RV Electrical 101

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RV Electrical 101

Understanding RV electrical systems can be confusing, and it was for us when we got started. So, we thought it might be helpful to share what we’ve learned in an effort to help others understand how the electrical system in their RV works, too.

Before diving into all of the ins and outs of how the system works, let’s start with some basic information about electrical systems in general.

Measuring Electricity

Most of what you need to know about an RV electrical system comes down to measuring various aspects of electricity. To do this, we have to talk about a few things.

The first measure is voltage and is measured in, you guess it, volts. It’s written as an uppercase V.

It can be useful to think of electricity like water flowing down a river.

Voltage can be thought of as the amount of water flowing. A small stream has a small volume of water flowing, like a low voltage system. Meanwhile, a huge, deep river has much more water capacity and is like a high voltage system.

Different electrical systems have different voltages. For instance, your cell phone charges at 5V. Your RV battery system runs at 12V. Home electrical systems run at 120V in North America and 230V in Europe. Meanwhile, high tension power lines can run at over 300,000V.

Note that higher voltage systems are more dangerous to humans and animals. A shock from a 12V system will hurt, but a sustained shock from a 120V system has the potential to kill you!

The second measure is current: Current measures the flow speed of electricity and is measured in amperes or just amps for short, written as an uppercase A.

You can think about it again like water flowing. Water flows down a gentle hill slowly. This is similar to a low amperage flow, like powering a small light. The same amount of water flowing over a mountain cliff moves much faster, like the electricity needed to power an electric motor.

Current is really important because faster flowing electricity generates heat. Sometimes a lot of heat! More current requires thicker wires, and if your wires aren’t thick enough or don’t have good connections, they can get hot enough to melt or even catch fire!

That brings us to the third and most important measure, which is literally just power. Power is determined by multiplying voltage times current and is expressed as Watts. This is written as an uppercase W.

If you think about the water analogy, this is like multiplying the flow speed by the volume of water. You can imagine how a wide, slow flowing river has more energy than a small, fast-flowing stream. Similarly, a high-voltage system with low current can have more power than a low-voltage system with high current.

Electric appliances measure power usage in watts. For instance, an old style incandescent light bulb might’ve been rated at 100W. Meanwhile, new LED light bulbs with the same brightness only use about 10W. An RV air conditioner rated at 10,000btu will use about 700W, whereas a small fan might only use 20-30W.

These power ratings become important when we look at battery systems a bit later on.

AC/DC: “shore power” and “12 volt”

RVs have two separate power systems, the DC, or Direct Current system, and the AC or Alternating Current system.

The DC system runs at 12 volts, and is commonly referred to as the “12 volt system”. The system is always on and running in your RV, as long as your battery is connected and charged.

Some 12V appliances that run on this system include: lights, electric tongue jacks, fans, and RV propane furnaces. RV fridges also require 12V power when running on propane.

The AC, or Alternating Current system runs at 120 volts, and is commonly referred to as “shore power”. This comes from the boating world when a boat is docked and plugged in. The AC or 120V system is only available if you are either plugged in to grid power, running a generator, or running an inverter. We’ll discuss these more in the next section.

Some 120V appliances include: air conditioners, microwaves, and most televisions. Most RV fridges can also switch over to run on 120V power.

Generating and converting power

Plugging in at a campsite powers your RV’s AC or “shore power” system, and lets you run 120V appliances. Different sites offer different levels of service including 15A, 30A and 50A service.

15A service is like one normal household plug. It won’t run most RV air conditioners, and you can only use one major appliance at the same time. For instance, if you try to run the microwave and an electric kettle simultaneously, you might trip a circuit breaker.

30A service can usually run your air conditioning and several other appliances at the same time.

50A service is for larger rigs and can often run two air conditioners plus many appliances all together.

If you are not close to an electrical grid, you can use a gas or propane generator to produce AC power in remote locations. They are rated by the maximum wattage they can produce.

