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USB powered desk fan

It is hot in my office and for some reason I don't have any available
power outlets near me to power a desk fan so I want to make a fan that
is powered by USB. I bought a cheap handheld fan that is powered by 2
AA batteries (3V) and I want to convert it to run off a 5V USB
computer port. I need to step the voltage down from 5V to 3V. What
type of resistor would I need to do this? It would be nice to make
the fan have adjustable speeds so would I use a potentiometer to do
that? What type and rating? I greatly appreciate your thoughts.
 
It is hot in my office and for some reason I don't have any available
power outlets near me to power a desk fan so I want to make a fan that
is powered by USB. I bought a cheap handheld fan that is powered by 2
AA batteries (3V) and I want to convert it to run off a 5V USB
computer port. I need to step the voltage down from 5V to 3V. What
type of resistor would I need to do this? It would be nice to make
the fan have adjustable speeds so would I use a potentiometer to do
that? What type and rating? I greatly appreciate your thoughts.

I am using this article as a reference for my design...

http://www.instructables.com/id/E5EU54XP26EP2871HG/
 
M

Michael Black

Jan 1, 1970
0
Charles Schuler" ([email protected]) said:
Sigh, it is the first of April.
But you can now buy all kinds of junk that plugs into USB ports merely
to get power from the USB port. Fans, LED lights, cellphones and IPods
so you can charge them, some things even more nonsensical.

Michael
 
C

Charles Schuler

Jan 1, 1970
0
Michael Black said:
But you can now buy all kinds of junk that plugs into USB ports merely
to get power from the USB port. Fans, LED lights, cellphones and IPods
so you can charge them, some things even more nonsensical.

A fan?
 
I would rather build the fan myself because if looks like a fun
project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2
standard AA batteries) then r=1.07 ohms. Are my calculations and
units correct? I went to radio shack earlier but could not find a
1ohm resistor or potentiometer. Do I have my units off in my
calculations? Am I thinking about this incorrectly?
 
C

Charles Schuler

Jan 1, 1970
0
I would rather build the fan myself because if looks like a fun
project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2
standard AA batteries) then r=1.07 ohms. Are my calculations and
units correct? I went to radio shack earlier but could not find a
1ohm resistor or potentiometer. Do I have my units off in my
calculations? Am I thinking about this incorrectly?

A fan has to move enough air to make one feel noticeably cooler. This is
mostly based on evaporation from the skin and air flow. People who can't
sweat don't appreciate fans. Battery operated fans normally must be held
about 5 inches from one's face to achieve any effect. USB power limits
would make for an anemic fan.

This is simply April 1, which follows March madness, el-regurgitatia.
 
S

Si Ballenger

Jan 1, 1970
0
It is hot in my office and for some reason I don't have any available
power outlets near me to power a desk fan so I want to make a fan that
is powered by USB. I bought a cheap handheld fan that is powered by 2
AA batteries (3V) and I want to convert it to run off a 5V USB
computer port. I need to step the voltage down from 5V to 3V. What
type of resistor would I need to do this? It would be nice to make
the fan have adjustable speeds so would I use a potentiometer to do
that? What type and rating? I greatly appreciate your thoughts.

http://www.geeks.com/details.asp?invtid=USB-X360-FAN&cpc=SCH
 
T

Tom Biasi

Jan 1, 1970
0
I would rather build the fan myself because if looks like a fun
project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2
standard AA batteries) then r=1.07 ohms. Are my calculations and
units correct? I went to radio shack earlier but could not find a
1ohm resistor or potentiometer. Do I have my units off in my
calculations? Am I thinking about this incorrectly?
Your calculations used the wrong data.
 
M

Michael A. Terrell

Jan 1, 1970
0
I would rather build the fan myself because if looks like a fun
project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2
standard AA batteries) then r=1.07 ohms. Are my calculations and
units correct? I went to radio shack earlier but could not find a
1ohm resistor or potentiometer. Do I have my units off in my
calculations? Am I thinking about this incorrectly?


A properly designed USB port only supplies 1/2 amp.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
M

Michael A. Terrell

Jan 1, 1970
0
It is hot in my office and for some reason I don't have any available
power outlets near me to power a desk fan so I want to make a fan that
is powered by USB. I bought a cheap handheld fan that is powered by 2
AA batteries (3V) and I want to convert it to run off a 5V USB
computer port. I need to step the voltage down from 5V to 3V. What
type of resistor would I need to do this? It would be nice to make
the fan have adjustable speeds so would I use a potentiometer to do
that? What type and rating? I greatly appreciate your thoughts.


