ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Old motor connections
by suzannemiller - 09/28/21 02:53 AM
How's all our Non-US folks doing?
by grich - 09/27/21 11:59 AM
Well I am back to stay (nearly 6 years)
by Bill Addiss - 09/26/21 11:09 PM
nec 110.3 (B)
by HotLine1 - 09/26/21 03:42 PM
New in the Gallery:
Now you know.
Now you know.
by Tom_Horne, September 7
February, North East Indiana
February, North East Indiana
by timmp, July 25
Who's Online Now
2 members (gfretwell, Scott35), 35 guests, and 21 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Apr 2003
Posts: 362
Member
So I am reading the back of the Lutron dimmer & fan control selection guide and it tells me dimming the lights 10 percent saves, 10 percent electricity. I learned that that this is not true. Can you guys straighten me out? The chart continues with 25 saves 20 percent, 50 saves 40 percent and 75 save 60percent.

Ob


Choose your customers, don't let them choose you.
Joined: Jul 2004
Posts: 9,663
Likes: 4
G
Member
Ten percent of what?
10% of the pot range?, 10% of the current? 10% of the light output? I think it is a throwaway line.
If they mean you are letting 10% of the wave through that might be accurate. Get out your log tables and start up your slide rules. wink
Dimmers certainly reduce the watts used when they are "dimmed"
The real question is how much light you are getting for your lighting dollar


Greg Fretwell
Joined: Jul 2002
Posts: 8,407
Likes: 2
Member
Yay!,
Marketing hype. clap

Joined: Mar 2005
Posts: 1,213
S
Member
It really depends how the dimmer works. As far as I know, most of the dimmers on the market now are of the switched type, which rapidly switches on and off a couple thousand times a second (I don't know the typical frequencies) to give you more of a duty-cycle type of dimming. This means the load still sees the same peak voltages, so W=V^2/R doesn't put us into exponential terroritory like rheostats would. On the surface looks like it would be linear- dim 50%, get 50% the light. However, at high switching frequencies, line conductors have considerable inductance, so currents while the switch is switched on are slightly higher than you'd get from looking at the resistance of the light bulb due to the building magnetic field, and the overall response curve isn't quite linear.

I'd imagine their claims are never exactly right since there are too many variables, but somewhere in the ballpark. Just don't plug in a CFL or LED bulb wink

Joined: Jul 2004
Posts: 9,663
Likes: 4
G
Member
I think the dimmers just gate the 60hz at given levels on the curve, selected by a pot and I believe a diac.

[Linked Image from gfretwell.com]


Greg Fretwell
Joined: Nov 2005
Posts: 826
J
Member
Greg,
I was thinking the same thing. They are usually just triacs with a variable hold off on the gate trigger. They add a snubber circuit to combat noise from the shatp leading edge at the trigger point. You'll always have some crossover distortion on them. I would guess that they all use sensitive gate triacs to allow the earliest triggering for maximum brightness.
Joe

Joined: Jul 2004
Posts: 9,663
Likes: 4
G
Member
If it is a "full range" dimmer there is usually a switch that jumpers out the triac when you are all the way on.


Greg Fretwell
Joined: Mar 2005
Posts: 1,213
S
Member
See... this is why there shouldn't be a timeout on the edit funtion. sleep

Triac makes way more sense. No idea where I picked up the idea that they were high-frequency switched.

Joined: Jul 2004
Posts: 783
L
Member
"Triac makes way more sense. No idea where I picked up the idea that they were high-frequency switched."

Switch mode power supplies?

Larry C


Link Copied to Clipboard
Featured:

Tools for Electricians
Tools for Electricians
 

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
mxslick
mxslick
Atomic City, ID USA
Posts: 806
Joined: October 2004
Top Posters(30 Days)
timmp 3
rick99 1
Popular Topics(Views)
283,621 Are you busy
216,894 Re: Forum
203,237 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5