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Thread: "Enhanced Generator" from JPKBook

  1. #11
    Hi Jules,

    The triggering on 15 degrees before TDC should be about right for attraction mode. But it should switch off exactly at TDC !!

    With 5 magnets on the wheel you have 72 degrees of rotation between pulses. With 15 degrees of pulse duration you would have a duty cycle of 15/72 or 20.8%. This is about ideal.

    In order to trigger off at TDC there are several ways it do it. A 555 timer based circuit will work correctly at only a particular RPM because it is time based and not distance (degrees of rotation) based.
    Gary Hammond,

  2. #12
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    Quote Originally Posted by Gary Hammond View Post
    Hi Jules,

    The triggering on 15 degrees before TDC should be about right for attraction mode. But it should switch off exactly at TDC !!

    With 5 magnets on the wheel you have 72 degrees of rotation between pulses. With 15 degrees of pulse duration you would have a duty cycle of 15/72 or 20.8%. This is about ideal.

    In order to trigger off at TDC there are several ways it do it. A 555 timer based circuit will work correctly at only a particular RPM because it is time based and not distance (degrees of rotation) based.
    Hi Gary

    Yes I concur with your reasoning. Is there a way to make a distance based option using a Hall sensor? If not then I guess the rotor will ‘stagger’ up to its optimum speed and sit in that speed niche, one determined by tinkering to find the maximum rotor speed.

    Jules

  3. #13
    Hi Jules,

    Quote Originally Posted by JulesP View Post
    Hi Gary

    Yes I concur with your reasoning. Is there a way to make a distance based option using a Hall sensor? If not then I guess the rotor will ‘stagger’ up to its optimum speed and sit in that speed niche, one determined by tinkering to find the maximum rotor speed.

    Jules
    I did it by using two hall switches at different movable locations. Both halls have to be on at the same time in an electrical series arrangement to bias the FET on for the required degrees of rotation (duty cycle). Moving both in the same direction changes the timing. The first one to switch on is also the first to switch off and determines the cut off point (turn off at TDC for attraction mode). The second one to switch on determines the point in the rotation that conduction occurs to turn the FET on (beginning of pulse 15 degrees before TDC).

    If the magnet spacing on your wheel is really accurate at 72 degrees, you can use any two separate magnet stacks with a hall sensor at each one. One hall would start the trigger event and the other would end the trigger event.

    Another, possibly easier solution, would be to run in repulsion mode by just inverting both the magnets in the wheel and the hall sensor. This would place the south poles of the coils and the south poles of the magnets toward each other, and the hall would trigger from the south pole of the magnets at TDC. You may still have to experiment with the location of the Hall to get it to switch on at exactly TDC. The duty cycle is not as critical when running in this mode and may if fact be shorter due to the hall being triggered by the south pole.

    P.S. - An easy way I found to check the timing (turn on point) is to use an old inductive automotive timing light. It strobes to let you see exactly at what point in rotation the timing is.
    Last edited by Gary Hammond; 09-03-2018 at 11:27 AM. Reason: add PS
    Gary Hammond,

  4. #14
    Senior Member Yaro1776's Avatar
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    Jules,

    Nice diagrams depicting the Hall positioning and it would certainly worth the effort to move the Hall to that second configuration just to see if it all works.

    Gary's recommendation is pretty dead on for an SG and his twin Hall arrangement is pretty simple and effective from a control standpoint.

    I am unfamiliar with how distance sensitive Hall devices are with respect to the magnetic field strength needed to trigger them. Also, one can describe that the magnet pole strength as a function of distance as being similar to a parabola - if indeed that is the case, then moving the Hall sensor away from the magnet face, ie. increasing the gap distance, should reduce the length of on time.

    You are just about there,
    Yaro
    Yaro

    "The Universe is under no obligation to make sense to you." -Neil Degrasse Tyson

  5. #15
    Hi Yaro,

    I am unfamiliar with how distance sensitive Hall devices are with respect to the magnetic field strength needed to trigger them. Also, one can describe that the magnet pole strength as a function of distance as being similar to a parabola - if indeed that is the case, then moving the Hall sensor away from the magnet face, ie. increasing the gap distance, should reduce the length of on time.
    The hall Jules is using is positioned with the back face toward the north poles of the rotor and the sensing face toward the south poles of the magnets. I suspect the north poles are turning the FET on and then when the coils are conducting the south poles of the coils are keeping the FET turned on too long.

