What's new
What's new

RPC Capacitor help

Kruzzz

Plastic
Joined
Dec 20, 2021
I just built my 1st rotary phase converter 5 horsepower idler motor, load will be leblond lathe 3hp. capacitors I can get to balance at 242 t1t3, 241 t2t3, 241t1t2 voltage but once motor is running they drop down to 230 t1t3 and 231 t2t3 witch make lathe struggle at high speed 1800rpm is that OK or should I up capacitor higher at idle like 251v and then when I run under load it drops down around 240v . I'm afraid of damaging idler motor at 250 V when it is wired for low voltage.
 
Most electronics are designed for +/- 10% in voltage. 110% of 240 is 264volts. Unless your idler is very old or has damaged insulation, you are fine to increase the voltage to 251 ad have it drop down to 240 when under load. It is possible to add capacitors on individual machines so the capacitors voltage boost is only present when that machine is run.
 
Good idea with putting capacitor on independent unit, as for idler motor it is brand new. Thanks
 
I just built my 1st rotary phase converter 5 horsepower idler motor, load will be leblond lathe 3hp. capacitors I can get to balance at 242 t1t3, 241 t2t3, 241t1t2 voltage but once motor is running they drop down to 230 t1t3 and 231 t2t3 witch make lathe struggle at high speed 1800rpm is that OK or should I up capacitor higher at idle like 251v and then when I run under load it drops down around 240v . I'm afraid of damaging idler motor at 250 V when it is wired for low voltage.

You did this backwards. When at RPC idle and no load the voltages should look unbalanced. When machine is on the lines are balanced with capacitors. You are
supposed to balance when the target is running.

This arrangement has worked for several 5 Hp motors over the years. Notice that C-Start minus C-1-to-3 equals 120uF. I use a timed relay to connect 120uf
in with C-1-to-3 for a total of 210uF. Then after a half second the 120uF is switched out and C-1-to-3 is 90uf again. All with oil capacitors.

C-Start = 210uF
C-1-to-3 = 90uF
C-2-to-3 = 50uF
 








 
Back
Top