[TheForge] grinder slow r.p.m.

[theforge@mailman.qth.net]

Most handheld power tools are driven by a universal motor.   These will 
run on DC or AC single phase, not polyphase, which is how the VFD's 
work.  You could regulate the speed of a single phase AC induction motor 
with VFD principles but as stated before, these hand grinders are 
universal motors.   Their speed is derived by the available current and 
the load on the motor.   In fact, they generally already have a speed 
regulating mechanism built in to prevent overspeeding, though it is a 
static device.  The unit Harbor freight sells is not a VARIAC.  VARIACs 
are a transformer with a variable tap on the secondary that generally 
provides from 0-120 percent of the input voltage.    The Harbor Freight 
unit ( and others, including the controls built into most new tools) are 
based on solid state devices that generally chop the voltage/current 
coming in, thereby reducing the effective current delivered.  A high 
tech version of the way we used to control the speed of electric 
handrills by blipping the trigger.

Charles

Mark Pesetsky wrote:

>
>You might try a motor speed controller.  HF sells one for twenty bucks
>and it will work on most power hand tools since they all seem to use
>universal motors.  I bought several of these a couple of years ago.   I
>use them for my old single speed jigsaws as well as my 4inch hand grinder.
>
>Charles
>
>
>The only problem with the VARIAC type of motor controllers is that you lose
>horse power.
>
>I use a VFD 3Phase Converter and a 2hp motor on my 2X72...ALLLLL sorts of
>ways to customize the settings on this unit.
>
>
>
>  
>