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.
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.
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).
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).
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.