Solar Panels

What Size Solar Charge Controller Do I Need? (Charge Controller Size Chart)

By:Michael Johns

What size charge controller do you need header

In this article, you will find out how to pick the correct size charge controller for your solar panel system.

The information below is about off-grid solar panels that you might use on an RV, boat, cabin, shed, or similar. Together we will go through the specification to consider when choosing your charge controller. Plus, I’ve created a size chart to help you select quickly.

Solar Charge Controller Size Factors

You will need to know a few bits of information to make sure a charge controller is compatible with your solar panels and batteries. Remember, the solar charge controller connects between the panel and the battery to regulate voltage and current.

So you need to ensure you have equipment with the correct voltage and current (amps).


The first thing to ensure is that the solar charge controller is suitable to regulate the voltage. This means it can take the voltage from your solar panels and match it to the battery. You will find your solar panel has a different voltage to your battery so it needs to be regulated.

It is likely you will have either a 12V or 24V battery system (12V is most common). So you should make sure you have a charge controller that outputs this voltage. Most modern controllers are both 12V and 24V, they will automatically detect and switch based on your system. You should still double-check these details. 

Amps (Current)

The amps, also called current, is the volume of electricity that is flowing through your wires. It is literally how many electrons are moving through your circuit. This will generally increase with the amount of solar panels you hook up to your controller in parallel. 

Solar charge controllers are sized in amps (A) so this makes life easier. We can use solar panel watts and battery voltage to get the correct size. 

To work out amps you divide watts by volts. For example, 100W ÷ 12V = 8.3A.

You can use the formula Watts ÷ Volts = Amps to work out charge controller minimum size.

The charge controller must be able to handle the amount of current you are sending in and out of it. You should check the maximum input wattage which is listed on the product specification. 

Solar Charge Controller Size Chart

The charge controller size chart below is designed to help you pick a controller size for 12V batteries. The suggested controller ‘Amps’ is its output and sizing. You should also check a product’s voltage and input. Larger controllers will naturally have higher input capacities but it’s worth double checking.

Solar Panel WattsCharge Controller Size (Amps)
1000 (1kW)90A
1200 (1.2kW)100A

What Size Charge Controller for a 100W Solar Panel?

For 100W solar panels you will need at least a 10A solar charge controller. This is because it will generate a maximum of 8 amps on a 12V system.  

What Size Charge Controller for 200W Solar Panel?

With a 200W solar panel you should use at least a 20A solar charge controller. In direct sunlight, your system will create upto 16 amps so you will need a size bigger than this current output.  

What Size Charge Controller for 300W Solar Panel?

A 300W solar panel requires a 30A solar charge controller. Your controller will need to cope with upto 25 amps output so 30A will work well.

What Size Charge Controller for a 400W Solar Panel?

Connected to a 400W solar panel you will need to use a 40A solar charge controller. This enables your system to output the maximum 33 amps it can generate in direct sunlight. 

What Size Solar Charge Controller Summary

I hope this article clears up what size solar charge controller you require.

Most off-grid solar panel systems are very similar. You simply need to check whether you have a 12V or 24V battery system and ensure the controller can regulate this voltage. 

Then you should ensure your controller can output a high enough current or ‘amps’ for your equipment. If you undersize your controller it will clip the current and reduce the energy being sent from your panel to your battery. This means it’s always best to go a little bit bigger to ensure you’re not missing out. 

And don’t forget to check the product specification for maximum solar panel wattage input to make sure all your components work correctly together.

Ready to buy? Check out my guide to the Best Solar Charge Controllers.