[TowerTalk] Reply - KW3000 with 1/2 inch Drill Motor - Wrongassumption in responses

[Roger (K8RI)]

Richard (Rick) Karlquist wrote:
> Dubovsky, George wrote:
>   
>> You will still lose torque with a pwm light dimmer. You will need something like an variable speed drive, where you vary the drive frequency and voltage simultaneously, essentially synthesizing a complete sine wave at an adjustable frequency. I use them on three-phase motors on my lathe and mill, but they are also available for single-phase motors. Not cheap, but less than the Hole Hawg ;-)
>>
>> 73,
>>
>> geo - n4ua
>>     
>
> The idea of the PWM method is that you have full torque when
> on, but are not on all the time.  You do lose horsepower, but
> not torque, 
You still lose average torque.  The motor has inertia and when hit with 
a series of pulses you still have a heating problem under load.
> AFAIK.  It's similar to pulsing the ON/OFF switch
>   
Which can also lead to excessive heating.

73

Roger (K8RI)
> on the drill.  I am not sure if there is any difference between
> a PWM motor speed controller and a light dimmer.
>
> A variable frequency drive sounds like something for an AC induction
> motor.  Most drills AFAIK are AC/DC motors, for which frequency is
> obviously irrelevant.
>
> If the above is wrong, someone correct me.  I want to get a
> Hole Hawg too, as soon as I figure out how to slow it down.
>
> Rick N6RK
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