Constant duty solenoid 02/09

Installed a constant duty solenoid, when activated sends/connects an auxiliary 10ga charge line to camper.

constant duty solenoid

Basic 3 or 4 pole CONSTANT duty solenoid.Either can be used, 3 pole is grounded thru the case, a 4 pole needs a ground wire, otherwise identical. The large poles are non directional, doesn't matter which, 1 from battery, other to load. The smaller poles also are non directional, Switched or ignition only hot wire is feed to the small pole, if 4 pole the other small pole is wired to a ground or to mounting screw. Power required to energize solenoid is minimal, but this should be wired to only work when engine running. When trigger wire is energized the solenoid closes and makes a direct contact between the 2 large poles.

I've thought about doing this a few times or at least change up existing wire to 8ga, though never enough to do it. But when I added the truck controlled relay for on road 12v use of our 3 way refrigerator (see relay page), I figured now was a good time. Since I'm trying to optimize the 12v, I looked at the existing wiring. That was the clincher. I knew the camper dealer just spliced into the factory trailer wiring harness, never more than causally looked at it. The truck factory charge wire is I think only 16 ga, might be 14but don't think so. Ether way the camper is 10ga, also the bed receptacle wire is 10ga,and it was spliced into the smaller trailer plug charge wire. So the charge wire starts out rather small. Lot to be gained by going from at best 14ga to 10ga wire, especially since it was just spliced with a crimp on connector.

I debated on how to do this. My first thought was to just disconnect the camper 10ga wire at the splice and replace from that point back into truck with 10ga. But that would still leave a splice, one, second was I don't what the charge wire goes thru in the engine bay before it gets sent to trailer harness. ..My plan is running a complete new 10ga wire from an additional camper plug to new charge line source, thinking new 10ga source plus existing charge source would be as good as an 8ga.

Since I'm adding a new 10ga charge wire and ground, I decide to replace the 2 wire plug i just installed for the fridge relay with a small 4pin trailer plug. I also wanted to use cable instead of wire on the camper pigtail. So off to the RV shop with a loose idea of what I was doing. The standard 7 pin camper plug was cheaper/better so picked up both ends, and to get a good seal I also picked up 4' of standard 7wire Trailer cord for the camper. (Its got 2- 10ga wires 1- 12ga & 4- 14 ga wires in it). I told the clerk what I was going to do and he suggested just a simple constant duty solenoid. He also suggested using the existing charge line to trigger solenoid., which I considered briefly. New solenoid will feed full power thru to camper when activated but closes when truck is turned off. Like a giant relay, so cant drain truck batteries. Cool, this will completely by pass all the truck relays/solenoid fuse box and spliced wiring. It will be an auxiliary direct 12v charge line w/ additional ground. The camper can draw from both the new wire and previously installed wiring. I'll also run my new fridge relay & pilot light wires thru the 7 pin plug.

additional 7 pin receptacle

Installed new plug where it'd easier to reach, If a wasn't so lazy Id mover the other one. I may to modify both receptacles and plugs, put screw in male housings one at 3:00 the other housing at 6:00 and add a matching notch in female ends so neither can be plugged into wrong place.

New constant duty solenoid

Installed the solenoid in engine bay, used existing ground screw. I have an auxiliary fuse block that's installed bout 6" from battery. From 30 fuse, ran 10ga to new solenoid. From solenoid 10 ga wire goes inside dash to amp gauge, from gauge back out to engine bay to new 30amp thermal circuit breaker. From breaker ran 10 ga to truck bed plug. Also ran a new 10ga ground from bed plug to chassis.

simplified wiring

switch & amp gauge

Thinking I really only need extra charge line/solenoid on when using the 3 way fridge, I used previously installed refer relay switch in dash for signal to solenoid, so single switch turned both the charge line & refer on. But I've since decided to add a separate switch for solenoid. Note that 8ga min wiring is recommended for adding a charge line and what most do, but 10ga is what I had and is in conjunction with existing charge line, plus I've limited this addition to 30 amps (twice what the refer draws).


Two pigtails


I made the new plug shorter so it cant reach main receptacle but I may go ahead and modify as mentioned, because the original plug 'could' reach new receptacle. Though the ground and hot are correct, the refer pilot feed might activate my turns signals or the fridge would only work when making a left hand turn, ha. But more than likely nothing would work and Id blow a bunch of fuses. Simple mod to avoid this happening cause at some point in time I can see it happening.

I've created a bit of a loop here in the wiring, I don't 'think' it will be a problem-if it is Ill just disconnect old camper hot lead splice at trailer harness. Also if I decide I need to, replacing the solenoid 10ga wiring to 8 it will be very easy to do.

In use: So far the refer stays cold- the batteries stay charged-so this worked, however I cant 'see' what's going on, So I added the amp gage mentioned above just to do it. It will let me see exactly what, when & how much the camper is drawing. Well once I figure out/verify what the gage readings mean. Since I've 2 charge lines Ill have to play with it, unplugging old one to see what the gauge reads with different loads, when the original charge line is connected/disconnected etc. The camper has the ability now to draw 30 amps from new line plus whatever from old line. Unfortunately I never checked what amps the camper actually drew before (though less than it took to required to run refer and charge batteries).



Finally loaded the camper, camper batteries fully charged, start truck, turn on new power supply solenoid-amp gage shows sending bout 2 amps to camper, turn on fridge & gage shows 14 amps at idle. Looks like everything is working. I can turn on/off the fridge from truck when its running - and turn on/off the solenoid charge line. I have a pilot lamp telling me when fridge is on/drawing 12v and an amp gage that shows how much current is being supplied to camper. I should see the fridge cycle (amp draw) when cooling. When I shut down the truck every thing automatically turns off, if I forget to turn off fridge/charge line. No more worries bout killing the batteries, running inside the camper to turn on/off the fridge when we stop. My plan is to make turning the fridge and charge solenoid switches on/off as part of starting/stopping the truck-Easy.

However if your really motivated I gather there is a place to grab ignition on power for activation on a diesel, where the ignition on source is hot or triggered after motor is started-but I'm thinking I'm done, least for now.

    Update 05/2019<
10 years + System still working awesome. Recent episode with adding a bypass switch to power radio noticed my amp guage separated. Got it fixed, tested at camper receptacle but backed up under camper to make sure.

Working-showing 14 amps, refer on 12v, solar off just like always. Decided, as I never had, is to check auxiliary charge without the trucks charge line connected. Generally I see 14 amps at the gage, camper loaded,refer on. Though last few years under 10amp, typically 7/8 amps due to added solar panel. But never knew what truck itself thru factory charge line was supplying. Assumed a few maybe 3-4 amps as refer is rated at 17amps.

Anyway- turned off solar, turned on refer, let it run a minuet on camper batteries then turned to run from truck. Plugged in camper aux line leaving main 7 pin unplugged. Started the truck let it idle a minuet the turned on refer and aux charge line. Amp gage climbed to about 19.5 amps. Plugged in the factory 7 pin with its charge line and amp gage dropped to just under 14 amps. Did this a few times. So trucks 7 pin is supplying approximately 5 1/2 amps. Surprised me that much.

What I don't know is if truck would supply more if the aux wasn't plugged in. Also didn't check what turning on solar does, it drops the aux charge by half 7 amps if at full output but didn't check cause camper is covered. Curious but not really. Mostly wanted to see if aux. charge line would supply full load-it does.

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