Building new PC, help with PSU?

[coolsti]

Hi,

have almost decided what my new PC will consist of, and am thinking of an
AMD Athlon64 3800+ processer, and an Asus motherboard using the
PCI-express interface for the video card. I don't want to move to a Dual
yet until they have been out on the market a bit longer, and for me the
move to this CPU (according to the CPU performance tests by Tomshardware)
will be an enormous performance increase over what we have now.

But I am totally uncertain what I need in the way of a PSU. Can someone
help me?

The PC will have at most 2 SATA hardisks, on-motherboard LAN, a DVD player
and a CD burner, and one (only) darn good video card. What should the
wattage rating of the PSU be for this? People recommend to me Antec, but
what model? Or can someone recommend something else for this setup?

Of course the lifetime of the PSU will probably be longer than the life of
this new PC before a future upgrade, so a bit more power would be better
than "just enough".

Thanks for any help!

Steve, Denmark

 

[Jan Alter]

Hi,

have almost decided what my new PC will consist of, and am thinking of an
AMD Athlon64 3800+ processer, and an Asus motherboard using the
PCI-express interface for the video card. I don't want to move to a Dual
yet until they have been out on the market a bit longer, and for me the
move to this CPU (according to the CPU performance tests by Tomshardware)
will be an enormous performance increase over what we have now.

But I am totally uncertain what I need in the way of a PSU. Can someone
help me?

The PC will have at most 2 SATA hardisks, on-motherboard LAN, a DVD player
and a CD burner, and one (only) darn good video card. What should the
wattage rating of the PSU be for this? People recommend to me Antec, but
what model? Or can someone recommend something else for this setup?

Of course the lifetime of the PSU will probably be longer than the life of
this new PC before a future upgrade, so a bit more power would be better
than "just enough".

Thanks for any help!

Steve, Denmark

430 Watt Thermaltake. I've used a couple of them and they seem to do a nice
job. Other folks rave about them as well. The cost is reasonable after the
$10 rebate ...$30


http://www.newegg.com/Product/Product.asp?Item=N82E16817153023

 

[Agent_C]

But I am totally uncertain what I need in the way of a PSU. Can someone
help me?

I'm running a Pentium Dual Core 3.4, with essentially the same
complement as you describe.

A quality 400 watt PSU, such as an Antec should be just fine.

A_C

 

[Paul]

Hi,

have almost decided what my new PC will consist of, and am thinking of an
AMD Athlon64 3800+ processer, and an Asus motherboard using the
PCI-express interface for the video card. I don't want to move to a Dual
yet until they have been out on the market a bit longer, and for me the
move to this CPU (according to the CPU performance tests by Tomshardware)
will be an enormous performance increase over what we have now.

But I am totally uncertain what I need in the way of a PSU. Can someone
help me?

The PC will have at most 2 SATA hardisks, on-motherboard LAN, a DVD player
and a CD burner, and one (only) darn good video card. What should the
wattage rating of the PSU be for this? People recommend to me Antec, but
what model? Or can someone recommend something else for this setup?

Of course the lifetime of the PSU will probably be longer than the life of
this new PC before a future upgrade, so a bit more power would be better
than "just enough".

Thanks for any help!

Steve, Denmark

A "darn good" video card, could draw from 4 to 10 amps from
the 12V rail. Naming the card might make a difference to the
recommendation.

Your processor is 8.25A from +12V. If the supply has 12V@18A,
the best video card money can buy, puts you over the limit.
Your other periphs might amount to 3 amps, and I'd want another
3 amps of margin. With a 4 amp video card, the 12V@18A is
a good minimal choice.

The more solid info you put in your hardware inventory, the
more accurate the answer.

The selection process is complicated by whether the chosen
power supply, is an ATX 2.0+ spec supply, or an earlier one.
The ATX 2.0+ spec, splits the 12V rail into two circuits.
Generally, that is more wasteful, as 12V2 only powers the
processor, and any excess capacity is not available to be
used elsewhere. So that is another factor that has to be
taken into account - splitting the computed load over
12V1 and 12V2, in the case of the more modern version
of power supply (typically with a 24 pin connector).
While some supplies may cheat, and use one 12V circuit to
power both 12V1 and 12V2, the power supply choice can only
be made by the specs the manufacturer provides, and the
assumption is, that 12V1 and 12V2 are separate circuits.

