Trailer power, DC inverter vs. generator


The only way you can get in trouble is if you buy a cheap DC inverter. Which, of course, I did. Harbor Freight routinely blows out big (>=2.5Kw) DC inverters pretty darn cheap. Don’t waste your time with anything smaller.

The problem with cheap DC invertors is that the AC power out is a crappy sinewave. Instead of some nice AC voltage curve, they’ll put out some kind of square wave looking thing. Any kind of “smart” electronics is going to hate that crappy sinewave.

A solution is to have nothing in your trailer that requires a nice sinewave. When you’re buying electrical things for your trailer, ask yourself “is this a dumb device?” I got in trouble with electric blankets. I had some awfully cold nights as I serially went thru electric blankets that seemed to only “intermittently” work. It took a while to figure out that while they liked paddock power just fine, they didn’t like DC inverter power. So I bought a 12V DC electric blanket, stuck it in a trailer cubbard and the next time it’s freezing cold and I have no paddock power, that 12V electric blanket is gonna be pulled into service.

Choosing the battery. Car batteries are not ideal for this because they are not designed for deep discharge. Get Marine batteries. Yes, they are more expensive. Sams Club has pretty good deals. Get two big-ass 12V batteries. All you care about is the Amp Hours that the battery can provide. Don’t pay any attention to the Cold Cranking Amps, or any other silliness.

Understanding Amp Hours. It’s how much current the battery can provide current, while maintaining a reasonably high voltage. 100AH is the ability to provide 100A for an hour, or 20A for 5hr.

Consider 2 big-ass 12V deep cycle batteries wired in parallel, instead of a single battery.

Isolating the battery. Go to Amazon and search for “200Amp circuit breaker switch”. This will allow you to fuse the big wire(s) going from the trailer batts to the inverter, and also give you an easy means to isolate the batt(s). I found that if I left the batteries connected to other stuff while the trailer was parked for a month, the batteries were always pretty discharged when I picked up the trailer. This got fixed when I put in a switch that isolated the batts from everything. It was probably the inverter pulling current even when it was off, but that’s only a guess.

Charging your battery. Get a dumb charger, not a smart one. The problem with smart chargers is that they need to be turned on. Often you have to hit more buttons in order to select a mode. What you want is some dumb-ass thing that will charge your batteries whenever you connect your trailer to paddock power.

Charging your battery with your truck. As long as you don’t do something dumb that blows the fuse in your truck in the Trailer Aux Power circuit, you can connect your trailer cable aux power to your trailer battery. This means that whenever your truck is connected to the trailer, it’s charging the batteries.
Ways to screw this up. Your truck Aux power prob has a 30A fuse, so you don’t want to pull huge current on this circuit. Connecting trailer cable to truck when your trailer batteries are flat could blow that fuse. As would shorting the battery wire in your trailer while you’re connected to your truck.

Be respectful of 12V power. 12V isn’t much. Doesn’t take hardly any insulation to stop it. That’s why you can handle it safely. However, big batteries are capable of huge current, so if you fuck up just right, it could be memorable. I almost lost a finger, some years ago, when 12V on the race car found a way to ground itself thru my wedding ring.

Wiring in the Inverter. The key is big-ass wires to the trailer battery(s). In order for your inverter to provide 1000W to your coffee pot, it has to pull about 100A from your battery. You ain’t gonna do that with some little sissy wire or ground connection that consists of a single screw into the frame of your trailer. What will happen is that that the voltage to the DC inverter will drop, causing the Inverter to brown out, and your wires and ground connection will get hot.

Go find yourself some big-ass wire, like welding wire or something. And then double that stuff up. Double wires to the Inverter, and double wires/double connections to the trailer’s frame.

There’s another thread here that talks about choosing among the different kinds of generator. Keep in mind that if you want generator power at night, the generator is going to have to be reasonably quiet or you’ll be the paddock pariah.