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Re: [TCML] LTR/STR and spark length

Lamp dimmers have some limited uses in coiling.  I
have found that cheap, 120vac/600W lamp dimmers sold
at Wal-Mart and similar outlets make dandy speed
controls for vacuum cleaner motors (used on sucker
gaps).  I have also used dimmers as speed controls for
asynchronous rotary spark gaps based on universal-type
brush motors.  One ARSG was based on an angle grinder.
 Another was based on a small Black & Decker router. 
Dimmers controlled these with no issues.  Lastly, a
dimmer and a series motor run capacitor work well for
exciting a 12v car ignition coil from a 120vac outlet.
 I've tried this with various caps and ignition coils,
and it has always worked with no damage to the dimmer.

Not all motors will tolerate a dimmer.  Most AC
induction motors--even the cheap little shaded pole
motors--will seize up when placed in series with a
dimmer.  I've never ruined a motor or a dimmer this
way--the motors simply refused to rotate and made
scary buzzing sounds.

On the other hand, most brush-type "universal" motors
used in vacuum cleaners and many common power tools
respond very smoothly to dimmer speed control.

My cheesy, homebrew secondary coil winding jig uses a
gear motor from an ice cream maker (low RPM, lotsa
torque, great for coil winding).  Unfortunately, the
little shaded pole induction motor inside the thing
balks at dimmer speed control--won't budge.  With a
10A variac in series, the thing can be smoothly
throttled across its whole RPM range.  Sometimes, you
just gotta bite the bullet and shell out for a variac.



--- neal@xxxxxxxxxxxxxxxx wrote:

> Hi Scott,
> You think a dimmer wouldn't work properly even on a
> cooling fan? I do have a
> smaller (5 amp)variac that I could use, but like
> previously suggested, I may
> not adjust the flow at all. If I had to, I could go
> the baffle route. I've
> heard this before about dimmer switches. What is the
> problem with them, in
> relation to coils? Thanks for your help,
> Neal.
> Quoting Scott Bogard <teslas-intern@xxxxxxxxxxx>:
> >
> > Neal,
> >      Never use a dimmer with anything coil
> related, it will not work
> > properly.  Many of us have been down this road, it
> never ends well.
> > Either buy a variac, or in this circumstance I
> would suggest that you
> > just build a baffle like Bart said.  It can be as
> simple as a piece of
> > cardboard taped to the back or your fan covering
> it partly.  Best of luck!
> >
> > Scott Bogard.
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