How Do I Kill a Starter When Plugged Into Shore Power?

OK... This is what I want to do. Just so I never can have a malfunction and try and drive off in my van connected to shore power. I have a lot going on and in my life and I don't ever want to drive off while connected and I want to make it so the starter will not engage while the battery charger is on.

Here is my problem. I would just naturally just use a relay that would flip when the van is plugged in but I have a 2 battery system which there is always at least 12.6 v on the back end so that won't work. I need something that detects that I am plugged in from the voltage rise from 12.6 to 13.7 and trips a relay that shuts off the ignition wire.

What do I do?

I put this circuit in my Chev PickUp. It detects when the engine is running (Vbat>14V), pulls in a relay, and connects an auxiliary battery (used to power ham equipment) in parallel with the main starting battery. Relay drops out, isolating the two batteries when the vehicle is parked, preventing discharging the starting battery if I want to use my radios while parked.

The relay I used was a special one that required the series resistor R6 (27Ω). If you use one of the automotive "sugar-cube" relays, then you can leave out R6. The trip-point is adjustable. The circuit has hysteresis.

Should work for your application if you use the normally closed contact of the relay to break your starting circuit (not ignition). With the circuit active, the starter will not crank if the charger is plugged-in. However, if the charger is unplugged beforehand, the circuit will allow the starter to crank. You cannot break the ignition wire, otherwise the circuit will detect the elevated voltage, and the engine will die again as the alternator comes on-line.

With the added advantage that the engine won't try to crank when it's running.

Mike.

Around here everyone plugs their vehicle, and most any machinery with an engine, into "shore Power" as you call it in the winter to run their engine block heaters and the simple solution to not driving away while still plugged in is to wrap the power cord around the drivers side door handle, mirror or window wiper so they can't miss seeing it when getting in.

If a person is so oblivious to that sort of obvious details around them they probably shouldn't be driving at all.

Personally I'd keep is as simple as possible, possibly incorporating a switch contact in the connector, that brings in a relay inhibiting the crank signal to the starter solenoid, anderson connectors are used for this kind of thing, you can get them in a range of currents, up to ones big enough for large fork lift batteries, you can also get accessories such as a microswitch that operates when connected to the mating plug/socket.
Nice simple circuit that is less likely to leave you stranded in a supermarket car park.

It occurred to me that I had solved this problem another way. Think about what happens if I jump into my beater farm truck without unplugging the float charger , and back -up (it has happened, several times)!

There are common magnetic coupling connections for mains current. Years ago, they were only low voltage (except for NASA rockets). Think of safety for deep fat fryers. Even Dewalt and others make them to avoid tripping. Of course, the coupling is special, but then you run a conventional plug to the power source.

John

Looks even simpler.
Fork lifts have the charging socket under the seat for a similar reason, plus the truck power is unplugged before the charger is plugged in.

I think the OP has left the building due to the obviousness of the solution.