Batteries for a small padlock alarm

[jkon]

I have a small padlock alarm that is powered by a 9 volt battery. I would like to power it with a 9 vdc wall wart adapter but would also want the battery backup just in case someone cuts the adapter power. I'd like to use a 9 volt rechargeable battery with the wall wart hooked up somehow to also provide a trickle charge to the battery. Is this easily possible without getting to elaborate because I have about twenty of these padlocks to do. Thanks.

 

[seadolphine2000]

Re: Small Padlock Alarm

You can connect the adapter with the battery at the same time through a switch, that when the adapter is disconnected, the battery is connected through the switch.

Hope this helps.

 

[IanP]

Re: Small Padlock Alarm

You can try to solve this problem with 2 diodes ( Schottky, for low voltage drop) and a resistor: see drawing below ..
The power supply will have to supply ≈10Vdc for this circuit to work correctly ..
If needed, you can add another diode between power supply and R1 to prevent the battery being discharged through power supply. In this case power supply voltage should be around ≈10.5Vdc ..
Regards,
IanP