1x 12V vs. 2x 12V question...

[XXGG]

Hello to all.

I am thinking of buying a new Power Supply Unit, a Enermax brand.

I was wondering what is the pros and cons of 1x 12v line vs. 2x 12v ?

Is there a combinatin is hardware in a system that is good for one or

the another ?

I would really appreciate your detailed reply

Thank you!

 

[Ice Czar]

LOL, well I wasnt blind before that post


in a general way, most any supply that you will see with dual +12V rails, will have more amps between those rails than a supply with a single +12V rail, a rule that is not without exceptions

youd need those amps to power CPUs, GPUs and mobos that more and more employ that rail, the now join the fans and drives that previously where the sole consumers off the +12V rail

seperation of the rails was called for in the spec to isolate the drives, which can be very high but short draw items from causing too much instability for the CPU\GPU, not that big a deal with a really high quality power supply, since they have adequate means to regulate what is called overshoots and undershoots on a given rail (for instance sending +13V on the +12V rail would be an overshoot) but it does force less than top shelf manufacturers to employ a more fool proof scheme, ensuring that stability

more importantly is to look at the factors that can adversely effect the ability of a PSU to run stabily

the leading causes would be
overloaded, a supply trying to supply more amps to a rail than its really capable of
read calculate the load on the PSU accurately

AC line instability (surge or brownout, conversely a supply that is only rated to convert AC power in a very narrow window of AC voltage) read run a UPS and get a quailty supply

too hot an operating environment, something you dont normally see is the true engineering specs for a supply, which will include a line like, rated at full power 100% for 0-25C decreasing to 0% at 70C, so a supply will in a linear fashion decrease in capacityy as it heats up, you need to factor that in when buying a supply, and as far as is possible given your skills address means to ensure a reasonable operating temperature

and lastly, being able to wade through the marketing hyperbol that surrounds power supplies, where there is little to no universal standard they have to meet when advertsing
from deceptive clainms to outright lies, so establishing the veracity of ratings is why you have p0laces like this, and a (very) small cadre of competent reviewers

why dont you post the configuration of components you need to power and we will work up some numbers, include everything that would be powered, all drives fans, lights, ect

and no Im not going to correct all those obvious typing errors as they dont effect the actual meaning in this case, read around them

 

[XXGG]

Here is my hardware spec.

AMD Athlon64 3000+ (Winchester) Retail Heatsink & soon to overclock.
2x 512MB KingMax PC3700 DDR-SDRAM
MSI K8T Neo2-FIR
Western Digital 120GB 8MB IDE
Maxtor 120GB 8MB IDE
Pioneer 16X DVD-ROM Drive
NEC ND-3500A DVD+/-RW Drive
ATi Radeon 8500 64MB AGP (Engineering Sample) (Soon to be replaced with X800)
CreativeLabs Sound Blaster Audigy 2 oem
WinTV PVR-250 PCI
Onboard LAN
Logitech Z-640 Speaker
Floppy Drive
IBM Type-M PS2 keyboard (Built 1996, opened from original seal box November 2004)
Logitech Optical mouse PS2
Samsung Webcam USB
Lexmark Media Reader USB
Canon MP360 Multifunction Printer USB
20GB HDD External Enclosure USB 2.0
2x Vantec Stealth 12cm case fan

All currently being powered by Thermaltake 420W PSU.

-
I am thinking of buying...
Enermax EG465P-VE (single 12v rail @ 33Amp)
or
Enermax Noisetaker EG475P-VE (two 12v rail @ 16 & 15Amp)

 

[Ice Czar]

OK for starters some of the equipment was simply estimated so looking up the actual figures up might be worthwhile, specifically the WinTV PVR-250 PCI and audigy 2, I used a capture card that hits the +12V rail for the estimate and a SBlive, and AMD reference for all the USB devices (which arent on the +12V rail) I assume the external HDD enclosure has a seperate power source? same with the printer obviously

used 2300 rpm 120mm fans

and I used the X800 Pro at stock
http://www.xbitlabs.com/articles/video/display/ati-powercons_5.html
http://www.xbitlabs.com/misc/picture/?src=/images/video/ati-powercons/t2.gif&1=1

if its the XT or the EC youd should rerun the numbers (make sure to add the AGP + Aux)
same goes for overclocking they also have OC amp draws listed
I added a value in the SCSI field to get an additional .04A on the +12V rail to get closer to the real value on the card (it rounds 100ths)


http://takaman.jp/D/?M=PbQDQbdHhSAgHIiH3kG5@XDWHXVjoG5H@YbZAZavHEwXAMZ&english
theoretical maximum
+3.3V @ 4.8A
+5V @ 14.2A
+12V @ 21A

realworld worse case senerio with HDDs and Fans at 1\4 static draw post spinup and the TV PCI and sound at 1\4 as well (static draw = 1.35), CPU \GPU and mobo at 100% and an Optical at full draw spinup
+12V @ 13.5A with a supply @ 25C (20.5A with a supply @ 40C)

the Thermaltake 420 w\ 18A on the +12V rail would likely be overtaxed during some load senerios and operating temperatures with the planned upgrade so that was a wise call

the EG465P-VE w\ 33A on the +12V rail @ 25C (22A @ 40C) would certainly do the job
as would the EG475P-VE w\ 31A combined

would work good for that config, and there is likely some play still, but youd need to rexamine it again for further upgrades
a good thermal solution for the supply will increase its range (where its not exhausting the CPU) and a UPS always makes the job of a PSU far easier (Stable AC source devoid of surges or brownouts)

 

[XXGG]

I have used the following link http://www.3dcool.com/PWC.asp
to do some basic Wattage calculation and it recommeds
minimum of 471W PSU.

A Minimum of 471? Sure it is calculated as a maximum full load.
So.. does 471Watts sound reasonable?

I guess Enermax will do fine since I will/can't never get every single
component to run at 100% load. Or can it happen?

-----
Thanks for your reply again.

 

[Ice Czar]

well, wattage is often deceptive, which is why we ran the amp distribution
these days a typical wattage calculator like the one you linked is actually kind of dangerous for some configs, its really important to run the amps per rail and that can include what amps are on a given +12V rail if its a dual rail supply
at a maximum draw of all the components your more like 350watt
but youd need to be into the higher side of 450 to 500 watts to get a supply that will produce the amps youd need on the +12V rail at a reasonable operating temperature for most supplies, however here is an exception a
350 Watt that would do it
(if its kept cool enough that is)



generally when looking at a supply
ignore its total watts, that capacity will largely be unavailable as they are sort of "dual" compatible supplys (if your lucky) working with both older mobos\cpus that use the +3.3V\+5V combined rail to power the CPU, and newer boards that power the CPU off the +12V rail, so either application you have untapped capacity (that 350 above is an exception here being biased towards the +12V rails, an older supply will be biases toward the +5V rail and worse anemic on the +12V rail)

when comparing supplies to your baseline +12V amperage above (20.5A in bold) you can simply compare it to the listed value on the supply
but if you where using the 13.5A value, youd deduct one third off the rated amps listed on the supply

basically youll never see 100% load of all the components at the same time, which is why I ran the real world worse case senerio

fans and drives hit 100% when they spinup, then drop to 1\4 of the draw to maintain that speed, but while that is happening, the CPU and GPU wouldnt be at full load

 

[XXGG]

Thank you