Charging the house battery via the tow vehicle

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Larry Howard

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Been looking all thru this forum and the net.  Not finding my answer so here goes:  Have a 2018 Toyota tow vehicle and a 2018 travel trailer equipped with a Battery Disconnect Switch.  Question:  Does the Battery Disconnect Switch need to be in the "On" position for the tow vehicle to charge the travel trailer (House) battery?

Thanks.
 

SpencerPJ

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I'm not sure that the tow vehicle charges the Trailer battery  :))  Good question

What I do know is, if the Battery Disconnect switch is in the OFF position, there is not going to be any charging no matter what. 
 

brclark82

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As long as your trailer uses the 7way blade connection and your truck supports it, then yes it will charge the batteries. 

Also, you do need to have the switch turned to the ?On? position for this to work.
 

Arch Hoagland

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When I pulled trailers I always made sure the truck alternator did NOT charge the batteries. 

Reason being if there was a problem in the trailer that was drawing a bunch of current I didn't want my truck electrical system compromised by the trailer and leaving me stranded in a parking lot somewhere next to nowhere.

Had that happen once 45 years ago. Learned my lesson.
 

Gary RV_Wizard

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Reason being if there was a problem in the trailer that was drawing a bunch of current I didn't want my truck electrical system compromised by the trailer

That's why competent installers put fuses or breakers on the +12v line from tow vehicle to trailer.  Trucks factory equipped with tow connectors and/or trailer brakes have them.
 

Larry Howard

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Thanks Gary.  I have found your posts to be straight forward and no BS.  Good reads.  Newbie here.  70 years old and just starting our camping experience.
 

Roy M

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Arch Hoagland said:
When I pulled trailers I always made sure the truck alternator did NOT charge the batteries. 

Reason being if there was a problem in the trailer that was drawing a bunch of current I didn't want my truck electrical system compromised by the trailer and leaving me stranded in a parking lot somewhere next to nowhere.

Had that happen once 45 years ago. Learned my lesson.
Did you then depend on shore power to keep the batteries charged? A properly equipped tow vehicle should have an isolator that disconnects the trailer from the tv charging system when the ignition is off. When on the tv would charge the house battery(s).
 

Arch Hoagland

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Roy M said:
Did you then depend on shore power to keep the batteries charged? A properly equipped tow vehicle should have an isolator that disconnects the trailer from the tv charging system when the ignition is off. When on the tv would charge the house battery(s).

Yes shore power in those days kept my trailer batteries charged.
 

Gizmo

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You should know that with a 7-pin (Bargeman plug) the tow vehicle will only marginally provide charging to the house batteries.  This is because the wire run is simply too long for the gauge wire used for a thorough charge.
 

Back2PA

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Gary RV_Wizard said:
That's why competent installers put fuses or breakers on the +12v line from tow vehicle to trailer


What size breaker allows charge of a low battery while still providing adequate protection? (Assuming best/worst case scenario where you've added a large charge wire and have a very low house battery?)
 

Hanr3

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Make sure your truck is configured to provide power. Over the years a variety of things may or may not need to be added or connected to make this function work. Was all dependent on Brand and model year. Some needed a wire connected under the hood, or under the dash, or a relay added, or a fuse added, or all of the above.

I cannot speak for other trucks.
The first time I towed my 5th wheel home the dealer activated my trailer, however they choose my boat trailer configuration. My boat trailer doesn't have a battery, and thus power was not provided from the truck. It was a 4 hour drive home. When I got home I checked my 5th wheel battery charge, 1/4. It was full when I left. My 12v fridge was on the whole trip.

First camping trip with the 5er I configured the trucks trailer setting for a 5th wheel and then the power was provided to the 5er. I drove 2 hours to the campsite, with the 12v fridge on, and arrived with a full battery and cold beverages/food.

I have a 2016 F150 with towing package. I can configure up to 10 different trailers. Note, both my 5er and boat use 7-way RV plugs. I added back up lights to the boat trailer and decided it was easier to use one type plug. Cost me a little more up front, but has paid off over time. I use the backup lights to launch and retrieve the boat at night, plus it makes backing into a dark campsite or garage easier.


Just because your truck can charge the battery, doesn't mean that feature has been activated. Test it. Mine won't work until I apply the brakes. What does Toyoda require?
 

Senator

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My 2015 Keystone Alpine 3536RE does NOT charge the battery when the battery cutoff switch is off.

It's simple to check.  Have the switch on (or off), measure the battery voltage.  Then turn the switch the other way and measure again.  The higher voltage is the one that is measuring the alternator voltage.

If they are the same, it is charging.
 

Memtb

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Larry Howard said:
Been looking all thru this forum and the net.  Not finding my answer so here goes:  Have a 2018 Toyota tow vehicle and a 2018 travel trailer equipped with a Battery Disconnect Switch.  Question:  Does the Battery Disconnect Switch need to be in the "On" position for the tow vehicle to charge the travel trailer (House) battery?

Thanks.

  Most newer vehicles with factory trailer towing harness, will send very little charge to the trailer batteries. Likely, less than 5 amps, as the wiring is likely 14 or 16 gauge wiring. Meaning...it will take a very long time to charge a ?depleted? battery(s)!
 

Gary RV_Wizard

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A typical breaker/fuse for the 12v line to the trailer connector would be 10A or 20A, but it is supposed to be sized to match the gauge of the wiring.  In other words, the fuse has to blow before the wire melts.

Many trucks come factory pre-wired and the installer just connects to the existing harness, or the entire harness & plug is factory installed. I have no idea what Ford, GM and Ram are doing for wiring these days. Maybe others cn tell us what they have from the factory?
 

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