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.)
