Split charge relay 12V , 2 Batteries reverse current flow detection.

Hi guys.
Doing a little project for my vehicle 24hr cctv. I decided to go with split charge relay to charge both batteries simultaneously. While I can control the relay to close the circuit when the alternator kicks in and second batt starts charging, Id like the secondary battery to be disconnected right after the engine is turned off, but Ive into a problem where I cannot detect the reverse current flow from the secondary battery into the main one and my vehicle has stop/start feature meaning I cannot rely on "ignition" signal either. What would be the elegant way to deal with this?(split charge diodes have voltage drop which Id like to avoid)
Any Ideas??? :frowning:
Thanks :slight_smile:

Hi guys.
Doing a little project for my vehicle 24hr cctv. I decided to go with split charge relay to charge both batteries simultaneously. While I can control the relay to close the circuit when the alternator kicks in and second batt starts charging, Id like the secondary battery to be disconnected right after the engine is turned off, but Ive into a problem where I cannot detect the reverse current flow from the secondary battery into the main one and my vehicle has stop/start feature meaning I cannot rely on "ignition" signal either. What would be the elegant way to deal with this?(split charge diodes have voltage drop which Id like to avoid)
Any Ideas??? :frowning:
Thanks :slight_smile:

You could just add a simple if then statement
Like if battery voltage > 12.87 relay ==1 (on) else relay ==0(off)
This will then only turn relay on while engine is running

Take a feed from something that is permanently live when the vehicle runs ( eg feed to the wiper switch ) and power your relay off that . When you turn the car off the relay will drop out and disconnect your battery

I think I`ve done it , added a 10ohm resistor in parallel with split relay I can now see few milliamps flowing in the right direction while the alternator is running, when engine shuts off and current starts seeping back into the main battery I cut the power to the relay coil. If think this might work ok.
Thanks for your input guys :slight_smile: