why do we call the car generator "alternator" but not building one?

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Electric-Light

Senior Member
The three phase generator within the car used to supply power while the engine is running is called "alternator" because it's a generator that makes A/C, but we don't call back up power systems or portable power units "alternators".

Why?
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Good question. I think terminology is not always consistent from 1 person to another or 1 profession to another. Whoever came up with the alternator probably had his focus on having the AC power he needed but may not have had a background in electric power. I'm sure he knew what a generator was but started calling his unit an alternator simply for it giving AC current.

Just an educated guess, or hypothesis, for a chance to use a big word.:cool:
 

gar

Senior Member
110424-2338 EDT

Go to dictionary.com and separately enter

generator
dynamo
alternator

Dynamo was used as the term for DC generators in 1879. Somewhere along the time scale the usage changed to DC generator.

Cars prior to about 1956-58 used DC generators. With the availability high power silicon diodes in the late fifties it was possible to change to using the more efficient alternator. More efficient because the power coils are on the stator and not the rotor. Thus, better heat transfer. I believe Chrysler pioneered the use of the alternator in a car.

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broadgage

Senior Member
Location
London, England
"generator" is a generic term that includes both dynamos for producing DC and alternators for producing AC.
In common parlance the term generator is often somwhat misused when reffering to what should more correctly be called a generating set. This being an assembly of a generator together with an engine to drive it, together with cooling and controling components and a battery or other means of starting the engine.

Generator=basic rotating device to turn mechanical energy into electricity.
Generating set=complete machine or assemby to turn fuel into electricity.

Terms are not allways used correctly, for example the very small generators often fitted to pedal cycles for lighting are often called dynamos, despite the fact that they produce AC and should therefore be called alternators.

Vehicle alternators do of course produce 3 phase AC from the windings, and are therefore correctly called alternators, despite the fact that this is rectified internally to DC for battery charging.
 

broadgage

Senior Member
Location
London, England
Alternators have the ability to regulate output voltage
Not allways, they dont.
Vehicle alternators produce a regulated DC output suitable for keeping the battery charged.
Generating sets for standby purposes or for remote premises normally incorporate a voltage regulator.
But the alternator built into a wind turbine does not regulate the voltage at all. The output voltage and the frequency varies according to the wind speed.
The miniature alternators fitted to cycles for lighting are designed to give a roughly constant CURRENT at different road speeds, not constant voltage.
 

sgunsel

Senior Member
If you mean bicycles, the ones I had w(a "few"years ago) were small wheel driven dc generators whose output was not constant anything. Pedal fast and the incandescent lights could get pretty bright, obviously supplying both higher voltage and current. Maybe today they are more sophisticated, especially with LED lamps.
 

Besoeker

Senior Member
Location
UK
Interesting points.
Maybe it was called an alternator on cars firstly to differentiate it from the older DC generators. A differentiator in the marketing sense in that the alternator was seen to be a superior machine and this was used to effect as a bit of a sales pitch.
Electric-Light is right about portable and back-up units. You dont buy or hire a portable alternator - well you do really - but it is never called that.
We do a fair bit of work in the water industry on the potable side. In all the pumping stations I can recall visiting there has been a back-up Diesel generator. An alternator in fact, but always called a generator.
Oddly, or maybe not oddly, the term alternator has always been used in the power stations I've been in.
 
We do call part of the generator an "alternator"

We do call part of the generator an "alternator"

Look at typical diesel generator literature/specs, and you will see the engine and the alternator listed in different sections. We often choose to upsize the alternator on the same size engine, if feeding Switch Mode Power Supply type loads (UPS, rectifiers, computers). So, IMHO, an engine is required to power the alternator, and the 2 components make up a generator (generates power).

But then again, I've installed a lot of 400HZ MG sets, which use a motor (usually 480V 3-phase 60HZ AC input) to drive a generator with 120/208V 3-Phase 400HZ AC output, and never heard the 400HZ part called an alternator.

So my answer created more questions. (Like talking to the wife).
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
"generator" is a generic term that includes both dynamos for producing DC and alternators for producing AC.
In common parlance the term generator is often somwhat misused when reffering to what should more correctly be called a generating set. This being an assembly of a generator together with an engine to drive it, together with cooling and controling components and a battery or other means of starting the engine.

Generator=basic rotating device to turn mechanical energy into electricity.
Generating set=complete machine or assemby to turn fuel into electricity.

Terms are not allways used correctly, for example the very small generators often fitted to pedal cycles for lighting are often called dynamos, despite the fact that they produce AC and should therefore be called alternators.

