Accessory Activation via Ignition Switch Question

[Tanabi]

Hey there;

I tried to search for an answer but I'm being overwhelmed by results for keyed ignition which doesn't help me This should be an easy one.

So I am installing a 24 to 12 volt converter on my HMMWV and this particular converted comes with an "ACC" input; basically, if that ACC terminal is hot, the converter turns on, otherwise it disconnects to avoid battery drain.

Looking at schematics, I believe I could run a wire from the "IGN" terminal on my alternator to the converter ... and that should theoretically work? Is there a better/smarter way to do this?

I'm planning on doing a write-up of this install when I'm done so other folks can try it. There's some resources out there, but none of them entirely comprehensive with respect to things like wire guage sizes to use, ACC switch, current and working links to parts, etc.

Thanks guys!

 

[Milcommoguy]

Don't think the standard STOP RUN START switch is going to work for the accessory feature you're looking for. NOT that it couldn't turn the converter on and off when in the STOP RUN position... BUT you would have the other RUN circuits fired up like the IP solenoid, alternator feed, heater if on, etc.

Not enough info to determine what your really trying to do. Now say you had one of those "Keyed Switches" with an accessory position connections that might do the job? Looking to run 12 volt radio and the like might just add an auxiliary "12 Volts ON" switch. Then you could turn it on when you need the 12 Volts.

Just don't forget to turn it off, CAMO

Free advice for free..

 

[Tanabi]

Don't think the standard STOP RUN START switch is going to work for the accessory feature you're looking for. NOT that it couldn't turn the converter on and off when in the STOP RUN position... BUT you would have the other RUN circuits fired up like the IP solenoid, alternator feed, heater if on, etc.

Not enough info to determine what your really trying to do. Now say you had one of those "Keyed Switches" with an accessory position connections that might do the job? Looking to run 12 volt radio and the like might just add an auxiliary "12 Volts ON" switch. Then you could turn it on when you need the 12 Volts.

Just don't forget to turn it off, CAMO

Free advice for free..

I have a keyed killswitch, the Kascar one, but that works in tandem with the original truck 3 position switch so the 3 position switch is still there and is the way to start the truck.

To be more specific, what I'd like, is to put voltage on that 'ACC' line when the truck's toggle switch is in the RUN position (or when the motor is running, either way). I suppose I'd also be okay with it switching on when the killswitch is on, but that would be my least favored option.

I think the IGN line on the regulator is hot when the truck is in Run if I'm understanding the schematics right -- it would be pretty easy to test that so I will actually test it next time I'm at the truck, but I'm not sure if that's the good way to do it.

 

[Milcommoguy]

Still a bit confused here @&^#$ . Sounds like you answered your own question. Use the key switch to activate the converter. Key switch feeds the trucks STOP RUN START as a security element.

Trying to understand the plan. What really is the need for the 12 volts? What to play the radio with the truck disabled?

Let's think about this... Turn the key to on, converter connected to key switch goes hot 24 volts to converter remote on.

Converter comes on. 12 volts to the goodies.

Truck in STOP, no power drain there, BUT truck could be started or stolen.

Like I said, if truck is in the RUN position circuits fired up like the IP solenoid, alternator feed, heater if on, etc. an addition drain not needed.


Not trying to overthink this, but surely missing something in translation, CAMO

 

[Tanabi]

So I am using the 12 volts for the AC unit which runs off 12 volt, and also for any other accessories I may want to run -- cabin lights, backup camera, etc. I don't need any of this stuff to work when the truck is off.

Let me boil this down to a more simple pair of questions:

1. Is there a wire on the truck that I can tap into that has voltage on it when the ignition is in RUN?

2. Is there a wire on the truck that only has voltage on it when the truck is actually running?


I think the answer to [1] is the IGN terminal on the alternator, so I'm looking for confirmation there. [2] might not exist

 

[Milcommoguy]

Which alternator do you have? May not need all of this monkey motion? If you have the 200 AMP system.

There is a "SENSE" ( #5a and 560A ) used to energize alternator. Hot from the RUN position. Not what you really wanted ?

There is an "AC Tap" lead from alternator ( #2A ). Used to send a "frequency sample signal" to enable "The attempt to restart when running logic."

Basically an AC voltage from one of the three phases outputs.

It is possible to build a simple circuit to sample the "AC TAP" and turn on a relay providing power to the air conditioner.

WOW, Now I get it. Truck running Air ON, ONLY. Did I get it right this time around? CAMO

 

[Tanabi]

Which alternator do you have? May not need all of this monkey motion? If you have the 200 AMP system.

There is a "SENSE" ( #5a and 560A ) used to energize alternator. Hot from the RUN position. Not what you really wanted ?

There is an "AC Tap" lead from alternator ( #2A ). Used to send a "frequency sample signal" to enable "The attempt to restart when running logic."

Basically an AC voltage from one of the three phases outputs.

It is possible to build a simple circuit to sample the "AC TAP" and turn on a relay providing power to the air conditioner.

WOW, Now I get it. Truck running Air ON, ONLY. Did I get it right this time around? CAMO

I have the 200 amp dual voltage alternator. I think the SENSE will do it for me -- just a hot line from the RUN will be good enough, though the "AC Tap" would be a clever way to just engage it when running. I'll tinker with that.

But yes, you totally understand -- truck running, air on, only

 

[Milcommoguy]

It's all about what you want to do.

The way to go, here we go IMO... is ditch the converter . Use the 12 Volt alternator tapped to the rear battery. Get the kit. Better for many reasons 1, 2 & 3 along with a standard configuration.

You will have ALL the 12 Volts you should ever need.

Simple circuit > Sample the "AC TAP" line into a diode to a R/C network, driving relay or NPN transistor . This will then drive say a power contactor / relay / HEXFET to feed the 12 Volt buss to your needs.

It would only supply 12 Volts when engine is spinning. ( and alt is outputting) Add a bypass switch with LED to force 12 Volt buss active if needed.

See, simple. It's a HUMV... not a spaceship, CAMO

OK... your ROCKET SLED.

 

[Retiredwarhorses]

Do not use the 14v tap as a direct source, pull from the rear battery, use the 14v tap to prevent imbalance, same as the all modern military vehicles do.