Dimmer Switch as a Controller

[klmok]

The ordinary household dimmer switch does give some speed control for
say a 115V motor but is effective only for the top 1/4 end of the knob
setting.

Is there any way to changes the parts and the values of the components
so that it is effective for the full range of the knob setting?

 

[Tweetldee]

"klmok" <klmok@shaw.ca> wrote in message
news:3f4c56b4.133440985@shawnews.ed.shawcable.net...

The ordinary household dimmer switch does give some speed control for
say a 115V motor but is effective only for the top 1/4 end of the knob
setting.

Is there any way to changes the parts and the values of the components
so that it is effective for the full range of the knob setting?

You didn't say what kind of motor that you're trying to control with the
dimmer. If it's a synchronous motor, then the problem is with the motor,
not the dimmer. The synchronous motor speed is set mainly by the frequency
of the power source and the number of poles in the windings. As you've
experienced, voltage does influence the speed somewhat, but significantly
reduces the torque produced. These motors are more efficiently controlled
by changing the power frequency. But, that has limitations also, since
synchronous motors are built with a specific frequency range in mind,
usually 50/60 Hz. Power frequencies outside this range will overheat the
motor, leading to failure, or possibly a fire.
If you need to control the full speed range of a motor, then the best and
most efficient way is to change the motor to a universal type motor (the
kind used in AC/DC appliances such as drills, saws, food mixers, sewing
machines, etc.) where the speed is dependent on the voltage applied. These
motors are usually identified by the use of brushes and a commutator ring
inside the motor.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.

 

[Mike Berger]

And then don't use a conventional light dimmer. They don't control
voltage, they control duty cycle. You'll see all kinds of weird frequency
components and funny waveforms, which are fine for incandescent
lights, but not for motors.

Use a variac to control the speed of a universal motor.

Tweetldee wrote:

If you need to control the full speed range of a motor, then the best and
most efficient way is to change the motor to a universal type motor (the
kind used in AC/DC appliances such as drills, saws, food mixers, sewing
machines, etc.) where the speed is dependent on the voltage applied. These
motors are usually identified by the use of brushes and a commutator ring
inside the motor.

 

[Tweetldee]

"Sam Goldwasser" <sam@saul.cis.upenn.edu> wrote in message
news:6wfzjnc7v7.fsf@saul.cis.upenn.edu...

Mike Berger <berger@shout.net> writes:

And then don't use a conventional light dimmer. They don't control
voltage, they control duty cycle. You'll see all kinds of weird
frequency
components and funny waveforms, which are fine for incandescent
lights, but not for motors.

Use a variac to control the speed of a universal motor.

Actually, the speed controls of variable speed electric drills and
such are very similar to light dimmers, though with some sort of
correction for the inductive nature of the universal motor. A
Variac would work but would result in very low torque at low
speed while a phase control speed control can maintain torque.

A Variac does work quite nicely for shaded pole type induction motors
used in fans.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/

Yep, yep, yep!!! The speed control in a drill motor is almost identical to
a standard dimmer with the addition of a snubber around the triac (or they
use a snubberless triac). Otherwise, almost identical.
Cheers!!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.

 

[klmok]

On Wed, 27 Aug 2003 18:00:34 GMT, "Tweetldee" <dgmason99@att99.net>
wrote:

Yep, yep, yep!!! The speed control in a drill motor is almost identical to
a standard dimmer with the addition of a snubber around the triac (or they
use a snubberless triac). Otherwise, almost identical.

Aha. So how do you modify a dimmer switch to do that, that snubber
thingy? I used a motor as an example but what I really want is a
cheap variable power control switch for fun projects.

 

[Tweetldee]

A snubber is a series resistor/capacitor that is wired across the MT1 and
MT2 terminals of the triac. Typical values for the snubber are 47ohms/1W
resistor and 0.1uF/600V capacitor. The capacitor should be an AC rated
capacitor, like a metallized polypropylene variety.

-------+--------+
| |
----- ---
/\ \/ ---
----- |
/ | /
/ | \
| /
| \
| |
-------+--------+

The snubber will not affect the dimmer's operation in any way when used with
non-reactive loads, but will offer a good deal of protection when used with
highly reactive loads such as motors, transformers, etc. Snubbers are used
extensively in circuits that control large relays, and even across the relay
contacts.
Cheers!!!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.
"klmok" <klmok@shaw.ca> wrote in message
news:3f4ec6da.5520032@shawnews.ed.shawcable.net...

On Wed, 27 Aug 2003 18:00:34 GMT, "Tweetldee" <dgmason99@att99.net
wrote:


Yep, yep, yep!!! The speed control in a drill motor is almost identical
to
a standard dimmer with the addition of a snubber around the triac (or
they
use a snubberless triac). Otherwise, almost identical.


Aha. So how do you modify a dimmer switch to do that, that snubber
thingy? I used a motor as an example but what I really want is a
cheap variable power control switch for fun projects.