Wildhorse,
I understand your question and as for the "demand on the truck wiring" there is a fused circuit that protects the wiring in the truck. You can't "melt the wires" (if things are working properly) since the fuse (on Fords, it's under the hood) will open if you draw more than the wiring is designed to carry.
As for the trailer, if you have batteries connected to your DC electrical system, they serve as a "buffer" against excessive current draws during slide or leveling system operation. Without the battery, if you're on shore power or using a generator, you can place an instant (startup) load on the converter and damage it. Usually the damage is from repetitive use, not from a "oops, one time kind of use"... So, the batteries are in the system to protect the converter when it is powered by shore/generator power. When you're not on shore power and have the umbilical connected, you can't damage the wiring because the truck underhood fuse protects it from excess current draw. If, however, you did not have batteries in the trailer and plugged in the umbilical, you'd probably blow that underhood fuse from overloading the umbilical wiring with the slide motor current draw. So the batteries protect that circuit from overload as well.
What I addressed is the statement that when connected to the tow vehicle the "converter" controls XXX" As I interpret the schematics I've seen and as I understand the system, the converter is not a part of the DC charging system or the DC power distribution system when connected to the tow vehicle. The ONLY time the converter influences DC power is when it is "making DC from shore power or the generator".... In other words, when the truck is charging the trailer battery through the umbilical, the converter might as well be a brick. It's not connected to anything or even powered on.
So, in response to your last post. If you have batteries connected in your trailer, you can operate the slides/leveling system from them. If you want to "adequately recharge the batteries" you can do that with the converter by using shore power or a generator (larger wires will carry more current to recharge what was used)
If you attempt to recharge the batteries using the trailer umbilical, about the most you can get is 5 amps of DC power through the "fuse protected" wiring, so it will take significantly longer to recharge what was used during slide and leveling system operation. So from an efficiency perspective, it is not very efficient to rely on the truck to recharge the batteries. Even when towing it takes many hours to "top off a half charged battery".... You'd be better off using the generator/converter, it will recharge your batteries much faster and more efficiently. Towing all day will barely make a dent in a two 6 volt battery setup that is at 50% charge.....
I leave my truck plugged in during slide operation, not because it will "replace all the DC I use, but because it will help power the slides, preserving my battery charge (a little) so I can dry camp longer before I need to recharge the batteries....
Sort of: If I have 100 amps in my batteries and I use 20 amps deploying the slides, if I can get 5 amps from the umbilical, I'll have 5 amps more than if the truck was disconnected.... If I was on shore power, that wouldn't be necessary since I could recharge the batteries in about 30 minutes of converter operation....
Maybe you're more confused now than before, I hope not
