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Quality ATX12v PSU with -5 voltage output

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  • Power Supplies
  • Motherboards
  • ATX
  • Components
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Last response: in Components
September 13, 2009 11:12:56 PM

Anyone know of a well built psu with atleast 450 or preferably 500 watts that has a -5 volt output? When atx 2.01 was standardized they removed the -5 completely. It was an option in atx 1.2. It was required before 1.2 for ISA cards. Most modern motherboards, if not all of them, will not use the -5 voltage and that's why it was removed in the atx 2.01 revision.

The problem is that I want to use a psu on an old kk266plus motherboard that will also be able to power a modern motherboard (like an lga 775). The biggest problem is not the lack of a -5 voltage on the 20th pin, although that's MY problem, the problem is instead related to voltages. Old motherboards used to consume mostly from the 3.3 and 5 volt lines, and to a lesser extent from the 12 volt lines. (as an example, my 300w psu outputs 180w on the 3.3/5 volt lines and only 98 on the 12 volt line) To reduce costs they moved to the 12 volt line and now we have a circumstance where motherboards are consuming mostly from the 12 volt line and to a much less extent the 3.3 and 5 volt lines. This is espeically true for psu's and motherboards developed after the atx 2.0 revision. The problem occurs when you use an old psu on an old motherboard or vice versa. For example, the corsair cx450(450w) outputs 140w for the 3.3 and 5 volt lines, while my much older 300w psu outputs 180 watts. This means that my motheboard might request more from the 3.3 and 5 volt lines than is available. No!!!

Anyone have any suggestions? Are there any quality psu's that also have a -5 voltage rail? Most of the ones I've seen, like hte corsair psu's, do not have a -5 voltage output because they're trying to strictly abide by atx standards. I think that's a bit overboard. It only consumes 5 watts about, but I"m sure there're other reasons they removed it from the standards. Seems to me that it only makes backwards compatibility more complicated, although I can understand why they did it. They did it because most motherboards that would use the -5 rail are too old to use anyway. This is not always the case though, and that's why I'm here.

This is the best I could find so far:
http://www.ultraproducts.com/product_details.php?cPath=...

The problem is that anantech (spelling) gave it a terrible review. If only it had had PFC and other quality protective measures I think it would have been a much better power supply for those who're looking for a more backwards-compatible psu than is what you find most of the time with the latest atx standard(s). (the standards pretty much force you to spend a lot more for a compatible power supply so you can get the extra output to compensate for the voltage changes)

More about : quality atx12v psu voltage output

a c 246 ) Power supply
a b V Motherboard
September 14, 2009 4:32:09 AM

AH NUTS! I definitely remember reading a technical review of a different power supply that still had the -5 voltage. Unfortunately, I am growing old disgracefully and I forget stuff. Hmmm...might have been one of the older Seasonic 500 or 550 watt models that is still available. I'm not sure about that.

EDIT - It wasn't Seasonic. That was a recent thread where deletion of -5 voltage was mentioned. Must have been another psu.
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a b ) Power supply
a b V Motherboard
September 14, 2009 5:23:51 AM

You can probably supply the amperage you need on the 3.3V and 5V side by using 2xPSU. A ground lead from each psu connected together will give them a solid common ground. Then "simply" provide some (eg half) of the 5V and 3.3V feeds from one psu, and the rest from the other.

The -5V is another issue. But perhaps you can find a better quality psu that doesn't have a lot of 12V/3.3V but still carries a -5V, and pair it with one that does not.

OK, three PSUs is not an elegant solution, but it *will* work:

http://www.allelectronics.com/make-a-store/item/PS-4002...
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Related resources
a c 144 ) Power supply
a c 156 V Motherboard
September 14, 2009 3:23:55 PM

How do you know the old motherboard actually needs -5 volts?
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September 14, 2009 4:09:24 PM

jsc said:
How do you know the old motherboard actually needs -5 volts?


It has an ISA slot. That's what the -5 voltage line was for on most boards that I know of. The other problem is that the cx450, the psu I want to get, probably doesn't supply enough 3.3/5 volt combo for the MB. I'm not going to get a 2x or 3xpsu combo. That's probably too expensive for me and also not within my technical ability. I may just end up getting the older less reliable ultra psu from 2007 (v-series 500watt) unless I can find something better. It needs to also work with an LGA 775 atleast.
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September 14, 2009 7:23:59 PM

Here is what I've found so far:
TOPOWER ZU-550W:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
V-Series 500 Watt PSU:
http://www.ultraproducts.com/product_details.php?cPath=...

Both of these are atleast a couple years old. They're subpar as PSU's go.

What I'm looking for is an atx12v 2.0 psu that has a -5 rail. The reason I want an atx12v 2.0 is that it didn't require the removal of the -5 rail. That didn't happen until 2.01. So any psu that meets 2.01 or later won't have the -5. Many of the 2.0's psu's don't have the -5 rail either, but some of them do - the topower is an example. I wish I could find one that is better quality. I also require a pci-e connector and atleast 2 sata connectors. It needs to work for an lga 775 intel board. Many of the atx12v 2.0 psu's will also tend to put most of their output on the 12v rail. That means it needs to be atleast 500w - the combined output of the 3.3/5v need to be atleast 180w. Most of the more modern higher output psu's will not even hit 150w on the 3.3/5. So it's almost a necessity that the psu is atleast 2 years old.
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September 14, 2009 7:31:55 PM

Here's a link:
http://www.jonnyguru.com/forums/archive/index.php/t-794...

Says hte -5 was sometimes used for onboard sound. The kk266plus has onboard sound - doh. I've also read elsewhere that later motherboards developed after atx12v 2.01 had an onboard regulator that produced the -5 voltage from the -12 line. I know that there're a couple motherboards that still used the -5 (that's not a good sign for them).
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September 14, 2009 8:01:24 PM

Here's a good one:
OCZ ModStream OCZ52012U 520W
OCZ ModStream OCZ45012U 450W

Link:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Unfortunatley, I can't find a price that's under $100. There're very few places to buy it. It appears to be atleast 3 or 4 years old. It was a great psu for its time. Too bad. I don't want to spend more than $70 for something so old. I suspect that the warranty would all but have ended since some manufacturers determine the warranty period based on when the unit was made. Sine most of the psu's that will work for my MB and a new MB are old, I'm struggling.
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