Newsgroups: rec.arts.theatre.stagecraft Subject: Re: Mirror Ball Moters and dimmers References: <%[email protected]> From: Tomi Holger EngdahlDate: 09 Jun 1999 02:01:28 +0300 Message-ID: Organization: Helsinki University of Technology, Finland Lines: 50 X-Newsreader: Gnus v5.3/Emacs 19.34 "Robert Johnson" writes: > I want to use a standard dual D20 sensor dimmer module to control the speed > of a 3 rpm mirror ball motor. I called several theatre equipment dealers and > basically got, "the motor will be OK. It's the dimmer I'd worry about." This > led to a call to ETC tech support. There it was, "I had nothing to worry > about with the dimmer. It was the motor be concerned about." At the going > rate on motors I don't care; however, as I don't have a full complement of > dimmers to begin with I am reluctant to experiment. Can anyone shed some > light on this? Mirror ball rotators an many similar mains powed small rotators use synchronous motors (clock motors). Their speed is affected by the mains frequency. The voltage does not affect their speed. They either rotate if there is enough voltage or do not rotate if the voltage is too low. In some cases you can get a voltage somewhere in the middle and there they barely rote (quite randomly do not rotate or rotate). The bottom of line for this capter is that a light dimmer can't be used to control the speed of typical mirror ball rotator motor. The only thing you can do with a dimmer is to turn the motor on and of when needed. This will generally work with, but there are few things which can cause problems because the motor is very indictive and small load. Those facts cause that not all dimmers work correctly with this kind of load. Possible sonsequencies are damaged dimmer because of indictive spikes (unlikely with good dimmers). Another problems might be unreliable operation of dimmer channels because of of load which is highly inductive and propably below minimum channel load rating. The worst possible consequence of this is that the dimmer conducts only on one half phase, which would cause some direct current component to the output, which will quite quicly fry the motor. The third problem might be that the motor will run even when the channel is turned off if the dimmer happens to pass some current to the output even when channel is turned off (preheat current or current leakage through simmber network fitted in parallel with triac). This kind of problems can be easily avoided by using the dimmer channel in swiching (non-dim) mode and putting a resistive phantom load in parallel with the mirror ball motor (a normal light bulb works very well for this). -- Tomi Engdahl (http://www.iki.fi/then/) Take a look at my electronics web pages at http://www.hut.fi/Misc/Electronics/