Paul

 

[coolsti]

A "darn good" video card, could draw from 4 to 10 amps from
the 12V rail. Naming the card might make a difference to the
recommendation.

Your processor is 8.25A from +12V. If the supply has 12V@18A,
the best video card money can buy, puts you over the limit.
Your other periphs might amount to 3 amps, and I'd want another
3 amps of margin. With a 4 amp video card, the 12V@18A is
a good minimal choice.

The more solid info you put in your hardware inventory, the
more accurate the answer.

The selection process is complicated by whether the chosen
power supply, is an ATX 2.0+ spec supply, or an earlier one.
The ATX 2.0+ spec, splits the 12V rail into two circuits.
Generally, that is more wasteful, as 12V2 only powers the
processor, and any excess capacity is not available to be
used elsewhere. So that is another factor that has to be
taken into account - splitting the computed load over
12V1 and 12V2, in the case of the more modern version
of power supply (typically with a 24 pin connector).
While some supplies may cheat, and use one 12V circuit to
power both 12V1 and 12V2, the power supply choice can only
be made by the specs the manufacturer provides, and the
assumption is, that 12V1 and 12V2 are separate circuits.

Paul

Hi Paul

thanks for your very detailed reply. However, as you can see from the
information that my original post is lacking, I am definitely not up on
the technology issues as much as you are.

To answer your question, I have not decided yet on which graphic card to
buy, but am sure I will only include 1 and not 2 graphic cards in the PC.
Whatever power supply and graphic card I choose, I would definitely like
to have a little more power available in the event of an upgrade to a
graphic card later. So the PSU definitely should be overdimensioned a bit
from the start. But what is enough? 430 Watts, as the Thermotake that
another poster suggested? Given the general description I provided, it
should be possible to put a number on the PSU size in Watts that I can
safely go for.

I thank you very much for the time you took to give such a detailed
description, but I just have no understanding of the sizing in terms of
volts and amps. Since I am purchasing a new PSU and not re-using an older
one, I also wonder if I need to worry so much about how the power is
divided into various cables. I would imagine that a new PSU produced from
a reputable manufacturer would arrange the power in the way which is
optimal for today's equipment. Or am I wrong? If I, for example, choose an
Antec or Thermotake of a certain Watt power, do I also need to dig into
the specs to make sure the power is split or not split correctly? I must
admit I did not understand much of what you wrote.

Thanks again!

Regards,
Steve, Denmark

 

[Paul]

Hi Paul

thanks for your very detailed reply. However, as you can see from the
information that my original post is lacking, I am definitely not up on
the technology issues as much as you are.

To answer your question, I have not decided yet on which graphic card to
buy, but am sure I will only include 1 and not 2 graphic cards in the PC.
Whatever power supply and graphic card I choose, I would definitely like
to have a little more power available in the event of an upgrade to a
graphic card later. So the PSU definitely should be overdimensioned a bit
from the start. But what is enough? 430 Watts, as the Thermotake that
another poster suggested? Given the general description I provided, it
should be possible to put a number on the PSU size in Watts that I can
safely go for.

I thank you very much for the time you took to give such a detailed
description, but I just have no understanding of the sizing in terms of
volts and amps. Since I am purchasing a new PSU and not re-using an older
one, I also wonder if I need to worry so much about how the power is
divided into various cables. I would imagine that a new PSU produced from
a reputable manufacturer would arrange the power in the way which is
optimal for today's equipment. Or am I wrong? If I, for example, choose an
Antec or Thermotake of a certain Watt power, do I also need to dig into
the specs to make sure the power is split or not split correctly? I must
admit I did not understand much of what you wrote.

Thanks again!

Regards,
Steve, Denmark

The power supply has a label on the side. It specifies how much
power can be extracted from the outputs. The supply will have
+3.3V, +5V, +12V, as the major supplies, and each one has an
ampere limit. Generally speaking, a lot of the supplies have
enough 3.3V and 5V (and it is not possible to calculate all
the loads for those anyway). The major power consuming loads
work with +12V.

