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LED Dimmer suited for task?

bushtech

Sep 13, 2016
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I bought this dimmer and the 3 led lights that it's meant to drive from an electronics place.

Worked fine for about 10 hours after which I could hear some crackling in the dimmer, upon investigation I could see some sparking in the pot.

Led 1.jpg

LED 2.jpg
The heatsinked transistor is a BT137. The lights are 240V AC 6W dimmable. The pot is 500K. Markings on the cap CY250 and 104J1.
Is this dimmer man enough for the job or have I been sold a lemon?
 

kellys_eye

Jun 25, 2010
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I could see some sparking in the pot.
Where in the pot?

It looks like a very basic DIAC/TRIAC arrangement for dimming but doesn't seem to have any snubber components. Equally the track clearances between screw terminals is ABYSMAL !!! Dangerous etc. You may have heard arcing across them.
 

bushtech

Sep 13, 2016
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Thanks kellys_eye
Reinstalled the dimmer to check but couldn't reproduce the arcing, whatever is causing it has probably died.
Checking the pot: (in situ)
Note: DMM in 2M range
Left and centre pin (as per above photo): 0Ω
Left and right pin: 0.8MΩ from off click right through to max
Right and centre pin: 0.8MΩ from off click right through to max

What is the best way to sort this? Can this dimmer be made to work properly with some modifications or would it be better to build a dimmer using a 555 or some other design?
 

73's de Edd

Aug 21, 2015
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Sir bushtech . . . . .

You say . . .
Left and centre pin (as per above photo): 0Ω

Right and centre pin: 0.8MΩ from off click right through to max


Whereas, you are able to get much lower ohmmage at the other Left limit . . .akin to . . . .

Making one wonder if your pot has an end of limit burnt area out at about Right extreme ?
 

bushtech

Sep 13, 2016
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Thanks St Edd
Those readings persist even with the pot clicked off:confused: I think it's history.

Just need to know where to go from here as per Post #4
 

dorke

Jun 20, 2015
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LED dimmer ?
Not so ,it is a continuous phase control dimmer
mainly use for A.C. halogen and incandescent bulbs light control.

While a LED dimmer should be a DC current control circuit.
 

dorke

Jun 20, 2015
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They did,If you are trying to control a "pure LED" lamp .
Please post the data sheet of the your lamp.
In any case it shouldn't have died,the LED would probably blow though...
 

bushtech

Sep 13, 2016
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Thanks dorke. Led's still working. Wired a on/off switch in there ilo the dimmer.Data sheet is one of the PRC's usual things

Data sheet.jpg
This forum's resources area has an led section, thanks *steve*. It does list some dimmers and I have some 555's. But looking at the link: http://www.reuk.co.uk/wordpress/lighting/led-dimmer-circuit/ at the bottom of the page they state that it didn't work with MR16 leds and this is what I have, albeit mine are 240V and they are using 12V led's.

So a bit stuck here. Looking for the correct way to dim these critters
 

bushtech

Sep 13, 2016
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Thanks dorke

Yes they are dimmable. Light fitting takes 3 bulbs as in first photo, each 6W
 

bushtech

Sep 13, 2016
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The switch that it will be mounted into is well insulated including the plastic knob. Can I stick an opto isolator in there? Ooops I see there is one in there. Is there a better design somewhere?
 

kellys_eye

Jun 25, 2010
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Isolation isn't a specific requirement if, as mentioned, the circuit is built into an insulated enclosure and the pot shaft is likewise insulated.

The 'important' part would be the 0.33μF capacitor which should be X2 class and have a 'bleed' resistor (say 330k) across it.
 

bushtech

Sep 13, 2016
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Thanks kellys_eye. Had to go and google X2 cap- had never heard of it. This is what my preferred supplier has: https://www.mantech.co.za/Stock.aspx?Query=0.33uf+x2+capsand
I see the highest they have is 275V. Will that do or do I need 400V?

Also never dealt with opto couplers and when the designer says "any optocoupler" I get miffed.

Here is a selection from my preferred supplier again: (all 327 of them): https://www.mantech.co.za/Stock.aspx?Query=opto+couplerand.
What am I looking for? Any optocoupler wtf!

If this is a good design then I am going to build this
 
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