Charge Batteries from Tow Vehicle, using a Solar Controller.

GordonThree wrote:
So you're increasing the voltage, to more efficiently transfer power from the tow to the trailer? Where does the voltage doubler get hooked up, hopefully someplace close to the alternator or starting battery?

There is an improvement in "Voltage Drop" power losses, but that's not the main purpose: The main purpose of all this stuff is presenting a sufficient Charging Voltage at batteries. First, we boost to more than the batteries can handle - then we let the Solar Controller adapt the high-power, 24V "fake Solar Panel" output into the correct profile (Volts and Amps) which the batteries should be given, according to SOC.

Per the linked picture (#2 of 4), the Boost occurs under the hood - reducing current on all the wires before the Solar Controller, including the "Trailer Battery Charge" wiring from under the dash back to the Bargman connector.

GordonThree wrote:

My thought: Bypass the bargman. Run 4ga or heavier off the alternator to the rear bumper and use a PowerPole connector to mate with similar wiring on the trailer side, leading to the battery box. Question is; would a factory alternator handle the extra load?

Yes, it would. (Unless your Trailer batteries are huge and discharged, e.g. 500Ah at 40% SOC.) "Brute Force" puts all the batteries into a single string, and the Trailer Batteries will drag down the Voltage of the Starting Battery by absorbing power until they are all equal. And at the same time, "Battery Voltage Sense" under the hood sees the reduced battery Voltage as well - invoking a higher "Battery Charge" Voltage within the TV (by drawing more Voltage and Power from the Alternator.)

IMO, having done a little bit of both jobs (rewiring the 4Runner "Battery Charge Wire" and installing my new gadgets) - installing the gadgets was much easier, except for mounting the new dashboard "mode switch". And it avoids hanging an extra cable between TV and Trailer.

That durned "mode switch" took about 2 hours: I needed to trim the dash panel it in order to get into an "unused switch plug" which didn't really fit, and I also had to pull leads (12V, ground) from other wires under the dash. :M

The 4Runner's OEM "Battery Charge" wire was not bigger than 14-AWG, and actually looked closer to 16-AWG. I pulled a new #10, and the body panel disassembly/re-assembly was very time consuming (about 3 hours, total). In contrast, the "Relays-with-Booster Assembly" (at the TV) and the "Two Relays with a few wires coming out" were both assembled in the house (with beer and TV), plus about 1/2 hour installation in each vehicle.

So you're increasing the voltage, to more efficiently transfer power from the tow to the trailer? Where does the voltage doubler get hooked up, hopefully someplace close to the alternator or starting battery?

Nice work if it's working for you ... Too many moving parts for me, and I like complicated solutions to simple problems :)

My thought, not currently implemented: Bypass the bargman. Run 4ga or heavier off the alternator to the rear bumper and use a PowerPole connector to mate with similar wiring on the trailer side, leading to the battery box. Question is; would a factory alternator handle the extra load?

GordonThree wrote:
Is 24v standard for all diesels, otherwise where does it come from?

DanNJanice wrote:
Good question, it is unclear to me what the OP is talking about. If you had a 24V system I could see using the solar controller as described. I just don't know what vehicles have 24V electrical systems.

Sorry guys - I left out something important. I just edited the first post, to explain that a cheap Chinese "12V-to-24V" Voltage Booster gets inserted into the Bargman wire path when the Relays engage.

TV Relay Coils disengaged: 12V mode, bypassing the Booster.

TV Relay Coils engaged (powered by output from the controller switch on the dashboard): 24V mode, Voltage gets increased by running the connection through the Booster before reaching the TV's Bargman connector.

https://goo.gl/photos/DBtjLwMrpZ8sjmLYA

Here's a note on the Tow Vehicle Picture: There are 3 Relays (rather than two), because I didn't have access to the original "Trailer Battery Charge wire" under the hood, after the fuse. It's hidden within a gigantic bundle.

So, before the two 12/24 "switching" Relays, there is (1) a direct battery connection with a new fuse (30A), and (2) an initial Relay, which switches "on" whenever the engine is actually running.(My new Trailer Battery Charge" circuit is not activated by merely turning on "accessories".) I pulled the fuse for the OEM circuit.
- - - -
Meanwhile, in the Trailer: the schematic shows 3 Relays, allowing for an automatic switch of "Bargman 12V" back into the "+12V" power distribution, whenever the 24V coil Relay is not activated. But per above, we never want this if:

• The Trailer will never be pulled by a different, 12V-only Tow vehicle; and
• You can always remember to flick the "24V mode" switch when pulling the Trailer, and sun conditions aren't perfect.

Why "12V operation" is never desirable in this configuration:

If your "genuine Solar" is performing well, and your Controller has determined that your batteries and loads need "Bulk" or "Boost" charging, the the Controller attempts to keep the battery charging Voltage fairly high: 14.2-14.4 Volts.

But, you have connected the Trailer's +12VDC power distribution to the Tow Vehicle, via the Bargman. The Tow Vehicle has probably "decided" the alternator in a way which yields 13.9V (and maybe even less). Your Controller's attempt to run at "Bulk Charging Voltage" leaks power into the Tow Vehicle - and the "thirsty" batteries get much less.

Whenever the Solar conditions aren't great, you should flick the switch and run in 24V mode. And, if Solar conditions are great, you should probably leave the Bargman "Trailer Battery Charge" wire isolated, disconnected from the Trailer 24V system. ("12V mode" in the Tow Vehicle = 12V with other Trailers, but nothing in a properly configured "24V" Trailer charging.)

GordonThree wrote:
Is 24v standard for all diesels, otherwise where does it come from?

Good question, it is unclear to me what the OP is talking about. If you had a 24V system I could see using the solar controller as described. I just don't know what vehicles have 24V electrical systems.

Is 24v standard for all diesels, otherwise where does it come from?

In my configuration, an MPPT Solar Controller can receive power from either the "genuine Solar Panels" (rated ~ 330W max, 5A @ 67V under prefect conditions) or the Bargman Input (rated ~ 290W max, 12A @ 24V under any conditions). Maximum power draw on my MPPT, in "Boost" mode, also corresponds to ~ 290W.

Under Good Sun conditions, I leave it running "genuine Solar". But, under clouds or sub-optimal conditions (night, early morning, dusk), I flick the switch - and it disconnects the "genuine" Solar Panels, switching over to the fake "24V Solar Panel" instead.

The Solar Controller monitors Battery State and adjusts output Voltage accordingly. A PWM controller could perhaps be used, but wouldn't take more than 14.4V (average) from the Voltage Booster, and might attempt to draw more than 12A while connected. That would be a 'Bad Thing'(tm), and blow a fuse inside the sealed Voltage Booster.