Battery charging through trailer plug

[BobTaylor]

Just returned from a long trip to the western US (again). I discovered that I am not charging my RV battery through the trailer plug (factory towing option) I get no 12V through the + terminal on the trailer receptacle, ignition on or off. Do I have a problem or do I have to do something else to get this to work. I know that an isolation solenoid is necessary to keep the RV from running the truck battery down, but I've been unable to find out if the factory towing package includes this.

 

[JDecanter]

Check the in line fuse. Sometimes they are blown and other times just corroded.

 

[BobTaylor]

That was indeed the problem. I found the fuse in the standard fuse box. I don't know why I didn't think of that first. They taught us in Tech School USAF, that we were to check the fuses first. Oh well, that was 50 years ago.



Thanks

 

[HBarlow]

You've probably already figured out the OEM trailer battery charge line on our trucks is marginal at best. The wire is not of sufficient gauge and current carrying capability to do much more than prevent the trailer batteries from being fully discharged and the circuit isn't switched to isolate the truck's batteries from being discharged during a period of heavy current draw by the trailer when the truck's engine is not running.

I never have bothered to do it on this truck but on the previous two Dodge Rams I bought a continuous duty high current relay, supplied it directly from the battery, and used an ignition switched 12v low current power source to control the relay. I ran a large gauge wire all the way from the relay back to the seven pin connector at the rear of the truck.

I wish Dodge would do this at the factory.

 

[MrLuckey]

I could be mistaken but I thought I read somewhere that in addition the ECM monitors the current going through at least a couple of the trailer circuits and can shut them down if they get too high.



In either case I have one of the painless wiring circuit bosses on the bench that is going to provide power to my OBA system (just the pressure swx/rly side) and will also feed a relay for replacement wiring to the trailer/charging pin.

 

[Gary - K7GLD]

A large capacity blocking diode - about 35 amps at 50 volts or so - wired to allow current passage TO the RV, but block flow back TO to tow vehicle is also a good idea, to prevent the RV from draining the tow vehicles battery - as mentioned earlier...



They come in various, inexpensive configurations - Radio Shack sells some bridge rectifiers that would do the job, simply use only one of the rectifier bridge legs for the purpose...

 

[MrLuckey]

wired to allow current passage TO the RV, but block flow back TO to tow vehicle is also a good idea, to prevent the RV from draining the tow vehicles battery

Now I'm confused, if you allow current flow TO the RV you'll still allow the tow vehicle to discharge into the RV and drain your tow vehicle batteries. The setup you describe only keeps current flowing from the RV (ie generator running and charging RV batteries etc) TO the tow vehicle?



Say that you had hard wiring from 7-Pin directly to the tow vehicle battery, seems all the diode would do is keep the rv gen from charging the tow vehicle battery.



Sorry if I misunderstood!

 

[Gary - K7GLD]

Now I'm confused, if you allow current flow TO the RV you'll still allow the tow vehicle to discharge into the RV and drain your tow vehicle batteries. The setup you describe only keeps current flowing from the RV (ie generator running and charging RV batteries etc) TO the tow vehicle?



Say that you had hard wiring from 7-Pin directly to the tow vehicle battery, seems all the diode would do is keep the rv gen from charging the tow vehicle battery.



Sorry if I misunderstood!

NOPE you understood perfectly - I mis-spoke - right idea, WRONG application - sorry...

 

[jelag]

With the voltage regulator that changes with temperature its hard to charge batteries...

I've run a 8 gauge wire from the batteries to the trailer plug through a 50 amp circuit breaker and than ran the same size wire to the batteries from the male trailer plug...

I've also added an 8 gauge ground in the truck and trailer... I've installed a simple volt meter at the trailer batteries and seem to get at least 1 volt more now this change has been made... .

I've trimmed the existing wire from the truck wiring and put a piece of heat shrink tubing over it...

I've also tapped into this power source (4) 35 watt floods for back up lights on the back of the truck using a relay to trip this circuit from the backup light circuit in the truck...

Hope this helps... .

 

[BobTaylor]

Is there a convenient place to get the battery voltage to send to the trailer connector? Do I also understand that the ground on the connector is insufficient and that I should also increase its size? Would grounding it to the chassis at the rear of the vehicle be acceptable? Do you have a suggestion for the relay?

 

[HBarlow]

It is convenient to take power direct from the driver's side battery positive post.

A NAPA store can special order a continuous duty 50 amp relay. The relay comes in a small can and looks like an old Ford starter relay.

DC electricity must always flow in a complete loop back to the source so a ground wire must be as large and carry as much current as the supply. Ground may be provided through the hitch back to the truck frame but a ground from truck frame to the ground pin in the seven pin connector is always better.

 

[JohnBower]

The relay you're talking about is the old remote starter solenoid. It will definitely handle the 50 amps.

 

[MrLuckey]

NOPE you understood perfectly - I mis-spoke - right idea, WRONG application - sorry...

Whew, its been about 20 yrs since electrical engineering and I've forgotten quite a bit but I was hoping I hadn't slipped that much :-laf. I love this place, almost everyone seems to add value!

 

[HBarlow]

The relay you're talking about is the old remote starter solenoid. It will definitely handle the 50 amps.

Yes, I remember now. Didn't they originally have a push button in the bottom for starting under the hood? It's been a long time since I've seen one.

The parts I have bought at NAPA look like but are not an exact duplicate of the Ford item.

 

[FWC]

Solenoid needs to be a CONTINUOUS DUTY SOLENOID. If you use an intermittant duty solenoid they over heat and stop working(vehicle starter solenoids are intermittant duty).



FWC

2007 6. 7 QC LB DRW 6 Speed 4X4

 

[tkerrigan]

What would be a safe ignition on only trigger wire to use on a 04. 5 to operate the relay?