I wanted figure out what is wrong with my led setup.

I have 78 leds in series connected to a mean well elg-150-c500b data sheet

The leds are a few different colors they range vf 3.6v to 3.8v and max amps 700mA to 1000mA (all are 3W leds on a star heatsink).

Whenever I plug in the driver all the leds light up for a second then several leds blow, about 20 or so from the right of the panel dimly light up.

Leds that blow up (all same colors warm white):

1st run: 3, 78

2nd run: 2, 3, 5, 78

3rd run: 1, 3, 6

The leds that blow are to the right of the panel (where my incoming +/- connections are).

What I have tried so far:

  • Tested each led connections to ensure they are not leaking to the shared heat sink.
  • Added a 100k resistor as per the driver datasheet.
  • Tested each led is working using a 6v 550mA power supply.
  • Made sure the led polarity is correct on each led connection.
  • Tested the driver using 3 leds on my workbench, drew about 12.8v; the leds dimly lit up due to not having enough load (this is to be expected as driver needs 150v to function as it is cc).
  • Checked heat of heat sink was cold as normal after run.

Some things to note

  • The driver is case grounded and is connected to the shared heat sink via screws.
  • When testing each led connection, some leds extremely dimly lit up when one prong of the mm was touching the heat sink and the other the led connection.
  • On the 1st run I had a multi meter connected and noticed it sent the full 315v through the system.
  • The leds are connected to the shared heat sink using thermal adhesive.

I would like to know what can I further do to troubleshoot this problem and find a solution?

Also if one or more of the led connections are touching the shared heat sink could this cause the issue?

enter image description here

Edit. The other question is also mine, I wanted to delete it and re-ask the question in a more readable and informative matter.

  • \$\begingroup\$ Possible duplicate of Led light power issue (large crack sound when plugged in) \$\endgroup\$
    – JRE
    Commented May 4, 2016 at 10:08
  • \$\begingroup\$ I'm thinking bond wire issues internally at full load. Your 500 mA test supply isn't enough to trigger the issue. \$\endgroup\$
    – Passerby
    Commented May 4, 2016 at 10:10
  • 1
    \$\begingroup\$ Besides that you did not provide a datasheet for the LEDs, everything is running on assumptions here. Do some actual measurements, like the current at the point of switching on and voltages all around and be precise about the conditions and timings involved. \$\endgroup\$
    – PlasmaHH
    Commented May 4, 2016 at 10:26
  • \$\begingroup\$ I'm guessing breakdown between your LED modules and the heatsink. Post datasheets for the LEDs. And try mounting them all via thermally conductive but electrically insulating sheets, with either nylon screws or insulating washers under the screws. \$\endgroup\$
    – user16324
    Commented May 4, 2016 at 14:38
  • 1
    \$\begingroup\$ The leds may not have enough dielectric strength, if it's a 150V string or thereabouts, one end is probably at ground and the other will be at some high voltage. If the heatsink gets connected to one end somehow, that will place an increasing voltage between the leds and the heatsink at the other end, one poor led at the end will have 150V between it's terminals and the heatsink and may be arcing over, the led itself is ok, but the board it's on is getting fried. Well, that's if it's an insulation issue \$\endgroup\$
    – Sam
    Commented May 5, 2016 at 9:59

1 Answer 1


I bought adhesive thermal pads and stuck them between the star led and the large heatsink this worked fine.

I believe the LED was grounding itself using its heatsink which caused issues.

Since there was no data sheet for the LEDs it did take some patience to get working.


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