Re: [TCML] SRSG's Helping them to synch up, was; new video - feedback welcome

[futuret@xxxxxxx]

Steve,

It's good you found out for sure that the motor was not
synching, and that the higher voltage caused it to synch
at the required 1800 rpm.

If you set up the electronic phase shifter circuit, that alone
may cause the motor to sync up (to reach 1800 rpm).
I've heard reports of the phase shifter giving a little extra
voltage boost due to resonance and making motors synch up,
which were otherwise not able to sync up (which were not
otherwise able to reach 1800 rpm).  So the use of the phase
shifter circuit might solve all problems for you.  You should
probably try this first.  If it still doesn't lock, I mention some
other techniques below.

Another approach that can help is to increase the size (value)
of the motor run capacitor which comes with the motor.
This was probably a 2uF cap for your motor.  If you increase
this to 3 or 4 uF, this might make the motor reach 1800 rpm,
(even without using the phase shifter circuit).

Still another approach is to simply run the motor on a 140 volt
variac all the time.  If desired, you can reduce the voltage back
to 120 volts after it reaches 1800 rpm.  Motors require more
voltage to lock to 1800 rpm than is needed to *hold* them
at 1800 rpm.  It probably won't drop out of sync until the
voltage falls to 70 to 90 volts or so.  For short runs, the
motor can withstand 140 volts of course.

Still another approach is to add a small 24 volt boost
transformer to one side of the line properly phased to
give a 24 volt boost over line voltage.  This method has
been used with success by other coilers, and is a common
method for obtaining higher voltages.

You said you need 90% on the variac to lock the motor.
The 120 volt position is usually at 82% on the variac.
This suggests that you need about an 8% higher
voltage.  If your line voltage is 120 volts, 8% higher
would be around 130 volts.  You probably need an
extra 10 volts.  Off course it's desireable to use a
little extra voltage (beyond that) to insure reliable lock up.
As I mentioned above, the phase
shifter circuit alone may solve all problems.  (give reliable
1800 rpm lock-up, and permit easy remote phase adjustment.)
If it still doesn't lock (synch), then you may need to add one
or more of the other techniques I mentioned above.

John
--------------


-----Original Message-----
From: Stephen J. Hobley <shobley@xxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Fri, 29 Aug 2008 11:27 pm
Subject: RE: [TCML] SRSG new video - feedback welcome



On the recommendation of a group member that my AC line voltage may 
well be
below the 120v normal; I hooked the motor up to the Variac and this 
time flipped
the output switch to 140V. Turning through the variac gave me the usual
"hunting" sounds but then at about 90% it stopped hunting and gave a 
continuous
tone - this looks like the 'sync' I need. So I guess my original SRSG
configuration is not really an S-RSG after all.

I need to get the AC voltage up to whatever the 140V setting on my 
Variac is
putting out to get this motor to run synchronous.

The Terry filter safety gaps where definitely firing on Thursday night, 
there
are some nice black circles on the brass spheres.

Thanks for all the feedback from the list - it really helps.

Steve

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx on behalf of bartb
Sent: Fri 8/29/2008 9:45 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] SRSG new video - feedback welcome

Hi Steve and Pete,

I'm inclined to agree with John F. The motor sounds as though it's not
synchronous. The pulsing is a little faster than I'm accustomed to
hearing, but your at 50Hz I think, so it would be a tad faster. The
pulse is very steady and it doesn't sound like the gap is hunting.
Hunting occurs in a synchronous gap when the motor torque is not quite
enough to keep the disc rotating (due to the weight of the disc). But
usually this type of pulsing is slower. This sounds like the gap is
asynchronous and running maybe 1450 rpm. The reason is the pulsing and
because I hear another much lower frequency in there as well as though
the rotary is running through peak, across zero, back up to peak, etc..
over a slow period of time (like 6 cycles over the period of the video,
thus 12 occurrences as the half cycles are what is heard). Are you sure
this motor is synchronous? Is the an off the shelf sync motor or a
home-brew type?

Regards,
Bart

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