Can I use an external magnetic ring for position sensing?

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  • #37244
    Michael Beglinger
    Participant

    I’d really like to avoid trying to mount the hall position sensors inside the motor. Can I mount the hall sensors near an external magnetic ring that has the same pole count / configuration as the rotor? With this setup the the hall sensors would not detect any magnetic field changes caused by the stator windings. Is that going to cause a problem?

    #37260
    rudydevolder
    Participant

    If your motor has hall sensors already you can do the same with me. I’m busy testing reading speed, direction and exact position using the 3 hall sensors of the motor. I have hooked up 52k + 20k resistors to make a voltage divider to lower the voltage level to 3v3 + using a 74hc14acp Smith trigger. It looks like it works fine. If I lower the resistors it takes to much current and the overall voltage starts to drop. This combination works fine for me and the Kelly controller doesn’t seems to be bothered by it.

    #37266
    Michael Beglinger
    Participant

    Thanks for the reply rudydeveloper. I think my situation is different than yours as it sounds like you have a motor with hall sensors that provide rotor position signals and you’re able to read those with a Smith trigger without affecting the operation of the Kelly controller. My motor has no hall sensors and I don’t know how I’d be able to mount them inside the motor in the proper location. My assumption (which may be incorrect) is that the hall sensors need to be mounted in the center of a stator pole. That seems to be where motor manufacturers put them. Somebody on a forum I found a while back put the sensors in the stator slots and seemed to be having timing issues.

    If the Kelly controller will work with sensors placed around an external ring of magnets that matches the rotor configuration, that seems be the safest way to go.

    #37271
    rudydevolder
    Participant

    Hi Michael, actually I am more about programming, I have almost no experience with hall sensors except that I observed that some sample software for Arduino is very badly written, not optimizing the timing, I found my Arduino sample on the Digi-Key website but I improved the code somehow to make the timing much more accurate. Maybe the timing-problems your friend has have more to do with software than the hall-sensors itself, did he check with a scope?
    If you want I can provide you the improved coding, I only changed very little. Used a timer of microseconds instead of milliseconds, using fast-read, and not reading the other sensors again if you know the status already and some other stuff. And it’s working great.
    There’s different types of hall sensors depending on your application, and Allegro is specialized in that:

    Good luck with your project.

    #37293
    Michael Beglinger
    Participant

    Thanks Rudy, if I get to a point where I need programming assistance I’ll be in touch.

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