Can somebody explain 'rails'?

[unknown9]

I've been told to 'watch my rails' when adding lights/mod's etc. I know how to monitor them, but what should i look out for? What exactly are they? I've been noticing my 5v rail has been jumping from 4.999 to 5.053 creating small waves in Asus Probe like so in the attachment. Thanks for all your info

[RamonGTP]

Rails are the 3 voltage lines coming from the PSU... 3.3, 5, and 12 volt... The fluctuation you're expierenceing is totally normal and is nothing to be alarmed over. What you want to watch out for is if any of the rails are too low, or too high.

[unknown9]

What you want to watch out for is if any of the rails are too low, or too high.

When is too low or too high (for future references)?

[RamonGTP]

I believe its +/- 5%

So the 12volt rail should not drop below 11.4, or go above 12.6

5 volt should go below 4.75 or above 5.25

3.3 shouldn't go below 3.13 or above 3.47

[Bovon]

As RamonGTP said, those voltages are about what to look for, but please..do not expect accuracy from the onboard voltage sensors the manufacturers install. They are general purpose sensors and have an overall accuracy of about 20%.

If you are that concerned wit your voltages, get yourself a decent digital voltmeter and compare the 12 and 5 volts from a molex connector against what the motherboard monitor says it is.

Right now, reading my 12 and 5 volts with a digital VM, I see 12.75 and 4.97 volts. Motherboard monitor at the same time shows me 12.55 and 4.72 volts. The digital voltmeter is obviously more accurate than the motherboard sensors.

The "term" rail is simply a term somebody assigned to the different voltages coming from a power supply. In electronics, these 'rails' will be called 'legs' many times..the proper term would be "the 12 volt circuit"... or, "the 5 volt circuit", etc. Lotsa writing to say the same thing others have come to accept when we say rail!!.. It really doesn't matter what its called, as long as everybody is on the same wavelength and knows what the other person is saying.

[unknown9]

Where would be a good place to buy a voltmeter? Computer stores? Hardware stores? I'm not too farmilar with them....

[DallasDon]

Most convient would probably be Radio Shack. As far as quality, you get what you pay for.

Another option is online, read the reviews of purchasers.

On another note, some mobos have a shutdown feature if the voltage fluctuates too much. Check the Voltage control section of the manual.

[Bovon]

http://www.bgmicro.com/

Use 'Go Shopping" button. Enter 'multimeter' in the search keywords box, or search category drop down menu, select (MET) meters. This option will give you every type of general purpose meter they stock...much better to simply enter multimeter in the "search keywords" box.

This will give you the following:

ACS1358 Multimeter Leads ITT Pomona Meter Leads $1.29
MET1014 Digital Multimeter Back Lit $15.95
MET1015 Digital Multimeter $44.50
MET1016 Small Multimeter Very Accurate $6.95
MET1028 4 Digit LCD Multimeter And Frequency Counter $47.55

The cheapie $6.95 meter will do you just fine for what you are wanting..if you want one, the higher priced models will have more functions, but the accuracy will be about the same. I have both a Fluke $200 meter and an elcheapo from BGMicro..voltage readings are very close when read by both meters. The Fluke will do many times more than the cheapie will however.

Shipping will be about $6 bucks..or was the last time I ordered anything...and I have been buying from these people for over 10 years.

Download their PDF catalog, and look on page 3 for multimeters..pictures of them will be on the page.

[John Prophet]

Just out of curiousity for the sake of this thread....

What kind of voltmeter are we talking about here...digital or analog?

Because obviously an analog (with the little needle like a speedometer) isnt going to really be too great for seeing exact levels..like say the difference between 4.96 and 4.88 volts etc.

So are we pretty much talking about digital voltmeters then yes?

BUT...my question is..are we talking about tiny MOMENTARY little voltage drops....or are we talking about the voltage actually "sagging"?


Basically my question is....can you really see these differences with a voltmeter or are we talkling about a millisecond voltage drop which cant be seen on a voltmeter?


Just curious.

JP

[Bovon]

These are digital voltmeters...look at the PDF catalog on page 3.

No meter can catch fast voltage fluctuations..that takes a `scope or other instrument that can detect these momentary up/down fluxes..which are usually not important...all power supplies will gain or loose a minute voltage as more or less current draw hits the source..it take a micro second for the regulator to kick in and the output to recover. Such as this cannot be seen on some system like motherboard monitor anyway.