RE: Dimmers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:57 AM 11/25/2003 -0700, you wrote:
>Original poster: "Philip Brinkman" <peeceebee-at-mindspring-dot-com>
>O.K., You got me curious... I took apart my dimmer, it has a linear
>variable resister... resistance lowers voltage, or so I learned in
>electronics 101, this is how the volume control for your radio works, I
>don't know what a triac dimmer is, I don't have an ossciliscope, to measure
>wave form, all I know is it works perfectly on my neon sign transformer. I
>made a jacobs ladder, the arg length varies, I use it on my tesla coil, the
>spark length varies. I'll buy a voltmeter to check it out, but I'm pretty
>sure the volts go down as the resistance goes up.

Precisely.. as you increase the resistance, the capacitor charges more 
slowly, delaying the time when the voltage across the cap gets high enough 
to "fire" the triac.  Actually, most dimmers use a device called a Quadrac, 
which is a triac with a diac (or similar 4 layer device) in series with the 
gate.  A triac will actually fire at a fairly low voltage, and, it would 
draw current on the gate anyway, keeping the cap from charging, so you want 
another voltage triggering device in series.   In older designs, a neon 
bulb was used for this function.