Ventilated motors: What has to be taken into account?

Question:

• What has to be taken into account if "ventilated" motors are in use?
• Why are no position controllers present by the "Modular system" controller's list in case of ventilated motors?

Solution:

A look into the catalog:

The technical data of maxon motors can be found on maxon's website (e.g. www.maxongroup.com) or maxon's catalog. The maxon catalog lists recommended or typical in use controllers by the "Modular system". Please find the most up-to-date maxon catalog always by this link:
-> http://epaper.maxongroup.com 

• The different EC60-flat motor types are present by page 322 - 324 in maxon's catalog 2022/2023.
• The different EC90-flat motor types are present by page 325 - 330 in maxon's catalog 2022/2023.

The following controllers are recommended by the 2022/2023 catalog depending if an "EC-flat", "EC-flat Open rotor", or "EC-flat ventilated" is in use, e.g.

• "EC-flat" and "EC-flat Open rotor":
  
• "EC-flat ventilated":
  
  

Why is the EPOS4 missing in the "Modular system" list in case of ventilated motors?

The catalog's "Modular system" recommendations just list ESCON and DEC product types in case of ventilated motors because these ventilated motors are typically in use for applications running at constant high speed (i.e. some 1000 rpm) when "nominal" torque has to be supplied.

Position control applications?

In case of position control applications, motors are also operated at low speed and standstill and might still demand for some remarkable torque to hold the motor shaft's position (e.g. in case of robot or exoskeleton) or start motion again in a high-friction or high-load state again.

It has to be taken into account that "ventilated" motors cannot provide the specified "Nominal torque" and power at low speed operation or standstill position control. The higher power and higher torque advantage of "ventilated" motors compared to "Open rotor" decreases when the speed decreases. Based on this there are not much position control applications still demanding for "ventilated" motors and an EPOS4. One reason still to choose an EPOS4 might be the need for a bus interface which is just present by the EPOS but not the ESCON (-> ESCON or EPOS: What controller should I select?).

Technical basics

Ventilated motors demand for some 1000 rpm to take advantage of the cooling effect due to a constantly strong cooling air flow by the ventilator (mounted on the motor shaft). As long as the motor runs at high speeds the air flow for cooling the winding is present and the "ventilated" motors can supply the specified much higher output power and higher torque than possible by a motor with a closed rotor or just an "open rotor" although the same motor winding is present internally.

Important to keep in mind:

As a rule of thumb it can be stated that the possible power and torque (resp. motor current) of a ventilated motor at low speed or standstill is much below the possible specified "Nominal torque" at high speeds and is just close to the "no speed" torque of an "EC-flat" or "EC-flat Open rotor" with the same winding.

The "decreasing" torque output curve at low speed is obvious by the speed-/torque diagram present by the catalog, e.g.

• "EC90-flat 300W ventilated":
  
  => The possible torque output at low speeds or standstill is much smaller (just around 500 mNm) than the motor's specified "Nominal torque" (e.g. 953 mNm in case of the P/N: 607953).
  
  
• "EC90-flat 220W Open rotor" (with same winding):
  
  => The possible torque output at low speeds or standstill is smaller (just around 500 mNm) than the motor's specified "Nominal torque" (e.g. 729 mNm in case of the P/N: 607942).
  
  
• "EC90-flat 160W" (with same winding):
  
  => The possible torque output is highest at low speed close to standstill.

Comparison of EC90-flat resp. EC60-flat within one diagram:

The above two diagrams are also attached to this document as graphic files (jpg) for better evaluation. 

Application aspects & motor selection:

Finally the torque / speed curve of "ventilated" and "open rotor" motors mean that you have to think about the actual torque demand of your application depending on the motor speed.

Motor windings of "ventilated" motors have a high risk to get damaged if these have to provide the specified "Nominal torque" at low speeds or standstill for a long period of time or if motor's rotation can get even blocked during operation with still a high motor current applied.

Caution:

The ventilation and cooling effect is just present if the motor rotates at high speed levels!
If a ventilated motor is operated at low speed or has to hold its position (with nominal torque) at standstill for a long period of time, its winding will be overloaded and damaged!

Conclusion:

If the specified "Nominal torque" has to be provided even at low speed or standstill (which often has to be assumed by a position controlled application), a ventilated motor is often the wrong choice! This is also the reason why maxon does not mention position controllers for ventilated motors by the catalog's "Modular system" anymore. The "missing" position controller recommendation might force interested users to ask about it and there is some chance to go into discussion about the restricted usage of ventilated motors (like mentioned above) and an application's concrete requirements to decide about the feasibility on this base.

• If a "ventilated" motor's "Nominal torque" and power is just required at high speeds, it is o.k. to use it and combine if with an EPOS4 (with a matching output current rating).
  
  
• If a motor's specified "nominal" torque is required over the full speed range or even at standstill, forget about using a "ventilated" motor and select an "Open rotor" type. Select one which is able to provide the torque required by your application from zero speed. Combine this one with an EPOS4 then (like present by the catalog's "Modular system" list).

Remark:
Please note that the catalog and e-shop does not list all possible "Modular system" combinations.  Recommended "Modular system" components focus on typically used combinations and exclude "exotic" ones which might be still possible and in use by some applications but need some clarification about details in advance to ensure a reliable operation.

In case of an in-depth discussion about your application and a suitable motor and controller selection, please get in touch with maxon's local sales engineers or use the Support Center's webform to submit a ticket.