Be less than 3% voltage drop. I size for less than 1% typically. You can use this calculator to see how your added panels will affect your cables efficiency adding panels. You can also pair up your panels in series if you have a charge controller that is designed for those increased voltages. (MPPT) In that case the wire would be just as efficient as what you have even doubling the panels. If possible make the added 2 panels the same as the 2 you already have for total wattage, amperage and voltage.
As far as a combiner box you can build your own or buy one. I made my own using an ip65 rated box and some din rail.
What people are forgetting is the gauge of the wire determines the maximum current can flow thru it safely. In industrial application we would run 14/2 (14 gauge 2 conductor) from a bank of four 12 volt 250 w solar panels. We didn't have any loss over a 50 foot run. Where we put Flexible welding cable was on the output of the solar regulator to the batteries and between the batteries .
Max open circuit voltage of each panel is 20 Volts . The short circuit current is about 18Amps. These values depend on the weather and how much sun is hitting the cells. I have never seen more than 8 VDC at the input to the solar regulator. Solar panels are current sources not a voltage source.
Bill and Laura Asbell
My three 160 watt panels came with 10 AWG conductors which go into a 4"X4"X4" conduit box from Home Depot. Twelve feet of 4 AWG welding cable goes from the combiner box to the solar controller and 0 welding cable to four T-105 batteries. I used welding cable because of numerous very tight bends, and sized the conductors using the afore mentioned voltage drop calculator. The box has been in service four years without leaking.
Bill and Laura Asbell
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