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Varianle speed hand power tools
3

Varianle speed hand power tools

Varianle speed hand power tools

(OP)
Pardon my ignorance.

What is the basic principle of operation of speed control of modern variable speed AC hand tools like drills and sanders.  I'm assuming it's not a VFD

Thanks.

RE: Varianle speed hand power tools

In a nutshell:

They use a rare type of DC motor that accepts AC.  Since it's a DC motor its speed can be controlled by varying the voltage it gets.  The trigger is a potentiometer that controls the phase firing point of an TRIAC providing the power to the motor leads.

As the phase angle is increased more of each power line cycle is fed to the motor until 100%,(full trigger), full voltage, is fed.   

Keith Cress
kcress - http://www.flaminsystems.com

RE: Varianle speed hand power tools

I believe that the trend today is to use Switched Reluctance Motors (SRM) in Vaiable Speed Cordless Tools.  Cheap, no magnets, easilly wound coils, punched rotor and stator laminations, heat on the stator, no brushes/commutator (cost, reliability) and easy PWM speed control(one 25 cent IC if purchased in the millions).

RE: Varianle speed hand power tools

Sreid,
          That's interesting, I must check next time I go to Home Depot to see what % still use universal, how do you recognize a SRM without pulling it apart?
Regards
Roy

RE: Varianle speed hand power tools

Roydm,

I think the answer is "Take it apart."  No one seems to be using "Has an SRM Motor" as a marketing slogan.  That British Vacuum Cleaner does. The one that has no filters but separates the dust from the air via cyclonic action.

RE: Varianle speed hand power tools

The basic design has been around for 100 years but became pratical using power transistors and contol ICs.  The advantages were always apparent.  The joke was, "SRM are the motor of the future.  Always have been, always will be."  That's now changing.

RE: Varianle speed hand power tools

I think the speed control may be produced also by rotating the brush holder as in
repulsion motor -a type of electric motor for use on alternating current.
The motor has a stator and a rotor but there is no electrical connection between the two and the rotor current is generated by induction. The rotor winding is connected to a commutator which is in contact with a pair of short-circuited brushes which can be moved to change their angular position relative to an imaginary line drawn through the axis of the stator. The motor can be started, stopped and reversed, and the speed can be varied, simply by changing the angular position of the brushes.
Never the less repulsion motors are old and uncommon.
 

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