By Wolfe Rose
There is a lot of confusion for new RVers as to whether they need a converter, inverter or generator. What’s the purpose of each, and if one is needed, what type or size? How do inverters vary from the converters built into RVs, or are they the same thing? To answer all of that, we first have to understand that trailers have two complete power systems, and why.
Starting at your shore cord, you take in 120V Alternating Current (AC), similar to your 15A wall power at home. This is the 30A or 50A designation you may hear referenced. You can pull much more power through that cord than the outlets you’re used to at home, but it’s the same “type” of power – 120V provided as a sine wave. This type of power runs your RV’s outlets, air conditioner and microwave. These are normally allowed to go dead whenever you’re unplugged from shore power. When your water heater or refrigerator are in AC mode, those too may be powered by this – but remember each of those can also usually run just fine off propane as well.
The second power system your trailer contains are your batteries, which provide 12V DC – the same type of power as in your car, which has polarity (+ and – terminals). This power runs your lights, fans, furnace blower and the control electronics for your refrigerator and hot water even when they are primarily powered from propane. These are all run from your batteries because “camping” trailers were originally assumed to need to be independent from shore power, even if that capability is only used by some RVers while in transit these days. Those who still camp away from power use this power independence to “dry camp” at sites without electricity, or “boondock” without a designated campsite. The problem is that your battery quickly runs down since it’s not being replenished – especially with high-drain loads like your furnace blower. This is why boondockers often install solar or wind power to recharge their batteries.
Recharging the battery (and preventing it from running down in the first place) is the job of the converter, which can be thought of as a beefy AC-to-DC battery charger. Some folks replace or augment their converters with “smart” multi-stage automotive chargers. A 40A converter designation means the converter can compensate for up to 40A of DC draw, running your lights and furnace without pulling power from the battery. Think of this function as a “wall adapter” for your battery-powered trailer. In addition to carrying the load for your batteries, the converter also recharges your battery from prior drains. The converter is an important bridge between the AC and DC power systems, in order to maintain the DC battery charge.
That said, our boondocker in the woods still can’t use his microwave or air conditioning, because they exclusively gulp down AC, not the relatively meager DC that’s available. In the next installment, I’ll discuss how to create AC power without a shore connection.