I have a small PV system for my shed. Just setting up and testing at this point.

  • 90W panel
  • MPPT T20 charge controller - 20 AMP
  • 120ah 12 volt battery

Only one led light connected to load.

I am not sure if the battery is just not discharged enough for charging or my panel controller is not allowing the battery to charge? The icon for sun does not show anything at all. The panel is producing some load according to my metre.

https://ibb.co/miqQX8 https://ibb.co/kv03Ko https://ibb.co/nQTqzo https://ibb.co/bQ3qzo


  • Not near enough information. What is the voltage on the battery? What is the voltage on the solar input to the MPPT? How long are the various cables? – Harper - Reinstate Monica Jun 24 '18 at 15:57
  • I am new to all this, I will answer best I can. 12.5v on the battery. 8.8v from the solar input I believe, varies. Cables are about 6 ft, 12 gauge I believe. – mrlayance Jun 24 '18 at 16:42
  • 1
    wire size is good for that length. Assume those voltage numbers are good,... The battery voltage clearly shows it is not being charged at all, but has a reasonable state of charge, so it is not flat. If it were being charged voltage should be at 13+, and if near full charge it should be closer to 14V. Check the manual on your MPPT controller, but I suspect it needs a solar panel voltage that is higher than battery voltage (14V). Nominal 12V panels should give 14-19V, so 8.8v says either they're the wrong panel, broken, or they're in shade. – Harper - Reinstate Monica Jun 24 '18 at 17:16
  • To fully charge a 12v battery the voltage needs to be closer to 13.5v and as high as 14.5v a higher voltage can be used but it will shorten the battery life. There should be a charge controller to protect the array and the battery. – Ed Beal Jun 24 '18 at 19:07
  • My panel reads the following, max power 90w, pmax 5.14v, voltage at pax 17.5v. – mrlayance Jun 24 '18 at 20:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.