Re Charge Battery

[Chiefdeck]

Have 2020 2108ds. Have looked in manual and can not find answer. When driving down road and trailer is plugged in to truck do I need to have battery power on in trailer to re charge trailer batteries? I will not have refrigerator on when driving so I do not need any power in trailer so I would turn the battery disconnect to off. Will my batteries recharge or do I need to have battery disconnect turned on to power trailer to recharge trailer batteries.

[Goodspike]

I'm fairly certain you do, because there is not a second line running to the battery to charge. Mine only has two lines, the main line and the power for the tongue jack.

Also, as I brought up in another recent thread, check your tow vehicle manual. For GM Colorado/Canyons they should either be in tow/haul mode or have the headlights on because otherwise the variable voltage charging system might not maintain a high enough voltage to charge the trailer battery. I'm not sure how many modern vehicles use variable voltage charging, so I'm not sure how widespread that issue is. As an alternative to reading the manual you could just get a volt meter for your tow vehicle. Anything over 14 volts should probably charge the trailer battery.

[Jim_HiTek]

Fairly easy to check. Buy yourself a DVM (Digital Volt/Ohm/Amp meter). Hook everything up & measure the voltage across the battery, than start the engine. Wait a couple minutes and again measure the voltage across the trailer's battery. If it's 13-14 volts or higher, it's being charged. If the same as it was before you started the engine or below, it's not.

With that procedure, you can now operate the disconnect switch and see what happens to the voltage.

[BobC]

If Jim's test indicates it's not charging, depending on how your tow vehicle's hitch socket is wired, you may or may not have 12V for charging at your hitch socket. I had to add it to my motorhome.

You also should make sure the trailer plug is appropriately wired as well. Neither is a difficult add if either or both are missing.

Both are easy to check with a multimeter. You should read full battery voltage between the #4 terminal and ground on the trailer and full charging voltage on #4 at the tow vehicle (which should be running). Here's a link to a wiring diagram:

https://www.ajtnt.com/Info/7-Way-Diagram

It's a good idea to print out and keep this diagram in your trailer for troubleshooting.

Let us know what you find out.

[Goodspike]

I think the bigger question is would the emergency brake still function with that switch off? I'm not sure how exactly you would test that, so I would say leave that switch on. I do recall the battery needs to be in place for the emergency disconnect brake to function, and the manual may be more likely to say something about that.

Also, if the only purpose of turning this off is to not have the refrigerator run while moving, I would re-think that. The refrigerators are not that powerful, so it's best to leave them on. But if you really want it off, then turn off the propane tank. That would be safer (but also not necessary).

[DavidM]

Comments on several points raised:

Many chassis do not charge trailer batteries unless they are in tow/haul mode or the headlights are on. Also some trucks, SUVs and cars some from the factory without the 30A fuse necessary to charge the trailer batteries. Easy to add if missing once you find the proper fuse panel.

Not sure how the battery disconnect switch is wired. It should be in the circuit from the battery to the converter and the breakaway brake switch is wired directly to the battery so the switch has no effect on emergency braking, but who knows.

Finally I always tow with the fridge in propane mode. It does need a bit of 12V power for lighting the pilot and operating the controls so turning the switch off may make it inoperable. But never try to run your fridge from DC. DC power is 1/2 or less the wattage of AC power and will quickly run down the batteries if not charged by the TV or the converter.

Also as noted, absorption fridges provide low cooling and take a long time to recover if warmed up any.

David