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Thread: The Role of Capacitors in LED Bulbs...

  1. #1
    Flashaholic* LEDAdd1ct's Avatar
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    Default The Role of Capacitors in LED Bulbs...

    I apologize if this was already posted. This issue has been discussed in various threads,
    but I don't think it has earned its own separate thread yet.

    Here is an article which goes into great detail on how good quality capacitors can make
    or break an LED "bulb".

    Link

    NOTE: This is a hobby for me, and so, some of the concepts discussed in the article
    are over my head. Overall, though, I think the author does a good job (from what I
    understand) of describing considerations when putting together an LED "bulb".
    "...and the diode multiplied and grew in brightness. And God saw that it was good."

  2. #2
    Flashaholic* Steve K's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    It's a good cautionary tale about the value of being able to read a datasheet when selecting the components for a design. Electrolytic caps have always been valueable, but have a lot of shortcomings that have to be accounted for. Among these is their temperature sensitivity, so it is important to select the appropriate cap and then do the thermal design such that the cap is kept out of heat that could shorten its life or degrade its performance.

  3. #3

    Default Re: The Role of Capacitors in LED Bulbs...

    Like and job or career, there are people good at their job, and those that are not. That applies to power supply designers and it was true before LEDs. Unfortunately with LEDs, there are a lot more people designing so the odds of running into a bad engineer are a lot higher.

    Semiman

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    Flashaholic* Pellidon's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    I can attest to this. As an early adopter or CFL lights, I had an issue with a desk lamp that would blow out the ballast circuit due to a lack of air flow to remove the heat from that circuit. LED lights would have a similar problem if not designed properly. The "bulbs" I have in a similar lamp today have great heat management and the LED bulb has been running flawlessly for a couple of years now.
    My doctor says I am a paranoid narcissist. I have the feeling I am plotting against myself.
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    Flashaholic* RetroTechie's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    Packing heat-producing parts (power LEDs) and heat-sensitive parts (electrolytic capacitor) together in a package with poor cooling like plastic E27 socket, is just asking for trouble. Which is exactly what practice is showing.

    The logical thing would be to put LEDs (with appropriate cooling) in one place in a fixture, the driver circuit elswhere in that fixture, and electrolytic capacitor(s) some distance away from heat-generating components in that driver circuit. The common "make LED-based 1:1 bulb replacement, leave fixtures unchanged" is an easy but short sighted, dumb approach if you ask me.

  6. #6

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    Cause we are just going to abandon billions of existing fixtures and lamps and spend who knows what for parts and electricians to replace them? .. Not going to happen.

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    Flashaholic* RetroTechie's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    I've seen that argument before, but it's flawed:


    • If fixtures were expensive and bulbs cheap: yes. But I can buy a simple desk light for say $20, and a LED bulb to go in it for $30. That lamp you have hanging over your table, was expensive some day. Not today - nor all the bulbs & electricity you'll consume in it, if you keep it around.
    • The argument may be true for existing fixtures, but not if you replace the fixture anyway. Following my previous comment, a logical thing would be to see new fixtures for sale that have 30.000+ hour (replaceable?) LEDs in one place, and an easy replaceable driver (circuit board) somewhere else. Yet, also most new lamps for sale are still meant to screw in same old E14 / E27 / GU10 bulb.
    • That would make sense if your existing supply of bulbs were expensive (so the new fixture could use all those 'expensive' bulbs already in your posession). In the case of incandescent bulbs: not (expensive). In the case of CFL bulbs: most probably not (expensive).


    Many existing fixtures have roughly independent 3 components: power supply (eg. 230V AC in), driver circuit (for example: an electromagnetic ballast / coil), and a bare lamp (for example a fluorescent tube). At what point did it make sense to integrate (2 of) those parts for LED bulbs? Repeatedly throw away an expensive 30.000+ hr power LED + other electronics because a $0.50 capacitor failed, just so you can keep using your $20 fixture? To me, that seems like at least somebody is failing at maths...

  8. #8

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    Fixtures with install cost are much more than bulbs. Not even close. Desk lamps are exceptions. You also assume a separate power supply is high quality and that replaceable led module easily integrates into 360 degree optics if so desired. Bulb issue is temporary as leds improve. Led is moving too fast to try to force a module standard at the consumer level.

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    Flashaholic* FRITZHID's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    This it's all old news among any electronics tech, beit engineer or amateur,..... Electrolytic caps fail.... Cheap fail sooner, it's that simple.
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    Too many bad engineers out there ... Just like any job

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    Default Re: The Role of Capacitors in LED Bulbs...

    Quote Originally Posted by RetroTechie View Post
    Packing heat-producing parts (power LEDs) and heat-sensitive parts (electrolytic capacitor) together in a package with poor cooling like plastic E27 socket, is just asking for trouble. Which is exactly what practice is showing.

    The logical thing would be to put LEDs (with appropriate cooling) in one place in a fixture, the driver circuit elswhere in that fixture, and electrolytic capacitor(s) some distance away from heat-generating components in that driver circuit. The common "make LED-based 1:1 bulb replacement, leave fixtures unchanged" is an easy but short sighted, dumb approach if you ask me.
    I totally agree but unfortunately the vast majority of the general public are unwilling to replace their fixtures. We definitely should be selling purpose-built LED fixtures in addition to LED bulbs. One problem with LED fixtures, besides the lack of standardization of LED modules, is that stores would most likely need to stock the same fixture in several CCTs to cater to all tastes. At least with fluorescent fixtures the end user buys the lamps separately, requiring only one fixture which can cater to any CCT. In any case, the heat issue you mention will diminish as LED efficiency continues to increase. In a few years we should be at the point where a 100 watt LED equivalent barely gets warm to the touch.

