Small 80mm fan need to drop voltage. HELP :)

[dbtoutfit]

Hi,

(Everything is in DC)

I have a (2) 80mm (rated at 12volt 0.14amp each) fans I need to use to cool my IC's.
My power source from the Stepper Driver board is 24v.

I was hoping someone could suggest a resistor I could purchase locally (radio shack etc) to drop the voltage to 12v for the fans.

I would like to either throw a resistor in line on each fan or one that both fans could be hooked to. I have limited space in my enclosure.

Thanks for your help.

Eric

 

[blueroomelectronics]

Why not buy a 24V fan?

 

[audioguru]

A resistor in series reduces the current. Then the current might be too low for the fan to start running because its starting current surge is up to 10 times its running current. A series zener diode or a voltage regulator IC would reduce the voltage and allow the fans to start.

EDIT: Two 12V fans can be connected in series and powered from 24V.

 

[dbtoutfit]

Well I have made an enclosure for these fans that I carry, they are clear blue and have lights in them and really make the case shine.

Eric

 

[dbtoutfit]

A resistor in series reduces the current. Then the current might be too low for the fan to start running because its starting current surge is up to 10 times its running current. A series zener diode or a voltage regulator IC would reduce the voltage and allow the fans to start.

EDIT: Two 12V fans can be connected in series and powered from 24V.

Man, so theres no simple solution to just drop the voltage with a resistor?

Uh oh..

Eric

 

[audioguru]

Man, so theres no simple solution to just drop the voltage with a resistor?

Sure. A resistor can reduce the voltage to another series resistance, not a motor.

Did you try connecting the two fans in series so that each gets 12V?

 

[dbtoutfit]

I didnt, I was hoping I could do that.

Eric

 

[Willbe]

Hi,

(Everything is in DC)

I have a (2) 80mm (rated at 12volt 0.14amp each) fans I need to use to cool my IC's.
My power source from the Stepper Driver board is 24v.

I was hoping someone could suggest a resistor I could purchase locally (radio shack etc) to drop the voltage to 12v for the fans.

I would like to either throw a resistor in line on each fan or one that both fans could be hooked to. I have limited space in my enclosure.

Thanks for your help.

Eric

86Ω, 2w or 3w. Standard values are 91 or 82.

If you want a stiff voltage source, you can use a 12v, 3w zener wired in series with the fan and the 24v, but I don't think the fan will have a problem starting in any case (it doesn't start under load).

 

[dbtoutfit]

86Ω, 2w or 3w. Standard values are 91 or 82.

If you want a stiff voltage source, you can use a 12v, 3w zener wired in series with the fan and the 24v, but I don't think the fan will have a problem starting in any case (it doesn't start under load).

Sorry Willbe I didnt see your post in time. I just wired them in series, they work great though.

When you say stiff? What exactly do you mean?

Eric

 

[Willbe]

When you say stiff? What exactly do you mean?

Low impedance, as opposed to the impedance the load sees if you use a series resistor.
Variacs and Lamp dimmers using Triacs are also low impedance, stiff, sources.
Some loads don't like being fed from a current-source-like (high impedance) source.

The highest impedance xformer sold as a voltage source or power source that I could find had an internal impedance of about 40Ω; higher than that, typically megohms, would be considered a current source. LED resistors, at 150Ω, are supposed to be current sources.

The "incremental" impedance of a Zener is much lower than Vz/Iz.