Start Capacitor sizing

[ceetee]

I have an electric motor for a heavy duty drill press that is missing the Start Capacitor. The motor runs good and is in good shape, how do you determine the right start capacitor for this motor.

The specs for the motor is:

1 h.p.
60 hz
110/220 volts
16/8 amps
Single Phase
4 pole
Heat 60 deg C
Class A
1720 rpm

Any help would be appreciated!! Thanks

 

[itspcb]

Hi,

I can't tell you how to determine the correct value, but a book I have suggests 50uF/HP at 220V, four times this at 110Volts. It's an English book so probably 50Hz.

In my limited (non-professional)experiance of small motors it's not critical.

Peter B
uk

 

[mpparent]

Well...you need to know your inrush current, full load kVA and starting power factor (any where from .15 to .3 lagging).

Inrush kVA * sin( cos^-1(pf)) = kVAR Cap. required.

Mike

I get 5.5kVAR with some assumptions made.

 

[aolalde]

If your motor has six terminal leads T1,T2, T3,T4 and T5,T8, then your starting winding (T5&T8)always works at 110 Volts. A trial starting capacitor for 1 HP, 60 HZ is 400 uFd.

For operation at 110 Volts, the power line 1 (L1) is connected to T1,T3and T8.
Line 2 (L2) to T2,T4 and T5.

For optimum torque, test the capacitor voltage drop and the starting winding voltage drop when the rotor is locked.
The capacitor voltage drop must be 5 to 10 % larger than the starting winding voltage drop.