Re: Charging from tow vehicle

On Wed, 5 Mar 2025 09:05:19 -0600,
  sticks <wolverine01@charter.net> wrote:

 On 3/5/2025 7:41 AM, Ted Heise wrote:
 

So I looked at the manual for the fridge, and it clearly
states it only runs on 12 V if the trailer is connected to a
running tow vehicle.  I guess the next step in better
understanding the issue would be to hook up the trailer and
check the battery status while the fridge is running on 12 V.

 

  Regardless, it seems pretty clear my Acadia tow vehicle is
  not producing enough juice to help.

 
If I want to look into getting a DC-DC charger and cable to
back of my Acadia installed, where would I start--is that a
GMC dealer thing, or an RV shop?  Other?

 
 OK, this is a good place for getting started on what I was
 suggesting we do to get some consensus on this charging of
 trailer batteries universal problem for us RVers.
 
 The first place to start would be the 7 prong plug in, on the
 tow vehicle, and the vehicle being towed.  I am going to take
 it for granted most of us would be using a 7 prong plug.  Any
 differences are minimal and easily solved.

Agree this is a good place to start, and you actually anticipated
my next step.  I've been puzzling over in my head on the lack of
charging while towing.  The Acadia does have a factory installed
7-pin connector right next to the receiver.

 So let's start on the tow vehicle.  It might surprise some of
 us that our plugs don't even have power in them as delivered
 from the factory. I have an F-150 and was quite surprised
 myself that I had to install an additional fuse to get my line
 hot.  It was wired, but not fused and inactive.  With today's
 CANBUS systems, it can be difficult testing this, and you
 really have to use a 12 volt test light and not a volt meter. 

My thinking was to take a reading from the LiIon battery app with
the battery connected to the trailer and then with the fridge
started (I think it may run off the batt for a minute or two).
Then I would connect the 7-pin to the running TV and repeat these
readings.  Does that seem like a reasonable approach?

I need a block of time to get out to the storage unit for this, so
in the meantime I figured I'd take some measurements at the 7-pin.
First I connected clips from my multimeter with the TV off. 
Surprisingly, I got some sparking, may have been from touching
across pins.  But once I had a good connection I got no voltage.

Now this could be from the line not being hot (e.g., because of a
fuse needed), or because a multimeter won't work.  But I vaguely
recall having gotten a 12-13 V reading from the pins some time in
the past.  So maybe the sparking blew the fuse.  I'm trying to run
down where that would be and will let you know what I find.

It's a pain to prop open the spring loaded connector cover to get
in there with meter probes, so I'm thinking I might look for a
7-pin plug with attached wires that would make the connecting for
measurements a little easier (and cleaner).

Another possible hitch (so to speak) is a small incident about a
year ago.  I was towing a rental trailer and went over a RR
crossing dip too fast and the trailer tongue popped off the ball. 
It yanked out the connector and adaptor (4 to 7 pin).  The mount
bracket for the 7-pin on the TV also got bent upward and toward
the front of the car, so it probably bottomed out going over the
dip.  So it's possible some connections got damaged, though
nothing was cut completely because I've used it with all the
signals and braking working since then.

In any case, the car goes to the dealer on Tuesday to get an
antenna repair, so I'm going to ask them to check out the 7-pin
while I'm there.

 Mine was wired with 12 gauge wire, and I did install a 12 gauge
 and a fused link that went from the umbilical directly to the
 battery on my Toad.  This, however is a regular automotive
 battery and not a Lithium battery.  This would NOT work for
 charging a lithium as it needs a converter/charger before the
 lithium, and even if I did have one, the trailer 7 prong is
 probably only going to be able to provide between 5-10/12 amps
 and that would not be enough to fully charge a lithium battery. 
 I think you need at least 20 amps to ever get a lithium
 charged.  (This is where having a bigger alternator could be
 useful, as you could get a 40 amp or bigger charger greatly
 speeding up charging.) Therefore, a DC-DC charger is the next
 logical option (setting aside a perfect solar charging
 install).

Yep, that all makes sense.  I'll be digging into that more after I
get the basics above figured out.

 The next question is what is available on the trailer.  Ted,
 for example can plug into shore power, and even use his 7
 prong, or so he thinks. So what exactly do you have on the
 trailer that deals with recharging the house batteries if
 anything?  Does it already have a charger that would be capable
 if you could only get it enough power?  When you're on shore
 power, does it also charge up the lithium batteries?

Yes, the LiIon battery charges up quickly when on shore power. 
The trailer has a Progressive Dynamics PD4000 Series Power Control
Center...

https://www.progressivedyn.com/pd4000-series/

According to the manual, it has a setting for lithium ion
batteries, and I believe I have it set correctly for that.

FWIW, the battery is this...

https://www.litime.com/products/litime-12v-100ah-lithium-lifepo4-battery?srsltid=AfmBOooYbGPTdOaEImeJqF-g0vqKIb27qtceloDoubGXsc1Pk8-UK_C4

 So, I think it is a certainty you cannot get enough power
 simply off the 7 prong to do much of anything.  So a DC-DC
 charger is a perhaps, but a 6 gauge or bigger line for power to
 the trailer is a must.  Now, you have to figure out what you
 already have on the trailer that you could use, if anything,
 and what you will need to get.  Next step is becoming certain
 of what is on the trailer now.

This all sounds right.  I think it's reasonably clear what's on
the trailer, but if I missed something, please say so.

   ...Would also be a good time to get a better understanding of
 what that solar plug it has installed actually does.  For
 example, does it just give a route for power from a solar
 source and charger/controller to the batteries, or does it
 actually have any of the hardware in the path?

I'm pretty sure the plug on the side provides only a physical
connection to the power center.  I'm pretty doubtful the control
center in the trailer would do anything to manage input from solar
panels, but maybe I'm missing something.

 please remember this is all new to me too, and I'm trying to
 work it out as we go too, so I've probably made some false
 assumptions.  That said, I think if we go step by methodical
 step, we can figure out how to properly deal with all this in
 an informed manner.

I really appreciate the help, can't say thanks enough!

--
Ted Heise      <theise@panix.com>       West Lafayette, IN, USA