DC GENERATOR

[bobby ocampo]

What is the common Field connection of a DC generator?:blink:

 

[ATSman]

Did you try Google?

 

[gar]

190612-1930 EDT

bobby ocampo:

I don't understand your question. Can you clarify what you are asking?

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[bobby ocampo]

What is the common conection of the field windings in a DC Generator? Series? Shunt? or compounded?

 

[gar]

190612-2106 EDT

bobby ocampo:

Any magnetic generator is going to require a non-zero magnetic field, and a conductor moving thru that field, AC or DC.

A DC generator will have either a permanent magnet, or an electro-magnet to produce its field. Your question as somewhat expanded implies an electro-magnetic field.

An electro-magnetic field implies one or more coils of conductive material wound around a magnetic material.

I think your question relates to how the one or more coils connect in the circuit.

Suppose there is one field coil that is connected to a battery for power to produce a magnetic field. Rotate the armature and an output voltage will be produced. This voltage is proportional to the product of the magnetic field intensity and the armature speed of rotation. If field intensity is constant, then output voltage is proportional to armature speed.

Now can you continue to clarify your question?

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[bobby ocampo]

My question is about the common connection of the Field windings in actual application. Based on your experience which among the field windings connection is most prevalent? Is it Shunt? Is it Series? Is it Compounded?

 

[gar]

190613-1933 EDT

bobby ocampo:

I will answer in a simple fashion that it is shunt. But that needs qualification.

Consider a shunt wound generator. What happens as RPM changes? Think thru this question.

The largest number of DC generators ever built were for automobiles. In a sense these were shunt wound, but not really. Why are they not a true shunt winding?

Compound wound generators were a means of providing somewhat constant voltage output with varying load if the generator was driven at constant speed. Over-compensation was a means to increase voltage with load.

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[GoldDigger]

My question is about the common connection of the Field windings in actual application. Based on your experience which among the field windings connection is most prevalent? Is it Shunt? Is it Series? Is it Compounded?

Shunt, series, or compound (series-parallel combination) connection is appropriate to a motor situation, where a single voltage source drives both the rotor and stator field coils. It is not a particularly appropriate characterization of a generator, where the exciting field must be controlled to regulate the output voltage rather than being directly proportional to either output voltage or output current.

 

[gar]

190613-2029 EDT

See http://www.circuitstoday.com/types-of-dc-generators

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[bobby ocampo]

Do you have statistics on the different kw capacity of a DC generator and percentage of each kw rating compared with other kw rating?

Is field winding connection different depending on the size of the DC generator?

 

[zbang]

Is field winding connection different depending on the size of the DC generator?

It will certainly depend on the use and how tightly you want to regulate. For instance, with a welding generator, you don't much care about the open-circuit voltage as much as about the current available, and you want it to self-limit into a short. Very different from a lighting plant.

What sort of application are you thinking of?


(This is like asking "what are the field connections of a DC motor?"- it depends on the application.)

ETA- how common are real DC generators now, anyway? Not in motor vehicles anymore; not for lighting; a bit for welding; not for railroads, etc. The only up-and-coming app. I can think of is inverter generators. Still in some MG sets, of course.)

 

[junkhound]

Nearly all DC systems I work with that are engine driven use AC 3 phase generators and full bridge rectification or PFC electronics to convert to DC.

Even railroad engines are 'switching' (pun intended) to AC motors and generators.

Nearly all wound brush commutation DC generators I ever worked with were shunt wound, with separate drive for the shunt winding.

 

[Besoeker3]

What is the common Field connection of a DC generator?:blink:

The ones I'm come across were usually shunt wound.
I dealt with quite a few in the paper making industry. Many were 4-quadrant meaning they could motor or generate.

 

[gar]

190617-1254 EDT

On the invention of the automotive voltage regulator see ---
https://ethw.org/First-Hand:The_Story_of_the_Automobile_Voltage_Regulator

My classmate's father invented a means of adjusting the relays in the regulator that lowered the cost of manufacture. Instead of a screw adjustment his invention was part of the relay frame that was bendable for adjustment. This eliminated screws, nuts, and adjustment time with a simple bending operation. Fewer parts and less time.

I worked in that electrical engineering department for a semester loading the regulators in test machines for contact life testing. Very many different contact materials were evaluated. Generally dis-similar contact materials were paired.

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[iceworm]

following Junkhound's post:
I don't think I have seen a new brushed DC generator in maybe 40 years, maybe 50 years - Not even welding generators.

Do car alternators even have slip rings any more?

bobby - I clearly understood your question. That isn't the issue.

We need some context. As in, regardless of the answer, what difference would it make?

 

[gar]

190622-2257 EDT

I did a search on automotive alternators and did not find any reference to any with no slip rings. It is possible to make one, but I doubt that it would be cost effective.

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[junkhound]

Pricey, but even wallyworld sells brushless car alternators.



https://www.walmart.com/ip/NEW-BRUS...=sem&msclkid=2dbe0ba894cf15e5b3b756a66db0b2c9

 

[drcampbell]

... Do car alternators even have slip rings any more? ...

As of a few years ago, yes, (except maybe in hybrid powertrains) and the manufacturers show no inclination to change. They're cheap (both the manufacturers and the slip rings/brushes) and low in mass (only the slip rings/brushes) and the brushes generally last longer than the vehicle.
(brushes on slip rings are much less stressed than brushes on commutators)

Automotive alternators usually have 12 or more poles and most often run at about 400 Hz.
(highly variable, as it's directly proportional to crankshaft speed -- the inductance of the stator windings limits current when it's spinning very fast)

Buses and heavy trucks often use brushless alternators. Their alternators will be turning for about 10x as many hours as the alternator on a passenger car, and those markets are much more sensitive to downtime and less sensitive to initial purchase price.

Permanent-magnet brushed DC motors are used for just about every automotive application other than traction motors.