Capacitors: a Case Study in LED Light Bulbs

[budm]

Good reading.

[tom66]

Re: Capacitors: a Case Study in LED Light Bulbs

I predict that although an individual LED will last 30,000~60,000 hours, the actual bulb assembly will only last 10,000~15,000 hours as that is the current limit for typical electrolytic capacitors -- and you can be assured that the average light bulb will not be using high end capacitors.

The solution to this is to therefore not use electrolytics at all. It's more than possible to build a unity power factor LED light which only uses ceramic and polypropylene capacitors up to around 10W output power with 85% efficiency. However, this would cost slightly more than an electrolytic capacitor based design, and ultimately since it would last longer, it would lead to a reduction in purchases of bulbs, so will be unlikely to be chosen by manufacturers.

[redwire]

Re: Capacitors: a Case Study in LED Light Bulbs

Looking at the new Cree 60W LED lamps (from Homedepot) teardown http://ledsmagazine.com/features/10/4/1 one is a Nichicon PW and the other looks cheap. But they have a 10 year limited warranty.

[retiredcaps]

Re: Capacitors: a Case Study in LED Light Bulbs

My fellow Canadian

http://www.youtube.com/user/electronupdate

has done a few teardown videos on LED light bulbs. I recall him talking about the electrolytic caps in a Cree bulb and how the company may be playing a game of statistics wrt to the capacitor life especially given their generous warranty.

About 10:30 into video ...

http://www.youtube.com/watch?v=n6DDFRBrSas

[retiredcaps]

Re: Capacitors: a Case Study in LED Light Bulbs

But they have a 10 year limited warranty.

A few potential problems with the above:

1) Will I find the original bill/receipt in 6 years?

2) Will Cree still be in business?

3) Is the cost of shipping more than what a new LED bulb will cost in 6 years? Shipping costs can only go up and if LED technology follows "Moore's law", it will get cheaper.

[tom66]

Re: Capacitors: a Case Study in LED Light Bulbs

Yes, a 10 year warranty in my opinion only works if you can just mail them back the bulb free post and they replace it. Or take it into any store and swap it for a new one. Otherwise they just bank on the fact that most people won't bother.

[redwire]

Re: Capacitors: a Case Study in LED Light Bulbs

The extreme teardown Youtube video was interesting... the bulb runs at 85°C-97°C matching 5,000hrs cap lifetime on the Nichicon chart... I would never run a 105°C cap that hot and expect it to last.
It looks like heat is the main cause of the lifetime problem. You've got 10W to dissipate and not much of a heatsink.

[japlytic]

Re: Capacitors: a Case Study in LED Light Bulbs

With warranty issues regarding the originin receipt going missing or fading, ideally LED lamps should have a serial number printed on them which is recorded with the customer's details at the time of purchase.

[smason]

Re: Capacitors: a Case Study in LED Light Bulbs

Cree are a leader in LED tech, and a reputable company from what I know of them.

The Cree 9W bulbs look very good. Still pricey for a light bulb ($15.00 here) I put 2 in our most left on locations.


There's a great Amp Hour episode with one of the founders of Cree.

[smason]

Re: Capacitors: a Case Study in LED Light Bulbs

My fellow Canadian

http://www.youtube.com/user/electronupdate

has done a few teardown videos on LED light bulbs. I recall him talking about the electrolytic caps in a Cree bulb and how the company may be playing a game of statistics wrt to the capacitor life especially given their generous warranty.

About 10:30 into video ...

http://www.youtube.com/watch?v=n6DDFRBrSas

Cool teardown, saves me ripping one open

It's all well and fine to do the math on the number of hours at 105 degrees, but that doesn't mean the cap just fails at 5001 hours.
Considering it's a reputable U.S. company and not a cheap Chinese manufacturer, I would hope that they have considered the characteristics of the cap as it ages, and done some over-engineering, so that after 5000 hours as the cap loses capacitance and gains ESR, that it's still within the specs of required capacitance for the given circuit.
Or I could just be wishful thinking.

It was also interesting that the ambient temp inside the bulb at the PCB was LOWER in an enclosed globe than it was in a desk lamp.

In my house, I've had 2 CFL failures in open (but downward facing) sockets, and none in enclosed globes.

[budm]

Re: Capacitors: a Case Study in LED Light Bulbs

I have changed almost all my lamps to CFL, I put the date I install so I can see how long they will last, so far they last about 2 years in the downward fixture, the upright fixtures one last about 3 years. I open them up and ALL of them has failed shorted out poly cap that sit between the two end of the filaments.

