How the CMTPO2 solar charge controller works. | how to use a cmtpo2 solar panel controller

I bough a solar panel which came with a CMTPO2 charge controller.

Unfortunately the instructions were difficult to understand, and faultfinding was impossible, so I have written this post to give you a quick understanding. 

Relate the letter in the below picture to the functions.


  1. Solid green light: This means its collecting energy from the sun and charging
  2. Flashing green light: This means it collecting energy from the sun but no required as batteries are full and not required by load device.


  1. Three solid red lights: Batteries are full
  2. Two solid red lights: Batteries are half full
  3. One solid red light: Batteries are approaching empty
  4. Flashing red light: Batteries are dead not providing any power


  1. Solid green light: There is a device connected and drawing power.


  1. Connecting the device which requires power.


1. Connection to the battery


  1. Connection to the solar panel.

2 thoughts on “How the CMTPO2 solar charge controller works. | how to use a cmtpo2 solar panel controller”

  1. I have worked out the circuit of a CMTP02 controller. From pictures I have seen other people post, there are many variations all called CMTP02, but may have different circuitry. The link is
    My tests at 12V agree with what you posted, except the load light. On my controller the load light is on as long as the battery has charge, it doesn’t matter if there is a load or not. It will go off if the battery is going flat.
    I haven’t started 24V testing yet.
    It is important to note there should be NO CONNECTION between the battery -ve, the panel -ve or the load -ve. Inside the controller all the -ve leads are connected, so connecting any two -ve wires will bypass the controller.

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