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Thread: Quick hall effect sensor + mosfet conversion to sg wheel

  1. #11
    the monostable circuit is useless, the input pulse duration affects the output pulse duration, back to the drawing board

  2. #12

  3. #13
    sucess, variable pulse width and timing, mosfet driven simply from optocoupler but not yet ready for high voltages, it produces the biggest spikes, and i cant dampen them enough with a battery to stop the neon protection on the mosfet from staying on, without the battery the neon is not yellow but bright blue / white.
    the wheel spins a reasonable speed with a very small duty cycle at around 200ma including the switching and i only have a single coil winding out of 8 connected (140ft x 0.5mm)

  4. #14
    I always thought that one of the essential essences of the SG is that it does not need or want a Hall sensor. Am I wrong?

  5. #15
    Quote Originally Posted by wrtner View Post
    I always thought that one of the essential essences of the SG is that it does not need or want a Hall sensor. Am I wrong?
    In a way you are spot on it is a 'school girl circuit' a bit sexist i suppose! however i think the idea was to create the "effect" as simply as possible, anyone can create the SG circuit without any electronics knowledge at all, making a good setup with a hall or optical really needs a scope and some basic electronics knowledge.
    the amount of inductive kickback with this circuit is higher than i have seen with any inductively triggered circuit (on the same spool).
    JB says that you have to build at a higher level if you want to go further, the sg is just a simple introduction to the idea.
    I will post my final simple schematic so everyone can have a go, my first one was incomplete so dont bother with it.

  6. #16
    i have been doing a few experiments just now, i have to say MUCH better with hall switching to see what's going on, you can pick a point on the magnet to look, and monitor output on the neon and battery input / output
    just tried some coil shorting which i have not been able to do until now, and have seen the sec battery charge with it with just a spin of the wheel by hand. might have to put in a reverse diode see if i can get the current loop.
    also have seen energy flowing back in little blips on the scope when the power is turned off, dont really know whats going on there, sometimes its high as half the supply voltage for an instant and then drops down to a volt, you put the wheel in a different place and it changes instantly not sure whats going on there yet.
    the coil shorting is interesting shows the forces at work "inside" the coil you can see the current flowing on the needle in reverse, and how different switching positions affect it.

  7. #17
    well thats the end of the mosfets thought they would last longer than that, not really sure what killed them, they were running cold and the wheel going well untill missed a few beats and then nothing...
    i stopped the neon lighting up using a full bridge, it seems without the trigger windings dampening the spike, it was no longer one sided. maybee to late for the mosfet...
    has anyone here got knowledge of gate drivers? im currently running strait of a h1d1 optocoupler into the mosfet gate clamped down with a 10k resistor, i have some bdc243c transistors and i have seen those on the back end of a cap dump circuit being used to drive the gates, anyone help?!

  8. #18
    Improved the mosfet driving circuit with a Darlington paired optocoupler h11d1 and bd243c and heavy resistor pull down loading, now getting square edged hits, replaced the mosfet with 600v rated coolmos pulled from a server grade PSU and installed pulse discharge capcitor on supply rail. its cranking FAST.
    200ah battery pushed from 12.7 to 12.9 in 25 mins under 800ma load and a 15 - 20 percent duty cycle, i have all the windings on the core parallel for now before i insulate for HV and run them in series.

  9. #19
    Hi Brain,

    Quote Originally Posted by Gary Hammond View Post
    Hi Brian,

    Give me a few days and I can post a schematic of what I did. I'm currently away from home on a mini vacation and posting this from a motel room using my wife's laptop.

    Back from vacation now, so here's the schematic of my circuit using two hall switches on two small PNP tranistors to trigger the five MJL21194's. The hall's are mounted separately for adjustability, but both are triggered from the south pole of the same magnet whose north pole is approaching the coil assembly at that same time.

    Hall Switched SSG.JPG
    Attached Images Attached Images
    Last edited by Gary Hammond; 09-05-2014 at 12:54 PM. Reason: added a more correct drawing showing neons
    Gary Hammond,

  10. #20
    Mosfet driver working really nice by the help of krill, got rid of the curve at the bottom of the square on the trailing edge, by using a transistor to short the gate / source
    i decided to finish the isolation and build a simple hv psu out of some junk computer bits and a vairac.
    made an air coil out of a full spool of copper, and joined it up, not going to give the best capacity either.
    turned it on and it worked first time, i can run from anywhere from 0 to 240v. most i have gone is 130 at the moment, mosfet temp is a reasonable 35 degrees C. most ive pulled from the mains is 98 watts!
    efficiency is not good, i need either a core in there or some powerful magnets and a flat coil. im going to series link an old 8 filler with a core and should work MUCH better.


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