Understanding Watts, Amps, Volts & Ohms: A Simple Guide

Angela Devaney

If you’re gearing up for an adventure on the open road, there’s a good chance you’ve thought about your campervan’s electrical system. Whether you’re planning to install new gadgets, set up solar panels, or simply keep the lights on, understanding the basics of electricity can make a world of difference. Don’t worry—you don’t need an engineering degree to get to grips with this stuff.

In this guide, we’ll break down watts, amps, volts, and ohms in plain English, and show you how this knowledge can help you design, install, and troubleshoot your campervan’s electrics with confidence.

Electricity in Everyday Terms

Before we dive into the specifics, let’s start with a simple question.

What Is Electricity?

Electricity is the flow of tiny particles called electrons through a conductor, like a wire. Think of it like water flowing through a hose. This flow powers everything from your campervan’s fridge to your favourite reading lamp.

Why Should You Care?

Understanding how electricity works isn’t just for electricians. It empowers you to make smart decisions about your campervan’s electrical setup, ensuring safety, efficiency, and reliability on the road.

What Are Volts? The Push Behind the Flow

Volts (V) measure the electrical “pressure” that pushes electrons through a conductor. Imagine water pressure in a hose—the higher the pressure, the more forcefully water comes out. Similarly, higher voltage means a stronger push for the electrons.

Volts in Your Campervan

Most campervans operate on a 12-volt system, which is standard for vehicles. Keeping everything at the correct voltage is crucial to prevent damaging your appliances and to ensure they run efficiently. Inverters convert your 12V system to 230V to power household appliances.

📌 Quick Tip

Always double-check the voltage requirements of any new appliance before connecting it to your campervan’s electrical system. Mismatched voltages can damage your equipment!

Practical Examples of Volts in Your Campervan:

  • Battery Voltage: Your campervan’s electrical system is usually either 12V, 24V, or 48V. This number represents the voltage. For example, a 12V system means your battery delivers 12 volts of electrical pressure to power your devices. The higher the voltage (like in a 24V system), the more efficient your system can be, but it requires compatible components.
  • Appliance Voltage: Many campervan appliances like lights, fans, and fridges are designed to run on 12V. However, if you’re using household appliances with an inverter, those typically require 230V (in the UK), which your inverter converts from your lower voltage system.
  • Matching Components: It’s important to match voltages when connecting appliances to your system. For example, a 12V fridge needs a 12V system, while a 24V fridge requires a 24V system. If the voltages don’t match, the appliance won’t run properly or could be damaged.

What Are Amps? The Rate of Flow

Amperes, or amps (A), measure the amount of electric current flowing through a conductor. In our water analogy, amps are like the volume of water flowing through the hose per second.

Why Amps Matter

Different devices draw different amounts of current. A small LED light uses fewer amps than a toaster. Knowing how many amps your devices use helps you:

  • Choose the right wire size (thicker wires for higher amps).
  • Select appropriate fuses to protect circuits.
  • Prevent overheating and potential electrical hazards.

⚠️ Safety First

Using the correct wire size is crucial. Undersized wires can overheat, leading to potential electrical fires. When in doubt, opt for a thicker wire to ensure safety.

Practical Examples of Amps in Your Campervan:

  • Current Draw: Amps tell you how much electricity is flowing through a wire. For example, if your fridge draws 5 amps from a 12V system, you can use that information to figure out how much energy it’s using (more on that below). The higher the amp rating of a device, the more current it needs to operate.
  • Fuse Ratings: Each appliance and wire in your campervan should have a fuse rated in amps to protect it. For instance, if your fridge draws 5 amps, you might have a 10-amp fuse in the circuit. If the current exceeds that, the fuse blows to prevent damage to your wire.
  • Wire Sizing: When you know how many amps an appliance draws, you can choose the correct wire size to handle that current safely. For example, a heater drawing 50 amps at 12V needs a much thicker wire than an LED light drawing only 1 amp.

