fake PC supplies

An example of Gresham's Law in action. Then it concerned bad money driving out good; now it's bad products. Look at what happened to floppy disks- the drive for low price reduced the quality BELOW the minimum required for safe data storage. Nobody wants to spend $1 each on floppies like we did not-so-many-years-ago. If I need to use one these days, I've got a box of 10-15 year old ones that I recycle. They are still better than buying new.

Similar thing has happened to food. Supermarkets sell cheap crap, small shops selling good stuff at 1.5 times the price go out of business (then the price of the crap goes up too).

Paul Burke

A healthy crowbar should fix that:)

Mike Monett

to

of

output

The devices are in the forced air cooling stream. They are also probably heatsunk.

Also they can be run at above recommended temps to some extent. Computer power supplies do not need to have a long life, since a new puter will usually be passed after 12 years.

standard

There are lots of goods like this on the shelf in UK, but we arent seeing any significant number of accidents as a result. With stereos its quite common that they are marked [[]] but are only single insulated. Been that way for decades.

NT

Unfortunately, that's not quite the same thing. The energy storage cap holds perhaps 5+ Joules of energy, which would be plenty to spike the output voltages quite high, in case of a malfunction, even if you disconnect the AC.

Quite. The quote is: "The love of money is the root of all *kinds of* evil". Quite different again... and spectacularly different from the oft misquoted version.

'properly' isnt one single fixed number. The further away from abs max you run it, the longer it lasts. You can run it up close to limit if you dont need it to last 5 yaers.

NT

Content-Transfer-Encoding: 8Bit

Clifford Heath wrote:

Normally I silently killfile anyone who is rude enough to hijack a discussion about electronics in an electronics newsgroup and turn it into another boring religion/politics discussion, but just this once I will correct the rude posters.

To be 100% accurate, you are both wrong. The actual quote is: Rhiza gar pas ho kakos esti ejstiv ho philarguria (Or, if your newsreader handles greek fonts, rJivza gavr pa'ß oJ kakovß oJ filarguriva).

When a Bible passage is quoted, the default assumption is that it's the King James Version. A distant second assumption is the New Internation Version, with all the others tied for last as far as being the default assumption for quotes goes.

King James Version: For the love of money is the root of all evil

New International Version: For the love of money is a root of all kinds of evil

R Adsett wasn't doing anything wrong by quoting the default english translation. Clifford Heath should not have "corrected" him by quoting another translation as if R Adsett had got the quote wrong - especially without saying what translation he himself was using. He also should have corrected the entire quote; he got "all kinds of evil" but missed "a root."

That being said, this is a passage where the changes in english language since the 1600s has changed the meaning for the modern reader. When the KJV says "the root of all evil", the 15th century reader understood it as meaning what a 21st century reader would get from "a root of all kinds of evil". Note that the difference between "a root" and "the root" is significant.

My ancient Greek is quite rusty and wasn't all that good in the first place, but from my reading, "a root of all kinds of evil" best conveys the sense of the original greek.

Can we go back to talking about electronics now? There are hundreds of newsgroups dedicated to religion, but only this one that is devoted to electronics design. Do you people really have to fill every newsgroup with religion and politics?

Umm, where are you getting that from? Not that I think they are that different in intent.

1 Timothy 6:10 "For the love of money is the root of all evel: which while some coveted after, they have erred from the faith, and pierced themselves through with many sorrows"

That King James which would be from where the quote probably originally entered the English language

Ah, the NIV translates as you've quoted. The version as I quoted would still be correct though.

Robert

:)

Actually, I was just reacting to a mis-quote that annoys me a bit. I wasn't really trying to discuss it's contents but point taken.

Robert

I'm not sure I agree. I have approximately 1000 floppy disks, most of which are about 1995 vintage. Of these, essentially none, not even the verbatim 'datalife' ones will format without errors.

Last year, I broke open a box of IBM OS2/warp (1994), and extracted the

40 or so floppies. None of them would format on any of 3 floppy drives I have.

Still pricey. BS EN 60065:2002 = $351.26 USD

Seems awfully expensive, especially when time and travel for the committee members are probably paid by their own companies.

