- #1
Guineafowl
- 762
- 366
- TL;DR Summary
- How to spec a start capacitor for an asynchronous induction motor, and the consequences of getting the value too high and too low.
A friend has a single phase, cap start induction motor with the following characteristics:
V 240/250
A 2.6
Hp 1/3
Rpm 1435 @ 50Hz
As for as I know it’s not fitted to a machine, but given the low hp rating I’d guess it’s for a drill press. So it would need only moderate to low starting torque. At the moment it won’t start spinning unless given a turn in either direction, and then only spins very slowly.
It’s so old the markings have worn off the original capacitor. Looking at various guides I have suggested a 50uF replacement, rated appropriately for voltage and designed for motor starting. It’s on the higher end of the suggested values.
While we wait for that to arrive, what would happen if the value is wrong? My guess:
Too high - excessive inrush current on starting
Too low - inadequate starting torque.
V 240/250
A 2.6
Hp 1/3
Rpm 1435 @ 50Hz
As for as I know it’s not fitted to a machine, but given the low hp rating I’d guess it’s for a drill press. So it would need only moderate to low starting torque. At the moment it won’t start spinning unless given a turn in either direction, and then only spins very slowly.
It’s so old the markings have worn off the original capacitor. Looking at various guides I have suggested a 50uF replacement, rated appropriately for voltage and designed for motor starting. It’s on the higher end of the suggested values.
While we wait for that to arrive, what would happen if the value is wrong? My guess:
Too high - excessive inrush current on starting
Too low - inadequate starting torque.