[retiredcaps]

Re: Capacitors: a Case Study in LED Light Bulbs

With warranty issues regarding the originin receipt going missing or fading, ideally LED lamps should have a serial number printed on them which is recorded with the customer's details at the time of purchase.

For the above, expect to pay additional $5 or so. While the serial number isn't a major problem, entering all the details takes time and training. Then someone has to maintain, backup, upgrade the database over time.

[retiredcaps]

Re: Capacitors: a Case Study in LED Light Bulbs

Cree are a leader in LED tech, and a reputable company from what I know of them.

I know very little about that whole industry, but from the amphour.com episode, I do believe they are reputable and the leaders in the field.

The Cree 9W bulbs look very good. Still pricey for a light bulb ($15.00 here) I put 2 in our most left on locations.

Too pricey for me. I can get 8 ccfls for around $10.

If "Moore's law" holds true, prices should be significantly less in 5 years or so. The danger with "Moore's law" is that the premium priced vendors or "technology leaders" have the most to lose and survival is not guaranteed.

I have seen the above scenario play out time and time again in my area of "expertise".

For example, will the average consumer pay 20% more for the Cree name when walking into Wal-Mart or will he/she reach for what is on sale? Does the average consumer even know the Cree name?

[retiredcaps]

Re: Capacitors: a Case Study in LED Light Bulbs

Considering it's a reputable U.S. company and not a cheap Chinese manufacturer, I would hope that they have considered the characteristics of the cap as it ages, and done some over-engineering, so that after 5000 hours as the cap loses capacitance and gains ESR, that it's still within the specs of required capacitance for the given circuit.

Today, Cree may be using brand name high quality capacitors, but there is no guarantee that they will continue doing so in the future especially if "Moore's law" plays out.

http://ca.finance.yahoo.com/q/ks?s=CREE

Profitability
Profit Margin (ttm): 5.21%
Operating Margin (ttm): 5.83%

And NO, I'm not short CREE. I have no idea of their product line-up, key selling points, average costs, etc so consumer light bulbs may only be a small part of their business?

And YES, I wish there was an energy efficient solution, but sometimes it is not the technology that is the most expensive thing.

[cheapie]

Re: Capacitors: a Case Study in LED Light Bulbs

These "Greenlite" 12W LED bulbs I got recently ($11 each) get too hot to touch... I'm sure they're not using quality caps at that price either. Their CFLs seem to do OK though. Most of the failures I've had with those were tube end-of-life, not ballast failure.

...I'm going to have to open one, aren't I? I get paid today, I might have to buy one and see.

[mockingbird]

Re: Capacitors: a Case Study in LED Light Bulbs

Would be nice to know which manufacturer he was designing for so we know from who to purchase bulbs from...

[lti]

Re: Capacitors: a Case Study in LED Light Bulbs

Greenlite CFLs are the only ones I've seen fail "normally" (with smoke, black residue, and discolored plastic). They were also unusually small for their wattage rating. The others silently failed, and only the ones in a certain light fixture showed any discoloration on the plastic base.

I didn't expect LED bulbs to last very long, but I didn't know they ran that hot.

[japlytic]

Re: Capacitors: a Case Study in LED Light Bulbs

One other thing from the PDF article I read, I suggest using solid polymer electrolytic capacitors in such units (one was 330uF/25V) - these capacitors (as used in motherboards) last a very long time.

[tom66]

Re: Capacitors: a Case Study in LED Light Bulbs

Solid polymer are expensive though. And they can be readily substituted for general purpose electrolytics and work -- they'll just fail much earlier.

[ben7]

Re: Capacitors: a Case Study in LED Light Bulbs

I have a project for my house, putting led lighting in the kitchen. My plan is not to use led bulbs, but to make my own fixtures. Each will put out about 800 lumens and consume around 8 watts. I think I will make three of them, and run them off of 48 volts DC.

The lame dollar store led lights are crap. They overdrive the leds, so the leds overheat and lose brightness substantially after a little while...

I use an led lamp in my room (my room has poor lighting, might be another project for led lighting), and it has been good so far for 4 years... it has arrays of leds, and commonly referred to as a "corn bulb". We got two of them, and one had an early failure, covered under warranty. Not sure how the ballast works, but after an hour, the bulb is only mildly warm - you can keep your hand on it.