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:
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:
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.