On Mon, 13 Dec 2010 18:02:46 -0800 (PST), "larry moe 'n curly"
wrote:

Jeff Liebermann wrote:

On Fri, 10 Dec 2010 12:11:00 -0800 (PST), Bob Villa
wrote:

Third, most flat panel sets are put together out of crappy components,
especially the capacitors.

Dell is hoping there are no more of those crappy-caps around!

Dell was not using "crappy" capacitors. What they were doing is the
same thing that almost every other manufactory is currently also
doing. They are rating their electrolytics as close to the bitter
edge of failure as possible. That saves a few pennies in cost by
using a lower voltage electrolytic but shortens the capacitor life. My
guess(tm) is that Dell's OEM supplier in China selected the capacitors
based upon faulty calculations, where it was designed to blow up in
about 5 years, instead of the 1-2 years specified in the class action
suit.

I don't know about Dell LCDs, but their computer motherboards of 5-8
years ago that failed at high rates were actually made with very good
brands of capacitors, like Rubycon, Nichicon, and Panasonic, not the
common crap found on many other motherboards . Unfortunately Nichicon
produced bad batches of their HM and HN series caps, marked HM(M) and
HN(M), from around 2001-2004.

I think you just demonstrated my point. It's not the brand or even
the quality of the caps. It's the voltage rating. In most cases, the
capacitors voltage rating is just too close to the operating voltage.
Filtering a 5vDC power supply line with 6.3v caps is just asking for
the caps to blow up. I've ranted on the subject before but am a bit
busy to dig out references right now. Short summary is that
electrolytics will derate substantially under high temperatures. The
ESR will also climb, causing increased self heating. Drops in
capacitance will cause increased ripple, which will produce increased
ripple current, which will result in additional heating. Manufacturers
can search forever to find a better quality 6.3v capacitor, but what's
really needed is to spend a few pennies more and use a 10v capacitor.

Electrolytic life calculators:
http://www.illinoiscapacitor.com/tech-center/life-calculators.aspx
http://www.cde.com/calc/
http://www.niccomp.com/Products/General/Alumlyticlifeexpect.pdf
http://powerelectronics.com/images/archive/ElectrolyticCap.pdf


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558