What size cable from solar charge controller to battery?

Undersizing your wires can lead to unwanted power and energy losses and potential safety risks. And, since copper wires are expensive, you also don’t want to oversize your wires too much.

Below you’ll find a calculator that will help you find the right cable size to connect your solar charge controller to your battery, along with a couple of examples that will make this more comprehensive.

What size cable from solar charge controller to battery?

The size of the cable that you need to connect your solar charge controller (MPPT or PWM) to your battery bank will depend on 3 factors:

• The Output Current rating (Amps) of your solar charge controller
• The Voltage (Volts) of your battery bank
• The distance between the output terminals of your charge controller and the terminals of your battery bank

Related: MPPT charge controller calculator

Based on these factors, the following calculator will determine the size of the wire that you need while ensuring minimal power losses (maximum voltage drop of 3%).

Please note that the results provided by the calculator are based on the assumption that you’ll be using a pure copper cable. Aluminum or Copper-Clad Aluminum wires are generally not recommended.

Below the calculator, you’ll find 2 examples.

Example 1:

For this example, we’ll make the following assumptions:

• The battery bank is rated at 24 Volts
• The MPPT solar charge controller is rated at 30 Amps
• The output terminals of the MPPT are 6 feet away (one way) from the terminals of the battery bank

After submitting these pieces of information to the calculator, here are the results:

The calculator has determined that we would need a 10 AWG (5.3mm²) pure copper cable for this setup. This means that we would need 12 feet of 10 AWG pure copper wire, 6 feet for the positive-to-positive connection, and 6 feet for the negative-to-nergative connection.

Example 2:

For this example, we’ll make the following assumptions:

• The battery bank is rated at 12 Volts
• The MPPT charge controller is rated at 30 Amps
• The output terminals of the MPPT are 3 feet away (one way) from the terminals of the battery bank

Here are the results:

Again, the calculator suggests a 10 AWG wire. This means that we would need 6 feet of 10 AWG pure copper wire, 3 feet for the positive-to-positive connection, and 3 feet for the negative-to-negative connection.