Reducing speed of a EBM-Papst centrifugal blower fan


I have recently bought a centrifugal fan from ebm-papst, a D2E120-aa01-04. It specifies the following wiring scheme:


I have wired the fan with the suggest 2uF/400V capacitor and the fan runs fine, if not too fast for our application.

I’m looking for a simple way to reduce the rpm of this fan.

The following link with suggested capacitors mentions that all fans with a PSC motor can be made multi-speed by adding extra capacitors. That would be our preferred solution, we do not need the flexibility of a VFD or variac.

I’m looking for some guidance on:

  • Is the motor in the D2E120-AA01-04 of the PSC type and can it’s RPM be reliably reduced with extra capacitors?
  • How would the additional capacitors need to be wired?
  • If only a single, lower speed would be required, can we simple replace the existing 2uF capacitor with a smaller one, or do we need to add additional capacitors next to the existing 2uF one?
  • For this fan-type, any suggestions what amount of capacitance would reduce speed to say 2/3 or 1/2?
  • Are there other, suitable external switches that we could use to get 2, or 3, or 4 different speeds on this fan?

Any help would be greatly appreciated!

Best regards,


Insofar as I’m unable at this time to find a datasheet for the specific product mentioned, I cannot verify its motor construction; incorporation of a PSC type motor would appear quite likely however.

Changing the value of the run capacitance connected to a PSC motor has the effect of altering the motor’s torque characteristics, and could conceivably be used as a means of achieving a limited degree of speed control. Because the operating point of any given air mover depends on the mechanical properties of the system to which the air mover is connected, specific suggestions are difficult to offer with any confidence. If you wish to pursue this approach, my suggestion would be to acquire a variety of suitably-rated capacitors in the vicinity of the suggested value and characterize the behavior of the system in context of your application witheach, being careful to note any changes in current drawn by the motor and resulting changes in motor temperature.

A potential disadvantage of this approach, assuming that the intent is to permit speed adjustment during operation, is that any switches used to alter the value of the connected capacitance are likely to experience some significant stresses and may wear or fail in a relatively short period of time. A phase control approach such as can be found in common ceiling fan speed controllers may be an alternative solution that would avoid this complication.

Hi Rick,

thanks for your comments and suggestions.

I have some caps underway that I can experiment with as you suggest.

To be clear, my goal right now is to achieve a fixed reduction in speed without switches for different speed settings.

I’m a little bit unclear about the best way to wire additional capacitance into the circuit above though.

There are 3 configurations that I have in mind and I’m unsure what, if any, difference there is between them from the perspective of reducing the speed of the fan:

  • A capacitor in series with the entire motor, either on L or N. This puts the extra capacitance on both coils.

  • An extra capacitor only on the secondary winding. This would change the existing capacitance that is already there. If this is an effective configuration, then I could also simply exchange the existing motorcapacitor by one with a different value and not increase the overall number of capacitors in the circuit.

  • An extra capacitor on the primary winding only. I have a feeling that this would be the least favorable, but I can’t really explain why.

From what I read on the internet, most suggestions are to put an extra cap in series with the entire motor, but I’m also curious what the drawback would be of only changing the run capacitor to a different value.

Best regards,

I’d start there.

Please bear in mind that much of the info on the 'net is worth what one pays for it…