Electricity Explained – Part 1: Volts, Amps & Ohms

Electricity Explained – Part 1: Volts, Amps & Ohms

Think you know electricity? Check out the first article in our new series, where we delve into electricity, understanding volts, amps and ohms — and how they affect each other.

By Matt Roda, Associate Professor, Automotive Technology, Mott Community College, Flint, MI

In my 30+ years as a technician and automotive educator, I’ve seen way too many techs shy away from electrical work simply because they didn’t understand it. Most of these techs end up doing undercar work because there is lots of it and you can usually avoid dealing with electricity, or they manage to fix an electrical problem but aren’t sure how they did it. With anti-lock brakes, stability control, electric power steering and other such items invading the undercar world, I think it’s safe to say there is nowhere to hide anymore if you don’t want to deal with electricity. In this five-part series on electricity, I’d like to help alleviate any anxiety and misconceptions you may have about electricity and have you tackling that electrical work like the pro you are.


Break It Down

Figure 1: Potential difference between the “ANODE” (negative) side of the cell and the “CATHODE” (positive) side of the cell.

We’ll start by breaking electricity down into three parts: Volts, Amps and Resistance (Ohms).

Voltage (volts) is the pressure that pushes the amperage through the circuit. It is created by having a “potential difference” on both sides of a cell. The greater the “potential difference” is, the more voltage you have in a cell (see Figure 1). If there is no potential difference on the sides of the cell then there is no voltage to push the electrons through the wire. In the automotive business we call this a dead battery.

Figure 2: The negative electrons are pushed from atom to atom of a conductor by voltage. This is current flow.


Amperage (amps) is the movement of electrons from one atom to another across a conductor, also referred to as current flow. These moving electrons are forced across a conductor by voltage and these electrons are what perform the work in a circuit (see Figure 2).

Figure 3: Voltage has a hard time pushing amperage through resistance in a conductor.


Resistance (which is measured in Ohms) will restrict the flow of amperage. As resistance increases in a circuit, the current flow will decrease in that circuit, if resistance decreases, current flow will increase (see Figure 3).

In automotive circuits, we need the amperage to make something work yet amperage will only flow if we have enough voltage to make it flow and no unwanted resistance stopping the current from flowing. The effect that volts, amps and resistance have on each other is called Ohm’s Law. Ohm’s Law states it takes 1 volt to push 1 amp through 1 Ohm of resistance; in simpler terms, volts divided by Ohms equals amps.

Figuring a car battery has 12 volts and a lighting circuit has 2 ohms of resistance, then 6 amps of current will flow in this circuit (12/2=6). In an automotive wiring circuit there are only two things that can change the flow of current in a circuit: voltage going up or down and resistance going up or down. Since the voltage in a running vehicle’s electrical system is usually between 13.5 and 15 volts, with a properly working battery and alternator, the main cause of most electrical problems is unwanted resistance. All electrical systems are engineered with a specific amount of resistance, but if this resistance goes up or down, that’s when problems occur.

There are five things that can create resistance in any circuit: the length of a conductor, the diameter of a conductor, the type of conductor (metal, copper, etc.), heat and the quality of a connection. The first four are engineered into a circuit and rarely change, therefore most of our automotive electrical issues are a “quality of connection” issue. This condition will present itself in the form of rust, corrosion, loose or ill-fitting terminals in a connector and broken or loose wires.

Think about a lighting circuit that has 0.5 Ohms of resistance built into it, 12/0.5=24 amps of current flow. If the ground screw rusts enough to add an additional 0.5 Ohms of resistance, the circuit now has a total resistance of 1 Ohm, 12/1=12 amps. The lights will illuminate with 12 amps but will be dimmer than they are designed to be with 24 amps. If the same ground wire is broken, the resistance will be so high that no amps can flow, therefore the lights won’t work. This is referred to as an “open circuit.” Since excessive resistance and open circuits make up most of our electrical issues in a vehicle, the more you understand about them, the better equipped you are to make the needed repair.

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In today’s competitive world of business, considering the coverage of a scan tool is an important decision that directly affects the productivity of technicians, but can also open opportunities for your shop. Buying a scan tool is difficult. In the past, we had more concerns over operation and operating systems, as the technology wasn’t up to par.Today’s scan tools leave that concern behind, with computer technology rarely in question, but now it’s important to shift our focus on what we can ultimately do with our scan tool. Initially, we ask, is the coverage adequate for the cars we work on? But, we also need to consider the additional benefits a scan tool can offer to a technician, such as technical data, repair information, repair times, technical service bulletins, recalls and troubleshooting procedures.Features such as this hold considerable value at the fingertips of a technician. But, there’s still more to consider. What direction will your shop, or you take in the future? As mechanics, we always knew we could fix anything. If need be, we’d work on a lawnmower, motorcycle, boat or tractor.Our mechanical skillset hasn’t changed, but multiple industries have faced the same challenges and advancements as automotive. And, while it’s probably out-of-sight, out-of-mind, if you decide to work on anything outside your normal repertoire, you’ll find it’s equipped with just about the same technology. Except one thing, the protocol.When you buy a scan tool, will it have options for motorcycle, marine and offroad vehicles? What about heavy trucks? They’re all valid ways to make money. They’re broken, and you can fix them. That is if your scan tool supports the protocol.Protocol is nothing more than an electronic language; the way in which a scan tool can communicate with different types and makes of vehicles. While all automobiles sold in the US since 2008 follow a standard CAN protocol, there are still different aspects of it depending on vehicle manufacturer, and there were multiple protocols pre-2008. Motorcycles, commercial trucks, off-highway vehicles, and marine all utilize a common type of CAN network which we are familiar with, but again with different protocols.When considering a scan tool, your primary concern is automotive diagnostics. But what else is it capable of? Can it open other options for service opportunities? Does the scan tool manufacturer support additional protocols and is this scan tool compatible with other equipment to capitalize on these other industries? Depending on your vision for the future, these are all important questions to answer.Another important factor is Advanced Driver Assistance System (ADAS) service and calibration. This is the hot topic in the industry, and the expanded need for service will be coming quickly. Your scan tool will need to not only perform the diagnostics on these systems, but will it need to have compatibility with ADAS calibration equipment. Technology isn’t slowing down, and you can’t afford to buy two scan tools. Make sure your next purchase has the options you need now and in the future. TS

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