Question about PSU

[Jake]

Hi,

I am looking to buy a power supply. I know my video card alone will
need 28a maximum on the 12v. If I get a power supply with 3 12v rails
with 18a each, will this be enough? Or will I need to buy one with say
38a on a single 12v rail?

Thanks

 

[Cuzman]

Jake wrote:

" I am looking to buy a power supply. I know my video card alone will
need 28a maximum on the 12v. If I get a power supply with 3 12v rails
with 18a each, will this be enough? Or will I need to buy one with say
38a on a single 12v rail? "


You don't need all 28A on one 12V rail, unless there is only one 12V
rail on the PSU. I wouldn't recommend buying a 20-pin motherboard and
PSU for a new build though.

The graphics card isn't the only item that uses 12V though, and you
might be building a system with 97 hard drives and 163 fans. I doubt
that, but you might do best to list your entire proposed system anyway
so people can give you specific recommendations.

 

[Paul]

Hi,

I am looking to buy a power supply. I know my video card alone will
need 28a maximum on the 12v. If I get a power supply with 3 12v rails
with 18a each, will this be enough? Or will I need to buy one with say
38a on a single 12v rail?

Thanks

The highest consuming video card is X1900XTX at 10 amps on the
+12V rail. That is no where near 28 amps.

The highest consuming processors at stock speed, might be the
Intel ones that have 130W TDP, and allowing Vcore conversion at
90% efficiency, that works out to maybe 12V @ 12 amps. An
overclocked Pentium D 805 can draw more than that, but you
probably aren't using that as the basis of a high end gamer.

Stating your hardware inventory (all the parts used in your
PC) would allow someone to estimate the necessary size for
you.

Paul

 

[meow2222]

Hi,

I am looking to buy a power supply. I know my video card alone will
need 28a maximum on the 12v.

Thats one freaky video card, suggest you reread the specs.


NT

 

[kony]

Hi,

I am looking to buy a power supply. I know my video card alone will
need 28a maximum on the 12v.

No, you don't know this.

If I get a power supply with 3 12v rails
with 18a each, will this be enough?

For what you really need, maybe.
"IF" you have a power hungry video card, you'd be as well
off not getting a psu with the 12V rails split 3 ways,
instead one where there are two or one and rated honestly
for at least 18A per the one used.

Or will I need to buy one with say
38a on a single 12v rail?

No, you don't need 38A and there are very very few PSU that
can actually supply 38A regardless of their misleading
specs. Those are peak and/or lab/low ambient temp ratings,
not what most can do in a real system.

As other posters already mentioned, you need to start by
providing a concise but complete itemized list of all major
power consumers in the system, including video, CPU, memory,
HDDs, optical drives and other cards if there are many or
they stand out as hungry devices. Also all USB or firewire
devices if you have a lot of them and need them on 5VSB
power.

 

[Htnakirs]

http://journeysystems.com/power_supply_calculator.php

 

[Jake]

Thanks for all of your replies so far...I'll admit 28a did seem
rediculous to me, but that's what the specs APPEARED to have said. I'll
include a direct quote. "Power supplies with 450-Watt capacity and 30A
current on 12V rail is recommended for single...product."
Does that mean 30a for the whole system (HDDs, CPU, etc)? (assuming
that everything else in the system won't take the amps above 27a or
so--to give a 10% leeway)

Now, I've been looking at other power supplies and have found one that
outputs very close to 38a on the 12v line with one rail (lots of good
reviews for this), and one that has 2 12v that output 18a and 19a
respectively. Which one do you guys recommend? Let's just assume, for
simplicities sake, that my system doesn't get within 10% of max
sustained power output. Is there an advantage to dual rails? Or is a
single, large one, better?

Thanks again. Sorry for the misinformation

 

[Rod Speed]

Thanks for all of your replies so far...I'll admit 28a did seem
rediculous to me, but that's what the specs APPEARED to have said.
I'll include a direct quote. "Power supplies with 450-Watt capacity
and 30A current on 12V rail is recommended for single...product."
Does that mean 30a for the whole system (HDDs, CPU, etc)?

Yes, when you have a single video card in that system.

(assuming that everything else in the system won't take
the amps above 27a or so--to give a 10% leeway)

Now, I've been looking at other power supplies and have found
one that outputs very close to 38a on the 12v line with one rail
(lots of good reviews for this), and one that has 2 12v that output
18a and 19a respectively. Which one do you guys recommend?

Generally best to have more than one.

Let's just assume, for simplicities sake, that my system doesn't get within
10% of max sustained power output. Is there an advantage to dual rails?

You obviously need to ensure that you wont overload one of the rails.

Or is a single, large one, better?

Nope, which is why more than one is the improvement seen later.

 

[kony]

Nope, which is why more than one is the improvement seen later.

Nope, there were more than one to adhere to the 18A limit
per *rail* which Intel now recants.

 

[kony]

Thanks for all of your replies so far...I'll admit 28a did seem
rediculous to me, but that's what the specs APPEARED to have said. I'll
include a direct quote. "Power supplies with 450-Watt capacity and 30A
current on 12V rail is recommended for single...product."

