# Simple battery backup circuit

#### Michel_e_r

Joined May 30, 2008
10
I'd like to design a simple circuit which is usually connected through an adapter and when it is not, it uses a common 12V battery or of the sort. How can I do this? I've thought of using relay and somehow make that work, but seems it will take more than that =P. Any ideas? Much thanks.

#### SgtWookie

Joined Jul 17, 2007
22,210
Your request is really quite vague.

What is your required voltage and current for sustaining the circuit?
DC or AC? AC gets quite a bit more complicated.

#### Michel_e_r

Joined May 30, 2008
10
12 volts and AC circuit =/

So, all I have is a power source adapter which is connected to the wall and when it is unplugged I need a battery to serve as backup to supply the voltage to the the rest of the circuit.

#### SgtWookie

Joined Jul 17, 2007
22,210
12 volts and AC circuit =/
So, 12VAC at what current?

So, all I have is a power source adapter which is connected to the wall and when it is unplugged I need a battery to serve as backup to supply the voltage to the the rest of the circuit.
OK, so if it's a "wall wart" that's supplying the juice, it may not be AC, it could be DC.

Still do not have much to go on here.

#### Wendy

Joined Mar 24, 2008
22,145
If you are using DC (say a wall wart and a battery) then simple diodes will do the trick. Just make sure the wall wart has at least a couple of tenths more voltage than the battery, and the switching is automatic.

#### Michel_e_r

Joined May 30, 2008
10
Thank you SgtWookie and Bill_Marsden for putting up with my vagueness..English is not my strong language . I didn't know what a wall wart was but it sure is what I have. I read through other thread of using diodes and I'm sure that is what I need but I just started with electronic and not sure as to how to put it all. Is there a circuit available I can use as reference perhaps?

Much thanks

P.S This whole thing is to connect lights..so around 100mA-200mA. Very similar to this persons project..except he had schematic for which i do not have and is what I need.