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Power Supplys'

E

eli

[H]ard|Gawd
Joined
Apr 30, 2003
Messages
1,648
The one thing I haven't delved deeply in, in regards to computer hardware are power supplys'. I know what brands make the best power supplies, but I hear people talking about more technical things. I hear some people talking about how their power supply gives their components unreliable power current. I also hear about hooking two devices together using the same power cables can cause problems. Like connecting a HDD and a video card to the same cable. Can someone give me a simple, "In a Nutshell" explanation on how power supplys' work? and how connecting two devices using the same power cables can cause problems?


Later,
Eli
 
im going to do this stupid anology because im bored.

think of the plug that goes into your power supply as an inlet to a water treatment plant (power supply), this plant now makes the water clean (useable) and feeds the water down to it's pipes (wires). Houses hooked up to the treatment plant (drives etc) need water for the people(components) to be happy. Hook up a few water hungry houses to the same line, house A(hard drive) and B(radeon 9800xt) kind of overcharge the line, each complains that one or the other is not getting enough or is taking too much water and not "sharing". to solve this problem, you hook each house to their own line, that they would rather not share with anyone else (greedy bastards). This makes each one of them happy, until a power surge (flash flood) goes through the pipes and takes both of them out :D

ok.... i'm done.

your power supply has different circuits to supply the juice to the components so spread out the load so one circuit is not getting the juice sucked out of it.

/passes out
 
that answers my question completely, thanks a lot. Are video cards and HDD's the only two things you dont want to share on a power cable?

Later,
Eli
 
That would be a great analogy, except...

1. If devices were pulling more power over 1 wire than it could allow, the wire would heat up and melt!

2. Only ATX-GES or similar high-end PSUs have truly different lines to attach to, and then it's only the +12v. Basically, all the physical lines in the PSU connect back to the same source.

3. Hard drives aren't high draw devices


So, in conclusion, that's a terrible analogy, and it's really voodoo when it comes to moving devices around on to different connectors.
 
Power supplies are rated in watts typically. Take the current on each rail times it's voltage and add them all together and that's what you get. Some companies measure these settings at different temperatures so that affects how much power you get during typical use.

Think of unstable voltages as when the air conditioner in your house kicks on the the light dim momentarily etc. Electrical components don't want the lights to dim because that would cause stability problems. Better supplies are good at keeping the voltages stable when one devices starts eating power.

The parts of your system that will be drawing the most power are the CPU(s), memory, and video card. However if it was made with an additional power connector on the card there's a good change that's eating your power as well. If it's putting off a ton of heat it's also eating a lot of power. When picking a supply you want one that can put out enough current on the given rail(12V, 5V, 3.3V, and some others). The 12V is the only one you typically have to worry about.

Each device having it's own direct cable, in almost all circumstances ,won't help at all. How stable the voltages are depend on the PSU in the system and how well it was built. ie if it's a cheap one your voltages are going to be more unstable and possibly cause stability issues for your system.

Better PSUs also tend to weigh more than others. Heavier PSU means better PSU in just about any case you'll come across. Better supplies also tend to be more resiliant towards voltage fluctuations in your house. For example if the air conditioner kicked on, the lights dim, and the computer gets restarted. That's a sign of a cheap PSU.
 
Completely understood, thanks. Is there some place to find out which components of a PC are the most power hungry? i dont want to hook up too devices, and have one of them fail. I know HDDs' and video cards dont make a good combination, but what else?

Later,
Eli
 
Old wives tale. Get the correct high quality supply and hook up at your convenienc.

Have fun and don't over think it
 
sorry, but thats not very encouraging. I have heard of people with problems hooking two power hungry devices together. Can someone give me a list or something of what devices not too hook up together.
 
Newer ATX V1.3 compatible PSU have seperate 12 volt rails to provide "clean" power to the mobo. Fans and motors can cause electrical interference for other devices hooked up on the same power rail. I know for sure that Enermax's newer PSUs have seperate 12 volt rails, and an "extra" dedicated 4 pin connector for the graphics card. (Other companies like Antec, PC Cooling, Vantec... should be offering this on newer designs too.) So now you've isolated your "main" components. Everything else is mostly motor related devices. Unless you're running some fans that draw current like a house air conditioner, you shouldn't have to worry too much about overloading anything. There's something to be said for common sense though. You shouldn't try to run 20 4-pin pass through extensions and every piece of hardware on the same power cable. If you're going to overclock the system, you should probably get a 430+ watt PSU. If you're only gonna have a couple of optical drives, floppy, and 1 or 2 hard drives you should be able to space them out across you available PSU leads and not have any problems with a 350 watt PSU. Making sure you're using a battery backup with voltage regulation will do you more good than trying to find a specific list of dos and don'ts for what to put on the same power cable. You're more likely to damage equipment from undervoltage power from the wall than you are from anything else.
 
<--- is writing a PSU FAQ this week because i'm sick of all the uncertainty around here about power supplies (now the question is will anyone read it...)
 
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