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- Newsgroups: sci.electronics
- Path: sparky!uunet!panther!mothost!white!sapphire.rtsg.mot.com!galena13!keating
- From: keating@rtsg.mot.com (Edward Keating)
- Subject: Re: Cost of running my PC?
- Message-ID: <keating.725743994@galena13>
- Sender: news@rtsg.mot.com
- Nntp-Posting-Host: galena13
- Organization: Motorola Inc., Cellular Infrastructure Group
- References: <1992Dec21.040252.19109@newstand.syr.edu>
- Date: Wed, 30 Dec 1992 19:33:14 GMT
- Lines: 77
-
- ldstern@rodan.acs.syr.edu (Larry Stern) writes:
-
- >I'm sure this is a simple one, but somehow it eludes me. I need to know how
- >much electricity my pc is using. It is a 386 AT clone with a 200W power
- >supply. I can find out the local rate for KW hours but how do I determine
- >how much current the pc (and monitor) is drawing?
-
- > Thanks,
- > Larry
-
- And after you`ve measured the power drain, you'll find out that the
- incandescent lights in the room draw more power than the PC.
-
- I recently was chartered to determine power drain and the heat generated by
- a network of up to 8 PC based machines used in a BBS by our local
- computer group (Chicago Computer Society). Some individuals using the nameplate
- ratings of equipment determined that we would need additional power lines in
- order to run the 10K Btu Air conditioner that would be required.
-
- Knowing that PC's do have switching power supplies, I decided to actually
- measure the power drain of some typical machines.
-
- An IBM PC (original PC) with 30Mb external powered hard disk, + monochrome
- monitor (IBM) draws 117w. (with 1 floppy disk spinning)
-
- An AT clone (1mb 10Mhz 286 + 2 Full height -power hungry- disk drives,
- NEC Multisync 1, HST 9600 and an external Alloy tape drive) draws
- only 150w.
-
- The NEC Multisync 1 specifications state power draw at 76w. Actual measured
- draw was 53w.
-
- The AT tech reference manual states the power draw of an AT to be 5 amps
- (600w!). I don't know what kind of cards need to be loaded into the machine
- to draw that much, but I suspect that it involves aircraft landing lights.
-
- My measurement setup involved measuring the AC current drawn by the device
- under test. (Current calculated by AC voltage measurement across a series
- .01 ohm resistor.) The power measured by this setup will be higher than
- the actual power drawn as it includes both real and imaginary factors.
- The goal was to find the maximum power so that the air conditioner and power
- requirements could be determined.
-
- Based on nameplate figures the other individuals calculated that without
- air conditioning, the room would rise to 110 F. The thermodynamic equations
- involved in their calculations included the roughness of the surface of the
- room air ducts and the height above sea level. Truly a sight to behold!
-
- Plugging in my measurements into the page and 1/2 of Thermodynamic equations
- provided by this other group, I replied that the room should not get above
- 80 F. (Assuming a 72 F ambient.)
-
- Well the BBS has been moved for about a month and the reports are that the
- room is between 74 and 78 with the heating thermostat set to 78.
- Just goes to show, nameplates are only a legal out for the manufacturer.
- You have to measure the real power if you want to know.
-
- Other trivial you might want to know:
-
- A sixty watt light bulb does draw 60 watts.
-
- Maximum power drain of a PC occurs within the first 10 seconds.
- (I did not measure inrush current, but the disk drive spin up can
- account for up to 40-50 watts extra on powerup)
-
- A USR HST 9600 draws about 10 watts.
-
- A 286 laptop with disk spinning draws about 19 watts.
-
- External powered disks draw about 30 - 50 watts on startup, but
- settle down to 15-20 watts after they have spun up.
-
- The floppy disk read with motor spinning does not affect a PC-AT's power
- draw. The original PC floppy disk draws 6 watts additional when active.
- (63.5 W rated power supply)
- --
- #undef .sig
-