I'm starting to make my wiring diagram and have a question. I will be putting in a power converter that has a battery charger. When I come from the pig tail connection from the car, do I connect the white and black wires into the converter first and then take them to the battery, or connect them into the battery first with a tie off to the converter. I started thinking (sometimes a problem) that doing it the second way might not charge up the battery correctly. The converter I'm getting is Progressive PD4000. I'm reading the wireing instructions and they just say battery pos and neg locations.
Consider this: as you no doubt know, the on-board trailer battery is there only to provide power to your internal 12V trailer power demands—cabin lighting
, water pump, frig, etc., as needed. NOT the outside running and tail lights
. This power is provided by the tow vehicle.
If there was NO converter in the chain, the pigtail harness pos and neg wires dedicated to the trailer battery are directly connected. The tow "reads" the trailer battery as just another demand source. When driving, the alternator provides the juice to keep it peaked, just like the tow vehicle battery. So the short answer is Yes, a direct connection to the battery is okay, even if you have a converter.
However, it is my understanding that (given the right gauge wire is used, and all is properly connected) running your tow vehicle power supply and return wires to your converter first, then back to your trailer battery works exactly the same without any loss. The advantage with this route comes when considering the battery charger component of your converter. As you know, the converter converts 120V AC into 12V DC only when "hooked up" to shore power. (Presumably, this happens only when parked!) The "charger" sends power to your trailer battery as needed—using the same converter-to-battery wire connection described above. No need for a second set or redundant wires.
The one hiccup I ran into (and has been discussed here on the forum) is keeping the trailer "isolated" from the tow when parked, but still connected via the harness. With the engine shut down, and under certain circumstances, the tow could drain the trailer battery and/or vice versa. In my case, a solenoid-like gizmo (Help me out here, folks!) was installed in my tow between the ignition and the battery, isolating the trailer from the tow unless the ignition is on.
Hope this helps.