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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