Is a 300w power supply enough for my system?

spodosaurus wrote:
wrote:
I've got a 5-year old 300w power supply (Antec PP-303X). I'm about
to add a IDE RAID controller and another hard drive, and a few more
case fans, and am wondering if I need a new power supply. Here's
what my system will have after the upgrades:

ABIT KT7-RAID mobo
Athlon Tbird 1.2 GHz
GlobalWin FOP32-1 heatsink
2 sticks of PC133 RAM
2 IDE 7200 rpm hard drives
Matrox G400 AGP video card with 16 mb
PCI 3ware IDE RAID true hardware controller
PCI network card
PCI generic soundcard
ISA modem
DVD-ROM drive
CD-RW drive
floppy drive
USB memory card reader
4 case fans
keyboard
mouse

I checked some of those online power supply calculators... the
Extreme PSU one and the Takaman one (which were set to 80%
utilization) said I need a PSU around 270w, and the JSCustom one
said I need a PSU around 300w. I've read that you shouldn't exceed
a PSU's wattage by 80%, and I also should have some "extra" wattage
in case I add more components in the future. So do you think my
300w power supply is enough?

In my opinion, it's not a good idea to push power supplies. There
rated limits are PEAK limits, not average. In your case, I'd go with
a brand name 350W PSU or higher. An Antec PurePower 350 (I think
that's the proper Antec model line) would be a minimum for me given
your system configuration. There are many other brand names that can
also be used, the example I gave was just that: an example of a
minimum.
Ari

quality over quantity usually makes the difference. who are you going to
trust? billy bob's eletro wonder or antec, seasonic, pc power and cooling?

sbb78247 wrote:
spodosaurus wrote:

wrote:

I've got a 5-year old 300w power supply (Antec PP-303X). I'm about
to add a IDE RAID controller and another hard drive, and a few more
case fans, and am wondering if I need a new power supply. Here's
what my system will have after the upgrades:

ABIT KT7-RAID mobo
Athlon Tbird 1.2 GHz
GlobalWin FOP32-1 heatsink
2 sticks of PC133 RAM
2 IDE 7200 rpm hard drives
Matrox G400 AGP video card with 16 mb
PCI 3ware IDE RAID true hardware controller
PCI network card
PCI generic soundcard
ISA modem
DVD-ROM drive
CD-RW drive
floppy drive
USB memory card reader
4 case fans
keyboard
mouse

I checked some of those online power supply calculators... the
Extreme PSU one and the Takaman one (which were set to 80%
utilization) said I need a PSU around 270w, and the JSCustom one
said I need a PSU around 300w. I've read that you shouldn't exceed
a PSU's wattage by 80%, and I also should have some "extra" wattage
in case I add more components in the future. So do you think my
300w power supply is enough?

In my opinion, it's not a good idea to push power supplies. There
rated limits are PEAK limits, not average. In your case, I'd go with
a brand name 350W PSU or higher. An Antec PurePower 350 (I think
that's the proper Antec model line) would be a minimum for me given
your system configuration. There are many other brand names that can
also be used, the example I gave was just that: an example of a
minimum.
Ari


quality over quantity usually makes the difference. who are you going to
trust? billy bob's eletro wonder or antec, seasonic, pc power and cooling?

Working on your reading comprehension would be a great place to start.

Jim wrote:
Humbug. Online estimation means squat, an average of devices they've gotten
figures for. If you can't add, use a hand-held calculator. Get the
amperage per voltage figures for the hardware you're going to use.

............
Jonny
ok, then let him spend that 20-100$ without need

On Wed, 25 Jan 2006 10:16:01 +0100, adsci
wrote:



Jim wrote:
Humbug. Online estimation means squat, an average of devices they've gotten
figures for. If you can't add, use a hand-held calculator. Get the
amperage per voltage figures for the hardware you're going to use.

............
Jonny
ok, then let him spend that 20-100$ without need

Actually most online calculators will overestimate more than
doing a conservative calculation. They tend to calculate a
hypothetical maximum draw from all parts simultaneously
which is never possible to achieve.

Don't know what you're implying, the figures will show minimum draw from a
prospective power supply.
The builder plans the prospective add-ons that may be added later and loss
from component level degradation of hardware being powered, and loss from
degradation of the power supply. Maybe you should stick with the brainless
method as requires thought and planning the worst scenarios.
.............
Jonny
"adsci" wrote in message
...


Jim wrote:
Humbug. Online estimation means squat, an average of devices they've
gotten figures for. If you can't add, use a hand-held calculator. Get
the amperage per voltage figures for the hardware you're going to use.

............
Jonny
ok, then let him spend that 20-100$ without need

In article om,
wrote:

Paul wrote:
Finally found a picture of the PP-303X. It is weaker than
the PP-303XP.


http://www.anandtech.com/showimage.h...-303x/side.jpg

There must be 2 different versions of the PP-303X. Here's mine:

http://www.thetechzone.com/reviews/c...ly/303spec.jpg

Anyways, you recommended the 430 model of the Seasonic in your other
post. I notice it has 150w combined on the 3.3v and 5v. In kony's
post, he said I should get one with 180w combined. What do you think?

