I can’t find an engine run signal, what can I do?
Engine run signal
An engine run
signal would give you a +12V when the engine is running an 0V when the engine
is off.
Switched ignition signal
A switched
ignition would give you +12V with the ignition on and the engine is not running and 0V when the ignition was off.
It is important
to find an engine run signal and NOT a switched ignition signal when
split charging because the split charge relay will engage and both batteries
will be connected together during engine cranking which can damage the leisure
battery.
The solution
If you can find
a switched ignition signal you can create an engine run signal by installing a
voltage sensing relay (VSR).
A voltage
sensing relay works by connecting a negative, switched ignition feed to the
input then the out put would become your engine run signal. For the relay to
connect the input to the output it needs to detect +13.2V on the input to
engage rather than +12V like a traditional relay.
Using a voltage sensing
relay (VSR) means you can use a switched ignition because the voltage on the
switched ignition would be below 13.2V unless the engine had already been
started and the alternator was charging the vehicle battery.