[TCML] Phase control and cap size

[Andrew Nettles <anettles@xxxxxxxxxxx>]

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.  
 
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.
 
So....I hooked up another 2uf in parallel for a total of 7 but the voltage rises a lot again....say about 10 volts at about 15 percent.   Is this normal?   Of course I'm going to try 6 uf next, but it's starting to seem like it's extremely sensitive to the point that I'm going to have to find some very small sizes of run caps.
 
Also, I'm using a 10A variac until I can get another one.  But if I use a different variac, I'll have to resize the capacitor, right?  I'm wondering if using a smaller variac would make things any easier.  Any input on this?
 
Thanks,
 
Andrew
FW, TX_______________________________________________
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