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Using a Wall Dimmer on LED Lightrope

D

D from BC

Jan 1, 1970
0
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker.

So.... how to get rid of the flicker and still use an ordinary wall
dimmer?

Could I put the dimmer in series with a bridge rectifier? That'll put
the flicker at 120Hz..

Or...
Maybe design a more appropriate dimmer?

D from BC
 
L

Lionel

Jan 1, 1970
0
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker. [...]
Maybe design a more appropriate dimmer?

That's the best way to go. My suggestion would be to run it from DC,
pulse-width modulated via a high current MOSFET or IGFET switch at
(for example) 1KHz. That should be reasonably cheap, & won't flicker
 
D

D from BC

Jan 1, 1970
0
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker. [...]
Maybe design a more appropriate dimmer?

That's the best way to go. My suggestion would be to run it from DC,
pulse-width modulated via a high current MOSFET or IGFET switch at
(for example) 1KHz. That should be reasonably cheap, & won't flicker

Mmm.... 170Vpk pwm on 40ft of lightrope (~300mA)...Isn't that make a
big EMI transmitter?
D from BC
 
L

Lionel

Jan 1, 1970
0
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker. [...]
Maybe design a more appropriate dimmer?

That's the best way to go. My suggestion would be to run it from DC,
pulse-width modulated via a high current MOSFET or IGFET switch at
(for example) 1KHz. That should be reasonably cheap, & won't flicker

Mmm.... 170Vpk pwm on 40ft of lightrope (~300mA)...Isn't that make a
big EMI transmitter?

It certainly can be, yes. The trick is to put a cap after the switch
output to remove the harmonics.
 
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker.

So.... how to get rid of the flicker and still use an ordinary wall
dimmer?

Could I put the dimmer in series with a bridge rectifier? That'll put
the flicker at 120Hz..

Or...
Maybe design a more appropriate dimmer?

D from BC

Going back to the original plan of a bridge rectifier - it may not
work because then the average power through the light-rope is doubled
(full wave not half wave), and it may overheat. You could compensate
for that by setting an upper limit on the dimmer, or rewiring the
series/parallelness of the lights in the tube.

Another alternative is to put a large capacitor in parallel with the
lightrope, as while the lightrope will still get dimmer through the
"off" parts of the cycle, it won't be fully off and that looks better
to the eye.
 
D

D from BC

Jan 1, 1970
0
Going back to the original plan of a bridge rectifier - it may not
work because then the average power through the light-rope is doubled
(full wave not half wave), and it may overheat. You could compensate
for that by setting an upper limit on the dimmer, or rewiring the
series/parallelness of the lights in the tube.

Another alternative is to put a large capacitor in parallel with the
lightrope, as while the lightrope will still get dimmer through the
"off" parts of the cycle, it won't be fully off and that looks better
to the eye.

Ahh..good point about the average power... I didn't think about
that..The lightrope has probably been designed to be max brightness
(with long life) with half wave.. (The lightrope has that internal
diode + LED's are diodes.)
I'll compensate with full wave..Thanks.

Seems a bit scary to put a filter cap in parallel with the lightrope.
Let's say power it's switched on right at the sine peak
(~170V)...That's a big inrush current spike.
Wouldn't that blow the dimmer(triac) + bridge rectifier combo?
D from BC
 
J

jasen

Jan 1, 1970
0
I'm dimming a 9ft piece of manufactured LED lightrope with an ordinary
household wall dimmer.

The nice thing about using a wall dimmer is that it doesn't get hot,
it's cheap, easy to get and no lightrope mods are needed.
The lightrope has an internal diode and internal resistors to run off
120VAC.

With the dimmer full on, I don't notice any flicker.
However, flicker seems more noticeable (but still subtle) when the
lightrope is dimmed.
I suspect some combo of LED curve + dimmer waveform + eye persistence
time to account for the flicker.

So.... how to get rid of the flicker and still use an ordinary wall
dimmer?

put a bridge rectifier and an inductor (fluorescent lamp ballast? or three?)
after the dimmer.

=======
----(D)---*-(+)--^^^^^----
X LOAD
----------*-(-)-----------
Could I put the dimmer in series with a bridge rectifier? That'll put
the flicker at 120Hz..

is it not currently at 120Hz ?
Or...
Maybe design a more appropriate dimmer?

probably the best way.
 
G

GregS

Jan 1, 1970
0
put a bridge rectifier and an inductor (fluorescent lamp ballast? or three?)
after the dimmer.

=======
----(D)---*-(+)--^^^^^----
X LOAD
----------*-(-)-----------


is it not currently at 120Hz ?


probably the best way.

Or use a transformer with a lower output voltage and a DC filter.

greg
 
D

D from BC

Jan 1, 1970
0
put a bridge rectifier and an inductor (fluorescent lamp ballast? or three?)
after the dimmer.

=======
----(D)---*-(+)--^^^^^----
X LOAD
----------*-(-)-----------


is it not currently at 120Hz ?


probably the best way.

IIRC a (triac based) wall dimmer doesn't rectify the line voltage.
Maybe call it 4 quadrant phase dependent switching.

Why the inline inductor after the dimmer? To reduce EMI?
The triac suddenly conducts at phase>90deg (and >270) across the
inductor and the light rope.
Wouldn't the inductor then return with a big nasty spike which will
stress the dimmer and the lightrope??
D from BC
 
D

D from BC

Jan 1, 1970
0
Or use a transformer with a lower output voltage and a DC filter.

greg

Nooooo! :p
Not variable, bulky, can get hot, expensive compared to wall dimmer,
needs to ordered and needs a box.
However, a linear supply will have no flicker.
D from BC
 
G

GregS

Jan 1, 1970
0
Nooooo! :p
Not variable, bulky, can get hot, expensive compared to wall dimmer,
needs to ordered and needs a box.
However, a linear supply will have no flicker.
D from BC

I was still using a dimmer. I have made variable AC lamp supplies using the transformer
and dimmer, but I don't remember if it was AC or DC.

greg
 
J

jasen

Jan 1, 1970
0
....


IIRC a (triac based) wall dimmer doesn't rectify the line voltage.
Maybe call it 4 quadrant phase dependent switching.
Why the inline inductor after the dimmer?

an attempt to reduce flicker. the load is basically a fixed voltage drop
To reduce EMI?
The triac suddenly conducts at phase>90deg (and >270) across the
inductor and the light rope.
Wouldn't the inductor then return with a big nasty spike which will
stress the dimmer and the lightrope??

No, inductors don't send spikes to triacs - triacs turn off when the current
stops. You do get a step however if the current isn't in phase with the
voltage.

The bridge recitifier howver should stop the current through the triac at 0V,

Hmm maybe it needs a 1 ohm series resistor just to make sure, because the
bridge will be forwards biased by ithe inductor abd so looking like no
resistance to the dimmer as voltage crosses 0.

Bye.
Jasen
 
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