Complete newbie here guys so please bear with my question.

I have bought 12W 6.6V solar panel that I will be using as phone charger. Beside that I have bought small USB solar controller which outputs 5V and max of 2A.

If I am understanding it right, 12W / 6.6V = 1.8 amps output by solar panel.

Now, this solar controller is limiting voltage to 5V, does that mean that I will get 12W / 5V = 2.4 amps that will get stabilized to 2A or 1.8A (solar panel - 12W / 6.6V).

Again, sorry for beginner question but I really don't know much about this, just starting to learn.

P.S. I am guessing I will get 1.8A because that is what panel outputs, but I just want to be sure.

  • 1
    \$\begingroup\$ Do you have a datasheet for your "solar controller"? \$\endgroup\$
    – The Photon
    Oct 18, 2017 at 17:17
  • \$\begingroup\$ @ThePhoton sadly i dont, but this is the controler that i got aliexpress.com/item/… \$\endgroup\$
    – Muxi Maxo
    Oct 18, 2017 at 17:19

2 Answers 2


You will never get more than 2A at 5V since that is all the controller is rated to give you.

Whether you get less than that will depend on how the controller converts the solar panel output.

If the controller is worth it's stuff, and at least 83.3% efficient, you should be getting the 10W (5V * 2A) it suggests when the 12W panel is lit well enough.

But then again.. this is cheap "e-bay" type stuff with no specs..so good luck.


The voltage output from solar panels is very dependent on the load. 6.6V is probably the open circuit voltage. It's the wattage that counts.

If the controller is up to snuff it will pass up to 10W from it to your output, plus a bit to do it's own thing.

BTW.. if you need 2A for your load, you will be way underpowered if there is a cloud in the sky with this setup. For decent operation, your panel rating needs to be significantly higher than your average demand.

  • \$\begingroup\$ hi trevor and thank you! i know that these are cheap panels, but still i wanted to know will i get 1.8A or 2A (since the panel is 12w/6.6v, i thought i will get 1.8). Thank you! \$\endgroup\$
    – Muxi Maxo
    Oct 18, 2017 at 17:37
  • \$\begingroup\$ @MuxiMaxo solar panels don't really work that way though. see edit. \$\endgroup\$
    – Trevor_G
    Oct 18, 2017 at 17:40
  • \$\begingroup\$ thank you! by "panel rating" you mean more watts? i mean, ideally it would work at 2A, but even if it is 1A, it can still charge the phone, only slower, right? i really have a lot to learn... \$\endgroup\$
    – Muxi Maxo
    Oct 18, 2017 at 17:45
  • \$\begingroup\$ @MuxiMaxo yes more watts. Or use two of them. Whether the charger will still work is hard to say. It depends on how the charger deals with a brown out on the 5V line and if the controller shuts down when the voltage sags. \$\endgroup\$
    – Trevor_G
    Oct 18, 2017 at 17:49

Trevor is correct about the controller not delivering more than 5 volts at 2 amperes for a total of 10 watts. Your solar panel can provide a maximum 12 watts at 6.6 volts which means the maximum current will be 1.82 amperes as you mentioned. Your controller is not likely 100% efficient and will take power to operate. I will assume your solar controller accepts 6.6 volts input. The controller cannot output maximum power unless the source can deliver that plus what the controller uses to operate. It would be good if you monitored the voltage and current into and out of the controller to know the electrical efficiency of this system. It would be even better if you could take reading every second


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