Re: Poor mans SRSG? Adjusting SRSG without Variac?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Bill,

At 01:23 PM 1/7/2001 -0500, you wrote:
>Without access to a machine shop, is it feasible to do the motor
>modification to convert an AC motor (1725 rpm) to salient pole
>synchronous (1800 rpm)?  What's the minimal set of tools required to do
>the job?

I just ground the flats with an angle grinder on my sync motors.  Works
fine as long as you try to remove equal amounts of metal so as not to upset
the balance too much.  This works better on 1800RPM motors as opposed to
the more trick 3600 RPMs.

It "can" be done with a big file if you have really big arms ;-))

Here are some snips about this since pupman-dot-com is down (grrrr...)
-------------------------------------

I just cut the flats on mine about an hour ago...

Mark the areas on the rotor you want to cut (or save) very clearly with a
black marker or something.  

Then cover the shafts and all the parts of the rotor (except the areas you
want to cut with plastic tape to protect them from the metal dust.  

Clamp the thing in a vice so it is solid.

Go rent, borrow, steal, or by an angle grinder.  It has a heavy duty
flexible grinding wheel 90 degrees to the motor.  It is a hand held metal
cutter from heck.  See you Sears catalog for details.  Get a couple 60 grit
(or close) grinding disks for it too.  You can file the flats by hand with
a file but it will take four years.  The grinder takes 1/2 hour if you go
slow.  Motors are pretty basic iron things and you really can't screw up.

Simply grind off the flats taking care to keep the grind flat (hold it
level) and stay within your cutting area.  Don't push hard and just slide
the cutter over the area in sort of a brushing motion.  It is really easy
and if you try to remove equal material, it will stay balanced and all just
fine.  When in doubt, cut less rather than more.  You can practice on any
chunk of metal.

The rotor will get hot so you may have to let it cool down between cuts.

Simply remove the tape, clean it up, and your done.

I had to add a shim to my motor because the shaft could move back and forth
more than I liked.  Mine used a 5/8 inner diameter fiber washer I found at
the hardware store.  It was only about 1/32 thick but it removed all the
play from my motor's shaft perfectly.  I just powered my motor up and it
runs perfectly and is in sync.  The current draw is 4.7 amps and the motor
is rated for 5 amps so it runs fine.

1800 RPM motors really don't turn fast enough to have to worry too much
about balance as long as your careful.
-----------------------------------------

Hi All,

	When I ground off the flats on my 1/4 HP A.O. Smith motor (they make nice
motors), I added a 5/8 inch inner diameter fiber washer to the shaft shims.
 This was to be sure that the shaft would not have a lot or back and forth
play.  Having the shaft able to move back and forth is not good for precise
gap spacing ;-).  It worked very well and I am able to set the gaps very
close without having to worry about them knocking.  I recommend shimming
the rotor shaft to remove the end play on sync gap motors.

Once again the angle grinder was able to grind the flats in the motor
without adding noticeable vibration.  As long as one is careful not to
upset the balance, this seems to work just fine.

I really like rounded tip electrodes too.  If the tips hit, the rounded
ends will slide off each other with no damage.  If they were flat, it would
break something...
------------------------------------------------------------



>
>Also, if I did manage to do the modification, is there some way to get
>by without a variac, as far as adjusting the spark gap is concerned?

You can put like a big light bulb or other low value "resistor" in series
with the NST to drop the voltage and the NST terminals.  Others may have
better ideas here...

Cheers,

	Terry

>
>	Thanks, 
>	Bill Vanyo  (planning first coil)
>