The Newegg listings of power supplies, include all the
amps ratings, and that is a convenient way to get the
necessary information.

I've copies a couple tables of supplies from a previous
posting. The first group are Antec Truepower2 supplies.
The second groups are Seasonic high efficiency supplies.
I'm including these, to show that each brand does things
a bit different, making it necessary to shop by "amps"
and not "watts".

VOLTAGE   +5V + 12V1 +12V2 +3.3V -12V +5VSB (Antec)

TPII 380W 35A  16A   16A   28A   1.0A  2A
TPII 430W 35A  17A   17A   28A   1.0A  2A
TPII 480W 38A  18A   18A   30A   1.0A  2A
TPII 550W 40A  19A   19A   32A   1.0A  2A (both normal and EPS12V version)

VOLTAGE --> 3.3V   5V  12V1  12V2   -12V  +5VSB (Seasonic)
S12-430     30A   30A  14A   15A    0.8A    2A
S12-500     30A   30A  17A   16A    0.8A    2A
S12-600     30A   30A  18A   18A    0.8A    2A

First of all, the currents shown cannot all be drawn
simultaneously. But, what we know about the computer, is
one output really gets hammered, while the other two are
not at their limits. The way the computer works, aligns with
how the power supply is limited. The overall "power rating"
is just one of those limits, and there are also limits on
the total amount of +3.3V and +5V, for example.

You will notice in the two product families above, that
the 3.3V and 5V are close to 30A each capability. The last
motherboards I measured, used about 15A from one of those
two rails, so there is a good deal of margin there. The
controller boards on hard and optical drives draw 1A from
+5V each, so there is a little more current drawn there.

You will notice that the 12V1 and 12V2, only have a
modest expansion with the power rating of the supply.
So, when we say "I'll buy a 350W" or "I think a 450W is
enough", really we need to look at the amps instead.
Notice how the Seasonic 430W is only 14A and 15A. while
the Truepower2 is 17A and 17A. That is a significant
difference between them. Thus the watts are not a
very good barometer of "value".

Your processor connects to 12V2. You need around 8.25A
for the proposed processor. With a little margin, like
about 3 amps, anything with 12V2 of 11A or more, should be
OK. All the power supplies in the above table are good
enough for that.

Now, we need to work out 12V1. 12V1 is on the main ATX
24 pin power connector. It powers the fans on the motherboard.
It powers the video card slot. By means of a Molex or
PCI-E power connector, it may also power the auxiliary
connector on the end of the video card.

For a basic system, my 12V1 looks like

Fans 12V @ 0.75A (three fans, a good one on CPU)
Video card 12V @ 4A (6600GT)
or 12V @ 10A (X1900XTX)
Hard drive 12V @ 0.6A (idling hard drive)
CD/DVD 12V @ 1.5A (spinup media, or maybe burning)
Margin 3A

Total (w. 6600GT) 6.85A + 3A (12V1)
(w. X1900XTX) 12.85A + 3A (12V1)

With the X1900XTX, all of the Truepower supplies can manage
16A, so anything from a 380W - 550W TPII would work. On
the Seasonic, the 500W or 600W would be needed. Thus, you
can see that buying a Seasonic based on a "watts" recommendation,
might not give the desired results. That is why the amps
thing is so important.

If you bought a 6600 video card, or a 7600, about 10A on
12V1 provides a comfortable margin. Now, your cheesier brands
of supplies could be used. But again, you have to check
the amps on 12V1 and 12V2 to be sure. Using the Newegg
power supply adverts, you should be able to find a
12V1 @ 10A, 12V2 @ 11A supply, for a budget video card.

