Solar wire size

Panel installed and working waiting for resettable fuse to get here then will hook that up and be done with it. I made my own tiltable feet for the panel I know it makes a difference everyone in the park I stay at in the winter has there panels tilted to the sun. Also by the time I was done it took over a tube of decor to seal things the way my parinoid mind was satisfied with. All that work just to charge 2 batteries.

This morning I ordered the 100w panel and the 20ft 10g wire with the 2 ends that match the plugs on the panel going to run it by itself to the control. Now also this morning I ran a new 10g set of wires from the control through the cupboards to the batterybox its just sitting there coiled up waiting for the panel to get here next week. It will replace the 12g wire that I have been using for 8 yrs problem I have is finding a 10g fuselink anywhere even on Amazon.

Don’t think about it, Gary. Use a solar wire size chart. Do it right, do it once.

We just had 1.3 kilowatts installed and the installer, Wayne the Rv prepper, only uses the lowest denomination and shortest distance between batteries and inverter.

I would suggest that you go to Handy Bob's site and read all his articles.

The RV Battery Charging Puzzle

Here's what he has to say on wiring:

*WIRING:* Resistance or impedance is the enemy. You have to overcome it and get the power to the batteries, not just to the output terminals on your charge controller. The system in my rig is efficient because I wired it with six gauge wire, for a total distance of only 12 ft from panels to controller. I ran #4 from the controller to the batteries. I spent about $30 for this wire and gained about $120 worth of added power when looking at what 6% of what my panels cost, which is about what I gained when going from 25ft of poorly routed #8 wire to 12ft of #6 wire. Big wire is even more cost efficient when you are looking at the difference in cost for a new installation. If your controller is located very close to the batteries like it needs to be, it will regulate the voltage to the batteries so they get what they need. You can run smaller wires from the panels to the controller than you run from there to the batteries, but make sure you can get nearly 16 volts minimum to the controller by looking at a voltage drop table. Big wire is cheap compared to the cost of panels, so err on the big side. You can either run big wire or install multiple smaller runs and split the panels up into several feeds. DO NOT tie the wires together at both ends. One wire will always have less resistance & carry more of the load. Find a voltage drop chart and limit your loss from the roof to the batteries to 3%. This way you can ignore the drop in the wires on the roof. You will find that voltage drop is directly proportional to the number of amps (higher amps equals more voltage drop), which is why you should wire for the number of panels you might need and not use the minimum size for the panels you initially buy. Use BIG wire, at least #8 for two panels and, and #6 for three panels and that is only for runs under 20 ft. I have installed a lot of #4 cable and wish I had it in my own rig.

From the controller to the batteries the wire size is critical. The
bigger the better. If you cannot design for less than a 1% drop due to the length of run, it is possible with better controllers (Morningstar Tristar & Prostar, plus a few others) to use remote voltage sensing and the controller will boost the voltage going out, so that the correct voltage reaches the batteries. Do not be tempted to use this as a way of installing smaller wires. Voltage drop in the run between the controller and the batteries equals wattage loss in charging. Fewer watts come out of the end of the wire than go in when the voltage drops. This means that using smaller wires here will cost you watts charging every day forever. This is a foolish place to save a few dollars.

A word on the stranded wire debate: Yes, you should use stranded wire
because it is better for DC power. However, the difference between
stranded building wire and finely stranded automotive or welding cable
is teeny, tiny electrically, so don’t obsess about it. The finely
stranded stuff is easier to work with, but the main thing to worry about is a UV rated shield on the roof, protection against damage when routing through the rig and the price. Buy what you can find at the right price and what you can deal with mechanically. There is nothing wrong with running big, stiff wires and then splicing short, flexible leads on the ends to make it possible to connect to terminals. The big wire is there to limit voltage drop, not to carry amps. You are not going to load it enough for the splices to get hot and fail.

Typically panels run 18-19v. So 200 watts of panel would be transferring 11 amps or so 200w/18v.

If the run is only 8 feet your voltage drop with 12 AWG is only about 1.5% That's fine, and that's at the panels full rated wattage which is something that rarely exists. Typically it is recommended to be below 3% voltage drop.

Going to 10AWG would give a voltage drop of about 1/2% less than the 12AWG. It is an advantage but a pretty small one. Is there a chance of adding more panels in the future? That would be a good reason to upsize the wires at this point in time.

I;m thinking I will just order the 20ft of 10g wire and run it across the roof into the cupboard were the 20amp controler is maybe 8ft away and leave the other panel on its own.

10 gauge would be better.
Low voltage systems need heavy conductors.

Wire size is determined by distance, amps and volts. You gave one out of three. Why assume Lance wired sufficiently?

I used homedepot extension cord (for wall outlets) and it has 14g wire. I get full recharge usually before I get out of bed. I have each panel on its own pair of wires all the way to the controller.
12g is better, but 10g might be overkill.