Meaning of rails

I'm not 100% about what is meant by rails, but my understanding of it is that if the PSU is rated for 250W, this power is divided up among the differnent connectors coming out of the supply. For example, the wires that connect to the mobo will supply up to 100W, the wires that connect to the CD drive will supply up to 50W, and so on up to the full capability of the PSU. Since the CD drives are powered by their own wires, or rail, as opposed to the same rail that powers the mobo, removing them will not increase power to the mobo. (granted, they do connect to the mobo via the ide cable, but this does not power the devices)

This is what I was getting at, but again take my basic knowledge with a grain of salt.

John

JohnK93 , you are right. For instance, the newer P4 connector, the one with 2 black and 2 yellow wires can be thought of as one rail, its 12 volts and it powers the cpu.
A combination of wires to get certain voltage is a rail.
So you test for 12 volts, 5 volts, 3.3 volts.
I dont have it down perfect but you can google that info.
If anyone wants it i can post or show you where this info is for your power supply.

k1n9k00p4. The best thing to do is disconnect all that you can to take the strain off your power supply. Just have one stick of ram and your hard drive and video, mouse and keyboard.
You can get a digital or analog meter at any hardware store for around $10. You can use the meter to check your various voltage levels of your power supply. All you need is a tutorial to do it. There is a very good tutorial at techrepublic.com. You have to sign up to get the tutorial but its a professional place anyway and they dont bug you so its worth it to sign up. You wont understand most of what is there, but the tutorial is very good. If you cant find it let me know and i will give you the correct page. I can even email you the tutorial, i made a copy of it long time ago.

here is a very very good tutorial on power supplies and different rails and voltages. I copied the whole tutorial into one word doc.
If anyone wants it just email me and i will send it out. Here is the article.

http://www.informit.com/articles/article.asp?p=31105&seqNum=4

heres another:

http://www.fonerbooks.com/power.htm

i have a copy of that as well

A bit of info to show us how much power a part will use.
But note that this power is taken from different lines and voltages as well, so you have power used on the 12 volt line, the 3.3 volt line, the 5 volt line and sometimes from 2 lines at the same time. This is what is meant by "rails". One rail is the 12 volt line, another rail is the 3.3 volt line, and so on.
Below is some info i copied from a source:

When it comes to the question of how much of a power supply you need; you should not judge your power supply by overall wattage alone. Take a look at the demands on each separate line. When looking at overall wattage, add the requirements of every device in your machine, then multiply that number by 1.5 (because you should be taxing from 30 precent to 70 percent of your power supply's capacity). Most of your individual components will actually list their specific power requirements. Use the below numbers for a general calculation. And remember, if you need to figure out wattage, multiply the voltage by the amps.

High-wattage AGP card 20 - 50W +3.3V
Average PCI card 5W +5V
Cached PCI SCSI controller card 20-25W +3.3V and +5V
Floppy drive 5W +5V
10/100 NIC 4W +3.3V
Typical Atapi CD-ROM 10 - 25W +5V and +12V
Typical Atapi DVD-ROM 10 - 25W +5V and +12V
Typical SCSI CD-R/RW 20W +5V and +12V
SCSI CD-ROM 12W +5V and +12V
RAM 8W per 128MB +3.3V
Ultra2 SCSI PCI card 5W +3.3V and +5V
5400rpm IDE hard drive 5 - 10W +5V and +12V
7200rpm IDE hard drive 5 - 15W +5V and +12V
7200rpm Ultra2 SCSI hard drive 24W +5V and +12V
10,000rpm SCSI drive 10 - 40W +5V and +12V
Motherboard (without CPU or RAM) 20 - 30W +3.3V and +5V
Typical Pentium II 30W +5V
1GHz and up Pentium III 34W +5V
Typical Pentium 4 65W +12V
Typical AMD Athlon (board w/ 12V conn) 70W +12V

Me again, if anyone wants a copy of any of this stuff, just email me.

Here are some sites with info on power supplies and multimeters for testing computers and anything else you might want to test with a meter. Bear in mind i got this a while back so some pages may have changed:


great one here, techrepublic, but you sign up for free membership, great info place too!! They dont bug you either. Plus, here is there multimeter tutorial:

http://techrepublic.com.com/5100-10586_11-5566528.html#

looks like a good one:

http://tritium.fis.unb.br/Fis3Exp/w...t/TUTnBRIEF/English/BI-T-Idx-Multimeters.html
http://www.fonerbooks.com/power.htm

http://www.acmehowto.com/howto/homemaintenance/electrical/multitesteruse2.php

http://channels.lockergnome.com/it/...n_how_to_diagnose_power_supply_problems.phtml

http://www.neoseeker.com/Articles/Hardware/Reports/motherboardvoltages/

http://ezinearticles.com/?Learn-How-To-Diagnose-Power-Supply-Problems&id=16307

http://mechatronics.mech.northwestern.edu/design_ref/tools/multimeter.html
http://autorepair.about.com/cs/troubleshooting/a/aa063001a.htm


http://www.extremeoverclocking.com/ - they have info but you have to find it