Can I drive a sensored brushless DC (BLDC) motor with a sensorless brushless DC motor controller?

Sensorless brushless motor controllers can work very well with a sensored BLDC motor

The quick answer is yes, you can, provided that you connect everything up correctly. That said, it is important to be clear about your reasons for doing this.

A sensored brushless motor is a brushless motor with sensors in it. A sensorless brushless motor is exactly the same as a sensored brushless DC motor with the exception that it does not have sensors installed. Many manufacturers make exactly the same motor (in terms of frame size and electrical specifications) but simply offer it in sensored or sensorless variants.

This therefore means that a sensored brushless motor can in essence be treated exactly like a sensorless brushless motor. To do this you must first ensure that the phase connections are wired in correctly but the hall sensors wires are ignored. It is important to remember that, if you do this, the motor that you are using will then become a sensorless motor so any performance characteristics that you were getting if you had been using a sensored brushless motor controller will now be different. However, there is no danger or issue in doing this and it is a (relatively) common option for those wishing to cut costs or where a motor with perfect mechanical specifications may only be available in a sensored option.

Performance characteristics may vary depending on the brushless motor controller

If you are thinking of using this method for a number of reasons then it is important to be aware that there may be particular issues that you need to be aware of. Generally speaking, the most important of these relates to lower speed or startup of the motor which may not (at least initially) be as smooth as it would have been with a sensored motor controller. The reason for this is that the rotor position of the controller will not be being communicated to the controller and this can therefore make control at lower speeds more difficult to achieve. Equally, the startup of the motor can be slightly more difficult in sensorless mode as it generally requires a forced commutation sequence for the controller to detect the rotor position. 

Depending on the nature of your application, it may not be a good idea to go down this route as lower speed options can be affected by driving in sensorless mode. That said, there are a lot of important motor characteristics that can all impact on the performance of the motor at different speeds such as the pole count, inductance and load on the motor. If you’re not sure on the best option for your project you can always talk to our team and we’d be happy to help.

Any technical information you may have on the motor which is based on it being run as a sensored motor will also no longer be necessarily accurate – this is especially true at lower speeds. If you are not entirely sure about this or have any questions please give us a call to discuss.

It is worth remembering that there is no obvious reasons to do this in practice with the exception that sourcing motors for specific applications is sometimes difficult and we have had clients in the past who have only been able to find a sensored brushless motor which met the torque/speed requirements their project required. Again, if you have any specific questions here please feel free to give us a call or email.

Customisation is always an option

Depending on the volumes that you are purchasing for your project it is also usually possible to talk directly to the manufacturer in order to get the sensors removed and a discount applied. At volume, it will undoubtedly be possible to save money by removing the sensors from the motor at the manufacturing stage.

It is likely that you will need to setup the sensorless brushless motor controller to deliver the correct drive pattern depending on the specification of the sensored brushless DC motor that you have. It is always important to take into account the number of poles and key electrical characteristics of the motor.

If you have any questions about the best way to setup your brushless motor and controller then please contact us. Our team can even set the controller up for you specifically for the motor that you have.

Category: Brushless Motor Controller FAQs
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