Help! Need elec advice

[e9999]

Panic mode here, my trailer battery is feeding power back into the truck and keeping things alive that shouldn't be. Were to leave tomorrow for a camping trip.
I need to fix this pronto.
Anybody knows if one can buy and use a diode system that would allow the current to go only 1 way but not the other, and withstand, say, 15 or 30 amps 12 VCD? Would be much easier than working out a relay solution.
thanks very much
Eric

 

[landtank]

I've got a relay in my truck and this is probably the most common solution. Any RV place will have them. There are 2 types, 3 pole and 4 pole. The difference is that the 4 pole you need to supply a ground while the 3 pole is grounded through the body of the relay. Basically yo wire it so it only supplies power to the trailer while the engine is on.

 

[Steve C]

15-30 amps would actually require a pretty hefty diode with heat sinks. It would need to dissapate about 30 amps * .7 volts = 21 watts. Plus the diode will drop about .7 volts while conducting. I would go with the rv store solution rather than trying to reinvent something myself, just to avoid any unnecessesary fires.

 

[e9999]

decided not to go with diodes, seems indeed like you end up losing close to 1V. Not good.

anyway, I sorta fixed the problem. Worst of it anyway. I installed a relay on the battery charge line just before the socket. Unfortunately, I did not have time to find a true hot-on ignition-only wire for the signal. Just used the power outlet in the luggate compartement (this is the 100) which is hot with ignition on and cold with key off. This way, no more power with key off. The not best part is that with the key on the first notch I still have back power from the trailer. But eh, that's just while turning it.
So, should be fine until I get time to tear the dash out...
Tapping into the power outlet was not too bad. I took out the quarter panel but it's not necessary if you check the colors of the wires and manage to sneak a peek in there. From there, I just went through and existing rubber grommet and down straight to the trailer socket.

thanks
Eric