Generator, alternator, dynamo naming semantics

[Circlotron]

Depending on where you live, many cars up until the early to mid 60s were fitted with a generator for charging the battery. After that, most manufacturers began to fit alternators instead.

The way I understand it, a machine that takes in mechanical energy and puts out electrical energy is broadly called a generator. If the machine produces DC it is a dynamo, and if it produces AC it is an alternator.

But as we all know, a car alternator has a rectifier bridge that enables it to provide DC at its terminals, so does that disqualify it as being called an alternator? And a car generator actually produces AC internally that is rectified to DC by the commutator and brush assembly, so does that disqualify it from being called a dynamo? Is there a hard and fast definition for each machine?

Also, AFAICT a Faraday homopolar machine and maybe a MHD setup are both the only true DC generators.

[IanB]

We have to think about what is the purpose of words?

On the one hand, if we know what a machine does, the function is more important than the label.

On the other hand, if we are trying to communicate ideas to other people, then what matters is that both people have a similar understanding of what a word means, so that meaning is conveyed.

Therefore, if most people in the auto industry understand an alternator to be a machine that produces AC with an external rectifier, then communication is best served by sticking with that term.

Similarly, if most people understand a dynamo to be a machine found in older vehicles that produces DC directly at the output, then again, communication is best served by sticking with that convention.

[IanB]

Note that some older vehicles had a magneto ignition system, which is yet another word to put alongside dynamo and alternator.

[Andy Chee]

The nomenclature is only confusing when you try to use terms across different disciplines.

For example, "dwell angle" would not be understood by electronics engineers, and automotive mechanics would probably not understand the term "duty cycle".

[NiHaoMike]

A lot of newer cars use starter/generators that are 3 phase permanent magnet synchronous AC with an external inverter/rectifier.

[SteveThackery]

Here in the UK I haven't heard the term "generator" used for cars, except in the most generic sense. I'm interested in vintage cars, and they always use the term "dynamo" (commutator and brushes, external voltage regulator). More modern cars use "alternators" (multi-phase AC with an internal rectifier and internal voltage regulator).*

As has been said, these are just convenient terms rather than scientifically precise.

*Decades ago some of the earliest alternators used external voltage regulators, but they weren't around for long.)

[David Hess]

*Decades ago some of the earliest alternators used external voltage regulators, but they weren't around for long.)

In the US, wound field alternators were replacing wound field DC generators with brushes and commutators in the 1960s, and both had external regulators.  External regulators were still used into the 1970s depending on the manufacturer.  I am not sure about foreign vehicles, but I think GMC switched over to internal regulators before Ford did.  Maybe they all had internal regulators by the 1980s?

[fzabkar]

*Decades ago some of the earliest alternators used external voltage regulators, but they weren't around for long.)

In the US, wound field alternators were replacing wound field DC generators with brushes and commutators in the 1960s, and both had external regulators.  External regulators were still used into the 1970s depending on the manufacturer.  I am not sure about foreign vehicles, but I think GMC switched over to internal regulators before Ford did.  Maybe they all had internal regulators by the 1980s?

From my vantage point in Australia, Chrysler was always the first to innovate in auto electricals, at least among the big three US car makers. Here in Australia they were the first with alternators, first with electronic ignitions and first with engine computers.

[.RC.]

I thought this was Dynamo?

[Siwastaja]

In Finnish this thing is, regardless of the type, called a "charger". Which is kinda true as its purpose is to charge the battery (just with mechanical input) but becomes a bit confusing when plug-in hybrids and other modern stuff is thrown in. Oh well, it was confusing to begin with because the thing which is plugged in a socket and then connected to charge your battery with two alligator clips always was a "charger", too.

[Stray Electron]

A lot of newer cars use starter/generators that are 3 phase permanent magnet synchronous AC with an external inverter/rectifier.

  A permanent magnet?  Really?  Name one.  Every automobile or truck that I know of uses an electromagnet so that they can regulate the power to it and thus regulate the output of the generator or alternator.  The only engines that I know of that use permanent magnets are some small engines such as small motorcycles and lawn mowers. 

  Again, it's mostly about semantics but in the automobile world a generator generates power (DC) from a rotating armature and it has a non-rotating field coil which uses a regulated input that controls the magnetic field and thus the electrical power output of the armature.  In these, there are large brushes to carry the output from the rotating armature to the outside of the generator and the brushes form a commutator converts the AC power in the coils to a pulsating DC output and there are no diodes.

   Electrically an alternator is built inside out compared to a generator.  It generates uses the rotating armature to create a rotating magnetic field. The fixed, non-rotating coils around the outside of the unit generate several phases of AC power that are then converted to DC by means of diodes that are colocated in the body of the alternator.  The major advantage of an alternator is that the brushes only power the field coil so they're much smaller and much more reliable than the brushes used in a generator. Also since there's less power flowing in the brushes you don't get as much electrical noise as with a generator.  Also an alternator usually generates at least three phases of power compared to only one in a generator so alternators are smaller and lighter than generators of the same output power. 

