strange hall sensor waveforms - noise?

6 years 11 months ago #29528711 by tonyo
I have a MBL1650C controller and two different motors.

Motor #1 has an external hall sensor module with a separate, shielded cable from the field wires. It runs great using the Roborun app.

Motor #2 has the hall sensors buried in the field coils and has the sensor lines and the field lines mixed together in one cable.

This motor runs roughly, I tried all 6 combinations of U/V/W and the smoothest combo is still pretty rough.

So I hung a scope on the hall sensor lines. The scope shows the proper 120deg. realtionship, but I also see a very slow leading edge on the hall output, and occasionally a full size pulse before the main transition (pardon the ascii graphics):


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The Hall RPM telemetry shows that the rpms go from, say, 2000RPM to -2000RPM very briefly, then back to 2000RPM, which is impossible, so I am thinking that noise is causing the controller to report wrong RPMs.

I split the cable open and separated the hall and field wires, this has reduced the roughness but the RPMs are still hiccupping.

Is there anything else I can do? Do the hall inputs need stronger pullups?

thanks,

tony o.

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6 years 11 months ago #29528712 by Griffin Baker
Replied by Griffin Baker on topic strange hall sensor waveforms - noise?
Add some shielding between the different wire connections.

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6 years 11 months ago #29528713 by tonyo
doesn't seem to be noise; I took the back of the motor off, separated all the hall wiring from the power wiring, reassembled the case, still have odd-looking pulses.

Then I put a 100ohm resistor from +5v to a hall input while looking at the signal with a scope.

The edges sharpened up, but still had a solid 420us pulse, then a pause of about 520us, then the main pulse of 5.18ms at about 4000RPM.

RPMs bounce between 4000 and -3000 RPM.

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6 years 11 months ago #29528717 by Griffin Baker
Replied by Griffin Baker on topic strange hall sensor waveforms - noise?
There is a 5k internal pull up and a 10nF capacitor to ground inside the controller circuit.

You can add another pull up outside and or a capacitor to ground. These should be placed very close to the connector.

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