What Are Watts? The Power Used

Watts (W) measure the rate of energy consumption or how much power a device uses. It’s calculated by multiplying volts by amps:

Watts = Volts × Amps

Understanding Watts in Daily Van Life

When you see a device rated in watts, it tells you how much energy it consumes when running. This information is vital when planning your power needs and ensuring your batteries can handle your usage. For instance, a 1,000-watt kettle will need more energy to run than a 5-watt phone charger.

💡 Handy Formula

To calculate how much power (watts) a device uses, simply multiply the voltage (volts) by the current (amps) or use the calculator below.

Watts Law Calculator

Enter any two values to calculate the third:


Practical Examples of Watts in Your Campervan

  • Appliance Labels: When you look at the label on your devices like a kettle or induction cooktop, you’ll see its power rating in watts. For example, if your kettle uses 1,000 watts, that means it requires 1,000 watts of power to run. This helps you understand how much power the appliance will draw from your electrical system.
  • Solar Panels: The power output of solar panels is also measured in watts. If you have a 200-watt solar panel, it can produce up to 200 watts of power under ideal conditions. This helps you figure out how much energy you can generate on a sunny day.
  • Battery Inverters: If you have an inverter in your van, its power capacity will be rated in watts. For example, a 2,000-watt inverter can power devices that use a total of 2,000 watts at once. So, if you want to run a 1,500-watt microwave and a 500-watt blender simultaneously, you’ll need at least a 2,000-watt inverter.

What Are Ohms? The Resistance to Flow

Ohms (Ω) measure electrical resistance—the opposition to the flow of current in a circuit. Think of resistance as a kink in the hose that slows down the water flow.

Resistance in Your Campervan (Mainly for Troubleshooting)

In practice, we’re rarely concerned with ohms unless something isn’t working as expected. In troubleshooting, continuity (checking if a circuit is complete) becomes critical. Using a multimeter, you can test if there’s a break in the circuit—like a broken wire or corroded connection—by checking the resistance.

Low ohms indicate continuity, while an infinite reading, often shown as -1 on a multimeter, shows there’s no connection or connectivity. 

A high reading might mean there’s a problem. “Might” because if the circuit passes through a motor, it may also have a high reading, but still has connectivity. Your water pump is a good example of this kind of circuit.

This is where measuring resistance can be a good thing, so long as you understand the components between the 2 points you are measuring.

It can help you quickly find issues like faulty connections, damaged wires or an earth fault.

🛠️ Troubleshooting Tip

If an electrical device isn’t working, check for continuity using a multimeter. A break in the circuit or a blown fuse might be the culprit.

Practical Examples of Ohms in Your Campervan:

  • Checking Continuity: If your water pump isn’t working, testing the wire for continuity (checking for a low ohms reading ) can help determine if there’s a break in the circuit.
  • Corroded Connections: A high ohms reading might indicate a corroded connection, preventing proper power delivery. Cleaning or replacing the connection can solve the issue.
  • Fuses: Testing a fuse with a multimeter in ohms mode helps you confirm if it has blown (infinite resistance) or is still intact ( low ohms).

Ohm’s Law: The Link Between Voltage, Current, and Resistance

You might hear us mention the power formula (Watts = Volts × Amps) quite a bit—that’s because it’s super useful and often the only electrical calculation you’ll need when working on your campervan. But there’s another fundamental formula that’s the backbone of electrical understanding: Ohm’s Law, which states:

Voltage = Current × Resistance
V = I × R

So, how does this relate to everything we’ve discussed?

Ohm’s Law shows how voltage (V), current (I), and resistance (R) are interconnected:

  • Voltage (V) is the electrical “pressure” pushing the current through the wires.
  • Current (I) is the flow of electric charge, measured in amps.
  • Resistance (R) is what resists the flow of current, measured in ohms.

While you might not need to use Ohm’s Law for everyday tasks, it’s helpful to understand that this relationship is the foundation of all electrical circuits. It explains why increasing the resistance in a circuit (like using thinner wires or encountering corroded connections) can reduce the current flow for a given voltage.

So, while the power formula (Watts = Volts × Amps) is your go-to for most calculations—like figuring out how much power a device uses or sizing your inverter—remember that Ohm’s Law is the underlying principle that ties voltage, current, and resistance together. It’s the reason why all these electrical concepts are connected, and having a basic grasp of it gives you a more complete picture of how your campervan’s electrics work.

