What Are Amps (and Amp-Hours) And Why Do They Matter?

We all use power in our homes, our RVs, our boats, and more. We get power-hungry as we live, work, and travel. Whether we’re using it out of an outlet or off of batteries, it’s important to have a general understanding of the concept of amps, or electrical current. But if you’re planning on using power off-grid or building out an electrical system, it’s critical for designing a safe system with properly sized wires.  

So let’s dive into what amps are and why they matter!

What Are Amps In Electricity?

The word “amp” (A) is short for “ampere”, one of the standard units of measurement used to define measurements of electricity. An amp is one unit of constant electrical current. “Amperage” is the strength of that current, expressed in amps (or “amperes”). If you were to think of electricity as water through a hose, amps would be the water. 

Amps Vs. Volts, Ohms, and Watts

To better understand the significance of amps, let’s have a quick look at volts, ohms, watts (close relatives of amps), and how they all work together to help us achieve our electrical needs!

Setting up the scene, we’ve established that amps are units of constant electrical current.

Volts

A volt (V) is a unit of electrical potential, so “voltage” is the potential for energy to move. This is a rather abstract concept to understand, so we can think of it like water pressure. Voltage, then, would be like water flowing through pipes. 

The word “voltage” is used to express available energy (per unit charge). “Current” (I) is the rate of flow and is measured in amps. In a water analogy, amps are the actual water flowing. Now we’re starting to see the relationship!

Ohms

Another piece of the electrical equation is “ohms”. Ohms is a measure of resistance, so ohms would be like the water pipe’s size in our analogy. 

Using our water-flow analogy, then, we can think of ohms (resistance) in this way: Increasing the resistance (ohms) is like decreasing the size of the water pipe, which would, in turn, reduce the water flow (current, measured in amps) that is driven through the circuit by voltage (the water pressure). 

Now it’s all coming together! We need to understand one more term in this relationship to bring the electrical team together – watts!

Watts

A watt (W) is a measure of power. More specifically, one watt is one joule of energy used per second, so a watt is the rate of consumed energy. For example, a 60-watt light bulb consumes energy at a rate of 60 watts!

Now let’s get back to amps and see how all of these terms work together. 

How Do You Measure Amps?

To measure amps, we need to use a tool called an “ammeter”. 

An ammeter (or ampere meter) measures the electric current in amps. It can measure direct current (DC) or alternating current (AC), but either way, it measures the current in amps (amperes). So the ammeter is an instrument that measures the flows of current in amps. (You may see ammeters represented by a circle with the letter “A” inside.)

How An Ammeter Works 

An ammeter measures the current going through a component. To use it, you must connect the ammeter in series to the component. “In series” means one after another. 

With an ammeter, you are measuring current, which is the electricity going through the meter. 

There are two primary types of ammeters:

Shunt Meter

An electrical shunt ammeter is commonly used in permanent DC (direct current) electrical installations. These devices are connected in series on the negative side of an electrical circuit, and all the current in the system flows through them. The shunt then reads out the current that it has been seeing.  

Shunts like this commonly double as battery meters because they also read the voltage of the circuit. As we learned before (Amps x Volts = Watts), so the shunt can also tell how much power (in watts) the electrical system is consuming or charging from the batteries. More on this later.

Hall Sensor (Amp Clamp)

Another way to measure amps is with a hall sensor. These devices do not need to break the wire to be installed and are commonly used in portable amp measuring devices we call amp clamps.    

An amp clamp has hinged jaws integrated onto a meter to clamp the meter onto a cable, wire, or another component to measure the current in that circuit.

The name Hall sensor comes from the term “Hall Effect” that the sensor uses to determine amperage. The term “Hall Effect” refers to the nature of the current in a conductor. A Hall sensor (or Hall-Effect sensor) is an amp clamp meter that measures both AC and DC current. 

The meter uses strong iron jaws to clamp tightly to the conductor being measured to concentrate the magnetic field around that conductor. As current flows through the conductor, the magnetic field passes through the Hall Effect clamp meter and produces a voltage that translates to a digital reading on the meter.

When Would You Use An Ammeter?

Electricians, electrical engineers, and electrical enthusiasts use ammeters to troubleshoot, design, and build electrical circuits. They can be very helpful in figuring out where and how much current is flowing in individual wires.  

Portable digital multimeters are available for troubleshooting and circuit verification. These let you verify that the current is what you’d expect it to be for a particular circuit. Digital multimeters measure voltage (Volts), currents (Amps), and resistance (Ohms). These multimeters are widely available on the market in various price ranges. You can find clamp-on digital meters or ones with probes, depending on what you wish to measure.

