fan speed

to control fan speed,(computer fan) is it done by resistance or by voltage

resistance and voltage will both change fan speed, since they both change the current

eerrmm, resistance? you can add a resistor and it will vary the speed, but you cant vary the speed with resisance itself, since its not a form of energy

Use a potentiometer. 100ohm seems to bring my vibra motors down to a very slow speed. Maybe use an 1kohm resistor. Ive never used a 1kohm resistor to slow down a fan. Maybe it will be overkill, meaning that at 400ohm resistance for example the fan will be off so you have a half turn left for nothing. Do abit of testing and find out what resistance switches your motors off. How? Well get a 10kohm pot and then turn it until the fan stops then measure the resistance then buy a pot which is equal to the reading you have and then you will have a full turn off to max speed fan.

PWM is the best, cheap enough way. Look around for soldering kits based on the 555-timer.

FireMyLaser said:

PWM is the best, cheap enough way. Look around for soldering kits based on the 555-timer.

Click to expand...

May you elaborate on this? Is there a way to use a 555 to randomly slow and speed up fans? Any links would be greatly appreciated.

Sorry, but I live in Sweden and got my kits locally :-[. The kit is called "motor/LED dimmer" if that helps.

Hmm i can see how it works because the 555 will push 200mA. The only problem with using a 555 is you will always get the same pattern. Slow---fast---slow---fast etc

It controls the speed very well and has a transistor so it can handle up to 1.5A and 5-12v.
I just got an idea, how about using a cheap RGB LED circut. They have 3 channels. Take one of them and connect it to a transitor in it's turn to the motor.
Now, the speed should fade up and down by it self, in theory.
Make two of these and make a spirograph...

The LED drivers dont have enough voltage to drive a fan....

PWM circuits work by sending pulses into a transistor (basically a switch triggered by a lower voltage), so you wire your fan to the transistor, and when the 555 sends voltage into the transistor, it allows power to pass into your fan, making it spin. The way it varies the speed, is by changing the amount of time between the pulses going to the transistor. The longer the space between the pulses, the slower the fan will go, if you make the time between the pulses less, the fan will go faster. Its basically turning the fan on and off at the right times to vary the speed. One problem with PWM is that at lower speeds, you can actually hear the high pitch coming from the fan. It's not to audible, but anyway...