How does my PSU work???

[spudnuts]

I have a question, how does my 12v rails on my power supply work?

What I mean is, are the rails split logically or does the first 3 connectors use one while the other 3 connectors use the other rail?

BTW, it's obvious that i'm running dual 12v rails. When connecting my devices, do I just want to make sure that they are evenly distributed between connectors? I have a few extra fans and UV light kits with in-line power connectors and I want to make sure i'm not over burdening a single rail.

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[G0AOZ]

Unless you have some special power supply unit, all the +12v (yellow) cables all go back to the same place on the PSU's printed circuit board in most off-the-shelf units. The reason there are several +12v (and +5v) cables is that by splitting the load there will be less voltage drop at the attached devices, and manufacturers can use thinner cables which makes them more easily manipulated within the case.

Balance your devices out as best you can on the cables provided. For instance, if you have two hard drives, put one drive on each cable. Fans and UV lights generally use less power than hard drives, so not so important to precisely divide them up...

ROGER - G0AOZ.

 

[felixc]

GOAOZ is right. All the 12V wires all go to the same location on the PC board inside of the power supply. Same for all the other voltages and the ground. In addition to the reduced voltage loss, there are multiple wires of the same voltage in order to let the connector pins meet their amperage ratings. This the main reason of the additional 4 pins on the ATX connector and the special 12 volts connector for the latest P4 and X2 motherboards. Exceeding the amps rating of the connector pins would make the boards lose their UL approvals.

 

[edfair]

The latest ATX specs call for splitting a part of the P4 connector to a separate supply in those supplies furnishing greater than 18A.

Full description and reasons can be found with a google search for "atx12 dual 12v supply".

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[spudnuts]

Thanks for the help, that pretty much helps me make the right decision.

Here's the deal, I have a PC with a Ultra Products X2 Connect 550W PSU and everything was running great until I bought a new VisionTek X1950 Pro XGE video card. All of a sudden i'm getting reboots and system freezing or dropping back to the desktop when I run 3d games.

After alot of research, i've come to the conclusion that my PSU just doesn't cut it. It has 2 12v rails (1 18amps and 1 17amps for a total of 35amps). I found out that this card needs at a minimum of 20amps by itself.

I just ordered a Thermaltake Toughpower 750 (750 watts, 4 12v rails, 15amps each for a total of 60amps). I think that should do it.

Thanks again for the help.

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[felixc]

Where did you see the requirement of 20 amps? (that makes 240 watts for this card alone, it is impossible) I'm curious because I've just built a system with an X1950Pro, with a 450W Antec power supply. I kept it running for hours looping on a 3D game and the air going out of the system wasn't even warm. The fan number 2 of the (temperature controlled) PSU wasn't even running.

This isn't to say that your trouble was not the power supply. Many power supplies do not meet their specs by far.

 

[felixc]

I saw on a web site that the power of the X1950 has been measured at 65Watts at peaks! And under 3O watts in office apps.

750 watts is a LOT of power. I hope that your system will meet the minimum load requirements of your new PSU. This can be another kind of problem.

 

[wahnula]

I hope that your system will meet the minimum load requirements of your new PSU. This can be another kind of problem.

Felixc, can you elaborate a little bit on this topic of minimum load requirements? It makes sense to me but to my recollection I have not heard much mention of this problem in the past. Thanks!

Tony

 

[felixc]

A switcher power supply will usuallly require a minimal load on one or more of its outputs, in order to be able to maintain its specifications on all of its output voltages.

Technobabble: This is due to the fact that all the outputs are tapped from a common transformer. But the internal switcher controller takes its feedback from only one of them, which needs a minimal load for a proper control.

If say the 5-volt output does not a minimal amperage, the other outputs may not be able to supply enough current and stay within their specs. Lots of say and may, because each power supply design has different requirements. You will find answers in the specifications of your power supply.

In the same range of ideas, the ATX power supply efficiency is a function of its load. Too lightly loaded, it will be less power efficient. A bit like the motor in a car.

Unless you have dual xeons, a full raid array, and dual graphics in SLI, I would be very surprised if the total consumption of your system exceeds 350 watts.

But the power supply that you purchased has a good reputation. YOu should be safe.

 

[spudnuts]

felixc,

I've checked everywhere and all the forums are saying the same thing. The latest i've found is that my VisionTek X1950 Pro XGE AGP card will need a minumum of 450-Watt power supply or greater, 30 Amps on 12 volt rail recommended (assumes fully loaded system). My current power supply max's out at 35amps and 550watts.

Remember, this is an AGP card. If it were PCIe and I was running it Crossfire the amps jump up to 38.

I don't know how you get an X1950 running 3D graphics to pull only 65watts, the lowest i've found is 165watts.

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[spudnuts]

felixc,

Sorry about my past post about the 65watts, I just noticed that that is what you found on the web and not what you had set up.

If you think 750 Watts is alot of power, you might want to look around at the power needs of the GeForce 8800 GTX and if your running dual SLI or even quad with 2 dual GPU cards, you might want to get a 1KW PSU.

Alot of reviews that i've been reading is saying that the basic power requirements for new gaming hardware will be 1KW.

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[felixc]

I agree with you, the power requirements for the future will go up.

ATI too recommends a power supply of 450 watts in a system that uses the X1950. You won't load a power supply at 100% of its rating, a typical fully loaded system would not exceed some 350-400 watts. Tom's hardware had an interesting article on the power supplies, showing that many of them do not meet their specs at full load. Thus the margin that ATI recommends for its cards.

http://www.tomshardware.com/2005/07/11/stress_test/

65 watts of power for the X1950 means 5.5 amps from the 12 volts, if all of its power was coming from that voltage connector. This is low.

Anyway, your system will rock for another year with a X1950!

http://www.tomshardware.com/2007/01/10/agp-platform-analysis/

Personally I would skip the 8800 generation of products. The first generation of products (both ATI and Nvidia) that support DirectX 10 will have their share of bugs and limitations. After this generation, the designers will optimize the hardware and the technology will allow for a better integration and lower power consumption. I'd have never bought an X1900XTX, but the X1950Pro (more or less next-gen) is quite a nice product and I'll probably put one soon in my AGP mobo too.

 

[spudnuts]

Nice article, makes me feel a bit more comfortable that i've not gone to PCIe yet. Don't really feel like fronting the money for a complete system overhaul.

I agree on the DirectX 10, it's the same as Vista in my book. I won't go no where near Vista until after at least the first service pack.

I've run a simple wattage calculation on my system and at idle i'm pulling 435watts. What makes me think the problem is my PSU is the Video change. It's the only thing that i've changed other then adding 2 more cathode UV tubes. I've disconnected all 4 cathode tubes, 1 hard drive and 1 DVD burner and my system runs without problems.

I'm really not going to know the full extent of my problem until I get the new PSU and test it.

I'm reloaded drivers, reloaded games, swapped video cards, you name it and i've pretty much isolated it to the PSU.

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[spudnuts]

Dropped in the 750 and everything is working well. I've posted my rig on my blog

http://www.spudsnuts.blogspot.com

No one comments or looks at it but hey, I don't comment or look at anyone elses blog either...lmao

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[felixc]

Oh I see why you computer didn't work, it's the power used by all those LEDs!!

Okay it's a joke...

 

[spudnuts]

Well, I do quite a few LAN parties and eye candy is very important....lol

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