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#57140 - 10/05/05 09:53 PM dimmers  
jw electric  Offline
Member
Joined: Sep 2005
Posts: 106
Asheboro, NC
Just wondering if someone could help me understand the difference between a low voltage dimmer and an incadescent or line voltage dimmer?


Mike

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#57141 - 10/06/05 07:06 AM Re: dimmers  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I'm not sure about "Low Voltage" dimmers, but I believe the scr-type controller in the dimmer for electronic LV transformers operates in reverse than the typical scr...

Instead of the current being let through at a certain point on the voltage wave (the trigger point) which would cause a bit of a surge, the current comes on at zero and shuts off at a corresponding trigger point.
From what I understand, this protects electronic LV dimmers from spikes while allowing the same average, (or RMS?) current flow through the electronics.

Standard dimmers can be used on most magnetic LV transformers.

[This message has been edited by Redsy (edited 10-06-2005).]


#57142 - 10/06/05 06:18 PM Re: dimmers  
gideonr  Offline
Member
Joined: Dec 2004
Posts: 161
Edinburgh, Scotland, UK
Non-magnetic low voltage transformers are essentially cheap switch-mode power supplies, and rectify the mains into a capacitor, then down convert it at a high frequency.

Trailing edge dimmers are needed to feed these capacitive loads, because the inrush current from a leading edge dimmer would stress the capacitor and rectifiers.

Trailing edge dimmers cannot use an SCR or TRIAC, and have to use a pair of MOSFETs or IGBTs which makes them more expensive.


#57143 - 10/06/05 10:01 PM Re: dimmers  
distributor x  Offline
Member
Joined: Jul 2005
Posts: 57
Canada
"Standard dimmers can be used on most magnetic LV transformers."

If I am not mistaken, when it comes to LV magnetic dimming, the dimmers must be derated by 20% to compensate for loss from transformer IE 600W LV magnetic dimmer is only good for ~450W (9 50W lamps).



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