Req: Circuit Help for use of SLA battery in Security Alarm Project

[charudatt]

Hello Friends,

I want help / circuit ideas on how I can use a 12V SLA battery in a (security alarm) project in which , when the main power supply fails , the Battery takes over and the main supply , trickle charges the SLA battery.

regards

[oldvan]

I've used this circuit in the past, works nicely.
http://shdesigns.org/gcellchg.html

[bobcat1]

Hi

You can use 2 diode connected back to back (cathode to cathode) and connect anode of each to power source (one anode to battery and one anode to PSU)

In order to charge the battery you will need to bypass the battery diode with a charging resistor (probably 10% of the battery current capacity)

another more efficient method id to use the LTC4412 from LTC you can find application schematic in data sheet   

All the best

Bobi

[DreamCat]

this can use p-channel mosfet as power switch.