Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: Pinspot Question
References: <[email protected]> <[email protected]> <0z4Ag.7677$L31.3878@trndny06>
"David McCall"  writes:

> "charles"  wrote in message 
> news:[email protected]...
> > In article <[email protected]>,
> >   MARTY  wrote:
> >> Please forgive me if this is a silly question.  I just wanted to check
> >> it is ok to plug pinspots into a dimmer rack?
> >
> > I have certainly done it - but some dimmers may not work properly on such 
> > a
> > light load.  You may need to fit a 'dummy' load on the channel to get the
> > dimming function to work properly.
> >
> > -- 
> > From KT24 - in drought-ridden Surrey
> >
> > Using a RISC OS5 computer
> >
> Dimmers are usually intended for incandescent loads.

Yes.

> Some pin spots are low voltage and have built-in transformers.

Most pin sports are made in this way.  

> Wouldn't that look like an inductive load to the dimmer?

The heavily loaded transformer (load is the bulb) in pinspot  
looks like somewhat inductive, mostly resistive load to 
dimmer. Dependign on dimmer design this might work well or not. 

When the light bulb of the pinspsot burns out, then 
what we have is a very inductive load... 


One warning: Some dimmers seem to work nicely with inductive 
loads but can have still one problem: their output waveform 
is not accurately symmetrical. This causes DC offset to the 
output power, and this DC offset can cause overhating of 
pinspot transformer increased resistive losses because of extra 
DC current heating effect, potential transformer core saturation 
because of extra DC on primary).  

There are situations where pinspots can be dimmer with 
dimmers successfully. Been there, done that.

> Many things have that used to have transformers have
> gone to switching power supplies. I don't know if that is
> happening with anything we use yet, but I wouldn't expect that
> a switching supply would behave on a dimmer.

Switching power supplies are quicly comign tolow voltage 
lighting power supply applications. Generally switch mode 
power supply and dimmerd do not like each other 
(can damage each other on some cases). But there are 
special switching power supplies that are designed in  
such way that they can be dimmer with either normal 
dimmers or some special dimmers (reverse phase). 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/