Alternator vs Generator : What’s the Difference?

Alternator vs Generator — What are the differences? This is a common question that people ask and once you know the answer you can understand why it can be confusing to so many. But as you will find out, there are several main differences between a generator and an alternator.

Alternator vs Generator: A Common Curiousity

When people talk about a generator, we immediately think of the portable generator that is used to supply electricity to our homes and businesses during a power outage, or for recreational purposes – like powering an RV. If we think about an alternator, it’s the device that produces electricity in our cars.

Though when we compare the technical definition of an alternator vs a generator, the opposite seems to be true. This confuses things. So what is the difference between a generator and an alternator? This is a simple question to answer. A generator produces Direct Current (DC) and an alternator produces Alternating Current (AC). This is where things don’t seem to make sense. The power we use in our homes is AC, yet we call the device that produces that electricity a generator. The electricity used in a car is DC, yet we call this device an alternator.

Before I compare an alternator vs generator, let’s get these naming conventions cleared up. The generator we use as a backup power supply is called a generator because it generates electricity, the name doesn’t refer to the technical design of the machine. In reality, the portable generator in your garage uses an alternator to generate an alternating current. The alternator in your car also produces an alternating current, but then uses a rectifier to convert the alternating current into direct current.

Maybe this all sounds even more confusing than when we began. Why not just use a generator to supply DC power for our cars? In the early days, they did. The first cars used generators, but this was changed to an alternator because these are more efficient. Because of the difference in the way the electricity is produced, it makes better sense to use a more efficient, and more reliable, alternator and then convert the electricity back to DC. In fact, generators are seldom used anymore.

The basic principle of a generator and an alternator is the same. Both convert mechanical energy into electric energy by means of magnetic polarization. Both can function as an electric motor if electric energy is supplied instead of mechanical energy. Though a generator will function just about as efficiently as a DC motor, whereas an alternator doesn’t make for a very efficient AC motor.

Okay, so what is technical the difference between a DC generator and an alternator, producing AC power. To clarify the alternator vs generator debate, I’ll explain how they work. I’ll start by explaining the difference between alternating current and direct current.

VIDEO | Alternator vs Generator Explained

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AC vs DC

Direct current is simple. Charged electrons move directly from one point to another. A battery has a positive terminal and a negative terminal. The electrons will move through a conductor from one terminal to another.

Alternating current reverses the flow of electrons over a controlled time period. The result is an electron pulse, contrary to the constant flow of electrons in one direction that we find with direct current. The electron pulse will happen several times a second and needs to be regular. This is known as frequency. In the United States conventional AC power operates at 60Hz, the electrons pulse between a live point and a neutral point 60 times per second.

Because of the exact frequency requirements, an alternator needs more sophisticated regulating devices than a generator.

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How does a generator work vs an alternator?

Both a generator and an alternator produce power by spinning a rotor (also known as an armature) inside a magnetic field created by the stator. Both the stator and the rotor are made up of copper windings. This is thin wire that is wound to create a magnetic field. So a generator has a stator, field windings, that is permanently magnetized and the resultant magnetic field, created by the spinning rotor, generates current that is transferred from the rotor by means of brushes.

VIDEO | See the Basic Mechanics of How A Generator Works

Because a generator produces the current from the rotor, the brushes need to conduct the full amperage of the current produced. This causes them to degrade easily. This is exasperated by the fact that a generator uses split rings that cause greater wear on the brushes.

An alternator uses the rotor in the opposite way to a generator. So the electric current is produced by the stator, or field windings. This allows the alternator to use solid rings and the brushes last longer. An alternator doesn’t need to use brushes at all. Many modern, brushless alternators use a capacitor instead and this means no mechanical wear from metal components making contact.

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Advantages of an Alternator vs Generator

We’ve already established that an alternator is more reliable and requires less maintenance. This is the main reason why alternators have come to replace generators in most instances. But there’s another reason why alternators are preferred. Although AC power requires more control, you have to manage both voltage and frequency (vs only voltage for DC), it is possible to control AC power more precisely. Using capacitors, one can manage the voltage and frequency with exact precision. Direct current can only be regulated. This means it’s possible to reduce the DC voltage to prevent overcharging, but the opposite cannot be achieved. You cannot step up a DC voltage if it is too low.

AC transformers can step up the voltage multiple times. This is of particular importance when you’re conducting the power over long distances. Electricity that supplies the national power grid can be as high as 138,000V. A series of substations use AC transformers to step the power up or down, depending on the distance from the end user. Bulk electricity supply experiences reduced power loss at a high voltage.

The main advantage to using an alternator to supply power for a car is the increased efficiency and better control over the voltage. An alternator has a parasitic power factor. This is the energy it draws from the engine to generate electricity. A generator requires a greater parasitic KW input for a lower KW output. Basically, a generator draws more power from your engine and produces less energy than an alternator.

A smaller, lighter alternator will provide all the power required for your car almost constantly. A larger, heavier generator will often draw power from the battery when the engine revs are low and the power demand is high. Old cars, that used generators, commonly experienced voltage drops under high demand. If you drove in wet weather, with the windshield wipers on full power and the lights on, the wipers would slow down and the lights would dim every time you stopped at a traffic light. The low RPM from the engine would not provide sufficient power for the generator to to meet the high demand.