double plug in question

[Bobby A]

I've often heard to NOT plug your trailer to shore power and to your tow vehicle at the same time, but I don't think I've heard what can go wrong if you do. NO, it didn't happen to me, we are trying to diagnois a problem with a fellow RV'er hear at the campground, and are exploring all possibilities. Any in site would be valuable information. Thanks, Bobby A

 

[danemayer]

BobbyA,

Everyone who ever stopped overnight and didn't unhitch had shore power connected at the same time as the truck. Anyone who ever started up their onboard generator without unhitching also had the same.

If your friend is having trouble with the trailer 12V system, perhaps our 12V Block Diagram and Diagnostic Guide would help. Some of the content might not be exactly tbe same, but there's a good chance SOB trailers have similar systems.

 

[Bobby A]

Thanks Dan, What happened was that they had the trailer hooked up to the TV overnight and when he got in the next morning the brakes on the trailer were locked up and the TV and trailer batteries were completely drained, so after jumping the TV that's when they noticed the brakes locked up. He then noticed that the brakes controller was extremely HOT, he immediately unplugged the brake controller. The trailer brakes disengaged and he relied on his TV brakes to get him to the campground. We were sitting around the campfire and we asked him if he had the trailer plugged into the TV and on shore power overnight at the same time and he said yes, so I was wondering if that is what caused his issue ?? Thanks guys,

 

[danemayer]

the TV and trailer batteries were completely drained, so after jumping the TV that's when they noticed the brakes locked up. He then noticed that the brakes controller was extremely HOT, he immediately unplugged the brake controller.

Could be a problem with the brake controller activating the trailer brakes, which would drain all vehicle batteries.

A simpler explanation might be that the breakaway cable might have come unplugged. That would have triggered the brakes and drained the batteries on both vehicles. After charging the truck battery, power would again flow to the trailer brakes. Unplugging the brake controller might open the path between battery and trailer brakes.

FYI, if the trailer were to come off the hitch, the emergency braking triggered by the trailer's breakaway switch relies on the trailer battery being charged. So towing with a dead battery is dangerous. And of course towing without trailer brakes is also pretty dangerous.

 

[Bobby A]

Could be a problem with the brake controller activating the trailer brakes, which would drain all vehicle batteries.

A simpler explanation might be that the breakaway cable might have come unplugged. That would have triggered the brakes and drained the batteries on both vehicles. After charging the truck battery, power would again flow to the trailer brakes. Unplugging the brake controller might open the path between battery and trailer brakes.

FYI, if the trailer were to come off the hitch, the emergency braking triggered by the trailer's breakaway switch relies on the trailer battery being charged. So towing with a dead battery is dangerous. And of course towing without trailer brakes is also pretty dangerous.

Thanks Dan, yes I agree traveling with no trailer brakes can be dangerous, his rig is a small ultra lite or something like that, so its not as heavy as our rigs and he does have a good tv. I will ask him about the emergency break when he returns this weekend. Thanks for all your help.