Many mobile power systems use an ammeter to measure the amps into and out of the house battery/batteries over time. You can use this to see how many amp-hours remain in your battery/batteries, to what degree they’re charged, and how long it takes to charge them using various methods. This information is critical for an RVer or boater because batteries supply the power they need for practically everything in the power system.  

What is a Shunt?

Permanently installing an ammeter shunt to continually measure the state of charge of your battery or batteries is one way to keep a close eye on the all-important amp hours.

A shunt acts as a low-resistance connection between two points in an electric circuit. So in our RV application, the purpose of installing a shunt would be to have a digital readout inside the RV, giving us a constant display of the state of charge of our battery system. 

The shunt would connect to the RV battery bank on the negative lead and to the display inside the RV. It would measure the amps coming into and out of the RV’s battery/batteries. This tells you how much you’re using and replenishing your battery capacity, and how much energy remains for use.

What Is Ampacity?

The term “ampacity” refers to the rating of wires and devices used in a system for a particular application. Ampacity is important because it refers to the maximum amount of current that a cable or wire can safely carry. (The bigger the wires, the higher the ampacity.) 

So when you choose wiring or cable for a particular application in your RV, for example, you absolutely must know the ampacity rating of that cable.

It is relatively common for electrical component companies to mark devices for load size or range in wattage, amps, or volts. You can use this information to calculate ampacity by dividing wattage by voltage. 

This important information is worth repeating: wattage divided by voltage = amps. The ampacity of a device needs to be higher than the amps that will go through it.  

Knowing this information and determining wire or cable size accordingly could be critical to your safety in terms of preventing electrical fires, as overloading a wire or device will cause it to get very hot and possibly burn up. 

It is key to remember that bigger wires = higher ampacity. 

Are AC Amps and DC Amps the Same?

While it’s true that both AC and DC refer to types of current flow in a circuit, the two are not the same. DC (direct current) refers to an electric charge (current) that only flows in one direction. AC (alternating current) refers to the current that changes direction a certain number of times per second (60 in the United States).

You can measure both types, but electrical devices are only rated to use one type. Do not connect DC devices to AC and vice versa without an inverter or charger in between. 

For mobile applications like RVs and boats, power receptacles have ratings in amps, 50Amp, 30Amp, 20Amp. These are the max amp ratings that these outlets can provide before their breaker pops. Many people get these amps confused with battery amps, but they are AC at a higher voltage. (120 or 240V)

While the 50 amp flow may be the same in a battery, remember the voltage is the pressure, and the battery pressure is only 12 volts. Thus the current may be the same, but the higher voltages’ power is much higher.

What Is An Amp-Hour?

The term “amp-hour” refers to a unit of electric charge. Where RV batteries are concerned, for example, we would use the term “amp-hour” to describe how much amperage a battery can provide for one hour. 

Let’s look at what this means in terms of real-world use:

Theoretically, a battery with a capacity of 1 amp-hour should be capable of providing a continuous current of 1 amp to a load (the device or appliance using power) for exactly 1 hour before becoming discharged. The same 1 amp-hour battery could alternatively provide a continuous current of 2 amps to a load for a half-hour. Or it could provide ⅓ of an amp-hour to a load for 3 hours. You get the idea.

Why Do Amps Matter in Electrical System Design?

When you’re designing an electrical system, it is critical to consider amps to know the wires’ size that you must use to maintain safety. 

Higher Amps Require Bigger Wires

As you may recall, the higher the amps, the bigger the wires needed to safely serve the system. You must properly size wires and cables not only to deliver quality power but also to prevent the occurrence of electrical fires.

Higher Amps Increase the Voltage Drop

Voltage drop occurs when the voltage at the end of a cable is lower than it is at the cable’s beginning. This drop often occurs at the end of a very long run of cable, for example.

The easiest way to reduce voltage drop is to increase the conductor’s (or wire’s) diameter. All electrical cables provide some resistance to the circuit flow, but it is important to take whatever steps you can to decrease that resistance when you’re designing your electrical system.

Finally, for RV and boat applications, people try to conserve battery power to the best of their ability. It is therefore important to remember that higher amps burn more battery power. 

Higher Voltage Decreases Amps

High amps is not always a good thing because the wires and devices need to be very big. To get away from having big wires, increasing the voltage will decrease the amperage for the same amount of power. The following example shows how. 

• 120 Watts @ 12V = 12 Amps
• 120 Watts @ 24V = 6 Amps
• 120 Watts @ 120V = 1 Amp

When designing your electrical system, it is best to bear in mind that running big, thick, heavy wires long distances adds weight to your rig. The wires can also be very difficult to work with due to their inherent lack of flexibility.

Understand Amps To Design A Proper Electrical System

As you can see, amps only represent one part of the electrical equation but are critical to understanding. To design a proper electrical system, we also need to better understand volts and watts because they all have to work together to become our coveted power supply!