While updating my knowledge on solar panels and batteries came across the video shared by Jason P...

[G+_Rud Dog]

While updating my knowledge on solar panels and batteries came across the video shared by Jason Perry this led to more searching found one video claiming if you don't place a diode in series with the output of the solar panel you might discharge your battery during no light time periods.

Idea being output from the solar panel would pass through the diode but block current from passing to the solar panel.

This is the first time hearing this and want to ask, can solar panels discharge your battery?

[G+_Black Merc]

This is true.. The added diode acts as a check valve(plumbers ref.) or simply a one-way door. The panel it self is a diode with special properties that react to light.

[G+_Damien Wessling]

I would have thought the controller/inverter would handle that function.

[G+_Rud Dog]

Damien Wessling thank you for commenting, in this case, the instructions stated the panel was so small and the current so low directly connecting to the battery was OK. Some suggest doing this could damage th battery so will wait and see if someone can confimr either way.

[G+_Black Merc]

Damien Wessling some do... Some commercial panels have a diode built in too.. Better to add one then to not have one at all. Worst case you loose 0.7v for adding one or your entire system drops for the unexpected drain over a long period of no direct sun(clouds, snow).

[G+_Dan Hockey]

When you have a cell or panel that's almost the same voltage as the battery it's charging then all you need is a blocking diode. Any voltage higher than your battery is when you need a charge controller.

[G+_Black Merc]

Dan Hockey partly true... You have to consider wattage of the panel/system. Ex. A car battery and a panel of 15watts... Simple math watts/voltage = current, 15/12 = 1.25amps but, that's maximum, at peak sun light, 1/3 to 1/4 of the day. The rest of the time your system will be relying on the battery.

 

I would not consider a charge controller unless your math tells you it's function is needed.(overcharge, overdrain of battery)

[G+_Dan Hockey]

Black Merc Battery chemistry will determine what you have to do for a charging circuit. Lead acid batteries are easy to deal with.

On you tube look for "DIY powerwall" there are people building their own home made "powerwall" and using solar to charge.

It gives a good example of how complicated things can get when using lithiun cells. Lots of good info though.