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Hall Effect Sensor Fun: Electronics 406 question

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  • Hall Effect Sensor Fun: Electronics 406 question

    Been having fun with hall effect sensors. Have used a unipolar hall effect sensor to create a pulse motor similar to the Bedini sensor coil style. I am planning to look at this further in terms of where one might like a pulse to occur, pulse duration, magnet spacing, magnet strength and so forth.

    I had another idea and quite bluntly it has turned out to be seemingly beyond me (i.e Electronics 406), that is to create a brushless DC motor using a hall effect sensor. Before going into the details of my attempt let me note that a Bedini SSG runs in both attraction and repulsion mode. This implies that the rectified inductive radiant spike is independent of the orientation that the electromagnet is charged in. This further implies that any "AC magnetic motor" where the coil collapses might allow one to gather an inductive spike. So I wanted to make a brushless motor, like the SSG but switching the coil from positive to negative.

    I had great initial success with this. I used a bipolar (i.e turned on by say North and off by South) latching (stays on until it sees the opposite magnetic field) hall effect sensor. I hooked it to two single pole double throw relays. When the hall effect sensor was on power flowed to one coil orientation, when off, to the other. I was quite pleased with myself ... until I tried a few magnets on the perimeter and things got close to 1000 rpms. The relays couldn't switch fast enough. Okay, easy enough, just go with transistors, this is when it all fell apart. Well, I never seem to know what's going to go easy with electronics, though it was easy with relays, this after a multiday battle has kicked my rear.

    So that is the question, how do you use transistors to switch from one polarity to the other on an electromagnet?

    What I finally came up with was 4 transistors (I'll try and diagram it if necessary). Positive to an NPN, negative to a PNP, negative to an NPN positive to PNP. Finally I had no shorts in the circuit and when an NPN and PNP were triggered the power flowed one way, when the other NPN/PNP were triggered the power flowed the other way. The problem then was how do you take the binary signal from a hall effect sensor and trigger one set of PNP/NPN transistors and then the opposite signal for the other PNP/NPN set, all without creating a short. As noted, kicked my hieney.

    I am new at electronics and may just be missing something but I am not a complete idiot, I think this is a genuinely difficult problem. I am not asking for any immediate response, just if you get bored and want to spend a few hours let me know what you come up with.

    I may perhaps use two sensors which would clear up the problem, the problem then is if the two sensors are not aligned and sensing the same thing, they would short because one would turn on while the other didn't turn off. Still it might be an answer.

    Another carrot for this question, what happens when one switches in a "nanosecond" between positive and negative polarity on an electromagnet? There should be some time when the coil is releasing its stored energy and the opposite current is energizing the electromagnet. What about the inductive spike, is it "snuffed" out as it were or does it not give a crap about the incoming opposite polarity current? What happens to the radiant spike in this situation??

    So again the question is, if you are bored or energized, how do use transistors to switch polarity on an electromagnet and how would this hook up to a latching bipolar hall effect sensor?
    Last edited by ZPDM; 04-07-2013, 03:53 AM.

  • #2
    ZPDM,

    you need the Bedini / Cole H bridge driver circuit, and you need 2 uni polarity hall sensors for it to work correctly..... and a 3 magnet timing wheel like JB shows on his window motor videos......

    MOTOR DIAGRAMS AND LAB NOTES

    THE 6TH PICTURE ON THIS PAGE

    Sequential Bipolar Switch Commutator
    Last edited by RS_; 04-07-2013, 12:38 PM.

    Comment


    • #3
      "Another carrot for this question, what happens when one switches in a "nanosecond" between positive and negative polarity on an electromagnet? There should be some time when the coil is releasing its stored energy and the opposite current is energizing the electromagnet. What about the inductive spike, is it "snuffed" out as it were or does it not give a crap about the incoming opposite polarity current? What happens to the radiant spike in this situation??"

      when you set up the timing wheel, and hall sensors, you want to create a Never on at the same time arrangement, as the coil is energized in ether direction, that small off time in between, is where you collect the spike into a cap, just before the reverse polarity pulse happens.......

      Comment


      • #4
        Originally posted by RS_ View Post
        ZPDM,

        you need the Bedini / Cole H bridge driver circuit, and you need 2 uni polarity hall sensors for it to work correctly..... and a 3 magnet timing wheel like JB shows on his window motor videos......

        MOTOR DIAGRAMS AND LAB NOTES


        THE 6TH PICTURE ON THIS PAGE

        Sequential Bipolar Switch Commutator
        RS_,

        Thanks very much for that. I am looking at the diagram you cited. I am encouraged that I see with Q1 and Q4 two PNP tranistors and Q2 and Q3 two NPN transistors. I may have been on the right track. I also see a bridge rectifier bridging the drive coil so I see that part is for gathering the spike. If I can make sense of the rest of the circuit I just may be able to do this.

        I still wonder whether you can get away with a single bipolar latching hall effect sensor. In any event will try and work on it again at some point going forward. For the moment I am running a monopole set up with a Hall effect sensor, trying different numbers, spacing and arrangments of magnets and seeing what RPMs I get with a 3 volt input.

        Thanks again, I think that diagram was exactly what I was looking for, now I just need to understand it.

        Comment


        • #5
          ZPDM,

          You were on the right track with the PNP and NPN setup on each side

          you might be able to use the bipolar latching Hall, if you add another small transistor to switch the polarty on one of the drivers sides. but you are not going to get very much off time in between, where with 2 hall sensors, you can adjust the on time Pulse duration and off time between pulses quite easily

          i have build several versions of this circuit over the years with various transistors........

          Comment


          • #6
            RS-,
            I got something running with 4 power supplies (lol) and two transistors! I've got a unipolar hall connected to a 3 volt power supply, another unipolar hall (opposite orientation) connected to another 3V. One hall triggering an NPN the other a PNP two nine volt batteries connected to each transistor and the coil hooked to both transistors. I'll diagram it if there is interest. It works great for what I was looking for, looking at different magnet arrangements and combinations. It has a serious drawback that, again I can diagram it, I don't think you can capture the inductive spike because one +9 volt is connected to another -9 volt lead, I'll try looking at some diodes but I doubt it. While I haven't yet done it, I am pretty certain this can be remedied with one or two more transistors breaking the other connections between the 9 volt batteries. Still having fun with magnets.

            Comment


            • #7
              RS_,

              I can't thank you enough for pointing out that circuit to me. I got it running today. In fact I made a video which if I get a chance I'll post. Will just say the Sequential Bipolar Switch Commutator is much better than the four battery contraption I had previously, and simpler, and I am now having no problem catching the inductive spike. Was a bit surprised it came together as it did, but now I can say it is a beautiful circuit and I'm having lots of fun with it. Am looking forward to experimenting more with it. Many thanks again.

              Comment


              • #8
                ZPDM,

                That is great that you have the Bedini/Cole bipolar switch going, it is my favorite circuit, and was the first circuit of Bedini's i built in 2000.......

                Jeremy and I have one going, running the window motor kit from the 2011 conference, that he has been learning on........

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