  One point of confusion is the term "Field Coil".  I contend that the field coil is always the coil that generates the magnetic field that makes all generators/alternators work.  So in a traditional generator that is the coil on the outside. But in a modern alternator that is the coil in the rotating armature.  But some people tend to follow the OLD normal, which was that the field coil was always the coil(s) around the outside of the device. 

  A dynamo is a very old term that used to cover all mechanical rotating electrical generators, including those that used brushes as commutators to convert the AC power in the armature to a pulsating DC output; and those that had slip rings instead of commutators and thus their output was purely AC.  The term dynamo also covered generators that used permanent magnets instead of electromagnets and thus had an unrelated output. 

   Today, outside of the automotive industry, anything that produces an AC output is generally called an alternator and anything that produces a DC out is referred to as a generator. But with today's inverter technology and small solid state rectifiers, the line between the two has gotten very blurry. 

  See some of the youtube videos is you need a more thorough explanation.

[Stray Electron]

Note that some older vehicles had a magneto ignition system, which is yet another word to put alongside dynamo and alternator.

  Somewhat but a magneto serves a very different purposes and it deserves it's own separate discussion.  It's designed to produce the high voltage electrical pulses for the engine ignition and not produce electrical power for auxiliary devices.  Thus while it does produce electricity from a device with a rotating mechanism, it is built and functions very differently.  Among other important differences, a magneto must have points (or a functionally similar device) to control the mechanical timing of the output power. And a magneto generates very high voltages which a normal generator or alternator doesn't.  Also AFIK all magneto's use a permanent magnet to generate their electrical field.  While it would be possible to use an electromagnet, I don't think anyone does since that would also require an external battery (and a charging system for it.)  Magnetos are used where the ultimate requirements are simplicity and reliability.  (Aircraft rotary engine ignition systems being a huge example.)

[Stray Electron]

The nomenclature is only confusing when you try to use terms across different disciplines.

For example, "dwell angle" would not be understood by electronics engineers, and automotive mechanics would probably not understand the term "duty cycle".

    Well dwell angle and duty cycle really do mean different things. Duty cycle means the portion of time that a signal in On out of one complete cycle which simple compared to computing dwell time.

     Dwell time (an angle) is the time that the points are closed in a mechanical ignition system. it's the time in which the ignition coil charges up so that when the points open and the magnetic field collapses the di/dt generates a high voltage pulse that is feed into the ignition coil(s).   But with engines that on time happens one, two, four, six, either or more times per revolution of the engine. And it also depends on if the engine is a two stroke or four stoke (or something else!) engine.  In two stroke engines there is one ignition pulse per cylinder per revolution but there is one one ignition pulse for each cylinder and for every other stoke on a four cycle engine.  And to confuse things further, distributors are usually driven at 1/2 of the engine speed in a four stroke engine.

    But before we go too buried in the details, the Dwell time happens a number of times during each engine revolution, i.e. each cycle.  In a four cylinder four stroke engine it happens four times per engine revolution.  IIRC 30 degrees is a pretty normal dwell time, that means that the points are closed for 30 degrees of the engine revolution and then opened and that repeats four times per engine revolution (per cycle). 

    So duty cycle means the total On time in a cycle and is expressed as a percentage; but Dwell is measured in degrees (or your unit of choice) and is a single event and it can happen multiple times per cycle.  In a single cylinder four stroke engine it would only happen once every other cycle! 

   Confused yet?   If you're not then consider that engines can run at various speeds so the time each Dwell takes will also vary in time (but not in angle).   

    Yeah, I think that I have too much time on my hands this morning.

[Siwastaja]

A lot of newer cars use starter/generators that are 3 phase permanent magnet synchronous AC with an external inverter/rectifier.

  A permanent magnet?  Really?  Name one.  Every automobile or truck that I know of uses an electromagnet so that they can regulate the power to it and thus regulate the output of the generator or alternator.

He's talking about some "light hybrid" configurations. The synchronous motor acts as starter motor, generator and torque booster all-in-one. Power is regulated through the control of the inverter, which enables bi-directional power transfer i.e. motor acting as a generator or a motor, just like in an EV.

[IanB]

It seems like permanent magnet designs are becoming the favored option for rotating electrics.

I noticed that the new tube trains arriving soon in London will be the first to use permanent magnet traction motors. It seems they are good for both efficient operation and regenerative braking.