They're trying to cover all bases by being conservatively
high. Around 24A is plenty in a decent PSU unless you're a
mad overclocker (or more than one CPU, more than one
high-end video card).

Does that mean 30a for the whole system (HDDs, CPU, etc)? (assuming
that everything else in the system won't take the amps above 27a or
so--to give a 10% leeway)

Most of the time a system peaking above 20A won't be
anywhere near 90% of that value. You'd have to have a game
where it put a fairly even load on both CPU and video, but
yes, their figure would have to be for the whole system and
it's just a generic guidline as they can't know if you had
some other need for a lot of 12V current such as a lot of
hard drives, a peltier, etc.

Now, I've been looking at other power supplies and have found one that
outputs very close to 38a on the 12v line with one rail (lots of good
reviews for this), and one that has 2 12v that output 18a and 19a
respectively.

You mean you found some that claim it.
Evaluate the brand first, not the label. Perhaps you have
but you make no mention of it.

Which one do you guys recommend?

That you stop trying to generalize and get an answer without
providing the details of what parts you have. Do not
randomly pick a number on a label, unless you just feel like
overpaying and then having some assurance you have more
power than you need (which can even then be a problem with
some generic PSU).

 

[Rod Speed]

Nope,

Fraid so.

there were more than one to adhere to the
18A limit per *rail* which Intel now recants.

No they dont.

 

[kony]

Fraid so.


No they dont.

Yes Rod, quit being contrary and do some research.

The 18A was an artifical limit that ultimately causes more
harm than good on any system that would really need 30A, or
36A as the op had suggested.

 

[Rod Speed]

Yes Rod,

No, gutless.

quit being contrary

Corse you never ever do anything like that yourself, eh child ?

and do some research.

Dont need to.

The 18A was an artifical limit that ultimately causes more harm than good
on any system that would really need 30A, or 36A as the op had suggested.

It aint that black and white, and it isnt even clear that
the OP does actually need those currents either.

Yes, multiple rails obviously needs the configurer to check
that the system isnt going to take more than the rated
output on any of the rails, but that does NOT mean that
there is no advantage in having more than one 12V rail.

 

[kony]

Dont need to.

Sometimes I laugh, sometimes I pity you.

It aint that black and white, and it isnt even clear that
the OP does actually need those currents either.

Yes, multiple rails obviously needs the configurer to check
that the system isnt going to take more than the rated
output on any of the rails, but that does NOT mean that
there is no advantage in having more than one 12V rail.

Actually I've never seen anyone mention their system didnt'
work right with one, ample capacity single 12V rail, but did
with dual rails.

The hypothetica benefit you might suggest, is also countered
by real drawbacks. Again, even the proponents of 18V/rail
in the spec have taken a second look and abandoned it,
contrasting the Intel PSU design guide 2.2 and today.

 

[Rod Speed]

Sometimes I laugh, sometimes I pity you.

Any 2 year old could leave that for dead, child.

Get one to help you before posting again, if anyone
is actually stupid enough to let you anywhere near one.

Actually I've never seen anyone mention their system didnt' work
right with one, ample capacity single 12V rail, but did with dual rails.

Irrelevant to whether more than one rail has some advantages.

The hypothetica benefit you might suggest,
is also countered by real drawbacks.

Yeah, yeah, you're the only one that understands the basics.

How odd that supplys with more than one 12V rail have been seen.

Again, even the proponents of 18V/rail in the
spec have taken a second look and abandoned it,

Pig ignorant lie.

contrasting the Intel PSU design guide 2.2 and today.

Pathetic, really.

 

[kony]

On Wed, 16 Aug 2006 06:41:53 +1000, "Rod Speed"

e 12V rail.

Irrelevant to whether more than one rail has some advantages.

Quite relevant as to whether a theoretical advantage is a
realized advantage.

 

[Rod Speed]

Quite relevant as to whether a theoretical advantage is a realized advantage.

Nope, what you may or may not have personally seen is
completely irrelevant to what real advantages there are, child.

 

[kony]

Nope, what you may or may not have personally seen is
completely irrelevant to what real advantages there are, child.

Show us even one example of a "real advantage", where it
made a difference, all else being equal. You're making up
nonsense as you go along.

 

[Rod Speed]

Show us

How many of you are there between those ears, gutless ?

even one example of a "real advantage", where
it made a difference, all else being equal. You're
making up nonsense as you go along.

Have fun explaining the ATX 2.2 standard, gutless.

Yeah, yeah, you know it all, they know absolutely nothing at all.

Yeah, right.

 

[kony]

How many of you are there between those ears, gutless ?

Someday Rod, I'll educate you about usenet. It's a wee bit
different than a P2P email.

Have fun explaining the ATX 2.2 standard, gutless.

I already mentioned ATX 2.2 in a prior post, perhaps you
should spend more time learning, less time trolling.

Yeah, yeah, you know it all, they know absolutely nothing at all.

Yeah, right.

Clueless one, it is they who changed their minds.