Re: Variac vs. Regular Dimmer (fwd)

---------- Forwarded message ----------
Date: Fri, 15 May 1998 23:50:40 -0700
From: Bill Noble <william_b_noble-at-email.msn-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Variac vs. Regular Dimmer (fwd)

standard wall dimmers are not designed to handle inductive loads - that
includes anything with a transformer or motor, as well as fluorescent
lights.  They will be destroyed instantly - or nearly instantly by the
inductive kickback from the load.  They are NOT zero switching devices -
they switch on at the phase angle that causes the diac breakdown to match
the RC charging network (the pot adjusts the time constant).  There are
dimmers for inductive loads and dimmers for motor control.  One of these may
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, May 15, 1998 8:49 PM
Subject: Re: Variac vs. Regular Dimmer (fwd)

>---------- Forwarded message ----------
>Date: Fri, 15 May 1998 14:00:30 -0600
>From: Gomez <gomez-at-netherworld-dot-com>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Re: Variac vs. Regular Dimmer (fwd)
>Tesla List wrote:
>> Can a regular modern household dimmer switch be used to changed the
>> output levels on a 15kV/30mA neon?  Or are the power requirements of the
>> neon too high for the dimmer switch?  (I believe those dimmers are
>> electronic now eh?)
>Theoretically, a standard 600W dimmer could handle the average power
>of an unmodified neon, since it's only going to draw about that much or
>a bit
>less.  And there are 1200W dimmers available as well.
>But there is another problem or two.  Cheap wall dimmers use triacs to
>their phase switching.  When triacs (or SCR's for that matter) switch,
>create spikes, and the sharp cut-off of the sine wave (especially around
>degrees phase angle, or 1/2 power) creates harmonics.  Both of these
>can create additional heating and/or saturation in your NST core and
>and interfere with efficient energy transfer.  It is possible that a
>power-factor NST (one with a cap added) might help, but I don't know for
>Another issue is that cheap wall dimmers use triacs for switching,
>higher quality (entertainment industry) dimmers and motor controllers
>back-to-back SCR's, one for each polarity of the sine wave.  The
>is that SCR's have one less junction than Triacs, and therefore _much_
>surge current capability.
>And finally, realize that even the most heavily filtered and
>Tesla coil puts voltage spikes, current surges, and RFI back into the
>line.  And if the discharge hits anything electrical that relates to the
>dimmer in any way, it will kill it.
>I've seen a dimmer get blown right out of the wall, including the utter
>destruction of the steel box it was mounted in, due to a secondary
>to a _grounded_ metal conduit that ran to the dimmer..
>In short, you'd be much better off finding a small (5amp) variable
>in a surplus store, flea market, ham swap-meet, etc.  That size will run
>small coil (a single NST) easily, will take a lot more abuse, and won't
>switching spikes and harmonics.
>.                personal email: gomez-at-netherworld-dot-com                .
>.          personal web page: http://www-dot-netherworld-dot-com/~gomez       .