How to disable the Orion XS when on shore power

I am installing the Orion XS 50 amp DC-to-DC charger on my boat to charge a new lithium house battery from the engine AGM battery (which is connected to the alternator). I want the Orion to charge only when the engine is running. The problem with using the built-in engine detection settings is it will think the alternator is running when I’m on shore power because I have a 15 amp AC battery charger to keep the engine AGM topped off. I don’t want the Orion drawing 50 amps off the engine AGM when it’s only getting 15 amps in. (I have a separate inverter/charger that will charge the lithium house bank on shore power). I feel like there must be a way to disable the Orion in this scenario.

The simplest would be for me to connect the Orion on the switched side of the engine battery off switch (which I keep off when on shore power) so it just doesn’t get any power at all when on shore power. Sadly, I don’t have good access to the engine battery off switch to do this so I’m exploring alternatives.

I could remember to turn off the Orion in the app when on shore power or wire a manual switch to the H/L port – but both of these require me to remember to do this. I’d like to have it detect this automatically. How have others done this?

Some potential ideas:

  1. Is there some way to wire the H or L to my Volvo Penta D4 electronic control unit so that it operates only when that indicates the engine is on?
  2. I could install some sort of relay between H & L that opens when AC shore power is detected and closes when it is not.
  3. Is there a way to configure the built-in engine on detection voltages to distinguish between alternator power (typically a constant 14.2 or so) from AC charger power (typical bulk-absorb-float)? I’m guessing not.

I’d love to hear how other people have addressed this given my setup must be pretty typical for a boat. Thanks.

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I think 2 is the easiest and is what I do usually.
For 1 you have to find the correct wire and that’s often not so easy in modern cars.

3 will not work, the Orion only sees the voltage it doesn’t know where it’s coming from.

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Another way is to connect from the on position of the engine off-on-start switch to the Orion H pin. That way the Orion only draws power from the engine battery when the ignition switch is on. Of course this doesn’t guarantee the engine is running but it is pretty close.

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Thank you. What sort of relay do you use? I found this on Amazon: OONO DPST 1NO 1NC 8Amp Power Relay Module, AC 110V 115V 120V Control Voltage https://a.co/d/d6RcmYQ

But it doesn’t look very reliable from the reviews.

I’m from Germany and use the Eltako ER61-UC or ER12-100 for that.
No sure if they are available in the US.

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You use an argofet isolator so that the Orion is isolated from the starter battery and only detects a voltage when the alternator is running.