speed control for a 12 volt fan

Thread Starter

Gompers

Joined Feb 21, 2007
18
Can anyone tell me if those small 12vdc ventilation fans can be slowed down

I added some resisters to drop the voltage, but so far no appreciable reduction of speed. Ed from Ct.
 

Thread Starter

Gompers

Joined Feb 21, 2007
18
Used a 9 vdc supply and added 7 ohm resister to the circuit. I intend to use a manual three position rotary switch to vary the speed in increments

The motor itself will be used to wind thread using various sizes of spools The blades have been removed and replaced with an applied spindle. Thanx, Ed.
 

hgmjr

Joined Jan 28, 2005
9,029
Used a 9 vdc supply and added 7 ohm resister to the circuit. I intend to use a manual three position rotary switch to vary the speed in increments

The motor itself will be used to wind thread using various sizes of spools The blades have been removed and replaced with an applied spindle. Thanx, Ed.
If the motor is a DC brushed motor, addition of a resistor is going to cause a problem.

The current drawn by a DC brushed motor increases and decreases with variations in the load. That means that when you need the motor to deliver torque to the load, the increase loading will cause the motor to draw more current and this added current will result in a greater voltage drop across the series resistor and drop the voltage driving the motor causing it to easily stall.

You have a few choices. You can use gears to mechanically reduce the speed, you can lower the voltage supplied to the motor, or you can use the circuitry that controls the speed using "Pulse-width modulation" (PWM).

The series resistor will only cause you grief. This is the voice of experience speaking.

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,029
Just use an LM317, adjustable regulator..... I do that on my dimmers, using a thermistor instead of a pot/pre-set....Daniel.
Good suggestion, lightingman.

Edward Schwalenberg,

Don't forget to include a healthy heatsink. I suspect there will be a good deal of power dissipated by the LM317 under certain conditions of voltage and load.


hgmjr
 

spar59

Joined Aug 4, 2007
57
You could try dropping the voltage using a zener diode or series string of normal diodes - you could vary the number of diodes using a switch. The output voltage will remain fairly constant at your chosen level irrespective of load with this arrangement.

If this is a small computer type ventilation fan they often only draw around 100mA so your 7R resistor would only drop 0.7V hence you wouldn't notice much of a speed change.

Steve.
 

Thread Starter

Gompers

Joined Feb 21, 2007
18
Spar, thanx for the reply. I used a 4vdc supply and 6,7,and 8 ohm resisters connected through a three position rotary switch Gadget wirks fine Thanks again I'm still learning how to navigate this forum Ed from Ct.
 

lightingman

Joined Apr 19, 2007
374
Yes..I use the LM317 to supply 2 x 100mm, 12 volt fans (in parallel)..... The LM317 is just bolted to a copper pad as part of the PCB, but it is placed in the path of 1 of the fans....When the unit is on, the fan is pre-set to run nice and slow, as the temprature increases the fans speed up....This has run for about 8 years now with no prob's...Good luck...Daniel.
 
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