[modeleng] Fw: modeleng Digest V2 #229
- From: "shep" <shep.28@xxxxxxxxxxxx>
- To: "Modeleng" <modeleng@xxxxxxxxxxxxx>
- Date: Sun, 11 Sep 2005 10:04:25 +0100
Dear Charles and Dorothy
Thank you for your clear exposition of this subject. I now understand a
little bit more about the mystery of vari-speed motors.
Cheers! Hubert
>
> ------------------------------
>
> From: "Charles & Dorothy Brumbelow" <cbrumbelow@xxxxxxxxxxx>
> Subject: [modeleng] Re: Vari-speed motors
> Date: Sat, 10 Sep 2005 06:41:31 -0500
>
> I don't know what you mean by "ordinary AC motor" Hubert -- split phase or
> a
> variant thereof I suspect. If that is what you are talking about, those
> motors all operate at some fixed fraction of being syncronous with the AC
> line (mains) voltage. A two pole in North America is usually in the 3500
> RPM range -- 60 cycles per second less slippage, a four pole is 1750, for
> example. (Yes, I know Hertz is the new word for cycles; it just doesn't
> seem
> right.) So any electronics to vary the speed of such a motor must do it
> by
> varying the effective frequency fed to the motor, and must control the
> current to maintain torque and minimize heating. Permanent magnet motor
> with converter controller might be the better choice for a small motor.
> Probably much easier to find and less costly, at any rate. Charles
>
>> Hi all!
>> Sorry to rabbit on and on about my construction of this little lathe.
>>
>> Now that various kind and clever friends have given me a variety of ideas
>> regarding the boring of the headstock of this little lathe, I am able to
>> proceed with detailed design. I notice that a variety of small lathes
>> and milling machines are now offered with vari-speed motors. If I could
>> use one of these, it would simplify the headstock design, as I could then
>> have just one pulley instead of a cone of pulleys. This single pulley
>> could perhaps be designed for use with a tooth belt.
>>
>> I am totally ignorant in the world of these vari-speed fractional hp
>> motors (mine would be quite small - say 1/10 hp). In the old days, you
>> had to use a DC motor, or a three-phase motor to be able to vary the
>> speed. But I believe that in the brave new world of electronics, an
>> ordinary AC motor can be adapted to vari-speed without losing torque at
>> the lower speeds.
>>
>> Any ideas? Thank you in advance!
>>
>> Cheers! Hubert
>
>
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