RV Electricity So Anyone Can Understand

The following is a post on RV electricity that was made by a Cool RV Stuff (FB Group) member who is also a journeyman electrician. His posts regarding RV power and electricity were so helpful and well done explaining the basics of RV electricity, we wanted to re-post it here and are doing so with Steven’s permission.

I’m back! There were lots of great questions out of my previous post about different voltages and adapters. I decided to make another post explaining a couple more things that people asked about.

The Basic Concepts

I am going to try to simplify electricity as much as possible. Think of your shore power cable for your RV/Camper as a garden hose and a bucket. Voltage is how much water pressure you have feeding the hose. Watts is how much water you need to fill up the bucket. Resistance is how big the hose is in diameter. Amps are how much water can flow through the hose. The key differences between 30 amp service and 50 amp service are the diameter of the hose is bigger and you have 2 hoses inside that 50amp cable.

Watt Electricity?

Watts! So there was confusion and were questions about, “I have a 50 amp trailer and a 30 amp plug. What can I run?” Here’s the deal.

Amps aren’t really what determines what you “can” run. The real number is how many watts do you need. To figure out what you can and can’t run you need to know how many watts the thing you want to run needs. In a 30 amp service the limit is around 3,600 watts. To figure this you take the amps (30) times the voltage (120). You get 3600 watts. For a 50 amp it’s the same calculation. 50×120=6000 watts but remember with the 50 amp service you have 2 hoses. 6000×2 is 12,000 watts.

ANY time you use an adapter to connect a 50 amp RV/camper to a 30 amp plug you knock yourself down to 3600 watts. As an example, a 13,500 BTU air conditioning unit (typical on RVs/camper) can use up to 3000 watts at startup and then once it’s fully started up it drops off to around 1300 watts. But a coffee maker can draw 1000 watts or more and that is what’s called a resistive load and will draw 1000 watts the whole time.

These numbers are not exact. Look at the electrical labels on your equipment and add up the wattage stated on the labels for anything you want to run simultaneously. Once you hit 3600 you’re done. I can’t and won’t tell you you can run your AC and a curling iron or really anything specific. Read the labels and know your limits — that’s the best advice I can give on that topic.

What About Converters?

Converters. This is really simple and just needs to be clarified. Converters convert AC (alternating current — household power/pedestal power/regular receptacles etc.) into DC power (anything that runs on batteries in your RV/camper such as lights, water pump, furnace, etc).

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The main purpose of a converter is to charge your batteries. People may argue this and I don’t really care. Think of the batteries like a water tank. The converter is the hose filling it with water at a slow pace but you wanna take a shower. You’re going to drain the tank faster than the converter can fill it. You can run some small loads on only a converter but don’t try to run slides in and out or landing gear/leveling jacks without batteries. You may overload the converter and burn it up.

So then What’s an Inverter?

Inverters. These do the opposite of Converters. They invert DC power to AC power. This is what makes it possible to run household items like TVs and coffee makers on battery power. However, going from 12 volts DC to 120 volts AC requires a LOT of amps.

Remember the hose analogy? Voltage is pressure. 120 volts is a lot more pressure than 12 volts so in order to get the same amount of watts out of the end of the hose, you need a hell of a lot bigger hose. That’s why it takes very large diameter and short cables to connect from the battery to inverters that are thousands of watts rated. 120 watts on a 120-volt system only uses 1 amp. 120 watts on a 12-volt system uses 10 amps. When you use an inverter, you’re changing the voltage but the watt requirement is the same. If you really want a good understanding of this, Google ohms law.

And Lastly, a Helpful Tip

Multimeters. I am a firm believer in always having a multimeter and testing power before I plug my trailer into any pedestal receptacle. I thought about making a video but Mike Sokol already did and here’s a link to it.

If you’re not confident using a multimeter, get a surge protector that checks power for you. Look at the lights and make sure it indicated power is correct. Always have the breaker off before you plug into shore power. Once your surge protector is plugged into the pedestal but NOT plugged into the camper turn the breaker on. If it shows power is okay, turn the breaker back off, plug in your shore power cable to the surge protector, and then turn the breaker back on.

Also, check out Stevens’s take on 30 and 50 amp outlets and adapters.

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