| LED Dimmers? [message #166890] |
Thu, 19 April 2012 22:01  |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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When I look on the internet for LED dimmers I see stuff that goes from a few dollars to over $50. What is anyone using for LED dimmers?
Are they effective, or do they make the lamps strobe, or change color temperature?
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: LED Dimmers? [message #166898 is a reply to message #166896] |
Thu, 19 April 2012 22:59  |
Chr$
Messages: 2690
Registered: January 2004
Location: Scottsdale, AZ
Karma: 1
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You have to reduce the current, not the voltage, but ultimately led's dim with lower voltages until they just stop emitting light.
Increasing the value of the current limiting resistor is one way to dim an LED, but you don't reduce the overall current draw.
LED's can also be pulsed to reduce brightness, but some people notice the flicker in the corner of their eyes. I'm one of those. Bugs the hell out of me. If you ever looked at a row of pinball machines with LED scoring, they look like they are bouncing, but this is not due to dimming, but due to refresh rate from the CPU as it updates the numbers by pulsing the segments.
Yeah, too much information.
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.
Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"
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| Re: LED Dimmers? [message #169510 is a reply to message #166890] |
Mon, 14 May 2012 08:34 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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You really need to go to a Pulse Width Modulation device for dimming LEDs. Supplies full (limited) current for very short period of time.
It may produce a flicker at some setting, but once you get past the persistent stage of human vision, you will not notice it. Everyone's vision persistent stage is slightly different frequency ranges, so you need to experiment with the settings. Settings within your personal vision persistent frequency will cause headaches, nausea, and other ill feelings.
www.youtube.com/watch?v=Lf7JJAAZxEU
www.dprg.org/tutorials/2005-11a/index.html
A Bing search turns up many references to these devices.
Tom Phipps,
MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] LED Dimmers? [message #169516 is a reply to message #169510] |
Mon, 14 May 2012 08:57 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Tom,
I haven't looked into that particular application, but seems to me a series
diode into a capacitor across the LED load could eliminate the flicker.
Ken H.
On Mon, May 14, 2012 at 9:34 AM, Thomas Phipps <tph1pp5@yahoo.com> wrote:
>
>
> You really need to go to a Pulse Width Modulation device for dimming LEDs.
> Supplies full (limited) current for very short period of time.
> It may produce a flicker at some setting, but once you get past the
> persistent stage of human vision, you will not notice it. Everyone's
> vision persistent stage is slightly different frequency ranges, so you need
> to experiment with the settings. Settings within your personal vision
> persistent frequency will cause headaches, nausea, and other ill feelings.
>
> www.youtube.com/watch?v=Lf7JJAAZxEU
>
> www.dprg.org/tutorials/2005-11a/index.html
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] LED Dimmers? [message #169533 is a reply to message #169516] |
Mon, 14 May 2012 09:58 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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| Ken Henderson wrote on Mon, 14 May 2012 08:57 |
Tom,
I haven't looked into that particular application, but seems to me a series
diode into a capacitor across the LED load could eliminate the flicker.
Ken H.
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Yes - but then it is very likely to eliminate the dimming ability you are trying to get with the pulse with modulation. The diode and cap is a smoothing filter and would act sorta like if you were feeding regular AC into it.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: LED Dimmers? [message #169557 is a reply to message #166890] |
Mon, 14 May 2012 12:26 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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It depends on the LED bulbs you are using. The ones with the internal boost converter will compensate for lower voltages, so you might not be able to dim them.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: [GMCnet] LED Dimmers? [message #169559 is a reply to message #169533] |
Mon, 14 May 2012 12:49 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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No, the cap should merely smooth the pulses into a fairly stable DC, at an
amplitude controlled by the width of the pulses -- basically "filling in"
the off periods. There will still be some ripple -- but probably
imperceptible to the naked eye with a sufficiently large capacitor.
Ken H.
On Mon, May 14, 2012 at 10:58 AM, Steve Southworth <midlf@centurytel.net>wrote:
>
>
> Ken Henderson wrote on Mon, 14 May 2012 08:57
> > Tom,
> >
> > I haven't looked into that particular application, but seems to me a
> series
> > diode into a capacitor across the LED load could eliminate the flicker.
> >
> > Ken H.
>
> Yes - but then it is very likely to eliminate the dimming ability you are
> trying to get with the pulse with modulation. The diode and cap is a
> smoothing filter and would act sorta like if you were feeding regular AC
> into it.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] LED Dimmers? [message #169562 is a reply to message #169559] |
Mon, 14 May 2012 14:02 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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PWM turns the LED on and off at a controlled rate. This produces the dimming effect, because of the persistent vision effect. They will be fully on or fully off, and trick the eye into thinking they are dimmed. A smoothing capacitor might help, resulting in a smoother transition, but cheap enough to experiment with. It would cause no failure of the LED, because of the current limiting effect of the resistor in series with the power input. High power LEDs are still expensive enough to hurt the wallet when you fry one with high current.
I was able to purchase nice strip LED lighting strips for IKEA that can be driven directly from 12v. Nice mood for soft background lighting in the coach. Avion had a strip of 12v automobile bulbs above the passenger side large window. I replaced them with the LED strip and am happy with the results.
LEDs are fun to play with, and are amazingly cheap, except for the high power ones.
Tom Phipps,
with a pocket full of LEDs.
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: LED Dimmers? [message #169626 is a reply to message #166890] |
Mon, 14 May 2012 19:44 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Here is an easy way to control LED brightness using a big 3
watt resistor in series with 3 LEDs powered by +12V (up to +14.4V).
The resistor is a 15 ohm. The LEDs drop 3.3Volts.
The current is (Battery Voltage - (3.3 + 3.3 +3.3))/ 15,
which works out to less than 1/3 of an amp. (~4 watts total)
http://www.gmcmhphotos.com/photos/cree-led-lights/p42474-led-lights.html
And the resistor doesn't make electrical noise as would a PWM circuit.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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