PWM Fan Controllers: 2-Wire vs 4-Wire

Last Updated: October 19th, 2021

There comes the time when it is necessary to control the speed of DC fans to reduce the power consumption and prevent the fans from being excessively loud. The simplest method to lowering the fan speed involves reducing the voltage delivered, but this results in power loss and is limited on the range of speed control.

Direct current fans, both 2-wire and 4-wire, can be driven by Pulse Width Modulation (PWM), which ramps the fan speeds up and down depending on the duty cycle of the input signal.

Any 2-Wire fan can be be crudely controlled by a PWM controller that cycles the power to the fan on and off to adjust the output fan speed. This controller can also be used to manipulate other electronics such as LEDs, efficiently lowering or raising the brightness. However, since fans store charge in a magnetic field, every time the fan is cycled off, the coils release a surge of current that can damage the internal and external circuits. At minimum this must be resolved by implementing a flyback diode.

The 4-Wire PWM controllers can read the speed of the fan and send a signal to the MOSFET controlling the fan's coils. This in conjunction with the circuit protection employed in 4-Wire fans prevents internal and external circuits from being damaged when the coils are cycled. The underlying principle controlling the fan is the same as the 2-Wire PWM, but the protection components are already implemented.

PWM for 2-Wire Fans

  • PWM for 2-wire fans controls the speed of a fan by switching the power to the fan on and off; a low duty cycle will result in a low fan speed and a high duty cycle will imitate the fan at full speed.
  • Power-based PWM can cause to damage to 2-wire fans without protection such as a flyback diode - 4-wire fans can also be damaged if they do not have circuit protection.
  • Under very low duty cycles DC fans can stall, overheat, and damage themselves.
  • Good for: crude fan speed control, LED brightness, adjusting power delivered under a fixed voltage.
4K vs 8K

PWM for 4-Wire Fans

  • A true PWM controller requires a 4-wire PWM fan, where a signal with a varying duty cycle can be used to control the fan speed by allowing more power through the internal MOSFET controlling the fan's coils.
  • The PWM controllers for a 4-wire fan are more quiet than ones for a 2-wire fan.
  • Higher minimum duty cycles and monitoring the tach signals prevents fans from stalling.
  • Good for: efficient fan speed control.
Print Example

Our 4-Wire PWM Fan Controller

  • 5V or 12V DC Fans
  • 4A Current Max
  • 15-95% Duty Cycle
  • Radial knob with Off/On position
  • Epoxy encased for circuit protection
  • No soldering required!
  • Made in USA with US, German, and Taiwanese components

4-Wire PWM Fan Controller

$20

Voltage: 5-12 VDC
Max Current: 4 A

Prusa MK3S

2-Wire PWM Fan Controller

$5+

Voltage: 5-35 VDC
Max Current: 5 A

Prusa MK3S
EbayAmazon

115 CFM 4-Wire Fan

$15

Voltage: 12 VDC
Power Consumption: 4.8 W
Static Pressure: 0.41 inH2O
Max RPM: 2600 RPM
Decibel Rating: 41 dB
Dimensions: 120x120x38 mm

Prusa MK3S
Ebay

178 CFM 4-Wire Fan

$18

Voltage: 12 VDC
Power Consumption: 18 W
Static Pressure: 0.94 inH2O
Max RPM: 4200 RPM
Decibel Rating: 54 dB
Dimensions: 120x120x38 mm

Prusa MK3S
Ebay

AC-DC Power Adapter

$9+

Voltage: 12 VDC
Power Rating: 24 W (Ebay)
Power Rating: Varies (Amazon)
Connector: 5.5x2.1-2.5 mm

Prusa MK3S
EbayAmazon

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