circuit design

[myp71]

Wow looks like I found heaven anyway I wonder if anyone knows how to build a battery backup system so when the A.C power goes out it will switch over to battery the battery would have to be different voltage like from 3-12 volts D.C<p>

[greg123]

Take a look at a simple circuit for an emergency backup light.<p>Should be lots of resources on the net

[myp71]

Thanks for your help Greg I'm looking at one of those emergency backup lights now but all i see is a transistor and some diodes the transistor leads go to the light then another one goes to the battery ground then the last one goes to all of the diodes and resistors thats were I get lost.I kind of thought that the circuit would be transtior based. I have a design now that is hooked up to a automotive relay with a wall transformer powering it all the time so when the power fails the relay goes to n.c then the light comes on but won't that hurt the ($.99 cent) relay? so will any transtior work like the one in the emergency light.
thanks everyone for your help again
Ryan

[Bernius1]

P71, depending on load current, you'll probably want to look at a hi-amp NPN-Darlington transistor. 2N6388 ??? MOS (NO-static!!) TO-220A case, 8A Max load. Or a hi-amp triac (mostly also TO220 cases), and run at the lower voltage. But the triac gate (assuming it's on the power side, not the load side)has to be energized AFTER the switch from a/c source to battery is made.

[myp71]

hi once again i was wanting to know if these circuits will work for me and which one will be better
this is circuit # 01<p>http://electronic-circuits-diagrams.com ... ges/10.gif<p>this is # 02<p>http://electronic-circuits-diagrams.com ... ages/2.gif