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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.”

motor

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

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.

2 comments

  • A Hall effect sensor (I think that’s what it is) came with my Chinese electric wheel. It’s in the form of a plastic ring of magnets about 50mm in diameter and a separate metal ring with a connection to the control box. There are no instructions with it, which is annoying…

    Reading your explanation above, I assume the ring of magnets must must be fitted concentrically with the wheel, and very close to the pickup ring… I will try to do this, but the plastic ring of magnets on my sensor is just pushed on to the axle stub, which meant that I had to cut it (to get the main cable through) and also enlarge the hole in the plastic to fit the stub axle. The sensor itself is a thin metal ring about 4.5mm diameter with a rectangular plastic object attached (presumably the sensor itself) and a wire going back to the controller. A ring of that diameter doesn’t have any obvious way of being attached in the right place… It’s trapped inside the fork and rattling about because of its very large diameter. Stick it on centrally with some tape wrapped round the fork ends, maybe? That’s about all I can think of, but it’s very rough and ready.

    I will try this and see how I get on. If anyone has any further information, I would welcome it (martin.corrick@protonmail.com)

    Martin Corrick on

  • A Hall effect sensor (I think that’s what it is) came with my Chinese electric wheel. It’s in the form of a ring of magnets about 50mm in daimeter and a metal ring with a connection to the control box. There are no instructions with it, which is annoying…

    Reading your explanation above, I assume the ring of magnets must must be fitted concentrically with the wheel, and very close to the pickup ring… I will try to do this, but it is not obvious how the parts are attached. It seems that the ring of magnets are just stuck on the wheel with their own magnetic attraction. Is that right?

    I will try this and see how I get on. If anyone has any further information, I would welcome (martin.corrick@protonmail.com)

    Martin Corrick on

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