Truck remote start and TC battery charging

I don't look at the truck as the primary charging source for house batteries, but it will maintain them and keep them from draining to an unsafe level under load. To get a full charge on the battery, you need a smarter charger that is sensing parameters closer to the battery. Depending on the battery chemistry, 80 percent charge may be good enough as long as you do not discharge bellow the battery threshold.

theoldwizard1 wrote:

A car/truck alternator is the WRONG TOOL to recharge house batteries, especially deep discharge batteries.. PERIOD !!!

BUT.....it is better than nothing.
13.2 is enough to put SOME charge back.
If you are driving for 8 hours, it might put back a significant amount.

Reading these threads is dangerous.
Now I need to pay closer attention to my alternator charging voltage......because after I got the "battery solenoid" replaced it now appears to stay above 14 all the time.

Even with my mechanical education I know that when alternator will put 14V into trailer wire, you will have full 14V on other end unless you start putting load on it.
When I drive for several hr with fridge on propane, my TC batteries will show 14.2V.
So what is all that whining about?

Z-Peller wrote:

Not entirely true. On my GM trucks back to 2009, the owners manual says driving in towhaul or turning on headlights will send full charge to trailer plug regardless of truck battery fully charged regulator issue.

What it says on page 4-82 is

If charging a remote (non-vehicle) battery, press the tow/haul mode button located at the end of the shift lever. This will boost the vehicle system voltage and properly charge the battery. If the trailer is too light for tow/haul mode, turn on the headlamps as a second way to boost the vehicle system and charge the battery (in the trailer).

But, previously on page 3-21 it says

The vehicle has Electric Power Management (EPM) that estimates the battery’s temperature and state of charge. It then adjusts the voltage for best performance and extended life of the battery.

When the battery’s state of charge is low, the voltage is raised slightly to quickly bring the charge back up. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gauge or a voltage display on the Driver Information Center (DIC), you may see the voltage move up or down. This is normal.

I simply do not believe the statement on 4-82 as it contradicts the statement "When the state of charge is high, the voltage is lowered slightly to prevent overcharging". Or maybe I should says, I don't believe that the proper voltage will be delivered to a trailer battery to recharge it 100%. It might keep it from being further depleted by loads in the trailer, but it will not be recharged.

Kayteg1 wrote:
It is not the fuse rating that limits TC charging via trailer plug.
It is size and length of the wire.
For reasons that I will never understand, the charging wire runs about 30 feet between alternator and TC battery. Since it is usually max #10 gauge, you have about 1.5V drop at 20 amp, meaning the fridge will deplete TC battery.

You are partially correct, but you are over simplifying it !

If you ran #00 gauge from the alternator to the TC house battery/inverter you would still only get about 13.2V ! That would probaby be enough to run your inverter, but it is NOT enough to recharge depleted house batteries. Why ? Because the PCM controls the charging voltage of the battery. Even on a big diesel, the PCM ASSUMES that it only need to replace the energy in the truck batteries that was used to start the truck.


A car/truck alternator is the WRONG TOOL to recharge house batteries, especially deep discharge batteries.. PERIOD !!!

The bottom line is, the alternator on any vehicle is designed to charge the starting battery. Period. END OF DISCUSSION. Heavy gauge wire will not help much to fully charge a house battery.

If you want to charge a house battery you need a special device called a DC-DC Boost Converter that will bump the voltage up to over 15V (regardless of the input voltage) and then a multi-stage solar charge controller connected to the house battery. Both of those devices have limited current capability so recharging a depleted house battery will take many hours.

Not entirely true. On my GM trucks back to 2009, the owners manual says driving in towhaul or turning on headlights will send full charge to trailer plug regardless of truck battery fully charged regulator issue.

That is different subject, but yes, my 120V fridge element is 360W, while 12V element is 260W.
In extreme situations that will make some difference.

Kayteg, you will see better charging and fridge performance if you run the fridge in AC mode from a small inverter while driving, rather than trying to run it in DC mode. An inexpensive MSW inverter will work just fine for this. I’ve tried both ways on my camper and the AC mode works so much better I unplugged the DC heater and never use it. If you’re going to run the fridge in an electric mode while driving, if possible use the mode that will perform the best. DC mode will only hold a pre-cooled fridge in moderate ambient temps. AC mode works as good as LP mode, and will work better than DC in temps above 85 or so.

I also ran new 4 awg charge wires to the camper through a Pollak 2-pin plug, and the truck alternator keeps the camper battery at a good state of charge. I make sure the fridge thermostat is on its mid setting so the AC heater cycles on and off rather than running 100% of the time. I didn’t do all that work on my truck and camper to recharge a depleted house battery (although it will to an extent), but to prevent the house battery from being depleted by the fridge.

On every Ford truck I’ve owned (four of them) the +12v pin on the trailer plug isn’t hot until the key is at least in then ACCY position. The 7-pin trailer plug charge wire has never been hot all the time, and I wouldn’t want it to be.

:):)

It is not the fuse rating that limits TC charging via trailer plug.
It is size and length of the wire.
For reasons that I will never understand, the charging wire runs about 30 feet between alternator and TC battery. Since it is usually max #10 gauge, you have about 1.5V drop at 20 amp, meaning the fridge will deplete TC battery.
And I really don't need 260 amp charging current for TC.

Kayteg1 wrote:
I have remote factory installed on my F350 and lack of power to trailer plug was disappointment.

What year F350 and what engine ? Do you have the factory HD Trailer Tow option ? The factory installed 7 pin trailer harness connector (Pollack connector) will have a +12V on pin 4. If not, check that the fuse is good AND you have the appropriate relay installed.

Kayteg1 wrote:
With dual alternators there is no question if the 260 amp would charge at idle,

Those 2 alternators will not put out anywhere near that power at idle and like most vehicles, the voltage will be cut back to about 13.2V, measured at the engine starting battery, shortly after the engine starts up.

Kayteg1 wrote:
Since trailer plug has limited amp and not too good connections, I have it on my winter project list, to add HD cables that would allow me run refrigerator on 12V ...

Pin 4 on your trailer harness connector should have a 20A fuse in the fuse box. That shoul be more than enough to run an RV refrigerator and they are not to fussy about the voltage being low.


I don't know how a TC harness is wired into your vehicle, but pin 4 on the trailer connector should be HOT AT ALL TIMES !