How large of a generator do you need? You can determine this by adding up the wattage ratings of all appliances that you need to use at the same time. Note also that some appliances, like air conditioners and microwaves, have a “peak” or “starting” wattage that is higher than their “running” wattage, so pay close attention to those numbers as well.

And remember from earlier that to determine wattage, you simply multiply voltage by amperage, so to have the equivalent of 120V 30A “shore power”, you’ll need a generator rated at 3600W or higher. An 1800W generator, meanwhile, will provide similar service to a 15A shore power connection.

The 120V system, when active, is used to power and recharge your 12V system. RVs have something called a converter that, true to its name, converts 120V electricity to 12V. These are coupled with a charge controller that controls how much power to send to your battery to recharge it and keep it topped up.

Solar power

What happens if you’re boondocking, or at a campsite without electric hookups? And let’s say you don’t want to run a noisy, smelly generator. Enter clean, quiet solar power.

Solar systems generate DC power and can directly power your 12V system, so you can run all your 12V appliances and charge your batteries. But what if you want to be able to use 120V appliances?

In that case, you need an inverter. This does the opposite of your RV’s converter, and transforms DC power to AC power, stepping up 12V to 120V.

This would be helpful to run something like a microwave or slow cooker, for instance. To run high wattage appliances like this, you need to make sure that your inverter has a high enough rating.

You also need to make sure that your wires are thick enough to handle the current. If your wires are too thin, they could get too hot, melt, or even catch fire!.

Finally, you need to ensure that your battery bank has sufficient discharge capacity. Some types of batteries can be damaged if they are discharged too quickly.

Storing power in batteries

Of course, solar power can only be generated when it’s sunny, so if you want any electricity when it’s cloudy or at night, you need to store that energy somewhere.

Before we talk about batteries, we need to introduce two new units of measure.

First, the watt-hour, represented as capital W, lowercase h. This is simply the amount of power required to run a 1W device for one hour. Second, we have the amp-hour, a related measurement often used to measure the capacity of automotive, RV, and marine batteries.

Watt-hours are a more useful measurement, since they translate well across different electrical systems. When calculating battery system requirements, I recommend making all calculations in watt-hours. You can convert amp-hours to watt-hours by multiplying by the voltage of the battery. So a 12V battery rated at 100AH gives you 1200WH of capacity.

There are more considerations when you get into the type of battery, but that will have to wait for a future post!

Calculating battery capacity is a bit more complicated than figuring out generator sizes. You need to know 1. How much power your appliances use, and 2. How many hours per day you expect to use them. You then make a list and add them all up. A simple example would be:

  1. RV lights: 50W for 1-2 hours = 50-100WH
  2. RV furnace fan: 150W for 2-3 hours = 300-450WH
  3. RV vent fans: 100W for 1 hour = 100WH
  4. CO detector, fridge, and other small devices that run all day: 10W for 24 hours = 240WH
  5. Laptop computer: 50W for 4-6 hours = 200-300WH

Adding them all up gives a total of about 900-1200WH, which (dividing by 12) means you’d need 75-100AH of usable 12V battery capacity for one full day of energy storage.

And keep in mind that different types of batteries have different percentages of usable capacity. Lead acid batteries, for instance, provide only about 50% of their rated capacity before their voltage drops and you can start damaging them.

People often ask about running air conditioners off solar and batteries. This is possible, but it requires a lot of solar, and a lot of batteries. Even a small RV air conditioner uses 700-1000W, meaning that you’d need upwards of 3000WH stored just to run it for a few hours a day!

I hope this post helped expand your understanding of RV electrical systems. If you still have questions, please be sure to leave them in the video comments or get in touch through our email address, contact@homearoam.com . I’ll answer them there, or even create some follow-up videos and posts to go more in-depth on some of these topics.

Until next time, keep on living the life you’ve imagined!

Mel, Jay & Benny

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