If there are no outlets, how are you powering your computer? If
there are no outlets, why hasn't the building inspector condemned your
office?

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
wow. lots of bird walking going on here. i just want to know if i can
put a resistor in series to reduce 5v to 3v and what the value of the
resistor would be. if anyone has the ability to answer this question
please help. otherwise please leave your 2 cents in your pocket.
 
M

Michael Black

Jan 1, 1970
0
wow. lots of bird walking going on here. i just want to know if i can
put a resistor in series to reduce 5v to 3v and what the value of the
resistor would be. if anyone has the ability to answer this question
please help. otherwise please leave your 2 cents in your pocket.
This has nothing to do with challenges.

If you asked "can I hook up a fan to a USB port", you'd likely get
the same sort of answers. The fact that you are "certain" that it
can be done is a failing of too many beginner's questions, they ask
something they think will be a solution, leaving out the intermediary
steps that likely are important to the ultimate solution. You've already
gone down a path, without being sure that path is the right one.

Michael
 
M

Michael A. Terrell

Jan 1, 1970
0
wow. lots of bird walking going on here. i just want to know if i can
put a resistor in series to reduce 5v to 3v and what the value of the
resistor would be. if anyone has the ability to answer this question
please help. otherwise please leave your 2 cents in your pocket.


You still haven't told us how much CURRENT the lousy fan draws. Of
its over 500 mA (1/2A) it can draw too much current and damage the
motherboard. You know WHERE you can put your two cents.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

jasen

Jan 1, 1970
0
It is hot in my office and for some reason I don't have any available
power outlets near me to power a desk fan so I want to make a fan that
is powered by USB. I bought a cheap handheld fan that is powered by 2
AA batteries (3V) and I want to convert it to run off a 5V USB
computer port. I need to step the voltage down from 5V to 3V. What
type of resistor would I need to do this? It would be nice to make
the fan have adjustable speeds so would I use a potentiometer to do
that? What type and rating? I greatly appreciate your thoughts.

Rather than a resistor 3 1N4001 diodes in series will be about right,
not that this is necessarily a good idea: if the fan seizes it could
damage your computer.

Bye.
Jasen
 
C

Charles Schuler

Jan 1, 1970
0
wow. lots of bird walking going on here. i just want to know if i can
put a resistor in series to reduce 5v to 3v and what the value of the
resistor would be. if anyone has the ability to answer this question
please help. otherwise please leave your 2 cents in your pocket.

Is it bird walking? Keep your 2 cents and hire a consultant.
 
I don't know how much current the motor draws. I bought a cheapo
battery powered fan from the drug store. It takes 2 AA batteries to
power it. That means 3V total and whatever the current of 2 standard
AA batteries are. Anyone know what the current would be for 2 AA
batteries? There is definitely a solution to this problem because we
all know that you can buy a USB powered fan at the store.
 
R

Rich Grise

Jan 1, 1970
0
I don't know how much current the motor draws. I bought a cheapo
battery powered fan from the drug store. It takes 2 AA batteries to
power it. That means 3V total and whatever the current of 2 standard
AA batteries are. Anyone know what the current would be for 2 AA
batteries? There is definitely a solution to this problem because we
all know that you can buy a USB powered fan at the store.

Go to the battery manufacturer's web site and look up the AH (Amp Hour)
capacity of your model of cells. Get a fresh set of cells, turn on the
fan, and see how long it blows before its output is useless. Divide the
AH capacity by the # of hours it ran, and that will tell you how many
amps of current the fan draws. You might get more life out of the
batteries if you turn the fan off for, say, 10 minutes every hour - but
be sure and record the "run" time accurately.

Or, you could stick an ammeter in series with the batteries and motor,
and measure it. :)

Good Luck!
Rich
 
L

Lord Garth

Jan 1, 1970
0
I don't know how much current the motor draws. I bought a cheapo
battery powered fan from the drug store. It takes 2 AA batteries to
power it. That means 3V total and whatever the current of 2 standard
AA batteries are. Anyone know what the current would be for 2 AA
batteries? There is definitely a solution to this problem because we
all know that you can buy a USB powered fan at the store.

Put in fresh batteries and run it until it dies, recording the time it takes
to expend the cells OR get yourself a current meter and measure the
demand of the fan OR just hook it up and hope for the best.

Case in point, my Sony Vaio laptop powers an external 2.5" hard disk
with no trouble at all yet my Dell can't run the same drive without
resorting to the external power pack.
 
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