RE: SRSG motor modification

["Colin Dancer" <CMD-at-datcon.co.uk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

>From the pictures on your website I'd say you've made a really good job of
the modification.  If the "hunting" noise doesn't occur until you add quite
a bit of load, then I wonder whether you motor is already attaining lock.
For the longest time I thought I'd failed with my first mod until I realized
that the problem was with my strobe!  What are you using to determine if
you've achieved sync?

With regard to the capacitor, as you say, it phase shifts the current in the
secondary windings.  This creates a rotating magnetic field which is key to
starting the motor, but if left connected also gives increased torque across
the whole range of speeds.  The optimum value of capacitor is one which
phase shifts the second winding by 90degrees relative to the first, and the
calculation of this value is very similar to the way PFC capacitors are
calculated (i.e. balancing the impedance of the winding against the
impedance of the capacitor).  

Colin.

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: 10 August 2000 01:04
To: tesla-at-pupman-dot-com
Subject: Re: SRSG motor modification


Original poster: "Garth van Sittert" <garth-at-mediasupplies.co.za> 

Thanks everyone for the replies!!

I tried a 20uF and then 40uF and 68uF but no luck.  The motor certainly did
spin up faster though at the expense of drawing about 5A while running.

Yes I was pondering the same thought about the wwwwWWWWWwwwwww noise (as you
so aptly described).  That noise occurs only if I load the motor quite a bit
by holding my hand around the spindle. (Very dangerous as the electrodes are
1/2 inch from my fingers and at that rpm ......).

How does the cap size affect the motor once it is running at full speed.  I
thought it only effects startup torque.  Or does it phase shift the smaller
windings during a run for more 'synchronous' control.

The pictures are now up for anyone to see if I am doing something wrong.
http://teslacoil.8k-dot-com

Thanks again for all your replies.  And many thanks to kVA effects for the
excellent graph and explanation on the 200+ BPS.

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 09, 2000 8:10 PM
Subject: RE: SRSG motor modification


> Original poster: "Colin Dancer" <CMD-at-datcon.co.uk>
>
> I'd second the suggestion to use a larger capacitors, but you need to be
> careful not to go too far.  If you make the capacitor too big, you can end
> up with the phase in the secondary winding nearer 180 degrees out of phase
> rather than the 90 degrees intended.  I found that with a 20uF capacitor
> (rather than the 4uF original) my motor ran raggedly at 1500 rather than
> 3000 rpm!
>
> If you motor is close to but not quite locking it should be making a
whining
> sound with a 0.5s - 3s period (as it gets near to lock and then slips).
>
> Kind of like,   wwwwwWWWWW.....wwwwwWWWW......wwwwWWWW....  :-)
>
> If that's the case, then it might be worth trying to get an lock using a
> variac to boost the initial voltage.  I found only an extra 30V was
required
> to get my 1/4HP motor to lock with a 6"disc, and after lock I could reduce
> the voltage back to 240V.  It's also worth trying for a lock without your
> disc attached.  If it won't lock with no disc then it's never going work
> when you add the extra drag of a rotor plus flying electrodes.
>
> Regards,
>
> Colin.
>
> P.S. A number of the images on your website seem to be zero length files
and
> I wasn't able to load the picture of your motor.
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: 08 August 2000 18:41
> To: tesla-at-pupman-dot-com
> Subject: Re: SRSG motor modification
>
>
> Original poster: FutureT-at-aol-dot-com
>
> In a message dated 8/7/00 4:47:35 PM Pacific Daylight Time,
tesla-at-pupman-dot-com
>
> writes:
>
> > Original poster: "Garth van Sittert" <garth-at-mediasupplies.co.za>
> >
> >  Thanks for replying.
> >
> >  The motor is 1/4 HP or 180W
> >  2850 rpm 50Hz
> >
> >  My armature measures: 4" long,  2" diameter.
> >
> >  The 2 flats I have made are 1" wide.
> >
> >  I have pictures of it at http://teslacoil.8k-dot-com/spark_gap.htm
>
> Garth,
>
> I tried looking at your webpage, but the pictures didn't load for
> some reason.  In any case, I'm thinking that maybe you need
> to use a larger capacitor than 6uF,  you could try larger ones
> such as 10uF or 20uF, and see it that makes it lock up OK.
> The flats should be plenty deep enough the way they are now,
> by the way.
>
> Cheers,
> John Freau
>
>
>
>
>