I am newbie in electrical engineering. Recently, I ordered a solar DIY kit package which includes a solar panel(10W, 12V, 1A), a solar charge controller and an inverter(DC 12V to AC 240V). I plan to use it to charge a 12V battery.

Here I have a question about this DIY package, To my understanding, to charge a 12V battery, the output DC voltage of solar charge controller should be higher than 12V. But the solar charge controler's rated current is: 10A / 20A / 30A / 40A / 50A /60A. According to the wattage(10W) the solar panel can generate, the solar charge controller's output DC voltage will be less than 1V. So, how this solar DIY package can charge the battery?


Solar Panel:

  1. Material: A-level polycrystalline silicon solar panel
  2. Maximum power: 20W
  3. Rated power: 10W
  4. Maximum voltage: 21V
  5. Working voltage: 18V
  6. Current: 0-1000MA


  1. Rated Voltage: 12V/24V auto adapt
  2. Rated Current: 10A / 20A / 30A / 40A / 50A /60A(Optional)
  3. Max. PV Voltage: 12V battery: 23V(Max.) 24V battery: 46V(Max.)
  4. USB Output: 2 way USB output,5V / 2.5A (Max.)
  5. Self-consume: <10mA
  • \$\begingroup\$ isn't rated current equal to the maximum allowable current? \$\endgroup\$
    – jsotola
    Commented Nov 3, 2021 at 0:29
  • \$\begingroup\$ @jsotola Thanks, I added specification. \$\endgroup\$
    – lei lei
    Commented Nov 3, 2021 at 1:00
  • \$\begingroup\$ The open-circuit voltage of your "12V" solar panel probably is substantially higher than 12V when it is illuminated by full sunlight. Probably somewhere between 18V and 24V. When they say "12V" that means, it is intended to work with a nominally 12V system. But even the battery in a 12V system isn't 12V. Battery voltage can be as high as 14.7V during charging, or maybe somewhere between 10V and 11V when deeply discharged. (Really, there's no hard lower limit. It's just, the lower you allow the battery voltage to go, the sooner you will be needing to replace it with a new one.) \$\endgroup\$ Commented Nov 3, 2021 at 1:20
  • \$\begingroup\$ @SolomonSlow Thanks. I can understand that if the solar panel direct connect to the battery. But I do not understand how the charging works if through solar charge controller. As I asked in the question, the solar charge controller's rated current is 10A / 20A / 30A / 40A / 50A /60A(Optional), then according to the rated wattage of solar panel, the output voltage of solar charge controller should be 1V assuming the current is 10A and wattage is 10W. 1V is far from enough to charge the battery. \$\endgroup\$
    – lei lei
    Commented Nov 3, 2021 at 1:34
  • 1
    \$\begingroup\$ Solar panel : 21V (18V). It'll be producing nearly 0.5A and the charge controller will step that down to 13 or 14V at about 0.7A. \$\endgroup\$
    – user16324
    Commented Nov 3, 2021 at 22:47

1 Answer 1


If the controller features MPPT (maximum power point tracking), then it'll be able to search out the best operating point for the solar panel given the amount of illumination falling on it. Usually this is done by varying the load on the panel while monitoring the current and voltage from the panel, and trending the load in the direction where the current * voltage product is greatest.

It won't be generating 10A to the battery, because the solar panel will never be able to generate that much power -- one hopes that the DIY package you got is designed so that you can change out the panel for a larger one, or add more panels in parallel to increase the current.

If the controller is any good at battery management, then when the battery is in a state of charge that can absorb the maximum power that the solar panel can produce, that's what it'll get (less any losses in the controller). If the battery needs less power than that, the controller will throttle the load on the panel to give the battery just as much charge current as it can safely handle.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.