Re: motor questions for RSG

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi John,

At 12:15 AM 8/6/00 -0500, you wrote:
>
>Hi again,
>
>	I Hate to be a pain about this but I would rather not do all the work of
>cutting into a motor to make it salient only to find out I should have
>gotten something else.  

No problem, Making sync motors is easy the "second" time, but the first
time is sort of scary...

>I have found some good prospects at ebay (thanks for
>the tip Pholp).  Some of these motors are 1725 rpm (just what I want) but
>some say CW or CCW rotation.  If I make it salient will it still perform
>this way and if so is this defeating me making it salient (so I don't have
>to rotate the motor in a cradle every time I fire up the motor)?  I did not
>see any starting cap on pics of any of these CW - CCW motors.

The direction of rotation does not make any electrical difference.  Many
motors can be easily jumpered to change the rotation direction.
However,...  If you use a center bolt like my gaps do, it is best to have
the direction of rotation CCW when looking at it from the front.  Thus,
when the motor suddenly starts, the bolt will tend to be tighten instead of
loosen. 

>	I remember reading a post from the archives where the writer recommended a
>capacitor start, induction run motor with ball bearings to use to modify to
>be salient.  I think the author said he was the person who in 1975 came up
>with the idea of grinding flats on a non-salient motor to make it salient.
>Is this recommendation still a good one?  There are many motors on ebay but
>I haven't seen any that specified 'ball bearings'.

I think Bill Wysock was the pioneer here.  Ball bearing last longer, but
for most of us, the sleeve bearing will last just fine.  Bill's coils have
lasted longer than many of us have been alive so he is really careful to go
with the best.  "i" like sleeve bearings because they can take a bearing
arc and survive quite well.  Ball bearings will quickly grind themselves up
if they get a weld spot.  But that is just "my" humble opinion.  

I don't know why capacitor start is recommended in "the" plans.  All my
motors are centrifugal switch start and they work fine.  Maybe cap start
motors have a more gentle starting torque??

>	As far as HP goes.  I would be using a 6" diameter 1/4" - 3/8" thick disk
>(material unsure as of yet maybe Plexiglas since I have this already) with 4
>electrodes on it.  I know John Freau has modified some very small HP motors
>and is running 5" or 6" disks just fine.  What minimum HP would you
>recommend to use to drive something like what I just specified?

My 1/4 HP gap motors seem to have wildly more power than is needed.  I
would avoid Plexiglass since it can easily shatter into nasty pieces.  I
would use G-10 or LE phenolic or lexan.

>
>
>P.S.  Would 1/4" thick, 6" diameter Plexiglas with 4 electrodes mounted 2.5"
>off center sound ok to use at 1800 rpm?  I will be running it with one 15/30
>NST and may try to in parallel later so I don't need a material that will
>have super hot arcs from pole pigs running by it.

You need to be sure the conductors cannot arc to the center shaft.  For 15
kV I would try to clear the center bolt to HV conductors by 1.5 inches.

I have a bunch of old pics of my big gap at:

http://users.better-dot-org/tfritz/RGAP.ZIP

They are not the best pics...  I will try to take new ones with my fancy
new camera and include my new gap too...

Cheers,

	Terry

>
>Thanks everyone,
>John M.
>