Vehicle alternators do of course produce 3 phase AC from the windings, and are therefore correctly called alternators, despite the fact that this is rectified internally to DC for battery charging.
+1

"Generator" is the generic term for the overall machine that accomplishes the task. Alternator is the part of that machine that creates AC, as opposed to a Dynamo being the part of it that would create DC. In a car, you are referring to just the component part, the alternator part, with the car engine being the rest of the "generator set". But in that context running the alternator is such an insignificant part of what the engine is there for that we end up only talking about the device as a component.

So technically is a Generator Set that makes AC really an "Alternator Set"? No, it's still a Generator Set, or Gen-Set, and it has an alternator inside of it. But we are a linguistically lazy bunch, and we like to boil down terms with a tacit understanding of context, so when we call them "Portable Generators" we all know what we're talking about.

It's really the same as "car" being used instead of automobile. Technically, a "car" is the part of an automobile that you ride in; the chassis and body. It's driven by the drive train that is powered by the engine, but being the lazy speakers that we are, we just took to referring to the whole shebang as a "car" because "automobile" is a mouthful.
 

Besoeker

Senior Member
Location
UK
+1

"Generator" is the generic term for the overall machine that accomplishes the task.
I'm inclined to disagree.
A generator converts mechanical energy into electrical energy.
Just as a motor converts electrical energy into mechanical energy.
Most rotating electrical machines are capable of operating in either mode. Or all four quadrants.

Are you old enough to have come across Ward Leonard drive systems?
It was a speed control system comprising usually an AC motor driving a DC generator (which had a controlled field).

It has the elements of a generator set. An input prime mover and an output generator, just like say, a Diesel generator set. But you wouldn't call it a generator. That refers to a specific part of the system.
 

gar

Senior Member
110427-0919 EDT

About 1/3 down just below the title "MASTER CHARGE: Alternators and generators"
in:
http://en.wikipedia.org/wiki/Alternator
Reference is made that 1960 was the first production use of the automotive alternator in place of the DC generator.

The word alternator has been used for a very long time to define an AC generator. In post #3 I had suggested looking at the dictionary definitions for generator, dynamo, and alternator. Additionally look at:
http://en.wikipedia.org/wiki/Alternator
http://en.wikipedia.org/wiki/Electrical_generator
http://en.wikipedia.org/wiki/Dynamo

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gar

Senior Member
110427-1144 EDT

It should be noted that pole shaping is used in the automotive alternator to produce a more square wave output and thus reduce the ripple after rectification.

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K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
"Generator" was the term used for auto generators until the "alternator" was invented. The term "alternator'' was used to differenciate between the two.
You are correct. I owned and operated a business that specialized in vehicle electrical systems.

The difference between the two was correctly explained several posts ago, about the function of the windings.

For some ungodly reason, generators are still in use in some types of equipment, like commercial grade wood chippers.

Alternators were a vast improvement over generators. Generators rely on residual magnetism to start charging. That means if the battery is taken out and replaced you have to 'spark' two terminals on the generator together before it will charge. That is known as 'polarizing'.

Generators don't put out squat for current when they aren't spinning fast. At an idle there usually isn't enough output to power accessories and charge the battery at the same time.

Generators are physically larger than alternators. An automobile generator is roughly the shape of a starter and about 3/4 the size.

Generators need two control wires coming from the regulator, which is always external. Alternators only need one or none and now days the regulator is inside the alternator. All the control wire does is turn the regulator on and off so it doesn't drain the battery down when the key is off. Alternators with self exciting internal regulators do not need a control wire. The only connection needed is the one to the battery. The case is the ground. Self exciting (SE) alternators are very popular among custom car and dune buggy builders.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
110427-1144 EDT

It should be noted that pole shaping is used in the automotive alternator to produce a more square wave output and thus reduce the ripple after rectification.

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I don't know what you are trying to say.

The rectification from three phase AC to DC is done by six diodes. Three are grouped together and are called the 'diode trio'. The other three are called output diodes. Three diodes control the positive side of the AC sine wave and the other three control the negative.

Looking at the output of an alternator on an oscilloscope (I own one made for this purpose) You will see a modified half sine wave. Each 'lump' on the wave is from a single output diode. If you see a pattern of two lumps followed by a zero space, you know that one of the output diodes has failed. A single failed diode will not render the alternator useless, it just reduces it's output. If I didn't have a scope I would need to remove and disassemble the unit to test the diodes.
 

