Re: [TCML] Phase control and cap size

[FutureT@xxxxxxx]

>--- Andrew Nettles <anettles@xxxxxxxxxxx> wrote:

>  
> I'm experimenting with different cap sizes for the
> phase  control circuit of one of those oriental
> reaction motors.  I heard  two different reports that
> a cap size of about 18 or 20uf was about  right so I
> ordered an 18uf.  When I hooked it up I got good
>  phase control but wayyyy too much reso-rise - lots
> of noise, immediate  voltage rise of 10v after barely
> turning the dial.  
 

 
Andrew,
 
There may be different sizes of oriental motors.
The small oriental motor I used needed only about
4 or 5uF for the phase shift capacitor.  Maybe it was
6uF, I don't exactly remember.  The smaller the
phase shift cap, the more sensitive it is (in a way)
to the uF value, since 1uF is a larger proportion of 4uf,  than
for example 1uF is, compared to 100uF for a larger motor.
 

>  
> I hooked up a 5uf and I get about 45 degrees  of
> phase control and the voltage drops.  Around 60
> percent  of the variac dial, I lose sync.
 
If this is an 1800 rpm motor, then 45 degrees of
mechanical phase shift is actually 90 degrees of
electrical phase shift.  This is because four spinning
electrodes are used.  It is not possible to get more
of a phase shift from this circuit.  It's 
normal for the voltage to drop at some point.  
Sometimes sync can be held for the full variac range.
In other setups, it may not be possible.  This is OK,
just don't turn the dial past 60%.  However 6uF, or 
maybe 5.5uF, may do the job for you and give full
variac range.  The amount of phase shift won't increase
however.  
 
I'm not sure if the size of the variac matters.  It seems
to me the inductance of the variac should be about the
same regardless of the size.  I'm not sure about that. 
It seems to me that the voltage rating of the variac would
determine the inductance.  
 
Also, my motor came with a 2uF run cap, which I changed to
a 4uF for more torque if I remember correctly.  
 
John




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