Sign in with
Sign up | Sign in
Your question

Two 12V rail

Last response: in Components
Share
September 3, 2009 8:01:49 AM

how will be power distributed in case of two 12v rails.

More about : 12v rail

a c 144 ) Power supply
September 3, 2009 8:16:51 AM

The label on the side of the PSU will tell you. Keep in mind that the total will usually be less than the sum of the rails.

For example, the label for my Antec 650 watt TP3 says that each of the three rails can provide up to 19 amps. But the total current is 52 amps.

What kind of PSU do you have or are considering?
a b ) Power supply
September 3, 2009 12:02:30 PM

The metal tag ratings on the power supplies include the SURGE RATINGS or >150% (common) of the maximum allowable continues load/capacity.

SURGE Ratings are the current surge or rush of electrical current that comes in to the load during power up. This came about to take care of the instantanous state of CAPACITIVE LOAD which are electrically DEAD SHORT at time-ZERO when power is applied. This condition happen in time periods of micro-seconds/mili-seconds. It is a real power load that must be accounted for to enable the load to stabilize. Power supplies are to ensure that the voltage specified (i.e. 12.) is retained to specification at that condition.

THATS THE REASON THE METAL TAG RATINGS ARE HIGHER THAN THE ACTUAL SPECIFIED CONTINUES LOAD CONDITION. These are two different electrical parameters that must be met.


SURGE current are common to electronic devices and applience since the bulk of our electronics are made of CMOS devices. Every transistor has in intrinsic capacitance on it and we have billions of it video cards and CPU. Every DRAM has capacitor per cell. Billions of Capacitors DEAD SHORT at time zero for a very short period of time.

Typical example of an ANTEC TP-550 with 12V rating of 20A per rail. In reality the continues load guaranteed is ~ 11 to 12 AMPS.
http://www.antec.com/Believe_it/product.php?id=MTc1OA==

Multi-Rail Supply(HIGHER COST): Distribute and Isolate your load. Separate NODE & LOOP:
===================================
Multi-rail supplies will allow you to isolate loads such as video cards and drives. Video card tend to have real time huge swings when apps switches from 3D to none 3D applications. Hard Drives voltages swings when the motors stops or start when apps put it on sleep mode or take it out. The acceleration control on servo motors inside the drive will require sudden increase in current draw. These are example of load changes that affect the voltage output of the supply and noise created by changing load condition.



================================
SINGLE RAIL PS(LOWER COST): (i.e. 12V 70A) Everything is shared in one common NODE & LOOP
================================
The combined noise and voltage variation created by the load is all shared by all loads. The noise from GPU variation is shared to other loads like Hard Drives. Same thing ...Noise from Motorize load such as Hard Drives & fans get shared with the GPU.

-------------------------------------

My personal preference is multi-rail supplies specially with multi-GPU setup that cost a lot of money. But again its more expensive and one has to manage the load and distribute it to different rails.

Its your choice

Good Luck


Related resources
a c 243 ) Power supply
September 3, 2009 12:14:51 PM

leon2006 said:
The metal tag ratings on the power supplies include the SURGE RATINGS or >150% (common) of the maximum allowable continues load/capacity.

Typical example of an ANTEC TP-550 with 12V rating of 20A per rail. In reality the continues load guaranteed is ~ 11 to 12 AMPS.
http://www.antec.com/Believe_it/product.php?id=MTc1OA==


1 ) That's the way most cheap sh!t psu's are labeled.
2 ) Bad example, Antec psu's are gauranteed to provide thier full rated power and it's been shown time and again that the OCP on good quality unit's is set higher than what is specced.
a b ) Power supply
September 3, 2009 2:03:30 PM

DellUser1
Read the specifications....

There is nothing wrong with the Antec Specs as shown on the webpage.

The Table defines MAX range that include SURGE RATINGS... There is a note below that defines that (Continouos or stabilized cond) MAX load which is 45A which is way lower than the summation of individual ratings for each 12V rail.

These are two distinc Power Supply Parameter. One includes the SURGE rating... The second defines the normalize load condition at time infinity.

Over Current Protection/ Over Voltage Protection are different electrical parameters than surge rating capacity parameters. OCP circuits are independent and separate than rail regulators.

The rules on these are defined by NEMA and IEEE as a function on type/classification of equipment and device.
a c 243 ) Power supply
September 3, 2009 3:10:05 PM

I have
Didn't say there was
The table does not include surge ( aka peak ) ratings it includes max rail ratings ( see my last post regarding that ). Yes, it's widely known that for the most part multiple 12v rails are not additive, there are exceptions though.
!