Power Supply Dual Rails

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bcorbin

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Anyone heard anything about a code in the EU (or maybe just a few European countries, dunno) that limits the size of any circuits in dwelling units to 20 amps (even appliances)? I know that Europe runs at 240V, and that would give them more power from the same amps, but......

The reason I ask is because of the recent trend in PC power supplies. If any of you has a PC with a big, honking graphics card that pulls 300W or more, you would understand my irritation with power supply companies. They advertise a 35 or 40 amp power supply, and then boast of dual voltage rails to "provide your CPU with its own clean source of power, separate from your video card". What this means is, you wind up with your video card given a 20A rail, and the rest of your PC the other 20A rail. Obviously, 20A at +12V DC isn't enough for a 300W video card.

I was told by some techies who say they are in the know, that the reason they are doing this is that for economic reasons, they just want to make one product, still meet the Euro requirements, then turn around and market a product shortcoming as a "beneficial feature" to us dumb Americans. I'm not so sure this isn't a case of black helicopter fantasies (it might just be to save on bigger capacitors, etc.), but I thought I'd see if you guys knew anything about this.
 
I'm probably a little slow today from all that turkey I ate, but I am not seeing a connection here between a 20 amp branch circuit limitation in a dwelling unit and an internal power supply in a computer. I think a 20 amp - 120 volt branch circuit in my house will power a 1920 watt power supply 24/7. And my Scottish cousin will have double that. I'm confused again.
 
The limitation I was told about was on any circuits in a house....even those that are part of appliances, not just the circuit to the receptacle which feeds the appliance. So I'm not talking a building code, obviously, but more of a usage code.
 
What does 20-amp supplied at 12 VDC have to do with the AC side? It does not work on a 1-for-1 amp basis. It works on a power basis So for your 20-amp @ 240 AC circuit is good for 4800 Watts, enough for 16 300-watts 12 VDC power supplies. Therer should be no problem with 2 DC supplies even on US 120 VAC 20-amp circuits.
 
bcorbin said:
....even those that are part of appliances, not just the circuit to the receptacle which feeds the appliance.QUOTE]

:grin: lol I think maybe you been had by another urban legend. How would you think that anyone is going to enforce the unenforceable ?
Click to expand...
 
I guess I should have supplied more details.

ATX re-wrote their new spec for power supplies, which limits any circuits associated with the secondary side of the power supply to 240VA. That would be 20 amps at 12V. I am trying to figure out why they would do such a thing. It all might have something to do with UL 60950 and SELV compliance. I'm just trying to figure out why. Who felt so strongly that some PC hobbyist plugging in a 360 VA power cord was unsafe that a whole standard had to be changed? There are some power supplies out there for sale that do not meet this spec. So obviously, it's not illegal in this country. I figured it might be illegal in some other country (was told somewhere in Europe maybe), and thus the industry nudge by way of a changed common spec.

***Edit. Intel writes the ATX spec***
 
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http://www.formfactors.org/developer%5Cspecs%5CATX12V_PSDG_2_2_public_br2.pdf
the above link is for ver 2.2 of the ATX specification. It appears to me that the max current allowed was always 240VA, and that this was part of the original specification's intent ? (this article is dated 2005).

I can think of many possible reasons why they would want to have a specification such as this, but since I don't know why I won't guess.

However, why do you think this in any way inhibits computer hobbyists ? You aren't limited to using only atx power supplies. There are a zillion ways to bootleg a nice power supply so you can use your computer as a baseboard heater or part-time fireplace.

Then again, one of these might work for you: http://www.legitreviews.com/article/436/1/[
 
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I don't think it "inhibits" hobbyists. I just said they were lying to hobbyists, by making the dual rail setup sound like an intentional improvement, when it's actually a design compromise. But hey, the marketing guy who came up with that probably got a nice fat bonus.

By the way, that power supply is just sick. I want.
 
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