Power supplies with solid polymer caps

[Arfa Daily]

So why do the good brands tolerate those conditions so well while the
same old junk brands don't? And contrary to what you say, most of the
caps aren't in hot spots but are running at under 60 Celcius

So, what exactly are you saying ... ? That better quality components
tolerate abuse more readily than cheapo crap ones ? Very profound ... I
don't think that is actually at odds with anything I said, is it ? I seem to
recall in my original reply to William that part of the reason that he may
have had good luck in regard to electrolytic failure, is the fact that he
has tended in the past to buy better quality equipment where the
manufacturers have been prepared to "design to a better spec with a few
cents more spent on components ..."

As far as your contention that most of the caps that fail are running at
under 60 deg and are not in hotspots, that may be true if you are talking
just mobos, which are a bit of a special case in that apart from all the
problems that have been caused in the past with boards built using caps with
fake electrolyte, the caps that fail are all decouplers on constant DC
rails, and are rated voltage wise pretty close to the continuous voltages
that are applied to them. Even accepting that, many of the decoupling caps
that do fail on mobos, are sited very close (by nature of the job that they
have to do) to LSIs which *do* run very hot.

The caps that I am talking more about in general, are on switch mode power
supplies, where they are subjected to huge stresses from the high frequency
pulse currents that they have to endure, and the self heating caused by this
in all but the most expensive types, very specifically specced for use in
these positions. Further, the ones that fail most regularly are, without
doubt, the ones positioned close to heatsinks. I replace hundreds every year
in the course of my daily work. Although the caps positioned on switchers
are by far the most common ones to fail, they are by no means the only ones.
I also replace many in other circuits, for instance audio output stages,
where failed ones are almost invariably close to heatsinks.

But the problems with junk capacitors showed up way before the switch
to lead-free solder, and only one of my RoHS mobos has so far popped a
cap, probably more because it's newer (late 2007), not because it's
better, but it has the same OST brand junk caps.

I don't dispute that junk capacitors have been failing for a long time, but
that is for the very good reason that they are ... well ... junk, not to put
too fine a point on it. However, if we take junk out of the equation, anyone
directly involved at the sharp end of electronic service will tell you, as I
do now, that over the last five years or so, the incidence of electrolytic
failure has increased a lot with the increased use of switchmode power
supplies in all sorts of consumer equipment, and the unstoppable rise of
Chinese designed and manufactured equipment, where many good design
practices, such as ensuring adequate ventilation, are not observed on cost
grounds. As to whether the increased process temperatures of lead free
soldering has had any effect on long term reliability of electros, I really
don't know for sure. I could be wrong, but it seems to me that over the last
couple of years, the incidence of electrolytic failure has increased even
more than the trend of the last 5 or 7 years, so it was just a thought in
that this was something else that had changed in that timeframe, and may
have been a contributory factor

The real fault lies with the makers of junk, period.

Some of the fault lies with the makers of junk, agreed. But not all, by any
means.

Arfa

 

[Baron]

As far as your contention that most of the caps that fail are running
at under 60 deg and are not in hotspots, that may be true if you are
talking just mobos, which are a bit of a special case in that apart
from all the problems that have been caused in the past with boards
built using caps with fake electrolyte, the caps that fail are all
decouplers on constant DC rails, and are rated voltage wise pretty
close to the continuous voltages that are applied to them. Even
accepting that, many of the decoupling caps that do fail on mobos, are
sited very close (by nature of the job that they have to do) to LSIs
which *do* run very hot.

The caps that I am talking more about in general, are on switch mode
power supplies, where they are subjected to huge stresses from the
high frequency pulse currents that they have to endure, and the self
heating caused by this in all but the most expensive types, very
specifically specced for use in these positions. Further, the ones
that fail most regularly are, without doubt, the ones positioned close
to heatsinks. I replace hundreds every year in the course of my daily
work. Although the caps positioned on switchers are by far the most
common ones to fail, they are by no means the only ones. I also
replace many in other circuits, for instance audio output stages,
where failed ones are almost invariably close to heatsinks.

Arfa

I'm in complete agreement with Arfa. Internal heating caused by the
ever increasing switch mode power supply frequencies is the most common
cause of failure. High external temperatures don't help one bit since
it reduces the components ability to get rid of internally generated
heat.

A place where I'm finding more and more capacitor failures is in the
memory supply voltage regulator circuits, sometimes causing CPU failure
in addition to memory damage.

 

[larry moe 'n curly]

To some extent, I don't think it is all the capacitors' fault, to be honest.
The places that electrolytics are found in today's equipments, tend to be
very stressful to them, when you couple in other factors such as the
international law on pain of death that requires designers to place
electros as close as is physically possible to anything that runs hot,
and then to mount the power supply or whatever board they're on,
upside down in the corner of the equipment with the least airflow,
it's actually not that surprising that these devices exhibit such
*apparent* unreliability.


So, what exactly are you saying ... ? That better quality components
tolerate abuse more readily than cheapo crap ones ? Very profound ... I
don't think that is actually at odds with anything I said, is it ?

