Re: Charging from tow vehicle

On Thu, 6 Mar 2025 17:56:09 -0600,
  sticks <wolverine01@charter.net> wrote:

 On 3/6/2025 7:54 AM, Ted Heise wrote:

On Wed, 5 Mar 2025 19:55:25 -0600,
   sticks <wolverine01@charter.net> wrote:

  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.

 
Okay, here are some aditional points of information.
 
I'm positive there is power coming out of the 7-pin connector,
because I've frequently operated the powered lift jack without
any battery connected (i.e., only the 7-pin connected to the
trailer).
 
Pretty sure there is power going into the trailer too, because
my memory (though not certain) is that the interior lights and
other 12 V things work in the same circumstance (i.e., no
battery connected, just the running TV).

 
 It looks like the PD 4000 power controller you have only does
 one thing that I can tell, that being to convert AC power into
 DC power.  It operates when it is plugged into shore power and
 charges the batteries, but will also provide power for the DC
 power outlets without the need for the battery.  So you can
 rule out using this controller for charging from the DC
 supplied power from the 7 prong plug.

I think that's probably correct.  Here is the (typical) exterior
wiring diagram from the manual...

https://panix.com/~theise/wp-content/uploads/2025/03/Lance-1475-ext-wiring-traced.pdf

This shows that the 7-pin does connect to the battery, and seems
consistent with the trailer manual statement that "Normally the
battery will be kept charged by either the tow vehicle charging
system while on the road or by the AC/DC power convertor when
plugged into AC service."  It looks like the TV is wired directly
to the battery and not by way of the PD4000 load center (though
it's also wired into the load center).

From some sites I've looked at while trying to figure this all out
(can't remember where) I've gotten the sense that the Acadia would
be trickle charging the trailer battery.  And of course the car's
system is designed for lead acid chemistry, so isn't going to be
very (or at all) effecive for charging the trailer's lithium
battery.  I also have the sense that the fridge must draw more
than the Acadia supplies and be drawing the difference from the 
trailer battery when towing.

The Lance manual also says, "The 30 amp main circuit breaker
located on the chassis in the car connector junction box will not
allow power into the trailer or the battery(s) to be charged when
an overload or short circuit occurs."  That said, I'm not sure
this junction box warrants further investigation so long as the
trailer is getting power.  Stil need to double confirm the trailer
is in fact getting power from the Acadia, and will try to get that
done tomorrow morning.

 So you do have some AC outlets in the unit I believe, and these
 most likely only work when the shore line cord is plugged in. 
 There might be a disconnect switch somewhere, but it probably
 just has a bank, or something like a electrical box that ties
 in all the AC outlets to the shoreline somehow.

Yes, correct, there are AC outlets in the Lance.  Looks like the
power goes from the shore line to the outlets by way of the load
center...

https://panix.com/~theise/wp-content/uploads/2025/02/Lance-schematic.jpg

     ...To get AC power without being plugged in, you would need
 an additional inverter that would change the DC battery power
 into AC for use at those outlets.  So far, you have not said
 you have such an inverter.

Pretty sure there is no inverter in the trailer (though it seems
there must be one in the Acadia to run its low power AC outlet).

 I think you're ability to use the lift jacks off the 7 prong is
 interesting.  I think it is probably wired mainly for trailer
 brakes, although it looks like the dry weight of your unit is
 around 3,000 lbs and 4,000 is the legal requirement for trailer
 brakes.  Do you have a brake controller in the Acadia and use
 trailer brakes on your Lance?

Yes, there is a brake controller in the Acadia, installed by the
RV dealer I got the Lance from.

 How else it could be wired into the Lance's volt system is an
 interesting question. You say you think you also get lights. 
 Sounds like there must be some other kind of control box then
 if this is true, and I would certainly follow the power lead
 off the 7 prong to find out where it goes.  Mainly, because it
 should NOT be going directly to the battery since it is a
 Lithium.  You simply cannot charge a Lithium battery properly
 from the alternator of a modern vehicle on it's own. It would
 never charge the Lithium, and it could harm the alternator.
 That capability requires the addition of the DC to DC
 generator.

So the diagram I posted shows the power does go from the Acadia to
the Lance battery.  Is that a problem?  I don't think there's any
other kind of control box, unless it's in the junction box under
the Lance tongue (or maybe in the Acadia's tow system).

 You say you get these lights "without any battery connected." 
 I'm assuming you mean you either have a disconnect switch, or
 you have the battery cable actually disconnected.  You see what
 I'm getting at?  If the interior DC circuits have no access to
 the battery, how is it they are getting power from the 7 prong. 
 Where does it get hooked into the system?

Yes, the interior lights go on with no battery in place (or with
it and disconnected), I think the wiring schematic shows it goes
into the load canter.

As I lay awake in bed last turning this over and over in my
mind, I seemed to recall the Acadia had a 110 V outlet in the
second row of seats.  Indeed there is when I checked it this
morning.  Rated at 150 W max, it seems I could use this with
my NOCO GENIUS 5 charger (max 75 W draw) to charge the trailer
battery in a pinch. Might could even use it to run the coffee
grinder.  ;)

 
 It looks like this unit is more for non-lithium batteries, but
 it does say it can charge them.  I'm not sure, though. 
 Doesn't seem to have enough power capability to do much of
 anything.
 

Gotta run to see the cardiologist now, but will come back to
this later today.

 
 Hope you got some good reports!

Thanks!  Just sporadic supraventricular arrhythmias, not a fib. 
Pretty benign according to the cardiologist.

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