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wbswenberg
User Rank
Platinum
Power Supplies
wbswenberg   8/2/2013 8:12:27 PM
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Usually the power supply is the last desinged and tested.  Pushed too hard to get the job done.  And given to the inexperenced to design.  Been on both ends.

Helped designed the charger for the power supply to charge the batteries for MX basing.  desinged a .2f cap bank for 208 VDC.  Used the bigest CD caps.  Looked like 6 pack of beer big boys.  

Critic
User Rank
Platinum
Degrees
Critic   7/16/2013 3:50:12 PM
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It would be nice if the editor would learn to type the degree (°) symbol.  It is very easy, unless the editor is using some weird kind of computer:  ALT-248.  Hold down the ALT key, and type 248 on the numeric key pad.  Make sure the Num Lock is on.

Critic
User Rank
Platinum
Cost.
Critic   7/16/2013 3:47:01 PM
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It's all about cost.  Consumer products are designed and manufactured to price points.  It is not about the character of individual design engineers or manufacturers.  They just give consumers what most of them want:  CHEAP.

Design tasks are often not completed (the way some of us think of a completed design) because of cost or time constraints.  The very best components are not used because they are just too expensive for the application.

BudM
User Rank
Silver
Bad caps
BudM   7/15/2013 12:18:39 PM
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I do volunteer works on weekend at Electronics recycle (since 1995), I fixed many PC, Monitors, TV that have failed due to bad bulging caps. The age of these failed products are about 2~3 years. Even Apple/Lenavo/Samsung/LG/Dell/Acer/HP/Sony. products have failed due to bad caps on the MB and in the PS. The sad is that we see 2~3 years old Flat panel TVs/Monitors are dropped off due to failed caps.

I use PANASONIC FM/FC/FR series which are made for switching Power supply for the repair works, I have yet to get the units back from the people we have donated the repaired units too due to same failing caps.

It is just poor quality caps are being used. Good site to see about bad caps: badcaps.net

notarboca
User Rank
Gold
Re: The Power supply as an afterthought?
notarboca   6/24/2013 2:43:14 AM
NO RATINGS
Visual inspection will fix a lot of problems, but understanding the mode of failure is key.  A very well thought out fix.

Bill Mullin
User Rank
Iron
Aluminum Electrolytic Capacitors
Bill Mullin   6/21/2013 6:33:35 PM
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Design News

 

On 6/13/2013 Sherlock Ohms wrote:

 

Aluminum electrolytic capacitors have a finite life. They consist of two strips of aluminum foil coated with a paste made of aluminum oxide, water, and other chemicals. If the water dries out, the capacitor's value drops and the internal resistance increases. At 25o C, the useful life is many years, but as the temperature increases, the life drops exponentially.

 Talk about incorrect tech!

 Aluminum electrolytic capacitors are NOT made of "two strips of aluminum foil coated with a paste of aluminum oxide, water, and other chemicals".

 FAR FROM IT!

 Aluminum electrolytic capacitors are made of carefully "doped" aluminum foil. The "doping" depends on the designed end use of the capacitors and amounts to a "trade secret" usually carefully guarded by the capacitor manufacturer. Funny thing here is that this was discovered (and confirmed in the lab) by a former General Electric scientist named "Alwin". I do not remember the man's first name. No matter. Alwin discovered how aluminum electrolytics actually operate.

For many years the major producers of these capacitors, Mallory, Sprauge, GE, Cornell-Dubilier, and others proclaimed that the anodes of these capacitors were "roughened" by etching the surface of the foil to increase the area. Nobody ever took the trouble to truly understand what was going on. Then, Doctor Alwin (yes, he was a certified PhD) did an experiment. He carefully dissected a small area of "formed" (etched) aluminum foil. Alwin gold-plated the foil to protect the "roughened" surface, dissolved the aluminum in acid, and examined what remained in a scanning electron microscope.

Holy Toledo!

What he saw were infinitesimally tiny "tubes" of gold. These tubes extended from what had been the surface of the aluminum foil at right angles to the surface and branching off in myriads of directions, but ALWAYS at 90° angles. To Alwin it appeared to be a plumber's nightmare.

However, Alwin had discovered exactly how the area of the anode foil was multiplied. Apparently, the folks at GE didn't know (or care) and Alwin left GE. He came to the Capacitor Division of General Instrument Corporation in Tazewell, VA in about 1971 when I was Marketing Manager of the GI Division. I had already written several technical books for  Howard W. Sams & Co. and I used this information in the 1978 revision "ABC'S of Capacitors". See pages 74 & 75.

