7 pin power question

[spartacus]

I am new to towing, and I have a question about the power running to the 7 pin connector. It seems that the power is live to the battery and not the ignition, so if (assuming I turn off every light, etc. in the camper) I leave it plugged in will it drain the tow vehicle battery? What if the camper battery is fully charged, will it still take power from the tow vehicle battery?

Thanks!

[Thomas G.]

The trailer will drain the tow vehicle battery if not disconnected. The usual solution is to install a relay wired to the ignition so it disconnects automatically. You can also install an isolating diode, but be sure to get one with a low voltage drop or it will hamper your trailer battery charging.

[floyd]

Originally Posted by spartacus

I am new to towing, and I have a question about the power running to the 7 pin connector. It seems that the power is live to the battery and not the ignition, so if (assuming I turn off every light, etc. in the camper) I leave it plugged in will it drain the tow vehicle battery? What if the camper battery is fully charged, will it still take power from the tow vehicle battery?

Thanks!

If what you say is correct, then a draw from the trailer will drain the TV battery.
Many systems use a battery isolator which will prevent this when the key is off.
I use an inline breaker and a manual 30A switch with an LED indicator light.
As you say, if the battery on the trailer is fully charged and has no load applied then it will not drain itself or the TV battery.

[Byron Kinnaman]

Originally Posted by spartacus

I am new to towing, and I have a question about the power running to the 7 pin connector. It seems that the power is live to the battery and not the ignition, so if (assuming I turn off every light, etc. in the camper) I leave it plugged in will it drain the tow vehicle battery? What if the camper battery is fully charged, will it still take power from the tow vehicle battery?

Thanks!

There's not a yes or no answer, it all depends.
When connected in the manner you describe any power consumption devices in the trailer will draw from both batteries, any devices in the tow will draw from both batteries. With nothing on in the trailer except the propane detector it will take several days to run both batteries down. A stop for lunch or even over night is NOT going to have much effect.
FYI, my factory tow package connects the battery in the tow directly to the battery in the trailer when the trailer is plugged into the tow. My standard procedure is to disconnect the trailer when camping, or a quick overnight sleep. I leave it connected for all rest stops including meal brakes.

Hope this helps a bit.

[Bob Miller]

A solenoid type battery isolator is readily available at most RV stores, as well as on line, for less than $20 and is easy to install. It assures that the trailer is disconnected from the TV battery unless the ignition switch is turned on

These are pretty much standard equipment on motorhomes to protect the engine battery from being run down by the coach when parked.

[Jon Vermilye]

I added an isolation relay when I wired the RAV4 charge line. Luckily, there was a 12V receptacle in the rear side panel of the RAV4 that I used to feed the sense coil of the relay.

If you have a 12V heater in your refrigerator & use it while driving, the relay is important - if you forget to unplug the trailer during a long lunch you may find everything dead...