You can get a lot of video card power measurements here.
Divide the watts by 12V, to get amps. So a 60W video card
would need 5A or so.

http://www.xbitlabs.com/articles/video/display/gpu-consumption2006.html

I hope that explains a bit why it is better to shop by
the output amps, rather than simply blindly grabbing a
bogus watts number. No two companies do their outputs
quite the same way, meaning one guy's watts aren't the
same as the next guy. (The worst example I can think of,
is a bargain supply 2 years ago. It was rated for a bit
more than 500W, but had a 12V@10A output. That amount of
power is not suited for any Pentium 4 based system, and
yet the "500W" sounds so impressive. I'm sure many of
those were bought by unsuspecting customers, and ended
up as door stops or boat anchors.)

HTH,
Paul

 

[coolsti]

I hope that explains a bit why it is better to shop by
the output amps, rather than simply blindly grabbing a
bogus watts number. No two companies do their outputs
quite the same way, meaning one guy's watts aren't the
same as the next guy. (The worst example I can think of,
is a bargain supply 2 years ago. It was rated for a bit
more than 500W, but had a 12V@10A output. That amount of
power is not suited for any Pentium 4 based system, and
yet the "500W" sounds so impressive. I'm sure many of
those were bought by unsuspecting customers, and ended
up as door stops or boat anchors.)

HTH,
Paul

Thank you Paul!

I have not read and digested your very informative and long reply yet, but
look forward to doing so today!

Thanks also for the tip to look at Newegg.

Now, heh heh, what can you tell me about video cards

Regards,
Steve, Denmark

 

[coolsti]

I hope that explains a bit why it is better to shop by
the output amps, rather than simply blindly grabbing a
bogus watts number. No two companies do their outputs
quite the same way, meaning one guy's watts aren't the
same as the next guy. (The worst example I can think of,
is a bargain supply 2 years ago. It was rated for a bit
more than 500W, but had a 12V@10A output. That amount of
power is not suited for any Pentium 4 based system, and
yet the "500W" sounds so impressive. I'm sure many of
those were bought by unsuspecting customers, and ended
up as door stops or boat anchors.)

HTH,
Paul

Hi Paul,

I now had a chance to look at your long second reply in detail and now I
understand what you are talking about

A question: With what I learned from your reply, I started to look at my
PSU choices again, namely the Antec and the Thermaltake, and I see a major
difference between the two. The Antec does split the 12V to a 12V1 and a
12V2, while the specs on the Thermaltake models that I looked at
(Purepower) only list one 12V. Does this mean that the Thermaltake is not
a good choice? Or is it a preferred choice because then the surplus power
on 12V2 can be utilized? I am a bit confused here.

But if the 12v1, 12v2 split is the better choice, seems I would go for one
of the Antec True Power models. I can see that the Antec NeoH, for a given
wattage rating, supplies much less amperes. And I can see that the Antec
SmartPower has variations rated at +-5% where the True Power is +-3%,
telling me it is perhaps of better quality. So of the three, seems the
TruePower 2 series would be better.

Comments?

Thanks again,
Steve, Denmark

 

[Jan Alter]

I enjoyed your explanation of where the power comes from on a PS to drive
the components on the system board. Explaining it as clearly as you did
should make it very reasonable for a lot of folks who never thought it out
to choose their PS a lot more knowledeably. For the most part I've relied on
overall watt capacity with name brand, but obviously that may not be enough.

Thanks,

 

[job]

Hi Paul,

I now had a chance to look at your long second reply in detail and now I
understand what you are talking about

A question: With what I learned from your reply, I started to look at my
PSU choices again, namely the Antec and the Thermaltake, and I see a major
difference between the two. The Antec does split the 12V to a 12V1 and a
12V2, while the specs on the Thermaltake models that I looked at
(Purepower) only list one 12V. Does this mean that the Thermaltake is not
a good choice? Or is it a preferred choice because then the surplus power
on 12V2 can be utilized? I am a bit confused here.

But if the 12v1, 12v2 split is the better choice, seems I would go for one
of the Antec True Power models. I can see that the Antec NeoH, for a given
wattage rating, supplies much less amperes. And I can see that the Antec
SmartPower has variations rated at +-5% where the True Power is +-3%,
telling me it is perhaps of better quality. So of the three, seems the
TruePower 2 series would be better.

Comments?

Thanks again,
Steve, Denmark

Split 12V is mainly for SLI as long as it's 16A+ each.If you don't plan an
SLI setup don't worry about Split 12V.

