Trailer plug power?

[tirnanah]

I see a lot of posts (on all of the forums I watch) where people suggest hooking the tow vehicle up to provide power for various things, even to assist with opening the slides... My dealer told me I could operate my tongue jack with nothing but the tow vehicle hooked up (no batteries at all, I did put one of the batteries on just to hold the terminals down to keep anything from shorting, and never tried the jack without the battery). I just can't fathom being able to pull enough power through that tiny little wire to operate something like a tongue jack (900+ lb tongue weight) or that it would even make a difference in opening the slide with the batteries installed.

I'm not arguing that power isn't provided. I realize that some power will go through into the trailer, but expecting any thing more then a trickle charge (at best) seem un-realistic? I would expect a MUCH heavier gauge wire to temper the amount of power lost from the front of the truck to the rear, much less the addition of a moveable contact point (trailer plug) and that wiring into the distribution box, then to the batteries.

Am I mis-understanding, or is there really that much power available at the trailer plug?

Thanks,
Doug

[JRTJH]

No, I don't think you're missing anything. The "thin wire" on my Ford isn't designed to carry a "large sustained DC load". In fact, there's a fuse under the hood for that circuit: Space #90 25A fuse for: Trailer tow battery charge.

Most DC motors that are large enough to lift a 900 pound load in a tongue jack or in fifth wheel landing gear will pull that much or more amperage starting the load. That's one of the reasons some people have problems with fuses in their landing gear. Replacing the fuse with a "slow blow circuit breaker" will often solve the problem. But, as you've pointed out, that "trailer tow battery charge line" is really intended to be a "trickle charge" for the trailer batteries to help keep them charged during towing. It's not really a "good source" of DC power for a heavy load, especially if there's no trailer battery to help "buffer the surge requirement"... There is a caution in the WFCO owner's manual and in the Keystone owner's manual which states to not operate the slides without a battery installed as the "sudden load" can damage the converter. The same holds true (in my opinion) with putting a "sudden load" on the tow vehicle alternator/voltage regulator.

I don't think it would "damage" the tow vehicle system or "burn the wire" if you used the tongue jack while the vehicle was attached, but to remove the trailer battery and rely on the tow vehicle to power the system is, at best very optimistic, and likely potentially damaging to the tow vehicle.

ADDED: It takes a 6 gage wire to carry the current from the battery to the trailer wiring system. Believing that somehow a truck system can deliver that kind of amperage with a 14 gage or 12 gage wire is, at best, very optimistic.

[Ken / Claudia]

I agree with John and either the salesman does not know what he is talking about or you miss understood him. I could understand him saying no shorepower is needed if you have the battery connected and it is a good battery, the jack can move with or without the TV hooked up.

[bobbecky]

The bigger issue is, if you are operating the jack, you are probably hooking up to your tow vehicle. If that is the case, you really need a battery installed in the trailer, if for no other reason than to power the electric brakes if the trailer becomes disconnected from the tow vehicle and the breakaway device operates while you are running down the road. No battery equals no brakes to stop a runaway trailer.

[randy69]

On dry camping I usually Unplug the trailor from the truck. I was told in case batteries go dead and you cannot start the gen. You replug to truck start it up and you will have enough power to start gen to recharge batteries. Is this right.?

[tirnanah]

I can't answer on being able to start the generator, but I do always unplug at the campsite (full hookups or boondocking) because it will draw down the battery to the point where the battery won't have enough charge to start your truck.

I always put at least one battery in, but I just can't believe the number of times I've seen someone say: "Oh, just plug your truck into your trailer and you'll have power for anything you need to do"... It just didn't add up for me, thanks for confirming I'm not missing something...

Thanks,
Doug

[Ken / Claudia]

Randy, Do not count on it working. Been there done that. Once I was dry camping. The batteries got low and would not start the genny. Plugged the truck in for 20 mins, running and still no go. Maybe if you run the truck for hours? it would charge up enough but, not right away at least with my ford.

[glenalt]

I had my 5er in storage and forgot to disconnect the battery. When I came back to hook up I had no juice for the front jacks. I had to hook-up my TV in order to get it to the right height for hook-up. I left the TV running and only waited a couple minutes and all was well.

[jsmith948]

Originally Posted by tirnanah

I can't answer on being able to start the generator, but I do always unplug at the campsite (full hookups or boondocking) because it will draw down the battery to the point where the battery won't have enough charge to start your truck.

Thanks,
Doug

On our Ford, the trailer charging wire must be wired through the key switch as there is no power present when the key is turned to the off position. We have never had the trailer cause our truck battery to discharge. A simple test is to put your meter on the 'hot' wire with the truck running, then have someone turn the key off.

[chuckster57]

Originally Posted by jsmith948

On our Ford, the trailer charging wire must be wired through the key switch as there is no power present when the key is turned to the off position. We have never had the trailer cause our truck battery to discharge. A simple test is to put your meter on the 'hot' wire with the truck running, then have someone turn the key off.

Ford puts the charge line on a relay that is energized when the key is in the run position. The circuit isn't through the ignition as its too much current.

[jsmith948]

OK - makes sense - the point being that, at least on our truck, there is no need to disconnect the trailer cord. The trailer can't discharge the truck batteries.

[JRTJH]

Being the "fatalist" that I am, and knowing that if something bad can happen, it will probably happen to me, when I'm in a situation where it "only gets worse," so I've made it a habit, if we're going to stop somewhere for the evening and not unhitch, to just reach in the bed and disconnect the trailer from the truck. It only takes a couple of seconds, I've almost always got the tail gate down for something anyway, and even though I "trust my Ford", there's a limit to the "trust"
If it'll bite anybody, it'll be me

It's probably just a carryover from the days when trucks weren't air conditioned and they only went a few thousand miles before they needed a water pump, or a fuel pump or a new generator, but being mechanical, if I can eliminate the possibility, and it's easy to do......

[chuckster57]

I hear you!! I still pull the umbilical. Like I said earlier in another thread old habits die hard.