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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