How much ripple for a ATX PSU is too much?

[gnif]

Hi All

My PC decided to start acting up the other day, random rebooting, etc... through a process of elimination I managed to identify the PSU as the fault. Now this is no cheap PSU, it is a Corsair HX1050 that feels like it is built well, and from what I can see past the fan, looks of decent quality. The device is still under warranty, so I am not going to open it, but I decided to power it up and stick it on my scope (which I am still learning to use).

I am seeing the switching on the output on all the voltages at around 20mv peek to peek every 14.5us, but on the 12V rail, I am seeing a 400mv spike. Now this PSU is on my bench and not under load, so obviously this is not a fair test. Is this normal or is this outside what would be expected for an ATX supply? or am I measuring this completely incorrectly because the PSU is not under any kind of static load?

[kizzap]

Are you bandwidth limiting the scope at all?

According to wikipedia, the acceptable ranges of ripple voltages up to 20MHz specify that ripple should be less then 120mV, so your supply seems to be outside of that specification.

It might be worth seeing if it causes issues in another system?

-kizzap

[jaxbird]

You can find the max allowed ripple in this design spec:

http://www.formfactors.org/developer/specs/ATX12V%20PSDG2.01.pdf

Max 120mVpp (20MHz) for the 12V.

It would make most sense to measure it under load, at least 100W.

[BravoV]

Make sure you turn on the 20Mhz BW limit before measuring the rail.

[Nerull]

Switching PSUs do not perform well without a load. Put a dummy load on it and see if it still does the same. My attempt to convert an ATX power supply into bench PSU had over 1V of peak to peak ripple before I stuck a power resistor across the 5V rail. Then it went flat.

Newer ATV12V PSUs need the 12V rail loaded instead, I believe.

[gnif]

Are you bandwidth limiting the scope at all?

Yes, 20Mhz.

It would make most sense to measure it under load, at least 100W.

I don't have a static load I can put on it at the moment, and procuring one is a bit difficult since at the moment the roads into and out of where I live are blocked due to fires.

[kizzap]

I don't have a static load I can put on it at the moment, and procuring one is a bit difficult since at the moment the roads into and out of where I live are blocked due to fires.

Chuck as many HDDs that you can on, the older the better

[Vgkid]

The unit uses good caps based on the review, but even new it had a higher ripple on the 12v rail. Maybe Phaedrus will chime in.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=245
^^ Review^^
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=245
^^Under Load^^

[gnif]

The unit uses good caps based on the review, but even new it had a higher ripple on the 12v rail. Maybe Phaedrus will chime in.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=245
^^ Review^^
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=245
^^Under Load^^

Well, that is certainly not what I see on my 12V rail, will RMA the thing.

[wraper]

The unit uses good caps based on the review, but even new it had a higher ripple on the 12v rail. Maybe Phaedrus will chime in.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=245
^^ Review^^
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=245
^^Under Load^^

Well, that is certainly not what I see on my 12V rail, will RMA the thing.

You forget ^^Under Load^^
How you can compare those pictures with what you get without load.

[Kjelt]

You can use one or two of the high power halogen head light lamps (55W) of a car as a load. 
They get pretty hot so mount them safely.

[dfmischler]

IIRC the ripple on an ATX supply is spec'ed right at the board (not the connectors) with a short ground lead.

EDN: Testing a power supply - Noise

[NiHaoMike]

A common problem is that consumer PSUs tend to have weak fans, causing the caps to fail early. An easy workaround (without voiding the warranty) is to externally supply better ventilation (such as pressuring the case), but the proper fix is to spend a little extra for a server grade PSU.

[codeboy2k]

I don't have a static load I can put on it at the moment, and procuring one is a bit difficult since at the moment the roads into and out of where I live are blocked due to fires.

You mean you are trapped and encircled by fires??   

Don't you think you should be building a personal quadcopter, and getting yourself out of there?? The PSU can wait...