Getting the right wattage on a PSU

  • Thread starter Thread starter Etno
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Etno

Hey folks,

I added up the wattage my system requires (not including USB devices)
according to the charts here
http://www.linuxhardware.org/features/01/11/07/1525211.shtml. It added up
to 281 watts. I then divided by .7 as your supposed to and got 401 watts.

I'm interested in getting a certain case which includes a 380 watt PSU. Do
you think the restriction not to go above 70% of your PSU's wattage output
is really a necessity? Would I get away with the 380, no problem, or should
I make the 400 my minimum? I've seen other sites that even recommend you
then multiply by 1.8 (http://www.pcpowercooling.com/maxpc/index_cases.htm)
because of the range of the 12V line. That makes my figure 505 watts if you
don't divide by .7.

Here's my setup (nothing integrated). What do you think? 380 is good or is
it pushing it? The guy at the PC shop was trying to tell me that 400 is
overkill.
Athlon 1800+
512 mb PC 2100
ATI Radeon 9000 Pro All in Wonder
Sound Blaster Live 5.1 Platinum
CD Burner
DVD Burner
Nic
Floppy drive
Hdd Controller Card (for >137 gb)
2 Hdd's (one 160 gb and one 120 gb)

Thanks for the advice!
 
Etno said:
Hey folks,

I added up the wattage my system requires (not including USB devices)
according to the charts here
http://www.linuxhardware.org/features/01/11/07/1525211.shtml. It added up
to 281 watts. I then divided by .7 as your supposed to and got 401 watts.

I'm interested in getting a certain case which includes a 380 watt PSU. Do
you think the restriction not to go above 70% of your PSU's wattage output
is really a necessity? Would I get away with the 380, no problem, or should
I make the 400 my minimum? I've seen other sites that even recommend you
then multiply by 1.8 (http://www.pcpowercooling.com/maxpc/index_cases.htm)
because of the range of the 12V line. That makes my figure 505 watts if you
don't divide by .7.

Here's my setup (nothing integrated). What do you think? 380 is good or is
it pushing it? The guy at the PC shop was trying to tell me that 400 is
overkill.
Athlon 1800+
512 mb PC 2100
ATI Radeon 9000 Pro All in Wonder
Sound Blaster Live 5.1 Platinum
CD Burner
DVD Burner
Nic
Floppy drive
Hdd Controller Card (for >137 gb)
2 Hdd's (one 160 gb and one 120 gb)

Thanks for the advice!
Click to expand...

I'm sure the 380 watt supply will be fine (assuming it;s a good quality one)

My own system is fairly similar and my 350 watt supply handles it without
any problems
 
Etno said:
I added up the wattage my system requires (not including USB
devices) according to the charts here
http://www.linuxhardware.org/features/01/11/07/1525211.shtml.
It added up to 281 watts. I then divided by .7 as your supposed
to and got 401 watts.

I'm interested in getting a certain case which includes a 380
watt PSU. Do you think the restriction not to go above 70% of
your PSU's wattage output is really a necessity? Would I get
away with the 380, no problem, or should I make the 400 my
minimum? I've seen other sites that even recommend you then
multiply by 1.8
(http://www.pcpowercooling.com/maxpc/index_cases.htm)
because of the range of the 12V line. That makes my figure
505 watts if you don't divide by .7.

Here's my setup (nothing integrated). What do you think? 380
is good or is it pushing it? The guy at the PC shop was trying
to tell me that 400 is overkill.

Athlon 1800+
512 mb PC 2100
ATI Radeon 9000 Pro All in Wonder
Sound Blaster Live 5.1 Platinum
CD Burner
DVD Burner
Nic
Floppy drive
Hdd Controller Card (for >137 gb)
2 Hdd's (one 160 gb and one 120 gb)
Click to expand...

Do you really expect that your Sound Card, CD Burner, DVD Burner,
and Floppy will all be operating simultaneously? They all take
significantly less power when quiescent.

However wattage rating on power supplies, especially "cheaper"
ones, are not what they seem. Proper testing would involve
placing them under full load and examining the regulation, ripple,
and noise on each line under those conditions. You almost
certainly don't have the equipment.
 
It is a good idea to use a power supply that is rated well above the power you are actually using. The amount of power you are using from part of the power supply e.g. 5v could be near the maximum and the power you are using from another source e.g. 12 volts could be much less. Power supply ratings are usually maximum output when cool; the sustained output when warm us usually much less. That said, most power usage estimates are high. I have measured the AC power used on PCs and always found it to be much less than one would expect, even with the power loss of the power supply.
 
Hey folks,

I added up the wattage my system requires (not including USB devices)
according to the charts here
http://www.linuxhardware.org/features/01/11/07/1525211.shtml. It added up
to 281 watts. I then divided by .7 as your supposed to and got 401 watts.

I'm interested in getting a certain case which includes a 380 watt PSU. Do
you think the restriction not to go above 70% of your PSU's wattage output
is really a necessity? Would I get away with the 380, no problem, or should
I make the 400 my minimum? I've seen other sites that even recommend you
then multiply by 1.8 (http://www.pcpowercooling.com/maxpc/index_cases.htm)
because of the range of the 12V line. That makes my figure 505 watts if you
don't divide by .7.

Here's my setup (nothing integrated). What do you think? 380 is good or is
it pushing it? The guy at the PC shop was trying to tell me that 400 is
overkill.
Athlon 1800+
512 mb PC 2100
ATI Radeon 9000 Pro All in Wonder
Sound Blaster Live 5.1 Platinum
CD Burner
DVD Burner
Nic
Floppy drive
Hdd Controller Card (for >137 gb)
2 Hdd's (one 160 gb and one 120 gb)

Thanks for the advice!
Click to expand...

The above will run fine from any good 300W power supply and many
235-250W models. Generic calculators almost always suggest a far
larger PSU that actually needed. A very high performance video card
or a half-dozen hard drives might increase what you need.

Buy a name-brand power supply with dual ball bearing fan(s), at least
the rear exhaust fan. Generic power supplies cannot be trusted to
deliver the wattage listed on their labels.

For future viability, you would buy in excess of what you need now,
like around 380-420W, with SATA drive connectors. On the other hand,
there's a large price difference, it might make sense to just buy the
300W now unless you have immediate plans for a high-performance video
card or adding a half-dozen hard drives.
 
Etno said:
Hey folks,

I added up the wattage my system requires (not including USB devices)
according to the charts here
http://www.linuxhardware.org/features/01/11/07/1525211.shtml. It added up
to 281 watts. I then divided by .7 as your supposed to and got 401 watts.

I'm interested in getting a certain case which includes a 380 watt PSU. Do
you think the restriction not to go above 70% of your PSU's wattage output
is really a necessity? Would I get away with the 380, no problem, or should
I make the 400 my minimum? I've seen other sites that even recommend you
then multiply by 1.8 (http://www.pcpowercooling.com/maxpc/index_cases.htm)
because of the range of the 12V line. That makes my figure 505 watts if you
don't divide by .7.

Here's my setup (nothing integrated). What do you think? 380 is good or is
it pushing it? The guy at the PC shop was trying to tell me that 400 is
overkill.
Athlon 1800+
512 mb PC 2100
ATI Radeon 9000 Pro All in Wonder
Sound Blaster Live 5.1 Platinum
CD Burner
DVD Burner
Nic
Floppy drive
Hdd Controller Card (for >137 gb)
2 Hdd's (one 160 gb and one 120 gb)

Thanks for the advice!
Click to expand...

It's a high quality PSU that I'm going for (Antec TruePower), so it sounds
like I should be fine using it despite being <400. Thanks for the advice
everyone.
 
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