[Siwastaja]

The control difference is that if you have wound field, you can regulate field current, which would be somewhat smaller than total current. But then the alternators use brushes to supply the wound field, and these brushes wear out. A permanent magnet generator generates voltage proportional to RPM, so for each phase, an actively driven half-bridge (e.g., six MOSFETs for a 3-phase motor-generator) is needed to operate it, converting the voltage up or down for the battery, utilizing the generators inductance. This bridge of course today costs next to nothing so it is slowly becoming an easier solution than the brushes.

[Xena E]

The way I understand it, a machine that takes in mechanical energy and puts out electrical energy is broadly called a generator. If the machine produces DC it is a dynamo, and if it produces AC it is an alternator.

That is my understanding.

Most terminology is misapplied as usual though.

American friends speak of a generator, for example, being perhaps something that powers the lighting on a vintage bicycle: this is fair, they invariably 'generated' AC.

Generator being the generic term, for anything that generates electrical power.

In the UK though the same device fitted to a cycle would mostly be called a dynamo, which to my mind, is wrong.

In the UK, traditionally, generator and dynamo were used interchangeably for the device used in vehicles to provide power to charge the battery and run the electrical equipment that output DC without the aid of an added rectifier.

Alternator is a less abused term although I have recently heard someone say, "DC alternator".

[David Hess]

A lot of newer cars use starter/generators that are 3 phase permanent magnet synchronous AC with an external inverter/rectifier.

  A permanent magnet?  Really?  Name one.  Every automobile or truck that I know of uses an electromagnet so that they can regulate the power to it and thus regulate the output of the generator or alternator.  The only engines that I know of that use permanent magnets are some small engines such as small motorcycles and lawn mowers.

The Honda Insight "parallel hybrid" is one.

The permanent magnet motor is mounted directly to the engine's crankshaft where the flywheel would normally go.  I have read that the motor is even timed to balance out the variation in angular momentum from the engine reducing vibration.

[Someone]

A lot of newer cars use starter/generators that are 3 phase permanent magnet synchronous AC with an external inverter/rectifier.

A permanent magnet?  Really?  Name one.

Mercedes
https://www.advance.mitsubishielectric.com/advance/pdf/2020/169_TR6.pdf
https://automotivetechinfo.com/wp-content/uploads/2021/09/Mercedes-Benz-High-Energy-48-Volts.pdf
Minor detail that most people do not care about.

[Circlotron]

The major advantage of an alternator is that the brushes only power the field coil so they're much smaller and much more reliable than the brushes used in a generator. Also since there's less power flowing in the brushes you don't get as much electrical noise as with a generator.  Also an alternator usually generates at least three phases of power compared to only one in a generator so alternators are smaller and lighter than generators of the same output power.

Another advantage of a car type alternator is the rotating field coil is wound on a bobbin or spool around the axis of the main shaft. This construction allows the field winding to tolerate being spun at very high rpms. This means two things - it can have a smaller belt pulley than a generator so it will still be spinning at a decent speed when the engine is idling, so it can till power all the electrical items and keep the battery charged when idling. At high engine speeds the windings won't fly off like they would with a generator with a small pulley. The surface speed of the small diameter slip rings would be slower at the same shaft rpm compared to the relatively larger diameter commutator, so less brush wear. Also, the higher operating frequency of the alternator because of higher rpms would make for less turns needed in the stator, so thicker wire could be used.

I did read somewhere that an automotive alternator has an efficiency of only about 50% and a generator is a lot better in this respect. The two diodes in series at any given time have a voltage drop, and the stator iron geometry is shaped to give inherent current limiting. Simplicity is the main feature here.

[David Hess]

The control difference is that if you have wound field, you can regulate field current, which would be somewhat smaller than total current.

When I designed and build a replacement regulator for one of my cars because replacement regulators kept overcharging or undercharging the battery, I measured a ratio between output current and field current of about 10:1.

[bdunham7]

But as we all know, a car alternator has a rectifier bridge that enables it to provide DC at its terminals, so does that disqualify it as being called an alternator? And a car generator actually produces AC internally that is rectified to DC by the commutator and brush assembly, so does that disqualify it from being called a dynamo? Is there a hard and fast definition for each machine?

For cars the Society of Automotive Engineers designates the term "generator" for any type of electromechanical device that produces power.  That includes the relevant parts of a hybrid drivetrain.  The term "alternator" was a marketing term that IIRC was first used by either Chrysler or Motorola to distinguish the new design from the traditional commutated DC generator.  The general term "alternator" was in use before automobiles even appeared on the market, but that was to distinguish generators with a final output that was actually AC from those that were commutated to DC.

[Andy Chee]

Surprised no-one has yet mentioned the use of the nomenclature "generator" in the context of small petrol/diesel generators, ranging from modern inverter generators, to old-fashioned 2-stroke generators, to diesel powered welders, to diesel generators for backup power for hospitals.