    The distance from the magnet does have some effect on how long the hall is triggered on. But it has to be close enough to trigger reliably each magnet pass. The width of the magnet more greatly affects the on time than the distance away does.
    Gary Hammond,

  6. #16
    Senior Member Yaro1776's Avatar
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    Okay Gary,
    Quote Originally Posted by Gary Hammond View Post
    Hi Yaro,



    The hall Jules is using is positioned with the back face toward the north poles of the rotor and the sensing face toward the south poles of the magnets. I suspect the north poles are turning the FET on and then when the coils are conducting the south poles of the coils are keeping the FET turned on too long.

    The distance from the magnet does have some effect on how long the hall is triggered on. But it has to be close enough to trigger reliably each magnet pass. The width of the magnet more greatly affects the on time than the distance away does.
    Good clarification of the Hall operation and distance issue. From a simplified approach the position of the Hall between the coil and magnet appears to be problematic. If as you suggest that the Hall/magnet field is the trigger, then the coil magnetic field is redundant and skews the control aspect in this instance - makes sense.

    I will note that the Hall device position is not centered on the magnets (Page 9 of the SPG.pdf). This vertical position, if varied up or down, should influence the total on time, when taking in consideration the magnetic field shape from a circular magnet (cone) versus a block magnet (rounded rhomboid or something). Why else does the author show the pic and the off center Hall position in the .pdf? Point of max field strength is always the magnet center. All very engaging, but of uncertain value to Jules at this point.

    I believe I am slowly being sucked into this project. Thanks for the diversion.

    Thanks guys,
    Yaro
    Last edited by Yaro1776; 09-03-2018 at 01:04 PM. Reason: Clarification
    Yaro

    "The Universe is under no obligation to make sense to you." -Neil Degrasse Tyson

  7. #17
    Senior Member Faraday88's Avatar
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    Quote Originally Posted by JulesP View Post
    Hi Yaro,

    I can confirm that my cores are all producing inward facing South poles so 'attraction' mode is the way to go. However my Hall sensor seems to have quite a wide angle of response in that it triggers about 15 degrees before TDC and switches off about 15 degrees after. I am therefore going to need to move it quite a bit towards the approaching magnet as indicated in the two attached diagrams I have drawn to show the issue.

    Alternatively, I am quite drawn to the electronic option of setting a time delay from the moment it switches on, and then an off time (hence a pulse width) using the 555 timer chip. Could be a neat option but I will need to bounce some design attempts of a few people

    Jules


    Attachment 7068Attachment 7069
    Hey,
    You can use a Mono-shot or Mono-stable multi-vibrator circuit using the 555 Timer. and set the required delay.
    Rgds,
    Faraday88.
    ‘Mass is spatial density of Matter (Particle) and Temporal density of Space (Field)’.

  8. #18
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    Gary,

    That's an interesting point - that the rotor facing side is turning the current on and then the South pole being created as a consequence is keeping the Hall triggered longer than it would otherwise. I guess this would not happen if the Hall sensor was of a type that only had one main sensing face as I perhaps yours do?

    I am going to try first to move the one sensor to the right, as per one of the two position diagrams I sent yesterday, and see if I can improve matters. If that doesn't work and I can't get the refinement of 'on' time and duration, then I will explore the double sensor arrangement. My coil positions are 72 degrees apart (to an accuracy of about 0.5-1 degree) so I could place the sensors by two different coils and build adjustment into them. I will first draw another diagram depicting that as it helps me visualise the sequence of events and, if I go down this route, will bounce the revised circuit of you. I note from what you say that this method is independent of rpm.

    Jules
    Last edited by JulesP; 09-04-2018 at 01:33 AM.

  9. #19
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    Quote Originally Posted by Faraday88 View Post
    Hey,
    You can use a Mono-shot or Mono-stable multi-vibrator circuit using the 555 Timer. and set the required delay.
    Rgds,
    Faraday88.
    True but it has been pointed out that this will work only at a specific rpm as it is time based. Ideally one wants a distance or angle based method so its independent of rotor speed.

    Jules

  10. #20
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    2 Hall Sensor operation

    Hi Gary,

    I have put together three drawings that simulate your 2 sensor setup and operation so I can figure out the best positions. It seems that my wide 'Trigger zone' will interfere with the clean cut off of sensor 1 at the appropriate moment so I have had to move it quite a lot further round to work. I hope the drawings and text on them are clear and I look forward to any thoughts.

    Jules
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