Charge Batteries from Tow Vehicle, using a Solar Controller.

MrWizard wrote:
your still using the T/V alternator
switches, relays, voltage booster, solar controller

Why not 'new wire, booster, (controller optional)
mount booster at TT, set output to 14.4v for charge {same as solar controller}
less conversion steps, less parts

Good question!
The #1 reason is: Setting a constant 14.4V output, rather than running through a nice charge controller, will pretty quickly overcharge and boil the batteries. So the Solar Controller is not optional: You need to have the Voltage adjusted according to SOC.

The #2 reason is: Voltage Drop and Power loss along the Bargeman path. If the Boost doesn't happen until the Trailer, you might be pulling fairly high current along that path. {The "+" Path is: The "Trailer Battery Charge" wire within the TV to the Bargeman; then going through the connectors; through the Trailer<->TV cable; then to the load center; and then back to the batteries. The "-" path is generally: Batteries to the Trailer frame (very short); into the Trailer<-->TV cable; going through the connectors; and then hooking into the Tow Vehicle frame (very short); back to the TV under-hood battery connector.} Boosting at the TV makes it run with half the current, all the way to the Solar Charge Controller.

The #3 reason is: More available power, with less chance for starting a fire. We all used a very short length of big wire (#8) and high-current Circuit Breakers (40A) to go into the Booster device. The current capacity of TV "Trailer Battery Charge +" wires is actually quite low - most vehicles are built with wire smaller than #12, even though the fuse is typically 30A. (My own 4Runner was built with #14.) Their excuse is "This is chassis wiring, within an electrical component system". I don't like that approach: By limiting the current to only 20A after a very short #8 wire, until we reach the Solar Control Battery Connections, we make the questionable wiring a bit more safe. (The neutral/ground return wire is sized larger within most Trailer cables, the problem is mainly with the +12V).

The #4 reason is: You need to consciously switch your Solar Controller from your hard-wired "Booster" input to your genuine panels, when you stop to camp. I feel that there's a very high risk of forgetting to do that. This way, it automatically switching back to Solar panels whenever your turn off the Tow Vehicle (for a long lunch, for camping, or for anything else). And anyway, you probably want to make that manual switch-back using switches - I just replace them with Relays, and add the "24V controller Relay" to make it automatic.

I'm definitely using the TV alternator to supply power into the Booster. But it doesn't typically run at full capacity, and if you're concerned you can simply avoid switching it "ON" until you're at speed , running fairly high RPMs. But most half-decent mid-size SUVs (4Runners, Traverses, Explorers) have no problem running pretty high loads, even at idle speeds. ("Pretty High Load" meaning 200-300 Watts.)

your still using the T/V alternator
switches, relays, voltage booster, solar controller

why not 'new wire, booster, (controller optional)
mount booster at TT, set output to 14.4v for charge {same as solar controller}

less conversion steps, less parts

time2roll wrote:
If I need that much power I am pulling 120vac back to the trailer.
I am certainly not feeding an expensive MPPT controller with some makeshift 24v supply system.
If you have a good MPPT you already have plenty of solar to charge while driving.
JMHO, good luck.

"Genuine" Solar panels don't work under clouds (or late in the evening, or early in the morning). This "Fake Solar" system is now in use by multiple Trailer owners, and we all use the "fake" whenever we're towing. It's more dependable than the "real" Solar system as weather conditions and sun angle change through the day, and it's totally reliable. Your characterization "makeshift" seems unfair: This is well-designed, and utterly incapable of damaging an MPPT Controller *or* the Tow Vehicle.

DanNJanice wrote:

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.

Re-read carefully - I use a $30 "Voltage Doubler" Boost Converter inside the TV, under the control of a dashboard switch. Switch Off = Towing a "normal" Trailer, or not Towing at all. Switch On = only when towing a Trailer with the Mod, capable of recognizing and handling high input Voltages via a Solar Controller. With the Boost Converter in the TV, the input to the MPPT COntroller is typically 26-29V.

red31 wrote:
https://www.redarc.com.au/products/product/in-vehicle-battery-charger-40a/

Great product. Devastating price.

smkettner wrote:
If I need that much power I am pulling 120vac back to the trailer.

that was my solution... bought a 12/3 outdoor cord and a bunch of that plastic wire loom tubing. ran it inside the box section of my trailer frame with the extra coiled up at the front.

boondock or wallydock in quiet, time to hit the road, plug into a bed mounted generator and charge up while I'm driving. might be hard to do with a FW covering the bed, but it works good with my bumper pull :)

If I need that much power I am pulling 120vac back to the trailer.
I am certainly not feeding an expensive MPPT controller with some makeshift 24v supply system.
If you have a good MPPT you already have plenty of solar to charge while driving.
JMHO, good luck.

Bob B wrote:
How much current will the 24V boost device provide?

The one I used is limited to 12A (24V), while drawing around 25A on the "12V" side. More expensive models can go a lot higher. I've only got 2*90Ah batteries, and my MPPT is limited 20A output - so this "little one" is a nearly perfect fit.

How much current will the 24V boost device provide?