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What is a hall sensor and why do electric bike motors need them?

Posted by Tom Lee on

Hall sensors are in most eBike motors, but not all. Ever heard of them and wondered what they are? They are magnetic sensors which help the controller to know what the position the motor is in as it turns, so that it can keep it turning. Read further for some more detailed info and photos.

Most eBike motors have “hall sensors” which help the controller to drive the motor.

In another post here we will talk about the practical aspects of motor control and hall sensors. But first, for those of you who are interested in physics, here is a quick blog about how hall sensors work.

hall sensors

“Hall sensors are a type of magnetic sensor – they detect the presence of a magnetic field.”


How does it work?

Hall sensors are a type of magnetic sensor – they detect the presence of a magnetic field.

The way this is done is by running an electrical current through a metal pad. When a magnetic field is nearby, the electrons (charge) get pushed by the magnetic field to one side of the metal pad creating positive charge on one side and negative charge on the other:


This imbalance of charge can then be measured as a voltage (across the pad). When the voltage is high it means there is a magnetic field nearby, when the voltage is low there is no magnetic field.

Hall sensors inside a motor


So how is this used exactly in an eBike motor?

Well, as will be discussed in the next blog how does hall effect motor control work, to control an ebike motor the controller needs to know the position of the motor at every point in time so that it can keep pushing it round. It works out the motor position from the signals coming back from the hall sensors (usually 3 of them). When the signal from the hall sensor is high that means that one of the motor magnets is going right past it, when the signal is low that means the motor magnet has already gone past.

So there you have it – a simple explanation as to what a hall sensor actually is.


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