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

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

Reply to
Chuck
Loading thread data ...

Chuck wrote in news: snipped-for-privacy@4ax.com:

IMO,in a proper design,the caps should not be getting hot. Caps should be sized and rated properly,with a fair amount of excess capacity,not sized/rated right at the margins. We have inexpensive thermal imaging available that can identify hot spots so that they can be corrected before the design is finalized.

--
Jim Yanik
jyanik
 Click to see the full signature
Reply to
Jim Yanik

Then you need all new technicians and engineers. They have to minimize lead inductance of the capacitors, at high frequncies. Unless you don't really want to remove the ripple.

--
You can't have a sense of humor, if you have no sense.
Reply to
Michael A. Terrell

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.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
 Click to see the full signature
Reply to
Dave Platt

On Aug 30, 2:48=A0pm, Jim Yanik wrote: > Chuck wrote innews: snipped-for-privacy@4ax.com: >

The caps may not be getting hot on their own but get damaged from nearby hot items. We had 16 Samsung digital tuners at work that had 1 cap that fails next to a diode on a heatsink. We replaced it with a very good grade cap but extended the leads just enough to lay the cap on its side away from the heatsink. Luckily room to do that existed.

G=B2

Reply to
stratus46

"Chuck"

** 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

Reply to
Phil Allison

Probably to keep you from touching the can, which is probably electrically hot. The life you save may be your own.

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). If the ESR is too high, usually due to underspecifying the voltage rating or capacitor type, it will get warm. There are derating curves for capacitors at various temperatures. There are also lifetime prediction calculators which include the operating temperature.

If you're shopping for a conspiracy theory, I guess the capacitors are badly specified or picking up heat from adjacent heat dissipating devices. A nearby resistor or heat sunk xsistor will heat up a cap quite nicely. The shrink tube will have little effect on the cap temperature. Black absorbs more heat, so it might be slightly warmer from nearby radiation. At best, maybe a degree or two.

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

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
 Click to see the full signature
Reply to
Jeff Liebermann

"Jeff Liebermann"

** Wanna try that again ??

** Only true of most Chinese made stuff.

.... Phil

Reply to
Phil Allison

Someone's idea of a black body radiator?

Reply to
N_Cook

Elevated internal current leakage in electrolytic caps will heat them up. The 'lytics with higher than normal internal leakage are the ones that troubleshooters will miss, if the only tester they have is an ESR meter.

Leakage tests aren't performed in-circuit, therefore it's a good practice to test new 'lytics when they're received and again before installing them if they've been stored for long periods.

I don't do much repair work anymore, but had a habit of checking ESR (Value and DA) and Leakage when new caps were received, and some new 'lytics would fail Leakage tests occasionally, quickly getting very warm at their rated voltage.

One of the most often repeated repair tips is to look for bulged tops and/or signs of external leakage wrt electrolytic caps. Generally, ESR checks are also advised, but electrolytic caps have other faults and failures which rarely get mentioned.

-- Cheers, WB .............

Reply to
Wild_Bill

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

Reply to
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 :-#)#

--
    (Please post followups or tech enquiries to the newsgroup)
  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
 Click to see the full signature
Reply to
John Robertson

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

Reply to
chuck

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.

Reply to
hrhofmann

En el artículo , chuck escribió:

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.

--
(\__/)   
(='.'=) 
 Click to see the full signature
Reply to
Mike Tomlinson

"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

Reply to
Phil Allison

+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.
--
----------
Kripton
 Click to see the full signature
Reply to
Kripton

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

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
 Click to see the full signature
Reply to
Spehro Pefhany

En el artículo , Phil Allison escribió:

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

You're full of shit, Phil.

--
 (\_/)
(='.'=)
 Click to see the full signature
Reply to
Mike Tomlinson

Usually anything on the hot side could use more insulation. Of course I mean on the hot side of the mains or line. Imagine an electrolytic bursting, there will be foil all over the place, conductive foil that is, or else of course the capacitor would never have worked.

They have to think about catastophic failures and ground faults, so sometimes if you want to know why they did what they did, so do you. It is quite possibly a containment issue.

It is still a money matter, if they could save one penny they would, but they have to figure out how many lawsuits and how much, things like that. Hey, the drug companies think that way, so sure as hell electronics companies will as well.

J
Reply to
Jeff Urban

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.