"Dave D" wrote in message
...

"Andre" wrote in message
m...
Hi group .

I recently scored a pile of 5V 1W fans . Problem is, for what I want
them for they are too fast, and suck too much current . (200 mA)

I am left with :-

1) Adding a constant current to limit current (and therefore speed)-
easy enough to do . How come there isn't a 100mA "constant current"
diode ?!?!?!
Also I'd need the regulator to drop less than a volt for this to work
.

Put two silicon diodes in series in the 5V supply, works perfectly.


2) Using a lower supply voltage (this would make things worse !)


How? That's exactly what you want to achieve!

3) Using a different fan . (too expensive)

4) Modifying the fan somehow to limit the speed (possible, adding a
capacitor across the Hall sensor output to limit the speed would
likely work but wouldn't solve the current problem)


Are you saying these are speed regulated fans? If so removing the hall
effect sensor might be the first step as they will always attempt to make
up
for your efforts to slow them down. Sometimes (often in PC fans) the hall
effect sensor is there simply to report the rpm to the device it is
connected to.

5) Pulsing the fan voltage so it gets 4V mainly with x % 5V pulses
(this would keep the speed reasonably constant) - anyone done this ?
The idea is to allow the logic to work so fan won't stall, but
limiting the current enough so that it keeps the speed down .


Rather like a sledgehammer to crack a nut! Try the diode idea first.

Dave


In my experience with 12V fans, a series resistor works nicely, as does
running them from a stiff 6V supply.
Unless you have something unusual, these fans do vary RPM in response to
power supply voltage.

You will have to determine the resistor by trial and error, since the fans
do not respond linearly to voltage.