Solar Charge Controller

Charge Controller Sizing and Selection

Each time you charge deep cycle batteries with solar panels, it’s necessary to use a charge controller in the circuit in order to protect the battery from overcharging or from over discharging. The exception to this rule is when using solar panels smaller than 5 Watts.

Solar Charge Controller

Solar Charge Controller

Choosing the most suitable charge controller is simple and only requires two steps:

Step 1 – Voltage selection

Select a charge controller that is compatible with the system voltage. The standard configurations are 12, 24, and 48 volts. If you are wiring your batteries for 24 volts you need a charge controller that is rated at 24 volts.

Some controllers are voltage specific, meaning that the voltage cannot be changed or substituted. Other more sophisticated controllers include a voltage auto-detect feature, which allows it to be used with different voltage settings.

Step 2 – Current capacity

Select a charge controller that can handle the maximum output current of the solar panel (or solar array). The maximum possible current that a PV panel can generate is the “short circuit current,” indicated as Isc in the panel’s label or specs sheet.

It’s recommended to include a safety factor for isolated events as well. For example, a solar panel with a LSC of 7.89 amp could potentially produce an extra 25% on a sunny day with very clear snow pack. (additional light reflected off the snow). This results in a possible maximum of 9.86 amp (7.89 x 1.25 = 9.86 amp). In this case, a 10 amp charge controller would be recommended.

Below you will find a quick guide to choosing the proper charge controller for several popular solar panel sizes.

12V solar panels 5W – 45W:
Phocos CM 04 Charge Controller 4A, 12V

12V solar panels up to 70W:
Flexcharge PV7D Charge Controller 7A – 12V

12V solar panels up to 120W:
Phocos CM 10 Charge Controller 10A, 12V
Phocos CMLup 10 Charge Controller 12/24V, 10A
Phocos ECO 10 Charge Controller 10A, 12V
Phocos ECO-N-10-T Charge Controller 10A, 12/24V

12V solar panels up to 160W:
Flexcharge NC25A Charge Controller 25A – 12V
Phocos CMLup 20 Charge Controller 12/24V, 20A
Phocos ECO-N-20-T Charge Controller 10A, 12/24V

24V solar panels up to 160W:
Flexcharge NC25A Charge Controller 25A – 24V
Phocos CMLup 10 Charge Controller 12/24V, 10A
Phocos ECO-N-10-T Charge Controller 10A, 12/24V