FAQs

Absolutely! A multimeter is an essential tool for anyone working with a campervan’s electrical system. It allows you to measure voltage, current, and resistance—all crucial for diagnosing issues and ensuring everything runs smoothly. With a multimeter, you can:

  • Check Battery Voltage: Ensure your batteries are charged and functioning properly.
  • Test Continuity: Find breaks in circuits or faulty connections.
  • Measure Current Draw: See how much power your appliances are using.

Even if you’re not an electrician, learning to use a multimeter can save you time, money, and prevent potential electrical problems on the road.

Great question! The use of ‘I’ to represent electric current comes from the French phrase “intensité de courant,” which means “current intensity.” Early scientists and engineers used this notation, and it became standard in electrical equations like Ohm’s Law (V = I × R). So while it might seem a bit odd, it’s a nod to the historical roots of electrical science.

Higher-powered appliances draw more current (amps), and when more current flows through a wire, it generates more heat due to electrical resistance. Thicker wires have lower resistance and can safely carry more current without overheating. Here’s why it matters:

  • Safety: Prevents wires from overheating, which can be a fire hazard.
  • Efficiency: Reduces energy loss in the form of heat.
  • Performance: Ensures your appliances receive the proper voltage to function correctly.

Using the correct wire size for your appliances keeps your electrical system safe and efficient.

If your fuse keeps blowing, it’s a sign that too much current is flowing through the circuit. Possible reasons include:

  • Overloaded Circuit: Too many devices drawing more current than the fuse is rated for.
  • Short Circuit: A fault in the wiring causing current to bypass the intended path.
  • Faulty Appliance: An appliance may be malfunctioning and drawing excessive current.

What to Do:

  • Check the Total Load: Add up the amps of all devices on the circuit to ensure they don’t exceed the fuse rating.
  • Inspect Wiring: Look for damaged insulation or loose connections.
  • Test Appliances: Disconnect devices one at a time to identify if one is causing the issue.

Always replace a blown fuse with one of the same rating, and if the problem persists, consider consulting a professional.

Voltage drop happens when the voltage at the end of a wire run is lower than at the source, often due to resistance in the wires. This can cause appliances to underperform or not work at all.

Ways to Prevent Voltage Drop:

  • Use Thicker Wires: Thicker wires have less resistance and help maintain voltage levels, especially important for long runs.
  • Shorten Cable Lengths: Keep high-draw appliances like inverters or fridges close to the battery.
  • Ensure Quality Connections: Tight, clean connections reduce additional resistance.
  • Upgrade System Voltage: If practical, moving to a higher voltage system (e.g., from 12V to 24V) can reduce current for the same power, minimizing voltage drop.

By addressing these factors, you’ll keep your electrical system running efficiently and your appliances performing at their best.

Conclusion

Understanding amps, volts, watts, and ohms might seem daunting at first, but with a bit of patience, it becomes much more approachable. Armed with this knowledge, you’re well on your way to creating a safe and efficient electrical system for your campervan. Whether you’re brewing a cuppa or charging your laptop, you’ll have the peace of mind that comes from knowing your electrics are up to the task.

Your campervan is more than just a vehicle—it’s your home on wheels. Taking the time to understand its electrical heart will pay off in countless ways. You’ll travel with confidence, handle minor hiccups with ease, and fully enjoy the freedom of the open road. 

So here’s to bright lights, warm meals, and the knowledge that you’ve got everything under control. Safe travels!

Angela Devaney - Expert in RV & Campervan Electrics - Mowgli Adventures

Angela Devaney

Angela Devaney, a former IT project management professional, embarked on an adventurous journey of full-time travel, which included touring West Africa in a converted overland truck and converting an ex-military 4x4 Sprinter van into a camper for a five-year South American expedition. She now utilizes her hands-on experience to create practical van life advice as a full-time digital media producer, reaching over a million users annually through her YouTube channel, blog, and newsletter. Angela also lends her expertise as the editor-in-chief of the Campervan Electrics Handbook.

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