 

[Paul]

Hi Paul,

I now had a chance to look at your long second reply in detail and now I
understand what you are talking about

A question: With what I learned from your reply, I started to look at my
PSU choices again, namely the Antec and the Thermaltake, and I see a major
difference between the two. The Antec does split the 12V to a 12V1 and a
12V2, while the specs on the Thermaltake models that I looked at
(Purepower) only list one 12V. Does this mean that the Thermaltake is not
a good choice? Or is it a preferred choice because then the surplus power
on 12V2 can be utilized? I am a bit confused here.

But if the 12v1, 12v2 split is the better choice, seems I would go for one
of the Antec True Power models. I can see that the Antec NeoH, for a given
wattage rating, supplies much less amperes. And I can see that the Antec
SmartPower has variations rated at +-5% where the True Power is +-3%,
telling me it is perhaps of better quality. So of the three, seems the
TruePower 2 series would be better.

Comments?

Thanks again,
Steve, Denmark

One way to look at the difference between the two types, is in
terms of the value to the customer.

When a power supply uses a single 12V output (the old pre-ATX 2.0+
supplies), the available current is shared for all the hardware.
If I am allocating a bit of margin, I only allocate say 3-4 amps
extra on the single output supply, but I need to allocate margin
on both outputs on the 12V1/12V2. Thus, I end up buying "more
supply" when I buy my ATX 2.0+ supply.

Also, the 12V1/12V2 designs, may not have a good balance between
outputs. If both the currents are close to equal, chances are the
processor output is not making good use of all its available current.
(I.e. I could be using an 8A processor, and connecting it to an 18A
capable 12V2, which is a waste of 10A of potential capacity. A
waste of money.) Since you can do the calculation, to figure out
how much 12V1/12V2 you need, that makes it possible to avoid
spending for an unnecessarily large supply.

One reason for the introduction of multiple output 12V supplies,
is to meet a safety requirement. I believe it might be IEC60950
and had something to do with the maximum amount of power available
on any one DC output of the supply. By limiting the power on
an output winding, there is a reduced risk of an uncontained
fire. But that standard has not stopped very nice supplies from
being built, and you can find power supplies with, like, a single
12V @ 34A on a common output. Even the three output PCP&C monster
supplies, have a large output like that on 12V3. It is up to the
power supply design, to make the supply as safe as possible -
flames are not supposed to shoot out of the supply, after all.

In terms of the analysis of what supply to buy, the existence
of both kinds of supplies, has doubled the amount of work I
have to do in one of my postings. The old supplies can be
used just as easily as the new ones, assuming you know which
hardware loads the 12V1 or 12V2, and so on. With a single
output supply, you just add all the 12V loads together. With
the dual output, the processor current goes on one output and
the rest is on the other. Add as much headroom (margin for
future loading) as you see fit.

I have seen one posting from someone, who suggested that some
of the 12V1/12V2 supplies, actually consist of a single output
circuit inside the supply. I can neither confirm or deny that
assertion, as I'm still using my old supplies here. (Maybe using
an ohmmeter between 12V1 and 12V2 would be one way to check.
A reading of zero would confirm they are joined together. Done
with the supply unplugged of course.) At least when I'm doing
estimates, I'll continue to assume that, when a supply states
12V1 and 12V2, that they are totally separate from one another.

The Truepower I have here, is supposed to have a separate output
circuit for each major output. That is how they can meet a 3%
spec (separate control circuits). There are three feedback wires
on my Truepower main power harness, and those wires sense the
three major outputs. The other method of designing supplies,
involves a shared transformer, and the voltage outputs are
defined by the turns ratio of the output transformer. For those,
the tolerance has to be a little wider, because the design is
a compromise between parts cost and good regulation.

As for the NeoHE, there have been a few issues with startup on
some motherboards. While Antec seems to eventually have responded
to customer concerns, and modded the supplies, I'm not in any
particular rush to suggest anyone go shopping for a NeoHE. I
don't like companies that pretend there isn't a problem, when
there very obviously is.

Paul