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Is it possible to measure the back EMF of a motor, using just the Arduino and no sensors?

Or what type of sensor do I need? One that measures current?

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There is no need to measure the windings of the motor... please see the great write up for full details using an Arduino to sense the back EMF on a PWM driven motor to control the speed. This can be applied to a 3 phase motor as well, see Back EMF.

This person uses the analog input and a voltage divider to sense when the EMF happened, basically he gets the motor running, then periodically grounds one side of the motor through the H-Bridge he is using to drive it, and the other side of the motor goes to a voltage divider into the Arduino... and it is also an open circuit at this time so the voltage generated is from the collapsing of the coil field so if it is 12V it becomes a safe 4V at the Arduino Analog input.

Now your question says "measure the back EMF", what I provided senses the back EMF... to measure it you just need to sample the Analog pin a bunch of times, and that will give you a reference of the max amplitude.

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You will need at least an external current sensor, the arduino has no way of measuring current built in. You will also need to measure the winding resistance of the motor beforehand. look to this answer for a good explanation: https://electronics.stackexchange.com/questions/54997/how-can-i-measure-back-emf-to-infer-the-speed-of-a-dc-motor

DC current sensors compatible with arduino should not be hard to find; just search one of the standard hobby electronics components sites.

  • Technically EMF is a voltage, not a current. – Chris Stratton Dec 11 '15 at 1:47
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Take a look at this website: http://www.vwlowen.co.uk/arduino/current/current.html

It shows how to make a create a simple current sensor with just a few resistors.

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    Links to external resources are encouraged, but please add context around the link so your fellow users will have some idea what it is and why it’s there. Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline. – microtherion Jul 28 '15 at 12:16
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    EMF is a voltage, not a current. – Chris Stratton Dec 11 '15 at 1:47

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