Battery backup

Hi,
I have developed an equipment whose current consumption is about 400 mA. Now it is required to add a battery back up for 4Hrs backup. Can I just connect a 12 V battery after my bridge rectifier (parallel to the present rectified DC). 5 voltage regulator is already there after this.
If I connect as above, will it cause damage to my transformer and 1N 4007 diodes (presently using 500 mA transformer) as the discharged battery may take more current? in that case is there any simple method to limit the charging current?
Somebody may please help.

You can connect a resistor between the bridge rectifier and the battery. The battery then provides power directly to the circuit.

Note that the resistor still has to pass the circuit current + the battery charging current (or else the battery won't charge).

If you want to charge the battery through the same transformer, then you should consider some charging control circuits which are freely available on internet. Otherwise, you can put a diode between the battery positive terminal and your circuit.

- Raj
Experiments with PIC16F628A