What Size of Wire to Use from Charge Controller to Battery?

If you’re building out your solar system then you might need some guidance on what size and length of wire to run from the charge controller to the battery.

Know what to keep in mind when sizing the battery to charge the controller wire also empowers you to make the necessary changes to your solar system, such as when you increase the solar panel size so that the system continues working optimally.

This post is therefore intended to provide some guidance on the optimal wire size to use to connect the charge controller to the battery bank.

What Size of Wire from Solar Charge Controller to the Battery?

The size of wire to use from the charge controller to the battery depends mainly on the maximum charging current of the controller and the length of the cable you plan to use.

Both the wire size and length are sized to minimize the drop in voltage so that as much power as is received by the charge controller from the solar panel makes its way to the batteries instead of being wasted in the wires.

In general, to minimize the voltage drop, keep the battery cables as short as possible.

That said, as a rough guide, 10 AWG wire is usually supplied with many charge controllers to connect the charge controller to the battery.

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Note: This is a minimum and you’d need to make adjustments to both the size of wire depending on the length and charge controller current.

The table below is an indicative guide of the wire gauge to use for selected charge controller current ratings for wire lengths up to 5 ft. The voltage drop is limited to 2%.

No.Charge controller rating (amps)AWG wire size from Charge controller to Battery
130A10 AWG
240A8AWG
355A6AWG
470A4AWG

Note: The limits the voltage drop along the cable lengths to 2% and assumes the cable lengths are not more than 5 feet.

You may also be interested in this post: The maximum cable length to use with your solar panels?

Tips to Select a Wire Gauge and Length for the Charge Controller to Battery Bank

  • Keep the wire size as short as possible. If the wire length is up to 5 feet, you can refer to the table above for charge controllers with charging current from 30 – 70 A.
  • Size the wire according to the maximum charge current the controller can handle. This minimizes both cost and time, in the end, should you upgrade the solar panel array to max out the charge controller capacity.

For cable lengths longer than 5 feet, refer to the table below as a guide.

AWG Wire Size141210864
Current carrying capacity (amps)152030405570
Solar panel Array Output current (amps)cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet)
14570115180290456
222.53557.590145228
41017.527.54572.5114
67.51217.53047.575
85.58.511.522.535.557
104.579.51828.545.5
1534.57121930
2023.55.5914.522.5
251.82.84.5711.518
301.52.43.569.515
402.84.5711.5
502.33.65.59
1002.94.6
Credits: Windynation.com

For a 30A charge controller for example, if the wire length is about 5 feet, you can use 10 AWG wire. Should you need to run longer wires of 10 feet, then you’ll use the larger 6 AWG cable to keep the voltage drops to under 2%.

What about when working with an MPPT controller – What wire size to Use?

Follow the steps above regardless of whether it is an MPPT or a PWM controller.

Size according to the maximum charging current from the controller and the length of cable you plan to run from the controller to the battery.

The Dangers of Using Undersized or Longer than Recommended Wires

If you undersize the wires, then you’ll have a higher voltage drop across the cable and less voltage at the battery.

You risk undercharging your battery bank and your batteries may not last their expected lifespan.

Closing Thoughts

To size the wire from the charge controller and the battery bank, it is advisable to size according to the maximum charging current from the charge controller and the expected cable run.

This saves time and cost should you increase the solar panel capacity to what the charge controller can handle.

Avoid undersizing the wires as the battery bank may not be charged optimally leading to early battery failure.

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