I'm in the process of designing a small solar regulator / charger (no more than 5A) for sealed lead acid batteries. I have put a working prototype together and all seems to be working.
However, after Googling solar charger circuit diagrams, I have found that a lot of chargers seem to short the solar output to ground via a dummy load resistor using a FET or transistor rather than just just disconnecting the solar panels using a FET or transistor.
In my prototype controller I am just disconnecting the positive of the panel using a P channel FET and it seems to be working fine.
From Googling and searching this forum extensively, I can't seem to find any reasons why one should short the solar panels to ground using a dummy load rather than just disconnecting the positive of the panels.
I am using an AVR micro controller to control the charge process using PWM. However, a lot of the circuits I saw using a dummy load used an analog method instead of a PWM micro controller. Is using an analog method maybe a reason that one needs to use a dummy load to stop charging but with a PWM method disconnecting the charge input is fine?
I cant seem to find any reason why one must use a dummy load to stop charging from the panels… It seems it won't damage the panel being disconnected or anything like that. Also, in my thinking I would say there would be more strain and possible damage on the system (FET and dummy resistor) if the output of the panel is shorted while not charging vs just being disconnected.
Does anyone have any feedback on what method I should use (dummy load or disconnect) in this controller I'm working on, and why?
Best Answer
http://www.backwoodssolar.com/products/diversion-loads
"If you use a windmill that does not have its own charge control, or use hydroelectric generating, a diversion control must be used, since those generators can be damaged if their charge is not absorbed in the batteries at all times".
Solar panels will sit happily with no load, while other kinds of generator will not.