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

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

I greatly appreciate your thoughts.
 
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 am using this article as a reference
for my design...

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

I greatly appreciate your thoughts.

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

martin griffith

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

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

I greatly appreciate your thoughts.
a standard USB port will only delivery 100mA before shutting down, you
have to talk to the USB port to tell it you need more power, up to a
maximum of 500mA. Measure your fan current, and see if it is less than
100mA, if not you need to put a micro inside your fan to talk to the
port, not a trivial task


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

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

I greatly appreciate your thoughts.

Perhaps this would help you:
http://www.dimensionengineering.com/appnotes/USBMini/USBMini.htm
Although i think that dc-dc converters are a little expensive.
 
J

Jan Panteltje

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

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

I greatly appreciate your thoughts.

I have a 'USB powered fan', it crashed my PC USB port repeatedly before I
soldered a AC adapter plug to it.
Forget it, it sucks.
USB is about 600mA max, and you likely have otehr stuff on it that uses
some power.
New mobo is expensive too... reboot is annoying.
30 Euro buys a huge Chinese fan with 3 speeds....
 
R

Rene Tschaggelar

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

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

I greatly appreciate your thoughts.

Why don't you just open the door of the fridge ?

Rene
 
J

Joel Kolstad

Jan 1, 1970
0
martin griffith said:
a standard USB port will only delivery 100mA before shutting down, you
have to talk to the USB port to tell it you need more power, up to a
maximum of 500mA.

Although the USB implementers would prefer it that way, many computers
(probably even the majority of them) don't have such fancy current limiting on
their USB ports and *will* pass a full 500mA (or more) to *any* device, such
as a 100% "dumb" fan. Relying on this behavior obviously doesn't make for a
robust design, but many ceahp USB "novelties" make use of that fact
nonetheless.
 
A

AZ Nomad

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

I prefer using 110V when I in the mood for destroying the circuitry on my
computer's motherboard. You can reach so many more subsystems that way.
 
M

martin griffith

Jan 1, 1970
0
Although the USB implementers would prefer it that way, many computers
(probably even the majority of them) don't have such fancy current limiting on
their USB ports and *will* pass a full 500mA (or more) to *any* device, such
as a 100% "dumb" fan. Relying on this behavior obviously doesn't make for a
robust design, but many ceahp USB "novelties" make use of that fact
nonetheless.
I had suspected that, but I thought that I should try and point out
the "correct" approach.

I'm not going to stick anything onto my laptop USB ports that is not
"proper", but maybe with cheap USB cards for a desktop PC, who cares


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

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

I greatly appreciate your thoughts.


Two words: extension cords.
 
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.
 
P

Paul Hovnanian P.E.

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.

That would be a ( 2 V / I_fan ) ohm resistor, rated at least ( 2 V *
I_fan ) Watts.
 
J

Jan Panteltje

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.

If you are such an idiot as not to listen to good advice WTF should anyone
help you anyways.
Now go an f*ck off.
 
N

Nico Coesel

Jan 1, 1970
0
martin griffith said:
I had suspected that, but I thought that I should try and point out
the "correct" approach.

I'm not going to stick anything onto my laptop USB ports that is not
"proper", but maybe with cheap USB cards for a desktop PC, who cares

I fit a USB to serial converter on almost anything with a
microcontroller (especially when it is a prototype). No need for a
bench power supply.
 
J

Joel Kolstad

Jan 1, 1970
0
Nico Coesel said:
I fit a USB to serial converter on almost anything with a
microcontroller (especially when it is a prototype). No need for a
bench power supply.

Aw, c'mon, you haven't lived until you've shorted a kilowatt or so transformer
and set the wire's insulation on fire! :)

I take your point though... the other day I was thinking of making a little
test board with a Max232-variant on it, when it occurred to me... hey... I
might as well just use an FT232R, and that way I wouldn't have to come up with
power from somewhere...
 
N

Nico Coesel

Jan 1, 1970
0
Joel Kolstad said:
Aw, c'mon, you haven't lived until you've shorted a kilowatt or so transformer
and set the wire's insulation on fire! :)

Many years ago I asked where a test lead had gone. A co-worker
answered, "well it is right there" while pointing at a black stripe
inside a transformer casing. They had been testing the transformer
while I wasn't there and they shorted it using the test lead.
I take your point though... the other day I was thinking of making a little
test board with a Max232-variant on it, when it occurred to me... hey... I
might as well just use an FT232R, and that way I wouldn't have to come up with
power from somewhere...

I have had very good results with the CP2102 from Silabs so far. Never
quits, driver never hangs and it has an internal 5V to 3.3V regulator
(100mA max).
 
J

Joel Kolstad

Jan 1, 1970
0
Nico Coesel said:
I have had very good results with the CP2102 from Silabs so far. Never
quits, driver never hangs and it has an internal 5V to 3.3V regulator
(100mA max).

Ah, thanks for the pointer. I took a look at the data sheet over lunch, and
while the CP2102 doesn't seem to have quite as many bells and whistles as the
FT232R, I do like the fact that it has substantially bigger internal buffers
(640/576 bytes for Tx/Rx vs. FT-232's 128/256), and it's nice that they
provide various utility programs for customizing the INF files rather than
making you hand-edit them as FTDI does!
 
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 can run the 3V fan with 5Volts, it will just run faster
 
J

jasen

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
yes.

and what the value of the resistor would be.

noone can tell from here. how much current does the fan use?
This is not something that can be determined (practically)
without measuring it.


Bye.
Jasen
 
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