What controls tow vehicle (TV) power to the trailer battery?

GHatfield

We just bought a used T@B 2019 320S (Boondock Edge) trailer and I'm trying to figure out if our TV (2014 Jeep Grand Cherokee) will charge the trailer battery as we are driving.  The Jeep is equipped with the factory installed tow package.  The 7-way plug does have a wire for +12 volts and when I checked the voltage it was about 12.9v without the car running and 14.3v with it running.  The wire carrying the 12v is probably no larger than 14 gauge.  These readings are without the trailer connected.  The brake controller is a Tekonsha P3.  Before buying the T@B we owned an Airstream Bambi (19') which I used the controller with.  But I never worried about charging the battery in the Airstream since 12v use while traveling was minimal.  But with the T@B we plan to run the refrigerator on 12v while traveling.  

My question is...  what controls the amperage flowing through the 7-way 12-volt line?   The trailer is equipped with a factory-installed MPPT75/10 solar panel and regulator.  So the trailer battery has two sources of power while underway, the TV and solar.  How do these two interact?  What controls what comes from each source? Obviously, I don't want to overload that relatively small wire coming from the TV.  



Thanks in advance for any insights.

GHatfield

I think I have answered my own questions, at least in part.  I just Googled "charging trailer battery from tow vehicle" and found a good explanation of what I think I need to do on e-Trailer.  So it appears that I need some sort of BCDC charger (e.g., Redarc) and a new, heavy-gauge cable from the TV battery to the BCDC charger. 

Questions:
 1.  According to e-Trailer, the Redarc units will accommodate an unregulated solar source also.  But will that work with the SmartSolar charge controller?

 2.  If I don't purchase a BCDC system, will the combination of 7-way low amp 12 volts plus solar power keep the battery charged while using the refrigerator on DC while driving?  I realize there are a lot of variables involved such as the outside temperature, but it would be interesting to know of other's experience of using the refrigerator on 12 v while driving without a BCDC system.   

Thanks in advance for any insights.  

Cbusguy

You don't need to purchase anything.   Pin 4 should provide 12 volt dc to the trailer.   Get your volt meter out and check it.   If no power and it appears to be hooked the fuse or relay may have never been installed
   

Worst case you need to run a new line from the battery, through an ignition switch controlled relay, to the trailer. No biggy and no need to spend a couple of hundred bucks on a magic box unless you want too

I installed a dc to dc charger to control the charge from my 250 amp alternator to my trailer.   I was charging my lithium batterys at 70 amps.   

Not needed except for extreme.cases

pthomas745

You can also use the Victron bluetooth app to see how much power your TV adds to the solar input.  Should be easy to figure out.

MuttonChops

There seems to be a full range of success to failure reported for running the Fridge on +12VDC while driving.

3-way Fridge has no temperature control on +12V or propane so you need to monitor.

+12V current draw is around 11 Amps,  most TV (without the DC2DC boosters) can only deliver a few amps of charging current . . . more for topping off not re-charging.

Most TV +12V to trailer is directly connected to the TV Battery.  Stop for lunch, leave Fridge on, get dead T@B battery and possible dead TV battery.  So install an ignition relay or train yourself to unplug the T@B (or turn off Fridge at every stop).

My first year it seemed running the Fridge on +12V was working well, second year as my driving hours increased and boondock days increased started to have Low Battery Voltage with Alde.  Am now doing +12V Fridge operation for short periods of time, use more ice in Fridge.  Am also considering a DC2DC unit - - - but for now have only increased battery size and carry a small gas generator.