"Steve" <no@spam.thanks> wrote in message
news:bqOdnT9CR9NIE0fenZ2dnUVZ_s2dnZ2d@texas.net...
> Olaf wrote:
>> "TheSnoMan" <admin@snoman.com> wrote in message
>> news:CW4Bf.4161$rH5.3472@newsread2.news.atl.earthlink.net...
>>
>>>Al Bundy wrote:
>>>
>>>>John Horner wrote:
>>>>
>>>>
>>>>>Al Bundy wrote:
>>>>>
>>>>>
>>>>>>Nomen Nescio wrote:
>>>>>>
>>>>>>"Electric motors develop maximum torque at zero rpm......."
>>>>>>
>>>>>>Is that so?
>>>>>>Unfortunately Nomen, you are a poser, just cutting and pasting things
>>>>>>you read. That leaves you making error after error in how things are
>>>>>>or
>>>>>>could be.
>>>>>>
>>>>>
>>>>>
>>>>>Well Mr. Bundy, I am afraid that Nomen is correct, at least for
>>>>>permanent magnet electric motors. Have a look at:
>>>>>
>>>>>http://claymore.engineer.gvsu.edu/~j...-71.html#54931
>>>>>
>>>>>John
>>>>
>>>>
>>>>Well John, you are wrong because you took a blanket statement and
>>>>qualified it to suit your answer. Again, nice pasting job though.
>>>>
>>>
>>>
>>>There are a LOT of varibles in electric motor design that can effect at
>>>what RPM peak effort is achieved. Generally though with traction type
>>>motors used to power electric cars and such, they achive maximum torque
>>>at zero or very low RPMs to get the load moving.
>>>
>>>--
>>>
>>>-----------------
>>>www.thesnoman.com
>>
>>
>> I think I may see where Mr. Bundy is saying. Without having read any of
>> the links provided, it makes sense to me that at zero RPM the motor is
>> putting out zero torque. Once any torque great enough to make the motor
>> turn is applied, then the RPM is no longer zero.
>
> What batshit!
I agree. (Good thing you didn't refer to bull shit, then I'd have been
offended.) After having thought about it after posting I realized a motor
can put out torque without turning. I thought of a drill with keyless chuck.
When the chuck tightens on the bit the motor is still putting out torque
>
> If electric motors put out *zero* torque at zero RPM, they'd never begin
> to rotate at all. Internal combustion engines DO have zero torque at zero
> RPM, which is exactly why you need an electric motor to start them!
>
> How much torque an electric motor does put out vs. RPM depends a lot on
> the design of the motor.
>
> DC and AC/DC commutator motors put out their maximum torque at 0 RPM (but
> will burn out if held at 0 RPM because only one winding on the armature is
> carrying the full load). An example of a DC commutator motor is the
> starter motor in a car, or the traction motors in older locomotives. An
> AC/DC commutator motor is the type used in vacuum cleaners, hand power
> tools, and blenders.
>
> AC induction motors put out their peak torque at a few percent less than
> their free running maximum RPM. As you lug them down, torque goes up at
> first, but lug them too far and torque begins to decline again, but it
> never drops to zero even at zero RPM. An example of an AC induction motor
> is a fan motor, AC blower motor, AC compressor motor, or shop air
> compressor motor. The most commonly used AC motors in the world.
>
> AC Synchronous motors put out their maximum torque at the synchronous RPM.
> They're used in heavy industry because they can be set to run at leading
> power factor to compensate for induction motors that run at a lagging
> power factor- save's the industry money overall.
>
> Variable-frequency drive motors are induction or synchronous motors driven
> by a variable frequency AC source, so that you can make them put out peak
> torque at any RPM you want. Modern AC locomotive traction motors are
> variable-frequency drive motors.
>
> But regardless of the type, ANY self-starting electric motor puts out SOME
> torque at 0 RPM. An example of a non-self-starting type would be a
> synchrounous motor without any start/damper windings... but that's a
> laboratory curiousity as all real-world electric motors have a provision
> to give them self-starting torque.
Makes sense to me. :)
