Electic car-trailer 12V question

[sschevel]

Never a dumb question right?
Perhaps it's been stated here except I could not find a good answer, and perhaps I already know it, but I want to ask just to make sure.

I have wired both of my trucks with the 7 pin plug, just planning ahead.
A few years later I put in the electric brake controller on my Explorer so I could tow other cars/trucks and purchased a dolly with brakes.

Now on both trucks I have never wired in the positive 12V line on the 7 pin plug. Never knowing what that one 12V wire would go do at the trailer end.

I can imagine that it would not charge a battery back there, but could perhaps trickle charge one?

I picture using it to power say the small 12V cooler back in the trailer while driving somewhere but it would not be of much other use.

So am I right? Or would that one small line also help like a "maintance" line on a trailer battery.

I know in my Explorer I have an isolated trailer light setup which has it's own 12V line direct from the battery where I could likely tap and run to that 12V pin on the 7 pin plug.

I just can not imagine what the trailer could do with that pin. What is it's intended purpose?

Thanks,
Guy

Oh, I hope to stop in on the SC get together and ask more "not so dumb" questions!
Guy

[Nitetimes]

If you run a 10ga wire back it will charge your battery. Anyone with an electric hydraulic dump trailer or utility trailer with a battery installed for various equipment charges their batteries that way. Just make sure you have a 30 amp breaker or fuse near the vehicle battery.

[SkipperSue]

I got this from the Airstream forums back when I got that trailer, I got it with all the wires cut loose from the trailer connector. I hope this might help, although the pic is a little hard to make out. This is showing a #8 wire going back from the car. I had thought about doing something similar with my TD, I got a 6 way plug as I won't be putting brakes on it.

[Dale M.]

You actually need the 12 volts wired back to plug IF your trailer has break away switch and battery to lock trailer brakes (if you have electric trailer brakes) if trailer gets loose from tow vehicle.

My Chev. pickup came with wire in place and with a 40amp fuse in master power panel (fuse/relay block) under hood....

Yes you can run any device in trailer from 12 volt vehicle supply, even charge TD trailer battery from tow vehicle. I personally would like to see isolation device between battery so trailer battery does not draw down tow vehicle when parked...

Think my system (Chev, Factory) disconnects 12 volts to plug when ignition is off... IF yours does not, might be good idea to put control relay in system...

As others have said, run 10ga wire back from battery add in line 30-40 amp fuse and some sort of isolation device, either diode or relay....

EDIT:...

Checked plug, it is HOT with 12 Volts at all times...IF it really matters...

Dale

[sschevel]

More pondering thoughts then.

I get the impression to go this way.

12V car battery - 10 gage wire - 30 amp fuse - trailer plug - 10 gage - trailer battery


Now for concerns about draining the car battery, as I imagine in my mind, there would be little time using the trailer and having it connected to the car so the drain hopefully would not drain 2 batteries (one car, one deep cycle type), otherwise sometype of automatic battery cutoff should be inline above. OR, once parked, remember to unplug the trailer while using the camper and still attached to the car.

In Japan I used one of those Coleman thermoelectric coolers and drained a Japanese car battery over a few hours out on the beach in the hot sun trying to keep some water cool. Once we got to the battery to jump it, I saw a tiny battery for their car. I've seen bigger ones in riding lawn mowers and snowmobiles!!! Course size does not always a good judgement of power, but I hope you understand what I am saying here. Tiny car, tiny engine (perhaps like 660 cc) and tiny battery.

I would hope that cooler would not drain a deep cycle batter two fast and I hope to do this;

1. Car to trailer connection driving down the road power to be used
2. Trailer power while getting camp set, run a few trips into town an hour or 3 at best.
3. Hook into "shore" power and charge up the battery again and power camp until time to leave then back to number 2 above until time to hit the road.


If the need arised for "dry camp" I would have to monitor the trailer battery and perhaps use a small power generator or plugging back into the car (engine running) to bring things back up.
Better thought came to mind, wire up a heavy set of cable in the car, when battery gets low, make a trip into town and take the battery with you and hooked up in the car.

Course there are many factors here.

1. The Coleman thermoelectric cooler.
2. Small portable DVD player for short nighttime viewing
3. A few small lights inside and kitchen.

All from 12V source. Any other 110 items could be breifly run with a 300-750 Watt converter, to charge cell or use some laptop......

I can not think of other power uses to draw only from trailer battery, so I do not think I could justify a power generator unless it was small / cheap.

Guy

[rbeemer]

Guy,

Think battery isolator wired on the trailer not the automobile. See Camp Inn's website for more info

[Gerdo]

I ran a #10awg thru a constant use solenoid to my 7 pin, 7 pin to my TD battery. Works great. If you plan on being out on multi day trips and are driving this will insure that your TD battery is charged. If you are in one place and run the TD battery down, just run the Tow Vehicle for a while and recharge. My solenoid is switched on with my Daytime Running Lights so when the Tow Vehicle is turned off the solenoid is off. I also have a switch in line with the triger line if I do not want to charge. Works Great. http://tnttt.com/viewto ... 3&start=60

[alexgray104]

In our current caravan (lunar lx2000 525l if anyones interested), there is an onboard battery charger that runs off of 240VAC when the hook-up is connected, I also plan on using one of these in the tear (pick one up from caravan breakers yard, too expensive to buy new). If you are gonna use maintained sites with AC hookup, why not consider one of these?

[Dale M.]

Now for concerns about draining the car battery, as I imagine in my mind, there would be little time using the trailer and having it connected to the car so the drain hopefully would not drain 2 batteries (one car, one deep cycle type), otherwise sometype of automatic battery cutoff should be inline above. OR, once parked, remember to unplug the trailer while using the camper and still attached to the car.



Guy

Exactly.....

Dale