Why do some manufacturers wrap the electrolytic capacitor that gets the hottest in a switching power

[Chuck]

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

 

[Phil Allison]

"Chuck"

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.

** What a load of bullshit !!

Putting a shrink wrap sleeve around an electro will not make it fail early.

I bet the sleeve is there for a totally non electronic reason - like being
able to put markings on it with a pen.



..... Phil

 

[Phil Allison]

"Jeff Liebermann"

Electrolytic caps do not normally get hot. There is a temperature
rise equal to the ripple current times the square of the ESR
(equivlent series resistance).

** Wanna try that again ??

Pro audio is the same as consumer audio, except for the price tag and
the hype.

** Only true of most Chinese made stuff.



..... Phil

 

[N_Cook]

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

Someone's idea of a black body radiator?

 

[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
tests).

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

 

[chuck]

What happens when you complain to Extron? And why - if they don't fix
the problem - do you keep dealing with Extron or Smart Technologies?

A company has to respond properly to design flaws or you change suppliers.

Seems simple to me.

If management says the items are cheaper then point out the downstream
repair costs are more than the few bucks it would cost to get a better
supply and thus a better reputation for reliability in the real world
(as opposed to the costing world).

John :-#)#

I work for a large university and have no say over what products are
chosen for our various projects. Extron doesn't support outside
repair so we don't have any contact with their service or engineering
departments. The reason we use the Sympodium is because some
professors demand them. Chuck

 

[Mike Tomlinson]

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

Maybe to prevent reading off the value for replacement? Built-in
obsolescence, in the same way the some makers grind the identifying
marks off the top of ICs?

You say in a later post that Extron don't support outside repair, which
lends weight to that theory.

 

[Phil Allison]

"Mike Tomlinson"

Maybe to prevent reading off the value for replacement?

** Absurd.

The most likely reason is to enhance safety.

The shrink wrap used on electros that run hot is prone to breaking and
exposing the metal outer.

Often, there is enough leakage to this outer to be a shock hazard.

A second layer of high temp wrap is a nice precaution.



.... Phil

 

[Kripton]

"Mike Tomlinson"

** Absurd.

The most likely reason is to enhance safety.

The shrink wrap used on electros that run hot is prone to breaking and
exposing the metal outer.

Often, there is enough leakage to this outer to be a shock hazard.

A second layer of high temp wrap is a nice precaution.



... Phil

+1
you can also have shrink wrap around the fuse in a smps
it is to prevent glass breaking in case the fuse breaks...
same for the caps, to prevent leaking and touching high voltage.

--

 

[Spehro Pefhany]

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

How about a photo?

There are two possible reasons that I can think of.
If it's a mains input filter capacitor, then it's likely for safety-
to beef up the very, very thin insulation on the capacitor body, so
they can get through the approvals process.

Otherwise, it could be to bolster mechanical support for the part so
it won't suffer failure form vibration, as an alternative to goop.


Best regards,
Spehro Pefhany

 

[Mike Tomlinson]

The shrink wrap used on electros that run hot is prone to breaking and
exposing the metal outer.

Often, there is enough leakage to this outer to be a shock hazard.

Unlike the shock hazard that's likely to be present on the adjacent
heatsink?

You're full of shit, Phil.