Dimmer output purity test

We are often told "never use dimmer outputs to power other devices, even if
you park them at full".  Admittedly some dimmer outputs have nasty waveforms,
but not all, and different devices react differently to various types of power
waveform distortion in different ways.  I decided to test the output of an
industry-workhorse Strand CD80 dimmer pack, to see how "pure" the full-output
waveform is and if it qualifies to, say, drive fixed-input power for a handful
of LED units, small moving lights and effects, or even some inductive loads
like motors or older power supplies.

With no load at all and *regardless of command setting* for the channel, the
output simply reflects the input power sinewave.  There is always a little bit
of "bleed" and if there's nothing to draw away that tiny current, the voltage
exactly tracks the pack input.  [This is why it's not safe to touch exposed
dimmer outputs, even if they're "all the way down" -- you *will* still get the
tingle you asked for.]  So we need a modest load, even if [as it was in this
case] a string of small "twinkie" lightbulbs.  Just that is enough to flatten
the waveform to zero output at 0% command input.

Output over the DMX-commanded range looks like the normal leading-edge triac
waveform we expect, and nicely free of spikes due to solid output filtering.
Here is what it looks like approaching 100% output, with the last hint of
switching still present just after zero crossings:
Triac switched output near 100%, Strand CD80 dimmer pack
As we push the channel up to 100% the switching artifacts almost completely
disappear, producing something very close to a simple switched non-dim output:
Triac switched output at 100%, no switching artifacts present
So in this case we can declare it safe to power other devices from these dimmer
outputs, as long as they're parked at 100% output all the time.  In fact, there
are per-channel test buttons on the pack itself which could simply be left
enabled on the outputs in question, and then the control input wouldn't matter.

This is useful to know about any given dimmer installation, as it can save the
extra work and wiring of having to run separate fixed power up to lighting
positions where self-powered devices are used, needing only a plug adapter
to feed them.  Load capacity would be calculated from whatever the dimmer
channel is rated for, suitably derated for continuous output -- thus, about
1900 watts on a 2.4k channel, etc.

Perhaps at a minimum, a simple "scopemeter" and a handful of tappable connector
adapters is something to add to a lighting electrician's toolbox, and add tests
like this to the standard venue checklist.

[Compare this page to my old rant(s) about dimmers from nearly 20 years beforehand.  We're still relying on that same technology!
_H*   210903