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Charge Controller showing low Voltage

img-7951.pngimg-7952.pngMy 100/50 has been working fine for over six months. Recently I noticed through the connect app that the batteries had failed to charge for a few days. Looking at the controller it was not charging even though it was sunny day. The PV voltage was showing at 12.6. I disconnect the solar inputs and measured 19.8 volts coming from the panels. reconnected the input to controller and back working. This has happened twice now and this time controller is saying 6v and I can't get it to charge. Any thoughts?

mppt smart solarcharger
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Paul B answered ·

if your panel voltage is only 5.57 volts then you have a issue with your panels ie a bad connection

also note that the panel voltage has to be 5v greater than battery voltage for the mppt to START charging.

as by the look you have 18 volt panels you would be better to connect these in series if you have more than one thus raising the open circuit voltage to 36 volts.



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Thanks for comment Paul - What I'm wondering about is why if I disconnect and measure the voltage from the panels with multimeter its actually 19 volts. why is the app saying 6 volts? is it a fault with the solar controller?

there is a bad connection somewhere. in the panel cables, check all the plugs.

another way is to look at the panels out put amps say its 5 amps. join the two panel wires neg and pos together thus this creates a short circuit but there amps coming from the panel should still be around 5 amps.

make sure the panel is in good sunlight to do this test


panels are constant current devices so basically no matter what the voltage they still out put amps


in your case I think this will be dropping to zero again indicating a panel or wiring fault

Thanks Paul. Thats a neat trick. I tested all the panels and they were ok. I took the opportunity to wire them back up in series instead of parallel and things are working ok. (the only part left out is the 3 to 1 joiners so im assuming it was them)