Hi Dave
Sounds good but I have three thoughts:
#1) - will the hall effect sensor work reliably with all the high current
(stray magnetic fields) around it? I would go with optical.
#2) - if you try to sense each of the six electrodes, you will not get the
absolute position of the shaft. You should go with one output per rotation.
#3) - switching the NST by the computer. What happens if the computer fails
with leaving the NST in the on position? I would program the CPU to deliver
a stream of output pulses (100Hz or so) and these would be fed into an
external circuit. If the pulses stop, the external circuit would trigger an
e-stop.
Dave
> -----Original Message-----
> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Dave Boyle
> Sent: Friday, September 19, 2014 06:07
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] Resin or fibergl - motor controller ideas
>
> We're all on the same page. I have a Cortex M0 based
> microcontroller and
> I'm setting up a system for assembly language programming
> using mcu on
> eclipse. I have an optocoupler that I will protect with a series
> capacitor and connect to the ac line to get a pulse stream of 120 per
> second. I'll get a hall effect sensor that will hopefully detect my 6
> copper clad tungsten electrodes spinning on my disk. If not
> then I can
> embed some bits of metal in between the electrodes which is
> where I need
> them anyways. Now I have a second stream of pulses that I can
> speed up
> and slow down by outputting to a power control device like
> the vfd. My
> algorithm will be based on a division by six but there will
> be lots of
> other things to do as well. I'll switch my nst's by a solid
> state relay
> so if the mcu ever fails they will disconnect immediately.
> This should
> become the standard method of phase syncing any motor into
> synchronous
> action. If I had a lab full of scopes and test equipment I
> might try and
> do the same thing with a cmos phase locked loop that sells
> for 29 cents.
> But I like the control that I get with an mcu.
>
>
> On 09/19/2014 12:55 AM, Dave Halliday wrote:
> > John was saying that if the Bodine motor was a hysteresis
> type synchronous
> > motor, it would lock in to one of a set of stable phase
> positions. (And
> > regardless of what type it is, Bodine is the go-to standard
> for bullet-proof
> > motors, great score!)
> >
> > If you were using the closed-loop controller, you could
> compensate for this.
> >
> > Your inputs would be
> >
> > #1) - the encoder on your motor shaft (paint a section of
> the shaft black
> > and put a dot of white paint on it and use an
> opto-reflector sensor to read
> > the difference)
> >
> > #2) - the incoming power frequency. Your Arduino is going
> to require power
> > so just tap this off the power supply before rectification
> and filtering.
> >
> > Your control would be a pot to adjust phase.
> >
> > Your output would be the control voltage to the VFD
> >
> > The Arduino would detect motor start and it would output
> the last known
> > control voltage (the value being read from non-volatile memory)
> >
> > It would find the difference between the incoming power
> frequency and the
> > output rotation of the motor and increment a counter to
> bring these into
> > sync. Counting to 3,600 would get you accurate to a 10th degree.
> >
> > Allowing for the mechanics to stabilize, I bet that you
> could have a perfect
> > gap within thirty seconds of starting the motor.
> >
> > Also, I would not use the Arduino for controlling the coil.
> With this much
> > power, relays, e-stop buttons, crowbars and deadman
> switches are a lot
> > better to use. A buggy line of code should not result in an
> injury or
> > worse...
> >
> > Dave
> >
> >> -----Original Message-----
> >> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of
> >> Dave Halliday
> >> Sent: Thursday, September 18, 2014 20:37
> >> To: 'Tesla Coil Mailing List'
> >> Subject: Re: [TCML] Resin or fiberglass perfboard for terry filter?
> >>
> >> And the three-phase motor in this case is being driven by
> a ' vfd '
> >>
> >> These are wonderful devices which take in single phase AC,
> >> rectify it and
> >> spit out three phase AC at variable frequencies (not just the
> >> plain old
> >> 60/50 Hz).
> >>
> >> The advantage with these is that when you are running
> >> machinery, you get
> >> almost full torque over the entire speed range. Using a
> >> variac to control a
> >> motor gives some variable speed capacity but the torque curve
> >> is horrid.
> >>
> >> Most vfd (variable frequency drives) have a control voltage
> >> input so you
> >> __might__ be able to do a loop - put an encoder on the motor
> >> shaft and use
> >> an Arduino to generate the control voltage to keep the motor
> >> in sync with
> >> the powerline frequency. You could implement variable phase
> >> with a counter.
> >> That might be a really cool project...
> >>
> >> Dave
> >>
> >>> -----Original Message-----
> >>> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Phil
> >>> Sent: Thursday, September 18, 2014 02:57
> >>> To: 'Tesla Coil Mailing List'
> >>> Subject: Re: [TCML] Resin or fiberglass perfboard for
> terry filter?
> >>>
> >>>>> " The motor is a 3 phase 208v 1/2 horse driven by a vfd.
> >>> Does it make
> >>> sense to grind flats on it's armature?"
> >>>
> >>> DON'T try grinding a three phase motor, AFAIK that only works
> >>> on single
> >>> phase units
> >>>
> >>>
> >>> Regards
> >>> Phil Tuck
> >>>
> >>> www.hvtesla.com
> >>>
> >>>
> >>>
> >>>
> >>> -----Original Message-----
> >>> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of
> >> Dave Boyle
> >>> Sent: 18 September 2014 02:38
> >>> To: tesla@xxxxxxxxxx
> >>> Subject: Re: [TCML] Resin or fiberglass perfboard for
> terry filter?
> >>>
> >>> The motor is a 3 phase 208v 1/2 horse driven by a vfd.
> Does it make
> >>> sense to grind flats on it's armature?
> >>>
> >>>
> >>> On 09/17/2014 08:50 PM, David Speck wrote:
> >>>> Dave,
> >>>>
> >>>> "Pretty close" is not good enough. When your gap drifts
> >> far enough
> >>>> away from optimum synchronization, the NST will fail permanently.
> >>>>
> >>>> Look at the old posts that describe how to file flats on a motor
> >>>> armature to convert it to a fully synchronous motor.
> >> Then, you can
> >>>> use a Freau phase adjuster to precisely set the phase
> >> angle of the
> >>>> motor without having to mechanically rotate the motor body.
> >>>>
> >>>> (Another) Dave
> >>>>
> >>>> On 9/17/2014 7:12 PM, Dave Boyle wrote:
> >>>>> Oh now you tell me! Hey what about if I operate my spark
> >>> gap motor in
> >>>>> the synchronous zone? At 1 or 2 beats per cycle with the
> >>> nst switched
> >>>>> off while the motor changes speeds? I have an led strobe
> >> synced to
> >>>>> the ac line light that I use to see when the disc is at
> >> the right
> >>>>> position. I can't get a phase lock but I can keep it
> >> pretty close.
> >>>>> Maybe I should build a custom inverter that will run the
> >> motor at
> >>>>> only those speeds that are safe.
> >>>> _______________________________________________
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