The Converter transforms AC Voltage to DC Voltage or 110V to 12V in an RV. An Inverter transforms DC Voltage to AC Voltage or 12V to 110V in an RV. Both transform voltage, but in opposite directions.
Converter versus Inverter: The Ultimate Transformer Battle
Okay, full disclosure, neither a converter nor an inverter will transform into a car, or a plane, or a robot. Nope, we are talking electrical transformers and more specifically about the difference between converters and inverters. The names are so similar that the question becomes, “how will I keep them straight?” Over the years I have had many conversations with customers about their inverter that turned out to be conversations about their converter and vice versa; they had the right information but they had turned the names around. An easy way I have found to remember which is which is in the components name itself. A CONverter decreases voltage, or takes the voltage in a negative direction. When thinking about the pros and cons of an issue cons are the negative aspects. It’s a bit of a stretch but a con is negative and a converter transformers voltage in a negative direction. Less of a stretch is an INverter which INcreases voltage.
RV Electrical Systems: DC and AC, Why Do I Need Both?
The simple answer is you don’t. The DC (12V) system runs the vast majority of the electrical components in your RV from the lights, interior and exterior, to the water pump, to the circuit boards on the gas appliances. Your RV is designed and equipped to be used with no AC Voltage for at minimum several days before you deplete your DC Voltage; which is referred to as boondocking or dry camping. The exceptions are an RV’s air conditioner and TV, which run on AC Voltage. As RVs evolve more and more they become a second home on wheels. After all; if I can’t microwave a burrito and watch the game I might as well be tent camping. Am I right? Of course I am! Excuse me, I get a little carried away but I take my comforts seriously.
Converters, Inverters, and Batteries: An RV Love Triangle
Whether we are converting or inverting the trail leads back to the batteries. A large part of the converters job is to take the incoming AC Voltage (110V), transform it to DC Voltage (12V), and then use the DC Voltage to charge the RV’s house batteries. The second portion of a converter’s job is to distribute the DC Voltage (12V), on separate fused legs, to the required components. This DC Voltage (12V) is sourced either from incoming AC Voltage (110V) that is transformed by the converter into DC Voltage (12V) or from the DC Voltage (12V) stored in the house batteries. The third part of the converter’s job is to distribute the incoming AC Voltage (110V), through a breaker panel, to the AC Voltage appliances.
An inverter uses the existing DC Voltage (12V), transforms it into AC Voltage (110V), and then distributes that AC Voltage to either a single dedicated outlet or through a breaker panel to multiple outlets used by 110V appliances. Unless your RV is plugged into AC Voltage (110V) the power available to your RV is DC Voltage (12V). The inverter will allow you to run the AC Voltage appliances but only as long as the DC Voltage lasts. See, now we are back to the batteries.
An RV/Marine deep cycle battery is designed to charge and discharge at a slower rate than a start battery, and a deep cycle battery will recover from being fully discharged where as a start battery often will not. This slower charge and discharge rate means that consumption of the DC Voltage is also at a slower rate, with a Group 24 12Volt deep cycle battery generally lasting two to three days. As you add additional batteries you add available DC Voltage, thereby extending the ability to boondock.
Deep cycles come in multiple levels of quality and in both 12volt and 6volt. Wait, 6volt? You’ve been talking about DC Voltage as 12volt this whole time! Relax, two 6volt batteries wired in series will produce 12volts, and are equivalent in amp hour storage to roughly three 12volt deep cycle batteries.
This is why many RV owners choose to go with 6volt or “golf cart” batteries if they use an inverter. Like their 12volt cousins, 6volt batteries come in the traditional wet cell variety as well as sealed options in the AGM (Absorbent Glass Mat) construction or a gel cell battery. An AGM 6volt battery is the best companion to an inverter due to its life span and the maintenance-free design.
Behind Every Inverter Is A Good Battery
Think of a battery as a box of peanuts. When we demand power from the 12volt system we eat those peanuts with our best cocktail party manners, one at a time with our pinky sticking out. When we demand 110volt power from the same battery, or box of peanuts, it is as if our teenage son has invited three of his friends over and they are eating the peanuts by the handful. Whom do you think will consume the peanuts first? In simple terms the more power you demand, the more peanuts…er, power you need to supply. No matter if the demand is 12volt or 110volt. 110volt will consume the power more quickly but the rule of thumb is as your power requirements increase, so do the requirements of your battery bank.
A typical bank of batteries on RVs equipped with the larger inverter/chargers is four 6volt “golf cart” batteries. Assuming that these are the wet cell construction batteries (AGM), this bank gives you roughly 440amp hours of 12volt power. As I mentioned earlier, a 6volt AGM is maintenance- free which helps to extend its life span. They also provide a small increase in amp hours. Taking our example of four 6volt batteries, AGM’s would supply 500amp hours of 120volt power. Experts tell us we should not discharge a battery more than 50% or there is the potential to shorten the lifespan of the battery, so in actuality a 440amp hour battery bank is really only good for 220amps hours before you will need to recharge your system. Of course, adding additional batteries to the bank will increase the available amps hours, thereby increasing run time.
Consumption – Or How Do You Eat Peanuts?
No matter how many peanuts you start with, if you don’t replenish them, eventually you eat them all. No matter the size of your battery bank, if you don’t replenish them, eventually you will drain the batteries. Even the biggest RVs have storage constraints making the amount of batteries you can carry limited. So until lithium batteries become affordable for the masses, you will have to maximize the performance of the current offerings. A battery bank is better used to power smaller loads for longer periods of time rather than large loads for brief durations. In fact, heavy loads like water heaters and air conditioners are not connected to an inverter because they would quickly deplete your battery bank; sometimes in minutes depending upon the load and available amp hours.
While there are ways to charge your batteries, or replenish your DC Voltage, using DC Voltage from solar panels or the alternator of the motorhome or tow vehicle, the most common method for recharge is plugging the RV into AC Voltage. This can be an outlet at home, at the RV park, or either an on-board or portable generator. (Did you know that most generators produce DC Voltage and then invert it into AC Voltage?)
Power To The People
We spent more time discussing inverters in this article than we did converters and this is based on the difference in complexity. On the surface both seem pretty simple and straight forward: I turn something on and it gets power from the batteries. In reality, the process involved for either a converter or an inverter to transform and distribute power is quite complicated; but a converter needs less attention than an inverter. A converter gets it’s incoming power from a theoretically endless supply; plugged in to an outlet or generator, while an inverter has a limited supply; the onboard battery bank, that must be monitored relatively closely to prevent depletion of the source.
In conclusion, no matter how you dry camp always remember your Ins and Cons. A CONverter reduces voltage from 110volts to 12volts, while an INverter increases voltage from 12volts to 110volts, but it is your battery bank that determines how long your adventure lasts.
Article written by Quinn Larson,
Guaranty RV Super Centers