Led conversion issue

Discussion in 'Solid State' started by Audi0, Jan 13, 2018.

  1. Audi0

    Audi0 Super Member

    Messages:
    1,065
    I just converted a Luxman to leds however I ended up blowing the leds to what was a mix up in resistors. When taking a reading on the circuit I get 8 dc and 4 ac as I remember. With this circuit I shouldn't see any acv right? Is this diagram wrong?

    20180113_120043.jpg
     

     

    Please register to disable this ad.

  2. w1jim

    w1jim I can fix it but good... Subscriber

    Messages:
    7,520
    Location:
    Boston western 'burbs
    You need a series current limiting resistor otherwise it’s essentially a dead short.
     
    Bill Ferris likes this.
  3. Audi0

    Audi0 Super Member

    Messages:
    1,065
    The resistor I had is missing from diagram. It was in place just after diode.
     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    41,190
    Location:
    Fort Dodge, Iowa
    What resistance and wattage is it ?
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    41,190
    Location:
    Fort Dodge, Iowa
    Whats the voltage and current rating on your LED's
     
  6. elnaldo

    elnaldo Addicted Member

    Messages:
    7,128
    Location:
    Buenos Aires GMT-3
    100 uF also looks too small for 6 or 9 diodes , perhaps that's why you read AC ( ripple).

    Try a larger cap and do the math again for the resistor. Or start with a large resistor and test different brightness. I usually do trial-error to find the desired brightness (usually at lower current than I calculated)
     
    Bill Ferris likes this.

     

    Please register to disable this ad.

  7. rcs16

    rcs16 Super Member

    Messages:
    3,632
    Location:
    Baldwin, Ontario, Canada
    It would be better to use a 3 terminal voltage regulator(LM317 or LM78xx) and a full wave rectifier if possible.
     
  8. quaddriver

    quaddriver 120 What's per channel Subscriber

    you need more math.

    first off, take the AC voltage and divide by RMS (root mean squared or sqrt2/2) or appx .707 to find the smoothed DC voltage. this is your stating point. V1

    now take the Vf of the color diode...most are 3.2v, but some colors are 2.2 or even 2.1

    Vd = V1-Vf

    In the parallel circuit, the Vd is presented to every diode. find the max or preferred current Id, usally 25ma Vd/Id = Rd or the resistor for EACH diode.

    if you use 1 diode, a noble idea, then the max current is Vd/Rd or some number that will be split essentially equally over EVERY path. and it might not be enough to light it.

    I get my mini 3mm diodes from parts express in packs of 100 and each order has given to me free, 100 470ohm (12vps) 100 100ohm 5v ps and I keep some 220ohm around (8vish) to keep the Id from anywhere from 11ma to 20ma. The 1N4005 should be good for 1A which is many dozens of lights. 100uf or a 220uf in 16v will be enough. You can use none, but you will get the 60hz effect like a cheap set of LED xmas lights.
     
    awillia6 likes this.
  9. restorer-john

    restorer-john Addicted Member

    Messages:
    5,737
    Location:
    Australia
    The standard drop for a Red LED is 1.7v, Orange is 1.9v, Yellow 1.9-2.0v Green is 2.0v, White is 2.8v and blue is 2.9v. Most LEDs are rated at 20mA max continuous (for 2,3 and 5mm).

    12V AC half wave rectified will give you 16.97v minus the diode drop, giving 16.4V approx. 100uF is inadequate smoothing. I would go 1000uF or more.- just watch the turn off time to extinguish the LED string.

    If you are using white LEDs, take 2.8V off the 16.4v and that gives you 13.6V you need to drop @10-20mA per LED. (20mA on a white LED is pretty bright BTW).

    For 6 LEDs @10mA (that's 60mA total), you'd need 226 ohms (use a 220ohms- 2 watt )
    For 6 LEDs @20mA (that's 120mA total), you'd need 113ohms (use 120ohms - 3 watt)

    For 9 LEDs @10mA (that's 90mA total), you'd need 151 ohms (use 150 ohms - 2 watt)
    For 9 LEDs @20mA (that's 180mA total), you'd need 75ohms (use 82 ohms- 5 watt)

    The wattage of the resistors allows for approx 50% of max dissipation. Mount the resistor up off a PCB or in free air- they will get hot.

    Modern LEDs are so consistent in their voltage drops, we can use a single resistor of sufficient rating, whereas in the old days, we had to use individual resistors for each LED to ensure equal brightness due to current hogging by mismatched LEDs. They are consistent enough (if you buy good ones) that series connection is also an option.
     
