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February 13th, 2002, 03:26 PM #1
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 Feb 2002
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How many amps foes a PC general use ??
Folks,
I have an older home and was wondering on average what type of amperage a PC uses?
I have a PC sharing a 15 amp fuse with an AC adapter and 4 or 5 lamps ( in two different rooms ) I am electrically illeterate so pardon me if this seems like a basic question.

February 13th, 2002, 03:31 PM #2
depends on the system. different hardware makes a huge difference on the uage of "amps"
what are the specs of the computer?

February 13th, 2002, 03:41 PM #3
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How many amps does a PC generally use ?
The system is a PIII 933 , 5400 RPM Hard Drive, 32 MB video card.
The PSU is a Q technology 230W rated, the cpu is being cooled by a Zalman Copper 6000 heatsink with fan. Case is well ventalleted  room is 12 x 12  not too bad on temp  can be somewhat stuffy  but nothing major.
Hope this helps  any ideas on how to safeguard on overloading would be helpful. My wife wants to add an air conditioner to the same outlet !!!!!!!!!!!!! I'm not worried about the system being damaged  just safety  !!!
Will a 15 amp handle an air conditioner, a PC and a few lights ???

February 13th, 2002, 03:51 PM #4
Current(A) = Power(W) / Voltage(V)
230W/ 120 V = 1.92A,
US(120V),Europe(230V)
As for the airconditioner I would run that on a seperate breaker.
This formula will not apply to the input current,230W is the amout of output power the power supply can produce.
There is also a spec. sheet attached to the side of the power supply.Look for "Input Current". See if you can also find input power and you can the apply that formula.Last edited by mad1; February 13th, 2002 at 04:09 PM.

February 13th, 2002, 03:55 PM #5
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How many amps does a PC generally use ?
Thanks !!

February 13th, 2002, 05:39 PM #6
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Current(A) = Power(W) / Voltage(V)
230W/ 120 V = 1.92A
Right formula, wrong figures. The result, 1.92 amps, is completely meaningless. The 230 watts are DC output, the 120 volts are AC input. You can't compare apples and oranges.
An average figure for the AC current draw of a 250watt power supply is 6 amps @ 115 volts, or 4 amps @ 230 volts. This info should be on a label on the power supply. This AC amperage usage is constant, regardless how much of the converted DC power is being supplied to system components.
An average 1719" monitor can draw 3 amps. With both of them running, a 15amp circuit can still supply a maximum of 6 additional amps, or 690 watts (6 x 115).
The biggest current draw of any system with a motor, and especially with a compressor, is at startup. An air conditioner that draws 4 amps (460 watts) while running may draw 78 amps (805920 watts) to start. Any hard drives in the system also need more power to start than to run.
Every 100watt light bulb in the circuit will draw 0.87 amps (100 / 115).

February 13th, 2002, 05:55 PM #7
So what would be an accurate way to compare them then? Can you explain why the formula doesn't work?
i.e. 230W != 115V x 6A.
I don't doubt you, I just want to undestand. I don't know jack.

February 13th, 2002, 06:04 PM #8
Psyco Logical,
Read my edit of the post,this was there prior to your post'
"This formula will not apply to the input current,230W is the amout of output power the power supply can produce.
There is also a spec. sheet attached to the side of the power supply.Look for "Input Current". See if you can also find input power and you can the apply that formula."

February 13th, 2002, 06:33 PM #9
jg1234
The previous posts are right .... and wrong.
The current darwn by a psu delivering 230W from a 120v supply is
W=V x A
Power = volts x current
Therefore A=W/V
substituting, A=230/120 or 1.92Amperes
so mad1 is right?, well in an ideal world yes but (there is always a but), power supplies even nice switch mode ones like the PC uses are not 100% efficient, this is what Psycho_Logical is getting at I think.
Switch mode PSU's are in the order of 90% efficient therefore the power drawn fron the AC supply would be about 10% more than the power available to the PC, about 2.11 Amperes (a long way from the suggested fuse rating of 7A). The reason for the large fuse rating is that there is a switch on surge form the PSU that can draw very high currents for a very short time.
This AC amperage usage is constant, regardless how much of the converted DC power is being supplied to system components.
If this were not the case, then a PSU which is powered up but not supplying current (you can get ATX psu's to turn on with no connection) would still be drawing 230W from the AC and supplying nothing, all the power would have to be dissipated as heat !!! get yer eggs and bacon out .
So, to get to the question, I dont know the answer.
Given that the PC may draw(momentarily) say 5A, each 100W lamp (momentarily) over 1A, and an unknown but presumably quite high surge form the AC unit, I would say, no it wont do it.
You may be lucky, but if you can run another circuit, the last thing you want (other than a fire) is the AC unit to cut in and the PC to reboot !!!!
GNothing moves faster than goalposts.

February 13th, 2002, 07:00 PM #10
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Re: How many amps foes a PC general use ??
Originally posted by jg1234
I have a PC sharing a 15 amp fuse with an AC adapter and 4 or 5 lamps ( in two different rooms ) I am electrically illeterate so pardon me if this seems like a basic question.
Be carefull about connecting too much to existing circuits in an older home. Many are burned to the ground each year from such. The cable used in many older homes had a combustible wrapping, unlike the more modern romex of today, and copper gets hot when too many amperes are drawn thru them, this somethimes will ignite the older cable wrappings.

February 13th, 2002, 09:27 PM #11
Example:
Input 115V @ 6 A
230V @ 3 A
OUTPUT 200 W
red: +5V @ 20 A
yellow: +12V @ 8 A
white: 5V @ .3A
blue: 12V @ .3A
black: ground
orange: p.g.
If you add up the numbers from the colors, you get about 200 W, but I still dont understand how 115V x 6 A = 230 W ?!

February 13th, 2002, 09:40 PM #12
newbie~wan
You're right, the 6A (115V) 3A(230V) relates to the fuse rating not the current drawn. The fuse will be rated significantly higher than the steady load to allow for switch on surges and other things like efficiency variations between individual PSU's.
GNothing moves faster than goalposts.

February 19th, 2002, 10:05 PM #13
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 Nov 2001
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 15
Right formula, wrong figures. The result, 1.92 amps, is completely meaningless. The 230 watts are DC output, the 120 volts are AC input. You can't compare apples and oranges.
The question is how many amps does a PC use. The VOLT AMPERE at the primary winding of the transformer is always equal to the VOLT AMPERE at the secondary winding. Actually, there is a loss consisting of the core and copper losses inherent in all transformers but let's just say its negligible to keep it simple
The amps at the input can be no more than 230W/110V = 2.09A. Supposing the stepped down voltage at the secondary winding of the transformer is 12 Vac, the amps before the voltage goes to the rectifying circuit should be 230W/12V = 19.16A
As someone has said, the fuse at the primary winding is rated 6A taking into account the inrush surges during energization of the transformer.

February 20th, 2002, 12:12 AM #14
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 Oct 2001
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Typical towers use anywhere from 0.8A at idle to about 1.2A full load. This is excluding the monitor.

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