Actually field current controls output current, not output voltage.IIRC the current at 12vdc is 2 amps.
Varying the field is going to vary the DC output voltage, rpm will also affect the output, do you intend to regulate it?
An alternator is not like a DC generator. The battery is what keeps the voltage near ~14V. Saying you can control the output voltage of an alternator by controlling the field is like saying you can control the current through an LED by controlling the voltage across it, or like saying you can control the voltage at the collector of a transistor by controlling the base voltage...How come I can vary the voltage output on an unloaded alternator by varying the field?
Just as it does on a DC generator.
The regulator keeps the Voltage at 14.5 volts loaded or unloaded.
That is what I have done, you need automatic regulation for precise control however, if the load is not very constant.thanks everyone
so variable DC supply can be used to excite alternator instead of battery in order to get 3-phase output .
Similar thoughts and feelings based on like experiences here as well.I don't agree, I have designed and marketed DC generator regulators that were virtually identical to the regulator used in automotive versions after the mechanical one.
The battery does not keep the generator to 14v it is the regulator, by varying the voltage and hence current through the field the output can be Varied.
You can run a Alternator without a battery connected apart from the initial excitation, and use a variable supply to vary the output voltage, empirical bench testing has shown it.
Both Alternator and DC generator both are exited by a DC field.
Exactly. Since the field (rotor) circuit acts as a resistor (~6Ω), you can consider the average field voltage (I=E/R) , or the average field current (E=IR) as the control input to the alternator....As I see it the voltage regulator circuit does its best to regulate the output voltage by voltage sensing and controlling the overall power sent to the field coil...
I have never, ever, said that an alternator voltage regulator senses current. The car's alternator voltage regulator senses the battery voltage, which depending on state of charge of the battery, will be somewhere between ~12.6V and 14.5Vdc....not current sensing to keep the output current constant regardless of what output voltage it has to make to do so.
I have never said "that a alternator ... charging system as being a constant current". I am saying that an alternator charging system is designed to maintain the battery voltage within +- a few mV of the VR setting, typically 14.2 to 14.5V.I am not sure how anyone could classify a alternator or generator system as being a constant current device when everything about its control systems suggests that they are designed to keep the output voltage as constant and stable as possible regardless of the current draw provided it's within the devices current supplying limit.
That is because you work on 1930's technology tractors. Load Dump is a well-documented and well-understood problem that surfaced as the electronics in cars became more complex. Just look at the difference in a voltage regulator IC spec'ed for use in automobiles vs one that is not. The suppliers of ICs for the automotive market have gone to great lengths to make their products immune to the effects of Load Dump. It is really bad practice to purposely induce Load Dumps to "test" a charging system.As for disconnecting the battery and killing everything electrical on the vehicle I say out rightly BS! I've done it countless times both accidentally and deliberately to every type of vehicle and machine I have ever owned and had to work on for charging system related issues and never once has anyone them ever had a single electrical or electronics device failure from it.
Not at all. Reread what I wrote, more carefully. If you disagree, refute the specific claims I made about how the Lundell alternator behaves in post #14. Don't just keep repeating yourself.Appears to be a somewhat of a contradiction?
Which is exactly what I just said in post #14.Actually the method of field control is virtually identical.
Then refute the claims I make in post #14. Explain why a Lundell alternator doesn't need current limiting. Explain why an alternator will create a load dump, while a generator does not. Explain why an open-circuited alternator generates hundreds of volts, while a generator will not.I agree that the field current directly varies the alternator output voltage. It only indirectly controls the output current.
There is thus no fundamental difference between a DC generator and an alternator generating rectified DC...
The Lundell alternator current is limited by the leakage inductance of the design.Then refute the claims I make in post #14. Explain why a Lundell alternator doesn't need current limiting. Explain why an alternator will create a load dump, while a generator does not. Explain why an open-circuited alternator generates hundreds of volts, while a generator will not.
They are inherently self limiting due to inductive impedance of the stator windings and its iron cores magnetic properties.Then refute the claims I make in post #14. Explain why a Lundell alternator doesn't need current limiting. Explain why an alternator will create a load dump, while a generator does not. Explain why an open-circuited alternator generates hundreds of volts, while a generator will not.
I work on vehicles and equipment with modern alternators and electrical systems that have been largely updated to modern designs. All of our farm machinery regardless of age have standard 12 or 24 volt system with 70 - 150+ amp alternators. The oldest vehicle I own and regularly drive now is a 1994 model with all modern EFI and whatnot.That is because you work on 1930's technology tractors.
From personal experience and observations I can say that years ago both DC generators and AC alternators used the same type of electromagnetic buzzing solenoid designs to control their voltage output. Also it's not that hard to transplant a modern alternators regulator system into a old DC generators voltage regulator box and have it control things rather than using its old buzzing solenoid design.I am saying that the way an alternator charging system works is a bit different than the way a generator charging system.
At a constant RPM, a DC generator's output voltage is proportional to it's applied Field voltage, Vo=k*Vf. The current out of the generator's output terminal is a function of the external load (within its useful range). It is a voltage source..., so much so that generator charging systems need to have a current-cutout circuit to protect the generator from excessive output current in the event that it is charging a badly discharged battery.
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by Luke James
by Luke James