So who gets the profit?

Mike Monett

My interest is adding ov protection to older supplies. I'd fire a latch that crowbarred the supply voltages and removed the ac supply. A led would indicate which voltage failed. A simple 40A npn on +12V and +5V would probably do fine. They wouldn't even need a heatsink.

Can you suggest a simple way to test the ov protection? If I understand correctly, most power supplies require a load to operate properly. So if you tried activating the ov protection by connecting an external supply to raise the voltage, the power supply may do wierd things.

Is there any other way to see how well the ov protection works?

Mike Monett

No it doesn't. NIV has "a root", not "the root." I cannot find a translation that has the exact text quoted.

The only SCRs specifically designed for a hard DC output crowbar, that I'm aware of, were MCR67/68/69. The latter 2 were plastic TO220 parts, but none were inexpensive.

The method is not really effective in devices with re-entrant or hiccoughing current limits.

Most mfrs have come to the justifiable conclusion that better reliability and guarantee of latch can be achieved by using small-signal devices farther back in the control circuitry. It's one of the main reasons you see two feedback optocouplers - the second is used to trigger a latch in the primary drive circuit.

You know the supply has latched if it has to be unplugged from the wall for xxseconds before it will restart.

RL

Off course they use the same "commercial Watts" as utilized in those 2 x 150W wallplug-adaptor-fed PC speakers.

Perhaps it's "500W PMPO".

Makes me think of early computer monitors that would do 1600 x 1200 pix; and >100Hz refresh. They would indeed - but not at the same time.

--
 - René

Yes those standards are pricey.

I have a copy ( a few yrs old ) of BSEN60065 which is pretty similar to 60950. Note : BSEN = the adopted British standard based on the IEC original. 60950 is specifically IT equipment whereas 60065 is listed as audio and video equipment now IIRC.

Graham

They *have* to be heatsinked !

If it's a TO-220 device as I suspect, that package can only safely dissipate 2W in typical free air conditions. That would make it good for only 2 Amps.

If you don't care about reliability ! It'll likely fail s/c.

They have quite long enough life to need parts to be properly rated.

Graham

[... for brevity]

Thanks for the excellent descriptions, Rob. I definitely will take your advise and check the ps very carefully.

Mike Monett

You can usually back-drive lower powered quasi-regulated auxiliaries as you describe. The test is also partially effective in testing an OVP circuit that is an independant thyristor crowbar. It may damage simpler linear post-regulator circuits, however.

Some redundant devices are designed to be immune to externally-generated faults. OVP may not be provided on some outputs.

Do not be surprised if the OVP thresholds are set higher than you might feel comfortable with - read the spec before testing. The test is incomplete if the unit is not demonstrated recover, on the removal and re-application of input power.

If a main output has remote sense lines, the output voltage may be alterable by disconnecting these and lightly loading them. This will cause an increased output voltage on the main terminals due to current flow in default-coupling resistive elements (usually internal 22 to

100R resistors couple the sense lines to the output lines when sense lines are open).

Some supplies have a 'margin' terminal that can be used to alter the output, but these may be idiot-proofed to limit the deviation made possible.

If you have access to the regulation circuit, temporarily wiring in a variable resistor, to parallel the shunting element in the voltage divider, will allow the same effect as margining. Some products may have an internal test point intended to induce an overvoltage condition when grounded, for use in automated testing.

You can purchase fairly simple 2-terminal crowbar protection modules that can be value-added-on. How effective these can be, on higher-current low-voltage supplies, is questionable. OVP is intended to prevent damage to hardware - not to protect data integrity - in the event of a PSU single fault.

If lower-than nominal voltages also present a threat - it might be worthwhile paying attention to how your computer handles the power-good signal line. This is often configured to indicate out-of-tolerance outputs, including undervoltage, but I have yet to see a PC that uses them sensibly.

If you're really concerned about the quality of the power provided by a PC supply, you should probably obtain devices that demonstrate the desired quality and performance.

I've been blind-sided by simple failures in the my own PC's supply signal lines - and power conversion is supposed to be my area of expertise. Ignoring PSU quality really doesn't pay in the long run.

RL