Do batteries charge while driving?

[cdoc83]

Hey all, I'm just getting into camping with a travel trailer and was wondering if the batteries "automatically" charge while attached to the tow vehicle? I have verified I have 12v+ at the correct pin on the 7 pole trailer plug but got wondering if simply plugging in is the equivalent of putting two batteries together of different charge levels (which, if I understand correctly, is really bad on the wiring and the batteries as they equalize)? Is there supposed to be some kind of inline resistance to ensure nothing bad happens, or is it fine to have a wire directly from the tow vehicle battery to the travel trailer battery (through the connector of course)?

[valhalla360]

Yes it will charge the RV battery but it will be slow. It won't cause any damage to the system. (don't leave it hooked up overnight or differences in battery charge could drain one).

With an RV fridge, the first question is does it have a 12v DC option. Some do but most run on either propane or 120v AC. If it has the 12v DC option, expect around 12amps as the heating element usually runs around 150w. If the truck wiring is in good shape and connected properly, that's about as much as you can expect.

If you want to charge the batteries, there are better options. Anything you get while driving consider it a bonus.

[PaulJ2]

With my truck the most i saw was about 15 amp. Usually about 10 amp was normal. #10 wire all the way. Had an analog meter in the circuit.

[rbpru]

The way my F-150 is set up, it provides some charging current while we travel.

Since the frig automatically switches to propane when the electricity is disconnected the frig electric is minimal, just enough to power the frig's brain.

It also, powers the antenna booster, CO detector, Radio/DVD player's brain, hot water heater brain while traveling.

When I turn the truck off a relay disconnects 12 volt feed line. We have never had the TT battery run down while traveling.

Safe travels

[bobndot]

I thought he meant to run the fridge on gas. The 12v board would operate the temp.
If that's correct then an average 6 cu ft rv fridge will only draw 1/2 amp or so. My rig keeps up with that just fine.

[KD4UPL]

cdoc83 wrote:
Cool, thanks! If it keeps the fridge from draining the battery while off propane I'll be happy!

If the wiring is factory on the TV and the TT it won't come even remotely close to keeping up with the fridge on 12v. You would need to change out the wiring to something several sizes large.
Running the fridge on 12v in a TT isn't really practical. In a MH it can work since the wiring between the alternator and the house batteries is much shorter and larger.
There isn't any reason to not just run the fridge on propane. That's how it's made to operate. Your refrigerator will run for several weeks if not months on one 20 pound tank under most conditions.

[Oasisbob]

Your batteries should charge while driving through the alternator. A volt meter will verify all is as it should be. Happy trails

[jeomelia]

If you want to run the fridge on 12v do the measurements with it on and good luck

[theoldwizard1]

dodge guy wrote:
It’s more of a maintainer circuit than a charge circuit. So if you have an inverter running like I do for my small dorm fridge then it will keep the trailer battery at the proper voltage.

Concur !

[pianotuna]

Hi,

If you mean running the fridge on 12 volt that would require 34 amps to be sent to the fridge. That just is NOT going to happen unless wire size is increased dramatically.

If you meant running the fridge on propane, then yes, it may work to keep the "house" battery charged. (but will not do significant recharging).

cdoc83 wrote:
Cool, thanks! If it keeps the fridge from draining the battery while off propane I'll be happy!

[RoyB]

The Truck Charge system is very close to the truck start battery and will use the status of the truck start battery to produce charging DC Voltages.

Essentially this is saying the truck charge system doesn't know the trailer batteries are in the loop. This is primarily due to the small charge cable wire size going from the truck alternator setup to the trailer battery distribution panel.

Yes you will get some charging from the truck alternator system setup but I would only consider this a trickle charge status.

I'm sure those on here with more battery smarts than I have may have a better way of describing this in laymen terms...

Roy Ken

[cdoc83]

Cool, thanks! If it keeps the fridge from draining the battery while off propane I'll be happy!

[theoldwizard1]

time2roll wrote:
To test put your voltmeter on the trailer battery. Then plug into your running vehicle. Voltage on the trailer battery terminals should pop up maybe a half volt if the vehicle charge system is putting power on the battery.

Rev the engine up to a fast idle and you should get about 12V +/-1V at the trailer house batteries. Still not adequate to recharge your batteries.

cdoc83 wrote:
First thing I'm going to do after work today! I guess it would be best to turn off the solar charger before testing anything?

Yes !

[cdoc83]

First thing I'm going to do after work today! I guess it would be best to turn off the solar charger before testing anything?

[time2roll]

To test put your voltmeter on the trailer battery. Then plug into your running vehicle. Voltage on the trailer battery terminals should pop up maybe a half volt if the vehicle charge system is putting power on the battery.

Just a slow charge due to vehicle voltage regulation and a long connection.
Maybe 5 to 12 amps into a low battery.