The DC-DC charger is a much more efficient and effective means of charging an auxiliary battery. With the old vehicle charging systems, connecting an auxiliary battery directly to the alternator with big wires to minimize voltage loss worked fairly well. It allowed the aux battery to play a more direct role in the voltage sensed by the regulator, and the alternator would keep it at a more fully charged state. There was always SOME voltage drop though, so it wasn’t perfect.
On today’s vehicles, I wouldn’t even attempt to make a direct connection to the alternator. I’m pretty sure you’d end up creating problems with the ECM. I’m not familiar with dual alternator setups, but I’m going to guess that unless the ECM allows that second alternator to operate independently, which I don’t think they do, you’re still not going to get as good charging performance as a DC-DC charger.
The Redarc I’m using is connected directly to the truck’s starting batteries, and is (as far as the alternator and ECM are concerned) just another electrical load on the system. No different than using the OEM 120v inverter that comes in many vehicles today.
The way mine is installed, it’s using a charging profile suitable for my AGM battery in the camper. Once the charger turns on, it will remain on for a fairly wide range of voltage from the truck, with upper and lower limits of course. I’m assuming other brands will work the same way.
The charger only turns on when the proper voltage is present on the ignition controlled circuit from the truck. When the engine isn’t running, the DC-DC charger is off. When the voltage from the truck goes down, the charger compensates by drawing more amps, when the voltage from the truck goes up, it draws fewer amps. It ALWAYS supplies the proper voltage to the battery it’s charging for whatever state of charging it’s in.
The charger can supply up to 40 amps of charging current, and the input circuit is fused at 60 amps. It also isolates the camper battery from the truck, and does not back-feed voltage from the camper battery onto the umbilical cord.
:):)
