Re: SRSG Newbie questions

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 6/1/00 11:39:26 AM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original Poster: "Bob Berg" <berg_bob-at-hotmail-dot-com> 
>  
>  Hello,
>  I'm preparing to build a SRSG that can handle up to 2 - 2.5 KW:
>  
>  What determines the diameter of the disk I should be spinning? I have seen 
>  many in the range of 7" - 12"  Which size is correct?
>  My next question is about motor HP.  How much HP do I need? I have a 1/4HP 
>  Reliance Cap start ball bearing motor.  It is rated at 3440 rpm -at- 60Hz. If 
I 
> 
>  make it syncronous through amature modification I know I will lose some 
>  torque, but is this  a good choice for a motor?  Or should I be looking 
for 
>  something bigger?   By the way the armature diameter is just about 2" if 
>  that means anything.
>  I also have a split phase (no cap)  , 1/2 HP  bushing motor - is this a 
>  better choice? Can split phase motors be modified the same way?

Bob,

Either motor can be modified and used for your gap.  The larger the 
rotor, the larger the motor must be.  Also the heavier the rotor, the
larger the motor must be.  Air resistance against the rotor and 
electrodes plays a big part too.  If the electrodes are large and/or
heavy, the motor must be stronger.  Also the speed is a factor,
the higher speeds may need more power to fight the air resistance.
The number of electrodes is also a factor; more electrodes = more
weight and more air drag.  The cap start motor will have more power
available to spin up the rotor I suppose.

The rotor can be large or small, but if small, you have to consider
the possibility of flashover between electrodes and hub, or the motor
itself.  For a 1/4 HP motor, I like to use a 8.5" to 9.5" rotor.  I often 
use 3/8" Lexan for a rotor because it's light and easy to work.  However
you have to make sure it doesn't get too hot in operation because
it will melt around the electrode pass through holes.  If you place
a metal ring around the rotor edge, it will dissapate some of the heat.
Also, small rotors have a longer dwell time, see below.

I would use 1/4" electrodes, or 3/8" electrodes for that power level.
If you use G-10, you may want to use the 3/8" thick type, or perhaps
the 1/2" will not be too heavy.  

The 3600 rpm speed is good, because it keeps the dwell time 
shorter, so there's less concern about "re-firing" while the gaps are
aligned.  The smaller your capacitor, the more of a concern 
re-firing is.

I use a 1/4 hp split phase motor (modified to make it sync), and I spin
a 9" lexan disc with up to (8) 3/8" steel spinning electrodes, and it 
locks up easily.

My other sync gaps are at:  
                   http://members.aol-dot-com/FutureT/
and at:         http://members.aol-dot-com/FutureT/TT-42index.html

Cheers,
John Freau