Shore Power 12V to vehicle

[baddog8it]

I have a new (old) truck camper and am still trying to sort out and fix various items. One thing that I have discovered that causes me concern is that when on shore power, there is 12V being supplied to the vehicle via the trailer light connector. I would think that the purpose is maybe to charge the vehicle battery... Is there any concern if I run the vehicle engine while connected to shore power and the trailer light connector is plugged in? I know that they're both positive 12V nominal, but concerned with 2 possible situations:

1. with vehicle running or not running, that the camper converter may not be properly regulated and overcharge (boil off) my vehicle battery

2. with my vehicle running, the vehicle voltage may be slightly different than the camper converter and cause some unknown problems.

I'd love any feedback.

Here's the specifics:
1985 Ford F350 pickup (the only electronics are the stereo and ignition)
1993 Jayco Jay Hunter 950 slide in truck camper

[Terryallan]

Your Ford is isolated from the Trailer when the switch is off. There maybe 12V going to the 7 pin from the trailer. But unless some one rewired the switch. It is going no farther. Same when not on shore power. the trailer draws no power from the truck as long as the switch is off. Ford has had that feature for years. Last I heard. GM, and Ram are doing that now as well.

One way to find out. Get a tester, leave the switch off, and test the battery charging pin on the 7 pin. If it doesn't light up. Good to go.


BTW. Fords also come with a relay that you have to install to activate the batter charging pin. unless you install the relay. the truck will not charge the trailer battery when running.

The relay is in a pack some where in the truck, along with a brake controler wiring harness. it could be in the dash, console or in the jack compartment.

[time2roll]

No issues. Even if you add solar charging, no issues.

[Joe417]

Add an isolation relay up at the fuse block. A 100 amp continuous relay is only about $20 on ebay. That will prevent the camper from drawing power from the vehicle when the ignition isn't on. Don't need that "oops", forgot to unplug and the vehicle battery is dead.

[Matt_Colie]

If it still has the 1993 converter, get it out of there. Since about 2000, a new line of smart converters has hit that will never boil a battery, will charge it hard when it needs it and burp it to keep it from stagnating. There is a company called "Best Converter". I have never done business with them, but others have.
Installing an isolater would keep you from accidentally killing main engine (truck) battery and that may be very worth while having.

Matt

[baddog8it]

Thanks all for the feedback. That makes me feel more comfortable. After digging out the documentation on that converter, I see that there is a battery charging module in it - probably very state of the art for 1993.

Yes, there is a mildly annoying hum.

Because of my concern, I have in the past always disconnected the vehicle wiring when connected to shore power. I'll probably continue to do this, but not worry too much if I forget to do it.

[DrewE]

In general, it should not be a problem. Basically, the higher voltage source "wins" and supplies power, while the other just kind of sits there.

If the converter is not supplying a proper voltage (which would apply to both the camper and the vehicle), then that's a problem that needs fixing in any case. If it's the original converter, it would probably be money well spent to upgrade/replace it in any case as it's likely a single-stage ferroresonant unit. Those sorts of converters do provide a reasonably regulated output--not perfect, but good enough--provided they are in proper working order and the incoming power line AC frequency is correct, which it pretty much always will be for utility power but might not be with a generator. They are, however, not super efficient and heavy and sometimes hum annoyingly.

A bigger concern for me would be that, if not connected to shore power and hence without the converter operating, the camper's electric usage could discharge both the camper's battery and the truck battery, leaving you stranded with no power and no way to start your truck. Adding a relay to shut off the trailer charge line when the engine isn't running is the obvious solution to that problem.

[BFL13]

Your Ford does not seem to have the relay that only lets power to the trailer plug when the ignition is on. Chevs are like that, but they have a fuse you can pull.

If your truck does not have a fuse like that, then you could snip the power wire that goes into the camper's plug (pin #4) which will mean no alternator charging, but no connection between camper "house" 12v when parked. The camper tail lights etc would still work.

Or perhaps you could put one of those relays in the Ford like newer Fords have if yours doesn't have one.

[Matt_Colie]

Baddog,

You have a lot to not worry about there.

If the converter is something newer dirt, then it won't care about the output from the main engine alternator.

Again, if that converter is a decent piece, it will not hurt the vehicle battery any more that it would hurt the bank in the camper.

What you should do is look up the model of the converter and find out how smart it is.

Matt