'Smart Solar charger' question

Thread Starter


Joined Feb 25, 2009
Hi all,

I am currently working on a smart solar charger with a group of people. This device will utilize Maximum Power Point Tracking and various smart battery chargers to allow a user to charge any of the big 4 families of rechargeable batteries (Lead-Acid, NiCD, NiMH, Li-Ion).

My questions stems from the use of supercaps in the circuit. Their use, as documented in the various papers over smart solar charges we've read, is to both store charge coming from the batteries and also to ensure that the output to the batteries is smooth.

Supercaps are low voltage-rated, obviously, and this presented a problem for us as our solar panel outputs at around 12 volts (43 watt rated solar panel). Our design as of now incorporates our supercapacitors in series to ensure they can handle the voltage across them while charging.

Anyway, the questions:

Unfortunately almost all of my knowledge of capacitor behavior stems from a voltage driven circuit. A solar panel is a current driven circuit, correct? Does this change the behavior of the capacitors? What changes need to be made?

Originally in our design, we had the ability for the capacitors to discharge in parallel to drop the voltage of the discharge down to the values on each individual capacitor. This was done to facilitate Li-Ion/NiMH charging that requires lower voltages, and to cut down on the need of a regulator of some sort (which lowers efficiency). We have been told by a professor that it SHOULD work in theory, but he doesn't know what will happen immediately at the switch. He feels as though there could possibly be massive amounts of current in the connection to ground.

If anyone knows anything about solar charging and can figure out any of these questions, or even explain the use of supercaps to us more clearly, it would be greatly appreciated.

Unfortunately no one in our group is familiar with power systems design, as it's never been taught to us. If we're missing a huge point, then it would be nice to be informed of it.