Could someone help with solar panel and charge controller wiring/sizing?

I have 3 x 100W solar panels, now fixed on my roof. I bought these in a kit (eco-worthy) that included an inverter and a PWM controller with it. I regret this now because I want to wire the panels in series to keep the roof tidy and I’ve also looked into MPPT controllers more and it seems I’d get more out of the panels with one anyway.

I understand I need a 30 amp charge controller (300W/12V=25 and round up?). I was planning on getting the Renogy Rover Li 30. The problem is the wire in the kit that connects the panels to the battery is 4mm^2 (or 12 AWG). I’m assuming that I should use a max 20 amp fuse (?) for this wire so does this mean I should get a 20 amp charge controller instead?

What’s my best solution?

Thanks in advance

Greetings & Welcome!

You want to size your wiring according to volt/amps/watts, and how long their length will be. There are wire size charts and calculators online.

Then you size your fuses/circuit breakers to be smaller that what the wire is capable of handling, and just slightly more than the largest loads expected. This is meant to protect the wire from getting hot, melting, shorting out, and starting a fire. Propane and electrical are the top 2 causes of camper fires and explosions.


"Never gamble with a non factory built camper,
your life could depend on it!" ~ Livin Large

Thanks for the welcome!

Ok, so the problem is that the wire on the solar panels is built in and it’s 4mm^2/12AWG. Will everything run ok if I run this to a 30 amp charge controller (with a 20 amp fuse in line)? Will I be losing any power from the solar panels?

Thanks again!


I’m not familiar with your controller, but I’ll attach a wire size chart below.

If I understand correctly, if you hook up the panels in parallel you’ll get up to ~25a @ 12vdc, in series would give you ~8.33a @ 36vdc. I have no way of knowing what your controller can handle, or how it handles it. They’re all different, but there should be a spec sheet with the controller to tell you. It might limit you to 12vdc @ xx amps, or it may not.

How the controller handles the conversion is important too, does it regulate amps, volts, or both? Will it regulate both power in and power out, or only one way? Many variables to deal with which is why success rates are low and costly. You also must determine how your battery wishes to be charged, to make sure your controller is capable of doing it. An isolator or a battery charger are capable of intelligent charging, but most controllers aren’t, which means pre-mature battery death. (6-9 months vs. 5-7 years getting charged correctly.)


"Never gamble with a non factory built camper,
your life could depend on it!" ~ Livin Large