pic with 2 battery connection

Hi,


my application is I want to use two 12V battery, with my circuit. In which when one battery is working than another must be charging and vice versa. So if my battery b1 is discharged to 11V from 12V than battery b2 must be connected to my circuit and battery b1 should be connected in charging and vice-versa. for this application i design voltage divider circuit that divides voltage linearly to 5v. this is given to pic18f4550. pic will convert this analog to digital and when change is more than 1 volt, it high the particular pin. Now, the program is completed and i want to connect relay at output of pic. So which relay and relay driver circuit should i use? any other simple logic for my application???

I suggest that you use a 12 V relay, with contact rating at least twice the charging current.

If you are switching the load as well, the contract rating should be at least twice the load as well.

To power the relay you can probably use 2 diodes to take the maximum voltage from the batteries. I suggest you have the negative of the batteries connected to negative of your 5 V supply. Then just use a logic level N-channel MOSFET to turn on the relay. Connect one side of the relay to 12 V, fit a freewheel diode, and make sure your MOSFET is large enough to take the coil current and not get too hot.

HI,

I am using dc to dc converter and taking 24V dc from 12V input supply... is it right choice or not???

What are you running from the 24 V converter? How big is the load?

What are you charging the batteries from? What is the rating of the charger?