Leaky Dimmers
- Thread starterlilricky
- Start date
porkchop
Well-Known Member
.5 amp not .5 Ohm, yup. I need to stop doing math while doing several other things. I really meant for the resistor to be in series with the LEDs not parallel so the current would be limited by the draw of the LED itself and wouldn't result in pyrotechnics, but better advice has been given and followed already so I edited my previous post.
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taneglaus
Member
Interesting post. I had a similar issue with dimmer leakage on a cathedral set where I used incandescent candelabra flickering lights for candles. The lights were custom wired in parallel. When dimmed off, the center light would stay on. The lights on either side of the center would go completely off. I finally realized it was a dimmer power leakage issue. I had an extra 500 watt par can so I plugged it into the same dimmer and that solved the problem. This is a heavy duty dummy load, but it was at hand. It did create another problem in that the dummy load par can was backstage and actors would see this light on and not pointing toward the stage. They'd either tell me there was a problem with a light, or try to aim the light toward the stage...even though...even though...even though I repeatedly told to leave it alone. I finally had a tech hide the light from the actors.
JD
Well-Known Member
Are you sure they were incandescent and not neon? That "one staying on" would be more typical of the neon type, and yes that would be the exact outcome as they are pretty much open-circuit under a specific voltage. The firing circuit in the dimmer would pass more than enough to keep one ignited, but it would be the one with the lowest ionization voltage.
@taneglaus Understood and writing in full support. In the my amateur days in the 1950's I was using a combination of hot-plates and lamps on stands in a basement shop area as dummy loads for practicals such as colorful neon signs on the set of a bar or wall sconces with medium-based 120 volt flickering neon candle lamps in which the contacts within the globe were cut in the shape of flames and fired across the bottom of the metal flames before working their way up to the tips similar to a Jacob's ladder. Later on in the fall of 1973 I was using lamps on stands in the basement shop of a 2183 seat soft-seater. Still later, I was doing the same thing in the trap room of a newly built producing theatre. When I took a hiatus from building and running shows to play head electrician in a local IA AC servo automation and scene shop, we built the sets and automation for the German production of the Who's Rock Opera Tommy in 1995 in Offenbach / Frankfurt am Meine (Sp?) and Dave Grille the associate lighting designer specified redundant incandescent dummy loads for at least a dozen practicals built with North American 120 volt lamps each powered via 230 / 120 volt isolating step-down transformers as many of the transformers were housed within the bases of various props. The German rental supplier who provided all of the dimmers and control in Germany knew all about redundant dummy loads and rows of cute little 'traffic light' style fixtures hanging in rows adorned a wall in our dimmer room located in an off-stage room DSR. We didn't care if the dummy loads were red, green or amber so long as each load provided two small incandescent lamps in parallel for redundancy on every dimmer requiring a dummy load. That was 1995. In 1996 our same Canadian shop won the toss to build all of the AC servo automation and scenery for the Who's Rock Opera Tommy again only this time for London's West End, I want to say we were loading into The Shaftesbury this time but I could easily be mis-remembering the name of the theatre. What I remember for sure was the stage door was on a tiny narrow side street and rolled up to reveal the stage at least 8 feet below finished grade. Vertigo was the name of the riggers the British producers contracted for all custom on-site rigging and the British electrician contracted to handle the load in was primarily used to loading in touring arena rock acts and wasn't prepared for our requirements for dummy loads. He was a very pleasant and knowledgeable lad but this was 1996 and he was not at all familiar with our requirements for resistive and / or incandescent dummy loads. One of our practicals was a street lamp with a 240 /120 volt isolated step-down transformer conveniently located within the portable practical prop's base. The pleasant British electrician kept flashing it to full and our transformer GROANED and vibrated MIGHTILY! He kept insisting something was clearly wrong with our transformer or its wiring and I kept insisting all it needed was a dummy load. The fellow had years and many tours under his belt and kept looking at me like I was daft. I was getting nowhere speaking with him, we were apparently separated by our common language. In desperation I grabbed a nearby 240 volt PAR can and a two-fer as a dummy load then flashed my prop and he was stunned that it now illuminated to full brilliance and in near virtual silence. Having proved my point, I suggested all of our transformer coupled props would behave the same with anything resembling a 25 Watt, or whatever was commonly available, 240 volt incandescent lamp.
Looking back at the whole build in general, our Canadian shop was scrutinized more closely by Germany's TUV inspectors who were particularly picky regarding our pneumatically delayed E-stops as they were more used to E-stops instantly totally cutting power until we proved to them we could stop our AC servos faster and safer by commanding them to stop and keeping their motors powered for 1.5 seconds while the springs in the magnetically released brakes clamped and gained a firm lock on the drives. This was especially true, as we demonstrated, for yo-yo drums located high overhead supporting heavy vertical loads which were capable of slowly unwinding even when driven through 90 degree worm-gear driven drive-trains. Once the TUV-ites realized we were accomplishing our brief time delays via Sprecher Shu's pneumatic [Non electronic] delay modules developed especially to mechanically delay the operation of small contactors for the European market even the TUV-ites were impressed by our attention to THEIR details. Getting our automation systems past the Lords of London was a comparative snap once they realized our systems had been passed by Germany's TUV.
Toodleoo!
Ron Hebbard
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