And thanks to EVERYONE who's responded to this thread. I don't know
much about power supplies, so all the replies have been very
informative (as well as making things more confusing!).

Remember that the processor was going to be 5V@13A which is 65W.
If Takaman has the option to put the processor current on the +5V
rail, you should just be able to take the V*I for the 3.3V and
the V*I for the 5V, and see if the total power for those two
rails is close to 150W or 180W etc. Otherwise, you can add
the numbers manually and see how close it is getting.

In other words, you have three things to check. Is the 3.3V current
less than its max ? Is the 5V current less than its max ? Is
(3.3 * current_on_3.3) + (5.0 * current_on_5.0) less than the
combined limit stated on the supply ?

HTH,
Paul

Sean Cousins wrote:

Many PSU's have about a 75% efficiency and the 300w rating is only
peak rating.

With few exceptions, the rating is meant to indicate maximum continuous
power output. The exceptions include very bad and cheap supplies, such
as Q-tec, and Q-tec at least admits that its ratings are for peak power.

Paul wrote:
Anyways, you recommended the 430 model of the Seasonic in your other
post. I notice it has 150w combined on the 3.3v and 5v. In kony's
post, he said I should get one with 180w combined. What do you think?

And thanks to EVERYONE who's responded to this thread. I don't know
much about power supplies, so all the replies have been very
informative (as well as making things more confusing!).

Remember that the processor was going to be 5V@13A which is 65W.
If Takaman has the option to put the processor current on the +5V
rail, you should just be able to take the V*I for the 3.3V and
the V*I for the 5V, and see if the total power for those two
rails is close to 150W or 180W etc. Otherwise, you can add
the numbers manually and see how close it is getting.

In other words, you have three things to check. Is the 3.3V current
less than its max ? Is the 5V current less than its max ? Is
(3.3 * current_on_3.3) + (5.0 * current_on_5.0) less than the
combined limit stated on the supply ?

Takaman is down right now... but I did find this about the Antec
TruePower series:

http://www.antec.com/pdf/TruePower_inclusion.pdf

It says:

"Traditional power supply designs typically feature circuit sharing for
the 3.3V and 5V lines off the output
transformer. That means that as you increase the load on one output
circuit, the available capacity for the
other decreases - for example as you load up on devices that use 5
volts (like drives and PCI cards), you have
less and less ability to power devices that need 3.3 volt output (like
your CPU). In addition, by connecting
the two systems at this point you increase the chance of having
interactions between the output circuits - for
example, a sudden 5V draw could potentially cause the voltage on the
3.3V line to drop, harming system
stability.

In evaluating a power supply, one important thing to look for is the
'+3.3V and +5V combined output' rating.
The total amount of power you can draw from those two output circuits
combined is typically much less than
the sum of the individual ratings for 3.3V and 5V listed elsewhere on
the box. An example from a
competitor's 430 Watt model:
+3.3V rated 38A = 125.4 Watts
+5V rated 44A = 220.0 Watts
+3.3V plus +5V : 220 (Watts) Max.
Thus, according to the label, if one fully loaded the 5V circuit in
accordance with the manufacturer's
specifications, there would be essentially no power left on the 3.3V
line. Note that the total power available
on the 3.3 and 5 volt circuits combined is barely more than half of the
430 Watt rating of the unit as a whole.

TruePower has dedicated output circuitry for each voltage line, which
means that there is no combined output
limit other than, of course, that of the entire power supply. Each
voltage line can perform up to the
specification on the label, without regard to or interaction with the
loads on the other lines, until the full
capacity of the power supply itself is reached."

If I'm reading this right, I can get a TruePower and not worry about
any limit on the combined 3.3v and 5v output.

On 26 Jan 2006 01:49:32 -0800,
wrote:


If I'm reading this right, I can get a TruePower and not worry about
any limit on the combined 3.3v and 5v output.


That is true, but not necessarily useful for your purpose.
The point of the 3V+5V rating is a guide to relative
amperage capacity on 5V rail as some supplies overrate it by
far too much, while the combined 3V+5V rating tended to
remain a more accurate indicator.

So, essentially it doesn't necessarily matter whether you
choose an Antec with that design or not, either way you have
the same goal- a power supply that is either optimized to
provide a large % of it's output on the 5V rail, or a power
supply with far more capacity than you need which was
optimized for 12V amperage but as a result of having such an
overkill capacity, it also has enough 5V capacity plus some
margin.

It is not really a good idea to shoot for exact match on
amperage capacity, if you were able to accurately calculate
that you needed 14A @ 5V for example, it'd be good for the
psu to be rated at least for 18A, maybe even higher if
you're often running heavy loads and the PSU is rated for
peak rather than continuous output.

On 26 Jan 2006 01:41:28 -0800,
wrote:


Sean Cousins wrote:

Many PSU's have about a 75% efficiency and the 300w rating is only
peak rating.

With few exceptions, the rating is meant to indicate maximum continuous
power output. The exceptions include very bad and cheap supplies, such
as Q-tec, and Q-tec at least admits that its ratings are for peak power.

Actually, no.
Take Enermax for example. Many PSU are rated like that,
including that OCZ rated for 33A on it's 12V rail.