Dual Power Sources: Supplementing Solar w/ Battery

[HybridLogic]

Hey!

I'm trying to create something with some power cells, and I've run into the issue of inconsistent power supply.

I'd like to supplement power from a solar cell with a battery, but I'm not exactly sure how to keep the input to something at a set value. Basically, when the solar cell supply falls below a certain level, I'd like to supply the missing power with the battery.

Anyone have any ideas? I really don't know if any hardware exists for this already. The idea of using a microcontroller came up (and I can write assembly, so using one's not an issue).


Thanks for any input.

 

[mheslep]

See http://en.wikipedia.org/wiki/Diode-or_circuit

 

[Danger]

Good post, Mheslep, but I can't help thinking that there's an easier approach. The way an automotive electrical system works is that everything runs off of the battery, and the alternator keeps it charged. In this situation, the power cells can be subbed in for the alternator.

 

[mheslep]

Easier than two diodes? OP didn't discuss charging the battery from the PV. If he/she wants that they need something different.

 

[Pumblechook]

The problem with diodes is that they waste some power. Better maybe to use to transistors which are switched fully on by a control signal.

 

[mheslep]

Any kind of semiconductor gate will have losses in its on state. Power MOSFETS have the lowest switch losses. I don't know if that's any better than a good Schottky diode (.1, .2V forward bias). In any case, an transistor/FET that's turned on is effectively just a diode.