Charger connection

For a while now I have been pondering how to to charge the twin 12 volt batteries from a single 12 volt supply.
It sounds simple enough, but my issue was that I need to supply 24 volts to the flight avionics for everything to work correctly.

The solution was simple.

A 4 pole 12v relay.

In its de-energised state it supplies 24 volts with both batteries in series. When the charger plugs in it supply 12 to switch on the relay that in turns places the batteries in parallel and supplies the 12 volt charger to them.

Now with the charge circuit working i am off to a local model air field that has a lot of old timer glider enthusiests to see what they say before my first flight tests in a few weeks :)