Besoeker

Senior Member
Location
UK
Generators don't put out squat for current when they aren't spinning fast. At an idle there usually isn't enough output to power accessories and charge the battery at the same time.
I agree. Another aspect of this is that the automotive DC generators couldn't run at as high speeds as alternators. The pulley on an alternator is usually much smaller that on DC generators. For electrical machines higher rotational speeds generally result in smaller physical size.
 
The three phase generator within the car used to supply power while the engine is running is called "alternator" because it's a generator that makes A/C, but we don't call back up power systems or portable power units "alternators".

Why?
Hm, this reminds me an old question I wondered about since I was a kid. Why do we have separate starter and alternator? A motor is basically nothing else but the abverse of a generator?
 

gar

Senior Member
110427-1442 EDT

Depending upon how the pole faces are formed (shape) the output waveform of an alternator can be modified. See http://en.wikipedia.org/wiki/Alternator
Automotive alternators

Alternators have the great advantage over direct-current generators of not using a commutator, which makes them simpler, lighter, less costly, and more rugged than a DC generator, and the slip rings allow for greatly extended brush life. The stronger construction of automotive alternators allows them to use a smaller pulley so as to turn faster than the engine, improving output when the engine is idling. The availability of low-cost solid-state diodes from 1960 onward allowed car manufacturers to substitute alternators for DC generators (major American manufacturers had made the transition to alternators by 1962, for example). Automotive alternators use a set of rectifiers (diode bridge) to convert AC to DC. To provide direct current with low ripple, automotive alternators have a three-phase winding. In addition, the pole-pieces of the rotor are shaped (claw-pole) so as to produce a voltage waveform closer to a square wave that, when rectified by the diodes, produces even less ripple than the rectification of three-phase sinusoidal voltages.

Typical passenger vehicle and light truck alternators use Lundell or claw-pole field construction, where the field north and south poles are all energized by a single winding, with the poles looking rather like fingers of two hands interlocked with each other. Larger vehicles may have salient-pole alternators similar to larger machines. The automotive alternator is usually belt driven at 2-3 times the engine crankshaft speed. Automotive alternators are not restricted to a certain RPM because the alternating current is rectified to direct current and need not be any constant frequency.
The fundamental reason an automotive alternator can provide charging voltage at low RPM is that it is run at a higher RPM than a DC generator. This can be done because of mechanical factors. At lower RPMs a DC generator could provide a higher voltage, but for the same current capacity it would be larger. For a given physical size higher RPM means greater power output.

For a fixed diode configuration if you square up the input waveform you will reduce the ripple current.

Alternators were a vast improvement over generators. Generators rely on residual magnetism to start charging. That means if the battery is taken out and replaced you have to 'spark' two terminals on the generator together before it will charge. That is known as 'polarizing'.
This description needs clarification. I will describe the operation from the perspective of a Ford generator and regulator system.

The Ford regulator consists of three relays:
A voltage regulator.
A current limiter.
A cutout.

The cutout relay is a normally open type and has two coils. A voltage coil from the generator, and a current coil in series with the lead to the battery. The regulator I have is a 6 V unit from about 1950. The cutout relay pulls in at about 6.8 V. For this system to work the generator has to produce voltage before the battery is ever connected to the generator to provide field excitation.

If fact the generator is self exciting as a result of the residual magnetism of the field.

A typical Ford generator had two terminals, the plus armature, and the plus field. The negative side of the generator armature and field are connected to the generator frame and in turn to the engine and car chassis.

The positive field terminal on the generator is connected to the field terminal of the regulator. The field terminal is connected thru a series pair of normally closed contacts on the voltage and current regulating relays to the armature. The armature terminal of the generator is connected to the armature terminal of the regulator. From here the armature current flows thru the current regulator and the cutout relay to the battery terminal of the regulator assembly.

The armature voltage is applied to the voltage regulator coil and the the cutout coil.

The current require to operate the cutout relay at 6.8 volts was about 1.1 A. This current is distributed between two voltage coils and a series string of resistors used to dampen arcing of the voltage regulator contacts.

It should be noted that the voltage regulator contacts oscillate at a high rate. Quite possibly above 10 Hz. In the engineering labs on this product many experiments were run on various contact materials to improve contact life. In those days 1000 hours of operation for the regulator life was a goal. At 60 MPH that is 60,000 miles.

So a DC generator is self-exciting. It only needs two terminals plus the chassis ground. It will produce full output voltage to the vehicle without a battery.

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