What is the optimal RPM for charging a battery with an automotive alternator?

In summary, the conversation discusses the rotational speed of a generator's rotor and its impact on charging a battery. It is mentioned that the standard frequency for a generator is 3000 rpm for Europe and 3600 rpm for the US. However, it is possible to have a generator with a rotor speed of 6000 rpm and still charge a battery as long as the AC voltage is rectified into pulsating DC. It is also noted that the terminal voltage of the generator can be controlled by varying its speed and field excitation. The conversation also brings up the example of a car engine, which rotates at a much faster speed on the motorway. It is mentioned that automotive alternators are regulated to adjust the current in the field wind
  • #1
royp
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Hello,

I have a very basic question. And, admittedly, my knowledge is limited in this field.
It is about the rpm of a rotor inside a generator. I know, to be aligned with the existing grid, standard frequency (of 50Hz, Europe and 60Hz, US) will require the RPM to be 3000 and 3600 respectively.

But suppose I am having a generator with rotor rpm around 6000 and I want to charge a battery with the electricity generated. It is very localised and isolated. Are we free to have such high rpm without disturbing/damaging thinhgs?
 
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  • #2
The AC will be rectified into pulsating DC, then that is used to charge the battery. So long as the voltages are appropriate there should be no problem. Any transformers will need to be able to function on that higher frequency AC.

The rotational speed of the alternator in your car varies over a wide range as engine speed changes.
 
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  • #3
royp said:
But suppose I am having a generator with rotor rpm around 6000 and I want to charge a battery with the electricity generated.
You can control the terminal voltage of the (isolated)generator by varying its speed and field excitation.
But for charging a battery, the ac voltage has to be rectified first , as NO mentioned earlier.
 
  • #4
Yes, Many thanks. I did not mention but I was told that the output of an alternator can be rectified through a diode before being able to charge a battery. The specific thing I have in mind is the car engine; which, presumably, rotate much faster when the vehicle is on the motorway.
 
  • #6
Many thanks, Cwatters. It has some sound experimental result.
 
  • #7
royp said:
Yes, Many thanks. I did not mention but I was told that the output of an alternator can be rectified through a diode before being able to charge a battery. The specific thing I have in mind is the car engine; which, presumably, rotate much faster when the vehicle is on the motorway.
Automotive alternators are always regulated by adjusting the current in the field windings to get the required voltage. This is necessary to deal with variations of 10:1 in engine speed and to ensure the alternator will supply enough current even at below 1000 rpm.
Low power alternators usually have a simple regulator on the output to avoid overcharging the battery but they will not provide as much energy overall.
 
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1. What is an alternator/AC generator?

An alternator or AC generator is a device that converts mechanical energy into electrical energy. It consists of a rotor, stator, and diode rectifier and is used in many applications, including cars, power plants, and portable generators.

2. How does an alternator/AC generator work?

An alternator/AC generator works by using the principle of electromagnetic induction. The rotor, which is connected to the engine, rotates inside the stator, which is made up of copper wire coils. As the rotor spins, it creates a changing magnetic field, which induces an electric current in the stator coils. This current is then converted into usable electricity by the diode rectifier.

3. What are the advantages of using an alternator/AC generator?

The main advantage of using an alternator/AC generator is its efficiency. It can produce a large amount of electricity with minimal energy input. It also has a longer lifespan compared to other types of generators and is generally more reliable. Additionally, alternators can produce electricity at different voltages, making them versatile for various applications.

4. What is the difference between an alternator and an AC generator?

The terms alternator and AC generator are often used interchangeably, but there is a slight difference between the two. An alternator is a type of AC generator that produces alternating current, while an AC generator can also produce other types of current, such as direct current. In practical applications, however, the two terms are often used synonymously.

5. How do I maintain an alternator/AC generator?

To maintain an alternator/AC generator, it is important to regularly check and clean the connections and terminals, as well as the brushes and slip rings. It is also essential to inspect the belts and pulleys for any signs of wear and tear and to replace them if necessary. Additionally, keeping the alternator/AC generator well-lubricated and free of debris can help prolong its lifespan and ensure optimal performance.

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