Can I charge the car battery from the camper ?

Pintoplumber

We’re camping this weekend with shore power. Our new suburban has WiFi internet, you have to have the key turned to the 1st notch. Can I keep the car battery topped off if I’m connected to the camper? I’ve gotten texts and e mails telling me to go out and start the car that the battery is low when we were at the cabin in the mountains.

Dutch061

Most likely not, it will depend on if there is a relay that only closes with the vehicle running or not. If your vehicle has this relay, it will only close and allow current to flow while it is running. Can this be bypassed, I am sure it can.

Brad

Pintoplumber

I think you’re right. We went for supper with the 7 pin plugged in. I checked voltage when we got back, only 12.4. Seems like it’s not adding anything.

pthomas745

@Pintoplumber the relay for your vehicle is called an "Isolation Relay." Several threads discuss the simple test to see if you have one:

To check if you have a charge line from the vehicle, and to see if the vehicle has an isolation relay:

Turn off your T@B battery by turning off the battery switch.  

Hook your camper to the 7-pin, crank the engine. Turn on an interior trailer light. If it comes on, you have a charge line. Turn off the engine, if the light goes out, you have an isolation relay. If the light stays on, you do not have an isolation relay.

Pintoplumber

Well, I’m going to have to redo my experiment today. Apparently my surge protector wasn’t working all last night, didn’t discover it until this morning when the 120V receptacles weren’t working. We had the 3 speed fan on low all night, so I’ll give the converter time to recharge the camper battery before I try again.

Pintoplumber

Well, it looks like it’s working. The suburban battery was at 12.2 V this morning and 2 hrs later it’s 12.7

Pintoplumber

Well it works for our car setup. I used the internet from the car with the key turned on, off and on all weekend long. Keeping the suburban and camper connected with the 7 pin plug kept the suburban battery charged all weekend long.