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

[royp]

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?

 

[NascentOxygen]

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.

 

[cnh1995]

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.

 

[royp]

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.

 

[CWatters]

https://www.google.co.uk/url?sa=t&s...WMAB6BAgPEAE&usg=AOvVaw3Wy8qMOosbTYt7ksXZwLws

Mentions 12,000 rpm as possible.

 

[royp]

Many thanks, Cwatters. It has some sound experimental result.

 

[sophiecentaur]

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.