Re: [TCML] Phase control and cap size

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

My limited experience tells me that when I did it, the
size and manufacturer of the motor and variac affected
cap size. I ended up with cap sizes that were
sometimes different than what other folks used. I have
dozens of run caps I've collected over the years from
1 uF all the way to 45 or 50, so zeroing in was easy.
Run caps can be found in old refrigerators, air
conditioner compressors, and on the fans for air
conditioners. If you have a metal recycling place, or
transfer station, you might try there. I've also found
air conditioners and refrigerators dumped in vacant
lots, ready to be harvested.

However, mine ended up at 115 uF using a 1/4 hp 1,800
rpm motor with a 120 volt 45 amp Powerstat. At that
size, going up in 1 uF increments was less than a 1%
change, while 1 uF increments for yours is an order of
magnitude larger, on a percentage basis. So it would
seem that yours may well be more sensitive.

Though I've not tried it, microwave caps would
probably work just fine. Given their sizes, they could
help you fine tune.

Adam

--- 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.  
>  
> 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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> 



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