I seem to recall in my original reply to William that part of the reason that he may
have had good luck in regard to electrolytic failure, is the fact that he
has tended in the past to buy better quality equipment where the
manufacturers have been prepared to "design to a better spec with a few
cents more spent on components ..."

That better quality components tolerate abuse more readily than cheapo
crap ones ? Very profound....

I'm just saying that low quality is probably a worse problem than the
heat (power boards for LCDs are sparse) or high currents. The usual
suspects have the same specs as the good components do, at least when
new, and their lifespan specs are also identical.

 

[Daniel Prince]

Sure. However, they're very difficult to identify without back
tracking the part number or chopping one in half and looking for the
black goo inside. The clue is that they tend to be short and not very
tall, while conventional electrolytics are much taller:

Both Asus and Gigabyte make motherboards that they claim use all
solid polymer capacitors. I doubt that they would lie about
something like that.

 

[Daniel Prince]

Yeah, but along with the general decrease in quality, there has been
proportional decrease in price. It's price that driving the decline
in quality. Running the operating temperature and voltages near the
point of failure is one way to save on costs.


They wouldn't make junk if consumers didn't demand low prices. There
are usually "premium" versions of almost any consumer product, but few
can afford the price. (If you want quality, be prepared to pay for
it).

How much would the retail cost of a computer power supply or
motherboard etc. increase if they were made to last twice as long?
Five times as long? Ten times as long?

 

[Daniel Prince]

If I interpret your question correctly, it's meaningless.

Polymer capacitors (ie, plastic-dielectric caps, such as polystryrene,
Mylar, and Teflon) simply cannot produce the huge capacitances in small
spaces that electrolytics can. They cannot easily replace electrolytics.

How much bigger (in volume) are polymer capacitors than
electrolytics for the same value?

Are there any types of capacitors with substantially better life
than electrolytics that are small enough to replace electrolytics?
If so, how do they compare in price?

 

[Daniel Prince]

The problems start when there are competing products. I call it the
Walmart effect. Walmart, Kmart, and many online vendors specialize in
selling solely on the basis of price. If there are two competing
products, differing only a few pennies in selling price, *ALL* their
orders will go to the lower priced product, with nothing to the higher
priced equivalent. Walmart aggravates the effect by setting the price
at some artificial low level, and challenging their vendors to meet
their price goal.

It seems to me that there is a good opportunity here for other
retailers. If a retailer sold only electronic goods that were well
made and well designed, they could sell them for ten to thirty
percent more than the junk sold at Walmart and Kmart.

I think many consumers would be willing to pay a little extra for
devices that would probably last four to ten times as long. This
would be especially true if they had two (or more) cheap-junk brand
devices fail.

The retailer could require vendors to only use non-junk capacitors
with voltage ratings at least three times the voltage the capacitors
would be exposed to. They could also require that no part of the
device ever get more than 30 degrees warmer than the temperature of
the room it is used in.

The devices could have much longer warranties and the store could
advertise itself as "The quality store". I do not think this would
require excessive advertising, especially after the first few years.

 

[Allodoxaphobia]

The good part about all this is that problem products just don't last
very long. Soon after the problems are found, the replacements appear
in the stores. The replacements have all the latest features, use all
the latest designs, and follow all the latest fashion trends.

... and are cursed with brand new problems.

 

[Arfa Daily]

It seems to me that there is a good opportunity here for other
retailers. If a retailer sold only electronic goods that were well
made and well designed, they could sell them for ten to thirty
percent more than the junk sold at Walmart and Kmart.

I think many consumers would be willing to pay a little extra for
devices that would probably last four to ten times as long. This
would be especially true if they had two (or more) cheap-junk brand
devices fail.

The retailer could require vendors to only use non-junk capacitors
with voltage ratings at least three times the voltage the capacitors
would be exposed to. They could also require that no part of the
device ever get more than 30 degrees warmer than the temperature of
the room it is used in.

The devices could have much longer warranties and the store could
advertise itself as "The quality store". I do not think this would
require excessive advertising, especially after the first few years.

I do service work for several retailers of 'quality' consumer electronics,
and all are having a hard time of it. Their only customers now are those who
can genuinely afford the stuff. The others who aspired to being owners, and
saved their hard-earned for however long in order to enable them to become
owners, are long gone, with whatever spare money they have, going to keeping
a roof over their heads, and putting food on the table. Times is 'ard, my
friend ...

As I repair the stuff for a living, you would think that I would know
better, but even I buy what I know to ultimately be junk. Just a few weeks
ago, I bought a DVD player to replace the 'good' Tosh that I had owned for
some time. It came from the local food supermarket, and was some kind of
unknown junk name. But you know what ? It plays any disc region that you put
in it, any home burn disc type and format both CD and DVD, came with a
complete set of connecting cables, and even a full function credit card
remote handset. And what did it cost ? Fifteen quid, that's what. And it has
a year's full warranty. Even if it failed within the warranty period, it's
just a throw away item. Go buy another. Half a dozen pints of beer ...

Arfa