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LED Dimmer suited for task?

Discussion in 'Troubleshooting and Repair' started by bushtech, Dec 28, 2017.

  1. bushtech

    bushtech

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    Sep 13, 2016
    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?
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    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.
     
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  3. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Last edited: Dec 28, 2017
    bushtech likes this.
  4. bushtech

    bushtech

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    Sep 13, 2016
    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?
     
  5. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    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 ?
     
  6. bushtech

    bushtech

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    Sep 13, 2016
    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
     
  7. dorke

    dorke

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    Jun 20, 2015
    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.
     
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  8. bushtech

    bushtech

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    Sep 13, 2016
    Thanks Dorke

    So they sold me the wrong thing?
     
  9. dorke

    dorke

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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...
     
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  10. bushtech

    bushtech

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    Sep 13, 2016
    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
     
  11. bushtech

    bushtech

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    Sep 13, 2016

    Attached Files:

  12. dorke

    dorke

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    Jun 20, 2015
    Look at section d)
    Is the one you have a dimmable bulb?
     
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  13. bushtech

    bushtech

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    Sep 13, 2016
    Thanks dorke

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

    dorke

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    Jun 20, 2015
    This isn't a very safe device,it uses no isolation to drive the 555 timer from the mains.
    If you use it the least would be for the outer parts(frame/pot shaft and knob) to be well isolated (plastic).
     
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  15. bushtech

    bushtech

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    Sep 13, 2016
    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?
     
  16. kellys_eye

    kellys_eye

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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.
     
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  17. bushtech

    bushtech

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    Sep 13, 2016
    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
     
  18. kellys_eye

    kellys_eye

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    Check the data sheet - 275V AC but 560V DC - there are others in the range too.
     
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  19. dorke

    dorke

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    Jun 20, 2015
    This is the kind of stuff you better buy rather than make yourself.
     
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  20. kellys_eye

    kellys_eye

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    Jun 25, 2010
    But not from the same supplier you bought the original device.........
     
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