Re: Basic Stamp Controlled Spark Gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ben McMillen by way of Terry Fritz <teslalist-at-qwest-dot-net>" <spoonman534-at-yahoo-dot-com>

Hi Jeremy, Terry,
    Why not use a hall effect sensor? I realize that the
fields we're dealing with here are quite strong, but if you
were to find a sensor that was tolerant of background EM
fields (of the tesla coil type) and use a small neodymium
magnet to get rotor position, you'd essentially have your
'spike' to feed back into the MCU.. The idea here being
that the sensor would only give a 'strong' output when the
magnet passed by.. If you had a strong enough (and small
enough) magnet, and a bit of epoxy..

    I have no idea how feasable this is, or even if those
kind of hall effect sensors exist.. Tesla coil fields may
every well fry one on the first try..


Coiling In Pittsburgh
Ben McMillen


--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Jeremy,
 >
 > Please disregard my last post and this idea.  I went back
 > and checked and I
 > am not sure what the old VI scope picture was.  I redid
 > the test with my
 > big gap motor (1/4 HP 1800 RPM 10 inch disk):
 >
 > http://hot-streamer-dot-com/temp/030513-01.jpg
 >
 > I used much more trustworthy stuff to measure V and I:
 >
 > http://hot-streamer-dot-com/temp/030513-02.jpg
 >
 > This is the motor at start up:
 >
 > http://hot-streamer-dot-com/temp/030513-03.gif
 >
 > Kind of neet!  For the first second while it is spinning
 > up it draws 30+
 > amps!  This droops the voltage but it is still seeing
 > over 100 peak watts
 > during start up.  After the internal centrifugal switch
 > opens, it settles
 > down to this:
 >
 > http://hot-streamer-dot-com/temp/030513-05.gif
 >
 > The current is just a distorted sine wave.  "No" nice
 > spikes to lock timing
 > with!  I was bothered by the old waveform and was
 > thinking something my be
 > screwed, and something was...
 >
 > If anyone is interested, here is a perhaps more clear
 > view of the motor
 > start up and run:
 >
 > http://hot-streamer-dot-com/temp/030513-04.gif
 >
 > And here is a big data file of the data too:
 >
 > http://hot-streamer-dot-com/temp/030513-07.CSV
 >
 > Cheers,
 >
 >          Terry
 >
 >
 > At 09:37 PM 5/12/2003 -0700, you wrote:
 >
 > >Wow that's interesting... looks like a spike from
 > >a triac turning on -- do you use the phase-angle
 > >approach method of controlling your motor speed?
 > >('light dimmer' method...)
 > >
 > >I thought about using the microcontroller to directly
 > >drive a triac. Would start by setting an output high,
 > >which turns on an opto-relay which turns a triac on.
 > >Another opto relay will be in series with the triac's
 > >main gates and when it turns off (AC crosses 0 into
 > >a new halfcycle), we wait a few milliseconds and turn
 > >it on again. That would probably reproduce the wave
 > >form you have. Infact, I bet if I replaced the
 > >RC network in a light dimmer circuit with a pulse
 > >that's just as wide as it's charge time I'll
 > >accomplish the same thing. The trick is starting the
 > >pulse a few ms after the AC crosses 0.
 > >
 > >The new basic stamps support 'interrupts', an
 > >interrupt could be hooked in to run everytime the
 > >AC line crosses 0, (a timing triac turns off) wait a
 > >variable # of microseconds, then set an output high
 > >(turn on load triac).
 > >
 > >So it theoretically could 'drive' the speed of the
 > >motor and it would know exactly how fast it's going
 > >without any mechanical sensors. (Would require some
 > >sort of calibration, linear testing etc...)
 > >
 > >The same type of 'timing' triac could easily be
 > >used across the tank capacitor's drain resistors.
 > >(Turns off -interrupts the stamp- whenever the
 > >capacitor dumps.)
 > >
 > >
 > >--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > > > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 > > >
 > > > Hi Jeremy,
 > > >
 > > > Check this scope capture of a sync motor's voltage
 > > > and current:
 > > >
 > > > http://hot-streamer-dot-com/TeslaCoils/Misc/SRSG-VI.gif
 > > >
 > > > Note the very sharp current spike.  If you could
 > > > pick of the motors current
 > > > and high pass filter and detect the spike, you know
 > > > where the rotor is at
 > > > ;-))  Might be very easy to do...
 > > >
 > > > I could re run this test on my two sync motors just
 > > > to double check and be
 > > > sure if you need.  I could also figure out where in
 > > > the dwell the spike is.
 > > >
 > > > Cheers,
 > > >
 > > >       Terry
 > > >
 > > >
 >
 >


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