Battery charging while towing

[bigdob24]

I found out the my 2017 F 350 only puts minimum amperage thru the charging pin in the 7 way trailer connecter. So I wired up one of my upfitter switches to supply 12v under a 20 amp fuse to the RV while traveling. I can switch it on and off . It’s fine for the wire size and can go up to 25amp fuse if needed.
As I now have a 12v compressor conversion on my 2118 Norcold that wouldn’t cool . It draws around 10 amps when running .
Is this 12v now running back to the RV controlled by the converter / charger so there is not a worry about overcharging?

 

[wdk450]

The converter/charger is operated by 110 volts AC power input, so it doesn't do anything to regulate tow vehicle supplied charging current. The wiring from the truck has essentially put the trailer's battery system in parallel with the truck's battery system. The charging current is regulated by the truck's alternator regulator system. In most newer trucks (mine is a 2004 and wired this way) the engine computer senses the truck 12 volt level and sends signals to the alternator field windings to regulate this voltage.

 

[centerline]

I found out the my 2017 F 350 only puts minimum amperage thru the charging pin in the 7 way trailer connecter. So I wired up one of my upfitter switches to supply 12v under a 20 amp fuse to the RV while traveling. I can switch it on and off . It’s fine for the wire size and can go up to 25amp fuse if needed.
As I now have a 12v compressor conversion on my 2118 Norcold that wouldn’t cool . It draws around 10 amps when running .
Is this 12v now running back to the RV controlled by the converter / charger so there is not a worry about overcharging?

 

[centerline]

There is no worry about overcharging... but very likely to not be charging as much as you think it is...
After a full understanding of what allows and causes a battery to uptake a charge, and wire runs vs amperage drop, and the percentage of voltage loss thru the wire, it quickly becomes apparent that the trailer battery is going to have to be pretty low before the current passing thru the wire will get much over 6-8 amps passing thru it.. and unless the wire is large, the voltage will have dropped to the point that it wont charge the trailer battery, but just help replenish a percentage of the amps being taken out of it by whatever power consuming devices you have running...

 

[bigdob24]

Thanks for the reply's
Don’t want to get in an overcharge situation so sounds like I’ll be ok as it will just help keep the batteries full.
They are always maintained and topped off before a trip and the fridge only draws around 10amp when it’s running.
Thanks
BD

 

[wdk450]

This charging pin on the 7 way umbilical connector was originally installed to provide SOME charging current to the trailer's battery system to PROVIDE FOR TRAILER DISCONNECT ELECTRIC EMERGENCY BRAKE (LANYARD SWITCH) BATTERY OPERATION. Other loads gradually got added over the years in the trailers while going down the road, but this is why the charging current engineered in the tow vehicles is ususally so low.