Way to switch between two power supplies

[acerdisma]

Dear all,

what is the most power efficient way to choose between two power sources?
To be more precise, I have a solar powered circuit with a dc regulated output and a rechargable battery, and want to be able to automatically select the best of those two upon voltage level conditions (i.e.always keep a 3V output).

Any ideas/suggestions welcome!
Thanks a lot!

 

[acerdisma]

thank you VE1BLL for the time you spare...

all sounds good on your approach, but the battery is what makes this circuit tricky.
What I mean is that the battery type to use, imposes various restrictions and requires extra circuitry in order to avoid situations like overcharge, overdischarge etc. Since SLA batteries are ruled out due to size and weight isuues, we are left with recheargable NiCd, NiMH and Lion.

NiCd are also ruled out due to the memory effect they present, hence I have to use NiMH or Lion cells, both of which are not easy to charge (at least not as easy it is with lead acid cells)....

While NiMH need constant current to (fast)charge Lion require a constant voltage/constant current algorithm..which brings me back to the begining, wondering what to do....

 

[itsmoked]

You can get Lead acids in "D" size.

http://www.enersysreservepower.com/spl.asp?routine=spl

 

[VEBill]

Is size really an issue? After all, you have a solar panel that is, presumably, fairly large compared to any battery system that you might choose.

 

[VEBill]

http://www.analog.com/library/analogDialogue/archives/31-2/liion.html

The above link provides some interesting details on the care and feeding of LiIon batteries. It doesn't seem reasonable that you would be able to accomplish all that, while being powered by a solar panel (with the added amusement of clouds occasionally blocking out the sun).