Wiring a Solar Controller

DISCLAIMER: Working with electricity can be dangerous. I am not a professional electrician, nor do I have an extensive history with electrics. All the information provided has been gathered through advice and my own research and is specific to my electrical system.


items used in wiring up my solar controllr

TOTAL: £268.98

A very exciting (at least for me) part of the electrical system - wiring my solar controller. I have a separate post that details installing my solar panel on the roof which you can read here. In this post we’ll be looking at wiring it into my electrical system.

Click here to see my full wiring diagram and here to see the section being described in this post.

victron solar controller wired in place

Charger Controller

I chose the Victron MPPT 100/30 Charge Controller mainly because you can connect it to the Victron app via bluetooth and you can see all sorts of information (that I don’t quite understand yet).

100 refers to the maximum solar panel voltage (V) and the 30 refers to the maximum solar panel current (A) is the controller can handle. Checking the information for my particular solar panel, the maximum voltage it will generate is 24.5V and the maximum current is 10.6A, so that falls well under those numbers.

Wiring to Battery

Kill switch wired to a 40A fuse

After mounting my solar controller, kill switch and fuse to my housing, the first thing to do is to connect the charge controller to the battery. It’s important to do this before connecting the solar panel, because the instructions say so. 

I first measured out all the 16mm cable I would need and cut to size, then crimped and heat shrunk cable lugs to the ends of each of the cables. The charge controller takes a positive and negative wire and is fastened in place by screwing down the bare fibers of the wire into the controller, rather than using cable lugs. 

First of all though, there is a bolt on the left-hand side of the controller’s casing which can be used to ground the casing. I attached one end of some black 16mm cable to this bolt then fixed the other end to my negative busbar. If you haven’t read my other posts, I’ve grounded my negative busbar to my van’s chassis which means I can connect all my other ground cables to this busbar. 

Next, I fixed some more black 16mm cable to the negative battery terminal of the charge controller and connected the other end to the negative busbar again. 

For the positive wire, I connected some red 16mm cable to the positive battery terminal of the charge controller and then connected it to one of the terminals of the kill switch. I then connected the other terminal of the kill switch to the fuse holder, then the other terminal of the fuse holder to the positive busbar. 

I decided to use a 40A fuse as the charge controller won’t be pulling more than 30A. There is an argument that rather than using a fuse and a kill switch, I could just use a circuit breaker as that would essentially do the same thing but with less breaks in the cable - thus reducing the chance of voltage drop. 

Now that both positive and negative cables were wired to the charge controller, I switched on the kill switch and checked on my Victron app to check I had power. (I did).

Wiring Solar Panel

Rather than wiring the solar panel directly to the charge controller, it’s important to be able to stop the flow of electricity to the charge controller, so I fitted a circuit breaker in between them. 

There are some NEC regulations in America that state both the positive and negative connections need to be able to be disabled at the same time. I’m not sure if this is the same in the UK but I figured it was a good rule to follow, so I bought a dual 32A circuit breaker and a distribution box to house it. 

I cut the positive and negative wires and screwed them in place into the top of the circuit breaker, then I screwed some positive and negative cable in the bottom of the circuit breaker and connected the other end straight into the positive and negative solar inputs on the charge controller. 

I’m not going to lie, the next part was immensely satisfying. I loaded up the Victron app to monitor my charge controller and switched on the circuit breaker. Amazingly, I instantly saw power coming through from the solar panel to the charge controller. 

If you have any questions at all, feel free to ping me an email or drop me a message on Instagram!