Re: Charging from tow vehicle

On 3/5/2025 2:03 PM, Ted Heise wrote:

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?

In truth, I think it is pointless in your case.  I think we already have agreed now you simply cannot get enough power to charge your lithium batteries from the 7 prong.  I would, however,  like to know if there is power coming in, and going out to the trailer.  If there is a power wire hooked up on the 7 prong on the trailer, where exactly does that power go?  Obviously the trailer lights you can easily figure out, and they don't use power from the trailer battery.  They draw directly from the towing vehicle.  Usually the power tab is for trailer brakes, or an accessory of some sort or another.  Were you under the impression it somehow went to your battery?  Obviously it can't go directly there since it would be incapable of charging lithium batteries, so does it go to the controller you speak of later?  You need to find out exactly where that power goes, and here's why.
I sense there is a possibility you could use the controller to charge your batteries just as it does on shore power.  The question would be does it have the ability to invert DC to AC, which would be what you get when you plug into shore power.  However, if your 7 prong power tab is going to this controller, perhaps you can use this.  I'll try and read up on it tomorrow a little more.  But, though my View is a single unit, this is exactly what it does somehow.  On shore power it charges up the house batteries nicely.  Once I turn on the engine, it still charges up the house batts, but it uses the alternator and now DC current.
Now you don't need to use this and can easily just install a DC to DC generator as they can properly charge lithium batteries.  To me it seems like 20 amp is the sweet spot when trying to use a 12 volt system with a single battery and standard alternator to do this.  Larger alternator and double battery obviously gives more options.  You do have to get the 6 gauge or larger wire back to the trailer somehow, for either scenario.   You need to find out where that power lead on the trailer side of the 7 prong actually goes.
FWIW, this wiring in your case should not be all that complicated as you could simply go in the engine compartment and go right out the bottom, encase it in some hard shielding, and zip tie it right along the frame rails.  I did small portions of this on my Bronco, and that is going to be doing some off road stuff.  (though I've heard somewhere you like to bounce over railroad crossings 8-)  You just have to figure out what type of plug you want and where to mount it.  If you would rather not attempt this, this is exactly the type of work RV places do.  I'm rather fortunate in that I have a family owned fantastic Winnebago dealership who can do my work.  I would completely avoid Camping world, RV center, and any other of those large chain stores.  They suck.  Small independently owned auto repair places can also do this type of work, and you can find some good ones.

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.

I believe your Acadia is a 2022?  It almost certainly will be utilizing lots of the CANBUS technology.  What this means for the power plug on your 7 prong is that it won't send any voltage unless it senses a load. That's why multi-meters usually will not work to see if they are hot.  I had to figure this out the hard way myself and once I bought a cheap DC test light it provides a load to the system and lights up.  You can try a meter, but the only way to know for sure if you're getting nothing is to use a test light.  I have not had my TOAD pulled behind my view yet, and the only way I know it should work is because the proper plug did light up with a test light.  Got nothing with a multi-meter.

 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.

Just in case you're wondering, you cannot utilize the 7 prong for the 6 gauge or larger size wire you need.  It simply won't fit in those plugs.

 

  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
 

Excellent, I will give this a good looking over tomorrow hopefully.

 

  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.

Sounds like all you know of is the controller/charger mentioned above, and a plug in for solar something.  No other switches or anything else you can find?
I'll try and make a list tomorrow of what I have in my unit.  There's about 4 different things IIRC.

 

    ...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.

Yes, definitely need more information here.  Once you get a proper setup for alternator charging, more important is going to be the solar charging that's done while you are enjoying your stay.  Perhaps I'll learn more reading about that controller tomorrow.  I looked at that link provided a few days ago, but it really didn't give much useful information.

 

  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!

I do enjoy all the learning that happens when you work on things like this.  Let's make RORT great again!  Ha!
--
Better Days Ahead!
Darwinism Is Junk Science!!