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Default Why do some manufacturers wrap the electrolytic capacitor thatgets the hottest in a switching power supply in shrink wrap?

On Aug 31, 10:53*am, chuck wrote:
On Tue, 30 Aug 2011 15:31:52 -0700, (Dave Platt)

In article ,
Chuck wrote:

Extron has been doing this for years and of course it is the first
part to fail in their units. *Smart Technologies Sympodium power
supplies, that they have contract built in China, fail in a year or so
for the same reason. *Technicians and electronic engineers at my work
place can't think of a rational reason why these manufacturers do
this. *This is pro gear where reliability is a great concern so it
doesn't seem to be planned failure mode. *Thanks. *Chuck

I've heard it said:

*"When the question is `Why is company X doing seemingly irrational
* thing Y in their product design?', the answer is most commonly
* `Money',"

Electrolytic capacitors are normally shipped, by their manufacturers,
in a plastic insulating jacket. *It's the common method used to
insulate the cases against accidental shorts, and to allow convenient
marking (no separate marking process is required during manufacture,
since the markings are manufactured into the plastic).

Almost all "commodity" 'lytics are of this sort. *If you want caps
with another sort of jacketing (even "none at all") you'd probably
have to special-order them, there would be far fewer possible sources,
and the cost per piece would end up being significantly higher.

There's immense price-pressure and competition in the electronics
manufacturing business, even for "pro gear". *A matter of a few cents
per power supply can make the difference between a contract
manufacturer getting, or losing the bid. *The manufacturers thus have
a *very* strong incentive to use standard parts... and, in fact, the
cheapest and lowest-rated ones which will allow the final supply to
pass its paper requirements (which may not include long-life survival

I've heard that it's quite common for overseas contract manufacturers
to covertly "down-rate" parts, after they win a bid... that is, the
specific caps and resistors and etc. that they stuff into the
production lots, may not be the same as the ones they stuffed into the
samples that they submitted. *Unless you stand over 'em with a club,
and do a strict verification of what you receive, you may get
lower-quality subsystems than you had been originally offered. *You
might even get counterfeit parts (e.g. cheap 85-degree-C caps, which
have been falsely labeled as 105-degree-C, or generic caps falsely
marked to indicate low-ESR, high-ripple-current ruggedness).

If the final system survives to the end of its warranty period, many
companies seem to feel that this is Plenty Good Enough, and brings in
additional revenue for repairs and replacements.

To clarify, this isn't the standard cap wrapping from the factory.
This is a thick piece of shrink tubing that is put over the
capacitor's normal wrapping and then shunk tightly around the cap like
a blanket. *Chuck- Hide quoted text -

- Show quoted text -

Maybe the case is not at "ground" voltage, so the tubing is to act as
an insulator to prevent shocking anyone working on the eqeuipment.