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I have a BLDC motor and its controller. How can I see its back EMF graph using an oscilloscope provided I can see the phase-to-phase voltage graph?

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    \$\begingroup\$ You can turn it with a power tool and directly observe the BEMF phase to phase voltage. If you know the speed you turn the BLDC motor with, you can also measure your BEMF constant. Be careful about the definition of the BEMF, it sometimes is peak to peak but mostly in RMS. \$\endgroup\$ Commented Oct 20, 2022 at 6:52
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    \$\begingroup\$ I dont understand the question, so I googled: (1) BLDC Motor Back EMF Explained - Machine and Mechanism Design, 2010jun29 brighthubengineering.com/machine-design/…, (2) Controlling Sensorless, BLDC Motors via Back EMF - Steven Keeping, Electronic Products, 2013jun19 digikey.com/en/articles/… \$\endgroup\$
    – tlfong01
    Commented Oct 20, 2022 at 7:00
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    \$\begingroup\$ Steven Keeping's article says the following: Methods for detecting back EMF: There are several techniques for measuring the back EMF. The simplest is to compare the back EMF to half the DC bus voltage using a comparator. Figure 4a shows a schematic of such a system. , ... \$\endgroup\$
    – tlfong01
    Commented Oct 20, 2022 at 7:13

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Do not use the controller at all. Disconnect the motor from the controller. Connect oscilloscope ground to one of the phase wires on the motor and probe one of the other wires. Spin the motor with your hand or with a drill or with another motor. You will see the back emf on the oscilloscope. This is the phase-to-phase or line-to-line back EMF.

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