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converting watts to milliamps

C

Carl Farrington

Jan 1, 1970
0
Hi there,

Please could someone explain to me how to convert watts into milliamps? I
want to compare the power usage characteristics of two devices (one is a
2.5" hard disk, the other is an IDE Flash Disk) but one manufacturer lists
usage in watts, the other in milliamps!

thanks,

Carl Farrington
 
R

Rheilly Phoull

Jan 1, 1970
0
Carl Farrington said:
Hi there,

Please could someone explain to me how to convert watts into milliamps? I
want to compare the power usage characteristics of two devices (one is a
2.5" hard disk, the other is an IDE Flash Disk) but one manufacturer lists
usage in watts, the other in milliamps!

thanks,

Carl Farrington
Amps = watts/volts
divide the result by 1000 for mA
 
D

Dr. A.T. Squeegee

Jan 1, 1970
0
Hi there,

Please could someone explain to me how to convert watts into milliamps? I
want to compare the power usage characteristics of two devices (one is a
2.5" hard disk, the other is an IDE Flash Disk) but one manufacturer lists
usage in watts, the other in milliamps!

Assuming we're talking DC here (the AC formulae are slightly
different): Ohm's Law gives you everything you need.

P = IE, where P is power in Watts, I is the current drain in Amps,
and E is the voltage involved.

Taking this a step further, we get I = P / E

So: As an example, assume a 12V fan draws 4 watts of power. That's
4 over 12, which gives a current drain of about 0.333A, or 333mA.

We can double-check this by finding the resistance, and using
Ohm's Law again: R = E / I. Since we now know I, we can find that
R = 12 / 0.333 = about 36 ohms.

Now that we know resistance, we can use the formula P=I-squared
times R to find the power figure: P = .333 squared times 36 = 3.99
watts. Pretty close, heh?

You can also simply do P = IE, or .333 times 12 = 3.996.

Hope that helps. ;-)


--
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
kyrrin a/t bluefeathertech d-o=t c&o&m
Motorola Radio Programming & Service Available -
http://www.bluefeathertech.com/rf.html
"Quando Omni Flunkus Moritati" (Red Green)
 
I

Ian Stirling

Jan 1, 1970
0
Carl Farrington said:
thank you!

You may want to look at the detailed datasheets, and work out just
what your usage will be.
Active, sleep, read/write, spinup, ...
 
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