At GI, we took the knowledge and performed dozens of experiments with aluminum foil by altering the alloy of the pure aluminum with iron, foil thickness, applied voltage, etching chemicals, cathodic chemicals, and the paper impregnated with the chemicals. As a result, we were able to "tailor" the etching and oxide formation PRECISELY to the intended use of the capacitors. This caught our primary competitors completely off-guard and we changed GI from an "also-ran" in the capacitor business to the BIG DOG ON THE BLOCK.

Where is GI today? Gone. The Capacitor Division was wiped out by the GI CEO who wanted to be KING OF ICs and be done with passive components such as capacitors. I split and became Publisher of  Electronic Products magazine (then part of Cox Broadcasting).

 Getting back to Sherlock Ohms...

No doubt there was a crappy capacitor in the circuit (or a good capacitor was misapplied). However, I can tell you I learned a whole bunch as a designer of electronic flash systems back in 1949-1952. I had a lab full of exploded chards of electrolytics before I learned how to manage them.

Bill Mullin

William K.
User Rank
Platinum
Re: Old man river
William K.   6/21/2013 5:54:57 PM
NO RATINGS
Lots of products have been designed that last for 50 years, or at least 20 years. And none of them was anywhere near the price peak for the era. The difference is in the design philosophy, where the intention now is for consumer electronics items to be obsolete in six months, and then to fail at between seven and nine months. I cal this an attitude devoid of any integrity, and with an adequate amount of publicity some makers could be out of business, which might possibly serve as a lesson to others. But probably not, since policy decisions seem to be made by boards of directors and upper managers who also lack integrity.

Frank Karkota
User Rank
Iron
Re: Capacitors
Frank Karkota   6/21/2013 8:51:19 AM
NO RATINGS
In response to Howman, the power supply may have been a flyback. My designs are all radio frequency circuits and switching power supplies create too much noise for my applications and I stay away from them. I have a hard enough time with noise from linear regulators!

When I got into electronics, everything used vacuum tubes. Tubes were inefficient, and even worse, they had a limited life, as they slowly deteriorated. It was not uncommon to see tube-testers in drug stores, so that people could test their own tubes. Occasionally, the electrolytic capacitor would fail and the radio would have a 60 cycle hum. (We called them cycles back then!) As long as you replaced bad tubes, the radio or television would last forever.

With the advent of transistors, it seemed that the problems of tube technology would disappear. But the early transistors were germanium and they got leaky after months or years. Early radios actually had sockets for the transistors, party because of the failings of germanium transistors and partly as a carry-over from tube technology.

Today's semiconductors are very reliable. Just as long as the ratings are not exceeded, the failure rate is very low, surprising considering the complexity and large scale integration. The weakest part is the aluminum electrolytic capacitor. Unlike most parts, it has a memory of abuse by overheating, whether internal or external. Overheating is often caused by high current in the capacitor. Careful design can often reduce the current without sacrificing performance. Miniaturization of capacitors has exacerbated the problem.

Some of the receivers that I designed have been in the field for over thirty years, and to my knowledge, no electrolytic has ever failed. In my home I have had a number of consumer products fail and it has always been the aluminum electrolytic.

Consumer and commercial products should be designed to last at least as long as the technology is viable. The designer should assume that aluminum electrolytics are the weak part in the system and design the circuit to minimize the stress on these parts. If the aluminum electrolytics do not fail, the product could easily outlast the technology or even the owner.

Howman
User Rank
Iron
Re: Capacitors
Howman   6/20/2013 11:08:41 AM
NO RATINGS
After reading the article again, it must be a high-frequency transformer with DC rectification.  I suppose they would do this to limit the bandwidth of noise.  Is this topology common in consumer satelite gear?  It is unfortunate that the designer went to so much trouble to limit the noise of the power supply but was sloppy designing the last stage.  Good power supply design requires expertise in so many disciplines, it is hard to find someone that has mastered them all.  It is not something you learn in school.  It is only learned by doing.

RBedell
User Rank
Gold
Re: The complex issue
RBedell   6/20/2013 9:54:50 AM
NO RATINGS
William K., to my knowledge I am not related.  Possibly some distant relative.

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