Negative voltage on BLDC Hall Effect output

[Tin Duc Vo]

Hey everyone,

I was wondering if anyone knew why the Hall Effect sensor output of a three phase BLDC would go negative? The motor I am using has a Hall Effect module with 3 signals + power and ground. I hooked it up like in the picture below. For some reason, all of the signals spike to some negative voltage when they're not supposed to transition and then decay back to zero. I can't have this because it would destroy the other components. If anyone could help me with figuring out why this output is going negative, that would be lovely. Thank you .

[uncle_bob]

Hi

Most likely reason - because the sensor is grounded to the motor frame and that ground is not the same as the ground in your measuring setup.

Bob

[Tin Duc Vo]

Thank you, Uncle Bob. I actually did not ground the case of the sensor to the circuit ground because I did not think that would be so crucial, but I will try that now. Honestly, I do not understand why that would cause the circuit to do this, but if it works, I will report back. If it does not work, I will also report back ... but with a nice picture .