7 Way Plug Questions

[RottenRalph]

A friend has a travel trailer he tows with an older model truck that has a hard wired 7 way plug. The 12V constant power pin of the 7 way is wired straight to the battery.

The travel trailer has a 7 way plug with the 12V constant power pin that runs direct to the house battery.

My question is, if you stop for the night without plugging into shore power, should you unplug the trailer from the truck in order to keep from possibly drawing down on the truck battery? Should he add a relay in the truck's 12V constant power so that the truck's circuit is open when the key is off?

Thanks for reading!

[BFlinn181]

I think I would, (disconnect at night) but I'd also wire the 12 v (+) in the tow vehicle from an ignition source, rather than directly connected. A very simple modification, it would isolate the two batteries except when the alternator was charging. Also, make sure the 12 v from the TV is fused, or better, an auto reset circuit breaker. Probably a 20 amp breaker, so when they are hooked together the alternator doesn't try to charge with too many amps when the trailer battery has been run down.

[Dr4Film]

I have never done it when towing my 30 foot Pace cargo trailer as there isn't anything in or on the trailer that would drain the trailer battery and my chassis battery overnight.

Dr4Film ----- Richard

[Scarab0088]

That's really up to the owner.

Our previous (older) truck was set-up similarly...
When camping off shore ties, I pulled the plug to ensure there was reduced chance of stranding us with a dead TV battery.

I did not want to change the factory wiring, so I did not install a cut-out, but I did ensure there was a breaker in the powerline near by the battery.

The connection provides a charge to your RV batteries while driving down the road...so it is nice to have.
And knowing that the connection is there, you can use the extra juice in an emergency

[BFlinn181]

Originally Posted by Scarab0088

....And knowing that the connection is there, you can use the extra juice in an emergency

Problem is, the wiring between TV and trailer isn't heavy enough gauge to allow any real current draw. Yes, you could carry the trailer battery up to the engine and use jumper cables, but wired through the trailer harness, you are limited to how much current can flow through the wires. That's why I suggested adding an auto reset circuit breaker to limit the current flow, especially if trailer battery is down and the alternator tries to charge too heavily.

[Scarab0088]

By emergency, mean a few 12VDC lights, a 12VDC cell phone charger, or maybe a radio to listen to the weather in a storm.

You would never be able to run an inverter - of course.

And what-if you are stranded and unable to get to shorepower to run the converter/charger - just start the TV's engine and let it idle to provide a low amp charge to keep the coach batteries alive. This assumes there is no on-board gennie...which would be much better

Safe travels