What to tap to check whether alternator is running

Hello

I am hoping to install a DC-DC charger for my trailer, to be powered by the alternator in the Sequoia.

One problem with that setup is I only want the DC-DC charging my trailer batteries when the engine (specifically: the alternator) is running. Otherwise I'll inevitably get distracted and kill my truck battery at the most inconvenient time.

There's a feature in the DC-DC charger to make sure it only runs when it senses power on a dedicated input lead. But what can I tap into in the truck to connect that to?

Most things in the truck are on or off depending on whether the "key" is in the on position or not.

Is there something that only has power when the alternator is running? Ideally something I can easily get to?

Thanks in advance.

 

I'm not sure the specifics so someone will have to fill in the details, but most Toyota alternators have a plug going to them which tells the alternator to turn on. There's multiple wires in the plug usually, like three, but one of them I believe is a signal wire from the ECU to turn the alternator on. If that wire is 5V+ or 12V+ you could directly tee into it, if it gets grounded then you could tee into it to engage a relay to send a positive signal to your device.

 

Which charger are you looking to use? I'm using a Renogy and it has a built in voltage sense function. It turns on when it sees a voltage above 13.2 for at least 15 seconds, and immediately cuts off at any voltage below 12.7. If your starter battery is lead acid like me, as soon I turn the truck off the voltage drops and triggers the disconnect.

 

Gonna store both of those little factoids away for another day...