    Many existing fixtures have roughly independent 3 components: power supply (eg. 230V AC in), driver circuit (for example: an electromagnetic ballast / coil), and a bare lamp (for example a fluorescent tube). At what point did it make sense to integrate (2 of) those parts for LED bulbs? Repeatedly throw away an expensive 30.000+ hr power LED + other electronics because a $0.50 capacitor failed, just so you can keep using your $20 fixture? To me, that seems like at least somebody is failing at maths...
    I feel this might be a good niche market for people handy at electronic repair. Few people will consider repairing a $2 CFL to be worthwhile but a $30 LED bulb might make sense if the repair is $10 or less. Either that, or people can sell their failed LED bulbs for $5 or so on eBay to people like me who could fix them and even swap in more efficient emitters. BTW, the LEDs should last a lot longer than 30,000 hours in a properly designed LED fixture with good heat management. The 25,000 to 30,000 hour life we see LED bulbs rated for is exactly because the LEDs are being cooked due to the small form factor. A decent purpose-built LED fixture should offer lifetimes upwards of 100,000 hours. In fact, if put into new buildings LED fixtures can be designed to last the life of the building. 300,000 to 500,000 hours is certainly within the realm of possibility if LEDs are underdriven and well heat-sinked.

  12. #12
    Flashaholic* LEDAdd1ct's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    Quote Originally Posted by jtr1962 View Post
    I totally agree but unfortunately the vast majority of the general public are unwilling to replace their fixtures.
    The vast majority of the general public either can't afford to or won't put down that money.

    When most people shop with the lowest common denominator being cost, spending extra dough
    up front isn't going to happen.

    I think those of us who are fortunate enough to be able to indulge in this hobby are a very small
    percentage of the population. While there are professionals on this board, I think most of the folks buying and selling and trading LED/incandescent/etc. lights here have surplus money they can use to "play" with. How many people on this forum own one flashlight? Many people will say you only need "one" of a given item (one car, one bicycle, one pair of shoes, one can opener)...

    Our perspective is very different from that of the general public, who has never given a second thought to the 2D plastic flashlight in the kitchen drawer next to the rubber bands and twisty ties.
    "...and the diode multiplied and grew in brightness. And God saw that it was good."

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    Flashaholic* idleprocess's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    Quote Originally Posted by LEDAdd1ct View Post
    The vast majority of the general public either can't afford to or won't put down that money.
    I believe the case to be far more the latter than the former.

    The typical lighting fixture is a thoroughly simple and inexpensive piece of equipment that the average person is well-equipped to replace if they could be bothered. A ladder, a screwdriver, and perhaps a flashlight is all that it really takes to replace most ceiling-mount light fixtures - wires are pretty universally pre-stripped and the wire nuts used to terminate previous fixtures can be re-used.

    A well-designed, purpose-built, inexpensive residential LED fixture won't drop into an Edison socket in 5 minutes but doesn't require summoning an electrician either. It shouldn't be any more complicated than swapping out any other fixture - a 15-30 minute job at most - but inconvenience and fear of electrocution puts it into the "hire someone" category for many.

    When most people shop with the lowest common denominator being cost, spending extra dough
    up front isn't going to happen.
    Eh, the average buyer seemingly doesn't think they can afford anything other than a $0.50 incandescent because they don't understand the Total Cost of Ownership concept that CFL and LED bulb manufacturers have been unsuccessfully trying to convey for decades now. The purchase price of a $0.50 incandescent is typically less than 10% of its total cost of ownership, but that price is apparent to the average buyer while the de-coupled operating cost is all but invisible in an electrical bill seen at a later time that aggregates all consumption into a single number. One of my co-workers swapped all his incandescent lights for CFL in the summer and expected his next months' electrical bill to drop significantly ... which it didn't ... which disappointed him ... then he admitted he was on an annual average billing plan and maybe he shouldn't have been expecting a change.

    Our perspective is very different from that of the general public, who has never given a second thought to the 2D plastic flashlight in the kitchen drawer next to the rubber bands and twisty ties.
    Indeed - something often lost on the average CPF member when they start a thread along the lines of You wouldn't believe the types of flashlights I just saw [people] using for [purpose/event]!.
    I apologize that this letter is so long; I did not have time to write a short letter

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    Default Re: The Role of Capacitors in LED Bulbs...

    Quote Originally Posted by SemiMan View Post
    Like and job or career, there are people good at their job, and those that are not. That applies to power supply designers and it was true before LEDs. Unfortunately with LEDs, there are a lot more people designing so the odds of running into a bad engineer are a lot higher.

    Semiman
    You seem to be assuming that short lifetimes, and overstressed components are the fault of the design engineer. Not necessarily true.

    The blame also needs to be shared with consumers, who tend to buy the lowest cost products, regardless of the value. Suppliers of products know there's a vast market for cheap crap and are happy to provide same. Sad, but true...
    Last edited by brickbat; 11-04-2013 at 07:54 AM.
    Jim

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    Flashaholic* LEDAdd1ct's Avatar
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    Default Re: The Role of Capacitors in LED Bulbs...

    Quote Originally Posted by brickbat View Post
    The blame also needs to be shared with consumers, who tend to buy the lowest cost products, regardless of the value. Suppliers of products know there's a vast market for cheap crap and are happy to provide same.
    Wal-Mart is alive and well.
    "...and the diode multiplied and grew in brightness. And God saw that it was good."

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