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cduma

Thu Aug 06 2009, 07:19PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
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Posts: 300

I am designing a power supply tester for a school project. What do you think are good max/min voltage limits for an ATX PSU? Prototype V1 is just a proof of concept and only measures the 12VDC line and displays an OK if it is between 11.6VDC and 12.5VDC. My lab partner wants to just hook up a variable power supply and see what the minimum running voltage is and what voltage lets the magic smoke out of the transistors.

Steve Conner

Thu Aug 06 2009, 09:00PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

RTFATXSpecsheet!

(page 13)

edit: Not to mention STFW

cduma

Thu Aug 06 2009, 10:57PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
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I dont think that the ATX spec sheet would be of any value since I am worried about the other hardware getting damaged. Thanks anyway! The first spec sheet was very interesting and has given me numerous more things to test for to insure the PSU is operating in a satisfactory way.

...

Fri Aug 07 2009, 04:45AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Steve is trying to say that if the power supply outputs voltage in spec (11.4-12.6v, <120mv ripple) under its rated load it is 'working' and if anything else has a problem with that its not the power supply's fault.

thedatastream

Fri Aug 07 2009, 07:17AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Some ideas of things to test

A low resistance load that you can switch in to check if the ATX PSU shuts down on an over current condition.
Remove all loads to see what happens - does it shut down or keep running?
If you toggle the PGOOD line, does everythign work OK?
If you remove the power, does the power fail line come up within the right amount of time?
Cross regulation: heavy load on 5V and no load on 12V - what happens? Vice versa.
Transient load testing?
Surge current on the 12V line (hard drive spinup)?

This level of testing demands some kind of automation

Steve Conner

Fri Aug 07 2009, 09:41AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

cduma wrote ...

I dont think that the ATX spec sheet would be of any value

You asked for the max/min voltage limits. They're on page 13. So you're getting the exact answer to your question, straight from Intel. What more value do you want?

To explain further: That document describes a series of tests that a power supply must pass to qualify as an ATX power supply. So it also must be the recipe for building an ATX power supply tester. This level of testing would normally be done by engineers in the power supply maker's own labs, using standard test equipment like variacs, variable frequency power supplies and electronic loads

... especially the tests for "Startling noises" and "Emission of molten debris" aren't really suitable for a standalone tester

I'd consider a reasonable tester to be one that applied a decently hefty load to all of the outputs (again the document specifies how many amps per output, and so on) and checks that all the voltages are within the published tolerance bands.

cduma

Fri Aug 07 2009, 07:03PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
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Steve, thedatastream thank you very much for your help! You have given me great information. I never thought to check if a heavy 12V load would effect 5V, 3.3V etc although I did think to apply a heavy load. I was going to make a multi-tap resistor out of some #22 wire since I have some pulled from a xformer worth about 1.1 ohms.

cduma

Fri Aug 07 2009, 07:06PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

I dont think that automation would be required. I have some old equipment with those dials that have a whole bunch of switches.

klugesmith

Fri Aug 07 2009, 07:36PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

cduma wrote ...

...I did think to apply a heavy load. I was going to make a multi-tap resistor out of some #22 wire since I have some pulled from a xformer worth about 1.1 ohms.

You could make all the loads you need out of AWG 22 copper wire, and will learn a lot along the way.
How are you planning to measure the currents, or to measure the load resistances at their operating temperature?

Some alternative materials for home-made low voltage loads at tens and hundreds of watts:
Nichrome wire from heating and cooking appliances (much less resistance change for a given temp. rise).
Steel wire or strapping (inexpensive at hardware store; thicker/shorter/less sensitive than copper for a given resistance and power).
12-volt incandescent lamps (resistance changes a LOT but reaches thermal equilibrium quickly. Then for small differences in DC voltage, they behave more like a constant-current source than a fixed resistor. But inrush current is several times greater than rated current -- better check ATX PS spec in that regard.)

cduma

Sat Aug 08 2009, 08:27PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

Toaster coils do make a lot more sense. Now that I think of it I have a toaster I bought for that purpose.

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