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LED Worklight and teardown

robogary

My workshop areas have eight 4 foot double tube fluorescent worklights in the man-cave. I installed the 4 foot floursecent fixtures 35 years ago. 

As the tubes fail,  they get consolidated, and one by one empty fluorescent fixtures get replaced with LED worklights. 5 of 8 fluorescents are still in service.

One of the LED worklights failed after a couple years of service. The failure is weird, the worklight had turned into a strobe light. 

Maybe the light can be repaired ?

I dunno, but the opportunity to troubleshoot, reverse engineer,  and maybe even scavenge parts is too good an opportunity to pass up. 

The endcaps are removed from the light fixture. The simplicity is smart. An extruded aluminum tube body, diffuser slides into it, and an LED strip is mounted on the AL extrusion.

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The power supply leads were desoldered and the LED strip slide right out.  

The LED strip is on a thin fiberglas pcb with 78 COB LED packages soldered in place.The LED strip is labeled with 94v. 

Its easy to follow the traces to see the LED strip has 3 parallel circuits of 26 COB LEDS in series. 

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Since the LED fixture was strobing, the LEDs seem OK, but the power supply would collapse after being able to start. 

The power supply was tucked inside the aluminum extrusion, encased in an insulated tube.

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The power supply was first inspected for failed components. The parts are really packed in there. 

Voila !  Nothing smoked. That black thing looks like its had an overtemp near the body. Its labeled L1, ah...an inductor. 

After desoldering and removing, a closer look seems that the inductor had bitty wire leads soldered onto the stiffer component leads.

Ohm check shows its not dead shorted, and LCR meter sez its 1.86 mH. Darn, that seems reasonable. 

The inductor probably isn't bad so it will have to be reinstalled onto the power supply card.

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Next step is to do reverse engineering on the power supply card to identify components. 

Its for sure a 120VAC 60 Hz to ~ 80Vdc (?) switching power supply, and appears to have 2 stages.  I'll need to surf for info on switching power supply basics.

 If anyone who has alot of design or service experience on switching power supplies, it would be appreciated to share some insights and hints  :-) 

  • in reply to scottiebabe

    ROFL - I was thinking the same thing about  the experimenting challenge. I don't understand why these transformers arent stamped with their volts ratio and KVA  like a CPT.    :-) 

    I'm about 1/3 the way thru drawing the schematic. Its really tough to get a probe on some of the components and there is some unexpected funkiness to the circuit. 

  • I'm going to put on my tin foil hat here a little, when LEDS first hit the market for consumer use, they had an expected lifetime of 5-10 years. But as I drive around the UK with a large portion of the infrastructure being converted to LED, its like I am in a disco!  Strobe-ing really feels like the main failure mode.  I wonder if it is intentionally cutting costs, or even some sort of planned obsolescence that causing this. I look forward to reading about what component failure causes the strobing.  

  • in reply to e14phil

    I can't read your mind with the tin foil hat on. Please remove. :-) 

    I also wonder about counterfeit parts 

  • in reply to e14phil

     I also remember the promise of 100,000 hour life LEDs.  I guess they made no promises of the power supply circuit.  It definitely has to also be cost cutting.  I purchased LED Christmas lights and they were a HUGE disappointment - not lasting two full seasons.

      says it's the caps.  I may have to investigate - because now my curiosity is piqued.  Unfortunately, my LED light bulbs will provide me the opportunity all too soon.

  • in reply to e14phil

    There's a book called "LED: A history of the future of lighting" which is a fascinating read. It does mention some unfriendly things that parts of the lighting industry did from time to time (e.g. two companies had a monopoly on fluorescent tube ballasts, and they didn't want them to be replaced with energy-efficient electronic ballasts).

    Back in the 2000's there was some $1M US government prize for the first firm that could make an LED bulb that would be as good as a 60W tungsten one. I think Philips won that prize. It was technically difficult because of the shape and dimensions of the bulb (getting heat out, because of LED inefficiencies at that time).  Philips used some fancy heatsinking for that.

    The flickering can often happen when there's a faulty LED in the chain, sometimes knocking it makes a difference! : )

    For the last few years, I've not had an LED bulb failure (got perhaps 20 in legacy fixtures, i.e. they are not optimised to be LED lighting, but to replace tungsten), but they definitely dim after a couple of years of heavy use (since it's so dark in the UK for half of the year!). 

    Recently I used "bayonet to E22 Edison" adapters, because then there's more space inside the bulb for the electronics. There seems to be a much better choice of E22 bulbs than bayonet. So now there are super-bright lights in a couple of rooms, perhaps too much! But nice when working.

  • in reply to kmikemoo

    100% agree.  

    Light fixtures with motion sensors are my #1 nemesis. The PIR seems to have a absolute max life of 5 years before the TO5 metal can leaks and fails. Of course, the motion sensors cant usually be replaced anymore, being integral to the fixture.  

  • in reply to shabaz

    I have dismantled all the LED bulbs that were damaged at home and so far all the ones that have started to blink have been due to what Shabaz said, a defective LED, they start blinking, with a little bump they go back to normal but eventually time they melt and you see a black dot in the middle of the LED that was defective. Since they go in series, the whole set goes into the "I'll use it for some project" box.

  • in reply to shabaz
    shabaz said:
    I think Philips won that prize.

    Philips also produced the long life 'Dubai lamp'. Big Clive did a video on them a couple of years ago to see what's different about the design

    https://www.youtube.com/watch?v=klaJqofCsu4

  • in reply to javagoza

    Is that bulb 120V or 220V ?   I'm not sure if it makes a difference if the power supply is current limited, except the peak volts are higher.