ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

ECN Shout Chat
Top Posters(30 Days)
Admin 19
Recent Posts
Anyone hiring inspectors?
by HotLine1. 03/27/17 08:03 AM
Old decora style outlets
by Admin. 03/25/17 11:40 AM
ESA Arc flash course
by TheShockDoctors. 03/24/17 10:15 AM
fuse rejectors
by HotLine1. 03/24/17 07:53 AM
Another Forum Update
by Admin. 03/22/17 03:04 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
231,627 Are you busy
166,458 Re: Forum
160,717 Need opinion
Who's Online Now
0 registered members (), 63 guests, and 10 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#143621 - 08/13/05 11:05 AM lighting control  
james S  Offline
Member
Joined: May 2003
Posts: 107
West England
has anyone came across flourecent lights that are dimmed down to a set level with a 24 volt dc supply?my problem is when i diconnect the dc supply from one fitting the rest of the fittings in the room go bright,which is a problem given the type of enviroment they are illuminating.my idea was to find the resistance imposed across the dc supply and replace the fitting with the same value resistor enabling me to take the fitting out of service for maintenance with the remainding fittings dimmed.
any info would be much appreciated


Test Equipment:
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement

#143622 - 08/13/05 11:58 AM Re: lighting control  
britspark  Offline
Member
Joined: May 2005
Posts: 54
southampton united kingdom
James,
could you give a bit more information mate, what type of fittings, control gear manufacture etc, are the fittings all on the same dim pack ?

britspark


#143623 - 08/15/05 07:27 AM Re: lighting control  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Second the questions. What kind of dimmers are in use? Are they just varying the voltage or are they some kind of PWM (Pulse-Width Modulation) controller?


#143624 - 08/15/05 11:45 PM Re: lighting control  
aussie240  Offline
Member
Joined: Jul 2005
Posts: 223
Blue Mountains, NSW, Australia
If it's the electronic type of ballast with remote dimmer you're describing, the dimmer is just a typical potentiometer, so yes it could be replaced with a fixed resistor.
These ballasts rectify the incoming mains, with the resulting 340V DC fed into a high frequency (~30-100KHz) ferrite transformer via high voltage switching FET's or transistors. There's a controller IC that sets frequency and pulse width of the drive to these transistors, as well as incorporating other features like shutting down if the tube is too worn out to fire etc.
It is a more efficient way to run a fluorescent tube than an iron cored choke partly because fluoro tubes work better at hight frequencies, and also higher frequencies means less wire (ie. less voltage drop) wound on the inductive components. A further advantage is you eliminate the danger of the strobing effect near rotating machinery. The downside of these ballasts is that they're much more susceptible to damage by high voltage spikes on the mains.
The old way to dim flourescent tubes is to run them via a normal triac light dimmer and iron cored choke, but with the tube heaters permanently energised via a separate filament transformer. The range of control isn't the best...problem being that unlike an incandescent bulb, a fluoro tube needs a minimum voltage for the mercury vapour to ionise. By using the electronic ballast method you can keep the voltage high but just vary the RMS current through the tube by altering the pulse width.

[This message has been edited by aussie240 (edited 08-15-2005).]


#143625 - 08/16/05 04:19 AM Re: lighting control  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
240,
Great comments there mate!. [Linked Image]
I agree, the older form of dimming was probably more wasteful, with respect to energy use than anything we use today.
The best thing about HF Ballasts these days is the lack of Strobo-scopic effect, as you mentioned.
Where as a few years ago, you had to have a few fittings on different phases to prevent the same thing. [Linked Image]


Let's face it, these days if you're not young, you're old - Red Green grin


Member Spotlight
HappyElectrician
HappyElectrician
Penn USA
Posts: 31
Joined: December 2011
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.011s Queries: 14 (0.003s) Memory: 0.7675 MB (Peak: 0.9043 MB) Zlib enabled. Server Time: 2017-03-28 08:13:36 UTC