"Ignoramus19023" wrote in message
.. .
I am considering adding some run capacitors to my self starting RPC. I
am reading Jim Hanrahan's article at

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

and I am confused by something. I understand how self starting
RPCwould start with one cap between one leg 1 and leg 3 (the generated
one). That's how mine is wired. Jim makes a point that it works, but
makes unbalanced voltage.

But why would it start is capacitors are connected between 1-3 AND
2-3, like in this pictu

http://www.metalwebnews.com/howto/ph-conv/fig1.html

I cannot see how it would create assymmetric fields needed to spin up
the motor. Is that because capacitances across legs 1-3 are greater
than capacitance between leg 2-3?

I could try to use run caps at run time and start caps at start
time. In fact, I won a time delay relay for $9 on ebay yesterday, so I
could set the RPC to start on start cap (both caps between leg 1-3)
and then reconnect the same caps to become run caps, one between 1-3
and another between 2-3. Same TDR could, then, turn out output current
aftet time delay, allowing the RPC to spin up and switch to the run
mode.

As you can see, I am quite confused, but am willing to experiment. I
have 4 unused Furnas 75 A contactors that I can wire, with the time
delay relay, to do just about anything.

Idler: 10 HP

Capacitors: 92 mF each, 535 VAC rated, oil filled. I have 5 total, and
use 2 for the starting leg, so three are unused.

i

You are correct saying that it's because the capacitance between 1 + 3 is
higher than between 2 + 3.
My RPC, 10HP 440V 50Hz motor, has 40uF between 2 + 3, 60uF between 1 + 3 and
500uF switched by a start circuit between 1 + 3. The 500uF is a bit too
much, it starts very quickly (around 1/3 second) so I could probably drop
that to around 200uF.
Martin

--
martindot herewhybrowat herentlworlddot herecom