How To Connect a Solar Charge Controller (With Wiring Diagrams)

Every solar panel system requires a solar charge controller, which is required to charge the batteries properly and safely.

But wiring a solar charge controller can be tricky if you haven’t done it before. You must also buy the right size wire and fuses/breakers to complete the installation.

In this blog post, we provide a step-by-step guide with clear & intuitive diagrams to show you how to wire a solar charge controller in a camper van conversion.

This post will also show you how (or point you in the right direction) to:

• Calculate the right size solar charge controller
• Identify what wire size (AWG) you’ll need
• Ground your solar charge controller
• Test the charge controller for functionality

Lastly, this post will show you what tools and materials you’ll need to integrate a charge controller into your solar build successfully.

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Part 1: Wiring Charge Controller to Solar Panels

Virtually every solar charge controller will have two input ports that must be connected to the solar panels. One port is for the positive (+) red wire, and one port is for the negative (-) black wire. In the below image, you can see where these solar inputs are located on this Victron MPPT controller.

Note: “PV” stands for “photovoltaic,” which is another word for solar.

The image below shows a sample charge controller wiring diagram connecting the controller to two solar panels.

Note: This specific diagram is for camper van conversions, so we include an “entry gland” and “rubber grommet.” If you install a solar system for a home, you could disregard those two products.

To complete this section, you must know the following two pieces of information.

Solar Wire Size

This is the wire that connects the solar panels to the solar charge controller. The thickness of this wire depends on several factors. To learn more about which size you need, check out our solar wire size guide.

Solar Disconnect Size

This circuit breaker is installed between the solar panels and the solar charge controller. This disconnect’s size (amp rating) depends on how much current is traveling through the wires. For more information, including sizing, visit our solar fuse guidelines post.

Copy Our Diagram: If you have a solar array that is 440W (or less) and the panels are wired in series, you can copy our wiring diagram and use 10 AWG wires to connect the panels to the charge controller and use a 40A solar disconnect switch.

Materials List

Besides the solar panels and charge controller, below is a list of materials you’ll need. This material list works for solar arrays that are 440W or less, with panels wired in series. If your array doesn’t fall within these parameters, you can read our above-linked articles to help you size your materials.

Note: This recommended wire above only includes red wire. You’ll need to get a spool of black wire of the same wire gauge.

Ancor-branded wires aren’t the cheapest. But we recommend them because the wires are ‘marine grade’ and resist corrosion when exposed to harsh outdoor environments (UV, salty air, rain). This is critical since a portion of these wires will be lying outside on your van’s roof. Watch our Ancor wire product review below to learn more about them.

Tools List

To complete this section, you’ll have to cut the solar wire and strip off the insulation jacket. You’ll need a multi-tool like the one we recommend below to do this.

Part 2: Wiring Charge Controller to Batteries

Next, the solar charge controller must be wired to the designated batteries you want to charge from the solar panels. Every charge controller will have output ports that lead to the batteries.

The image below shows where these output ports are located from the same Victron MPPT charge controller.

The below wiring diagram shows how to connect a solar charge controller to the bus bars. We do not recommend wiring the charge controller directly to the batteries. Using bus bars as an intermediary will simplify your wiring process and keep your electrical wiring neat and tidy.

Our 12V installation guide shows you how to wire the bus bars to the batteries. 

Note: The specific products we list in this diagram above, like the 40A circuit breaker, assume you have a 30A-rated charge controller. If you have a different charge controller, we recommend reading our solar wire size guide and solar fusing guidelines to get the right products you’ll need.

Materials List

Tools You Will Need

You’ll need the following tools to crimp lug terminals onto electrical wire.

To learn how to use these tools to crimp your own lug terminals, check out our video below.

Part 3: Grounding a Solar Charge Controller

Most charge controllers will come with a terminal bolt that allows you to wire the solar charge controller to an appropriate ground point. Refer to the image below to see where Victron installs their ground terminal post.

However, if the charge controller is integrated into a larger 12V/24V DC system that is ALREADY grounded, then you do not need to ground the charge controller specifically. Since our camper van’s electrical system is already grounded from the bus bars, we did not utilize Victron’s ground point.

If you need to ground the solar charge controller, refer to the simple wiring diagram below to see how this is done.

Part 4: Confirm Solar Charge Controller Is Working

Once the solar charge controller is wired to the solar panels and the batteries, it’s time to see if everything is functioning properly.

If your charge controller has a display on the unit box, read the display unit to confirm that the batteries are being charged.

If you are using a Victron-branded charge controller, you can connect the controller to your smartphone via Bluetooth using the smartphone app.

We use the Victron 100/30 controller, and checking our solar harvesting data is beautifully simple. In this photo, I can see that 215 watts (15.60A) of power flow into my batteries.

Great!

By the way, if you haven’t yet selected your charge controller, we think Victron model charge controllers are pretty neat. Read our review to learn why.

Solar Charge Controller Wiring Summary

Congratulations if you’ve made it this far and your batteries are charging! You’ve successfully wired your solar charge controller into your camper van’s electric system.

Being able to charge batteries directly from the sun and being energy independent is one of the greatest feelings in van life.

For more van life solar content, we encourage you to check out our DIY solar guide for camper vans.

Happy building!

Appendix 1: Test Charge Controller for Proper Voltage

Now that you have wired your solar charge controller, it’s time to check the voltage readings to ensure everything was wired correctly. We can do this with a standard multimeter tool.

Check Battery Side Voltage

Set the multimeter to read volts and insert the positive and negative leads of the multimeter into the output ports of the solar charge controller.

Depending on your battery type and the battery’s state of charge (SOC), the multimeter should read somewhere between 10.5 and 14.6 volts.

If you get a reading between this range, your charge controller is successfully wired to the batteries.

Check Solar Panel Side Voltage

Next, connect the multimeter’s positive and negative leads to the charge controller’s input ports.

To get an appropriate voltage reading, your solar panels will need to be in full sun. No partial shading on the panels.

Under sunlight, check to ensure your multimeter detects a voltage coming from the panels and entering the solar charge controller.

FAQ

Is a Solar Charge Controller Required?

Yes. In most circumstances, a solar charge controller is required for the building of your solar system. These devices are essential to ensuring your batteries are properly charged and are not overcharged, which can degrade the batteries.

What Is the Best Wire Size for Solar Charge Controllers?

The best wire size for your solar charge controller depends on the size of your solar array. Read our solar wire size guide to identify the best wire size for your needs.

How To Mount a Solar Charge Controller?

Mount the solar charge controller on a non-flammable substrate. The electric terminals should be facing downwards.

Do not mount the solar charge controller directly above the batteries to prevent damage to the charge controller (due to off-gassing).