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

["" <dr.hankenstein@xxxxxxxxxxxxx>]

I had the same problem with my modified "1725 RPM" 3phase 1/2hp motor on Zotzilla...Not sure if I machined too much off of the rotor. The problem became more pronounced after I changed out the rotating electrodes from brass to much heavier tungsten. I suppose the additional "load" of the heavier tungsten electrodes caused the rotor to lag somewhat causing "slip" of the rotor. I noticed high current surges or pulses as the rotor was trying to lock up. I ended up bolting a box to the RSG frame which houses a "boost" xfmr and a DC relay with a large electrolytic. The boost xfmr/relay/electrolytic combination provide about 2 seconds of 280VAC to help start the motor. The motor load current actually exceeds the nameplate rating until the relay drops off; then restores to normal FL rating at 240VAC. Turning the motor start/stop switch on and off when the motor reaches near synchronous may also help lock it in. I have not tried the phase shifter because my motor has rubber mounts which allows me to change the "timing" on the fly, kind of like an old car with a conventional distributor...works well.

Picture of my RSG setup:  http://www.audiotesla.org/images/Zotzilla%20Pictures/zotzilla%20web%20images/IMG_5056.jpg

Regards,
Woo


> [Original Message]
> From: <futuret@xxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Date: 8/30/2008 10:43:43 AM
> Subject: Re: [TCML] SRSG's Helping them to synch up, was; new video - feedbackwelcome
>
> 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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