    Last edited: Jan 13, 2018
    Bill Ferris likes this.
  10. Audi0

    Audi0 Super Member

    Messages:
    1,065
    I ended up grabbing the wrong resistor and installed it. Which is why it went bang. thankfully I only had 1 installed to see how it would look. Plan was to convert it to warm glow leds. The 9 needed mentioned was a mistake. I need 18 just for the face. 1 for the needle and 1 for the stereo light on semi sperate circuit. The leds installed dont look right. I went from knowing nothing about this to reading how to do it over night. It ended badly.

    The current leds are all 12v. Have plenty of them. The warm glow are 2.7v and don't have enough to complete the lighting now.
     
    Last edited: Jan 16, 2018
  11. Audi0

    Audi0 Super Member

    Messages:
    1,065

     

    Please register to disable this ad.

  12. Audi0

    Audi0 Super Member

    Messages:
    1,065
  13. restorer-john

    restorer-john Addicted Member

    Messages:
    5,737
    Location:
    Australia
    LED conversion done properly is an art. You cannot go on datasheets for the LEDs, or voltages on the schematic. You have to measure everything, under the expected load to determine resistors and brightness levels you want.

    Due to their very low current draw (as compared to the incandescents), the usual dial lighting tapping on the tx/former will be sitting at a much higher voltage than the ratings of the bulbs that were in prior. Measure it unloaded and then load it up with the expected current draw of your string and measure again.

    Post the numbers here and we'll do the math if you like.

    I'm sorry, I'd pull them all out and change to flat top diffused LEDs, they give a spread light. Also use heatshrink to control the light leakage and secure the LEDs to the old holders in such a way the light is directed where you want it.

    What model Lux receiver is it?
     
    f0427ea likes this.
  14. quaddriver

    quaddriver 120 What's per channel Subscriber

    IMG_20171216_141511.jpg

    art.

    no spotlight effect. .79 solution
     
    f0427ea and restorer-john like this.
  15. Audi0

    Audi0 Super Member

    Messages:
    1,065
    Agree all the leds got to go for a complete redue. Personally I don't like the look of the leds I installed.

    Part of the issue is i mixed up postive and negative rails. Will have to double check. 12.38acv is what I got measured from positive lead to chassis. The other issue I had is there is small gap between the light bulb holder and the frame. If a lead touched it would short. Which explains the electrcal
    tape.....

    Amp in question is a Luxman 1500
     
    Last edited: Jan 14, 2018
  16. Audi0

    Audi0 Super Member

    Messages:
    1,065

     

    Please register to disable this ad.

  17. elnaldo

    elnaldo Addicted Member

    Messages:
    7,128
    Location:
    Buenos Aires GMT-3
    *another trick: I paint the flat top leds with white nail polish to have a better diffuse light.
     
  18. quaddriver

    quaddriver 120 What's per channel Subscriber

    lets get to the .79 solution. I discovered this by accident after reading about lens caps (hideous expensive!) and vellum. I would not know what vellum was if you fed it to me with cabbage so I asked the wife, and then, tried something. I am remodeling the house so I have some armstrong self stick tiles around for like closet floors and stuff. the backing paper is a weird semi organic, semi plastic paper to stick to the tile, but not let it dry out, but not stick real hard. It has a neato translucent property.

    So....

    I cut it into small rectangles and made is as long as the light housing is wide (no pictures, all my victims are together in the store...)

    then I folded the edges back to give a glueing surface, and used midwest/simply speaker glue to fasten it in side the housing.

    considering the viewing angle is from 25* to maybe 140* this sets up the focul length...25* - farther out, 140 - closer to the lights

    it then acts as a glowing screen in the target color, softening greatly the LED spotlight effect. the picture I gave is a fairly recent restore of a fisher MC-3010. If had 3 sickly glowing incandescants that were power hungry, now it has 6 3mm 5000K leds held to around 11-13ma and the meters have 2 and all the 8 track track lights, stereo etc, are leds in the correct color.

    so the .79 part? goto lowes or home depot and buy one tile for .79 so ugly, your wife wont want it, then just peel off the backing as you need it
     
  19. Audi0

    Audi0 Super Member

    Messages:
    1,065
    I threw in the towel and ordered bulbs. As they were 50 cents a piece.
     
    restorer-john likes this.
  20. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    20,146
    Location:
    SE PA
    Another fine Lux unit being put back to original condition and not screwed up with LEDs. Great info here to try on other units but getting an led lighting system looking nice and as good as the original lamps can be difficult if there are more than a couple lamps.
     
    restorer-john likes this.

Share This Page