Can I Use Any Capacitor as Long as It Has the Same Capacitance?

The question was "I lost a capacitor during maintenance of equipment that uses a single-phase power motor, and I want to use a capacitor I have on hand to replace it. Would that be okay?"

Was the capacitance of the capacitor to be substituted is same as the original capacitor?

Yes, I've checked the capacitance of the capacitor. They had one with the same capacitance as listed on the motor nameplate. If the capacitor's capacitace is large, the vibration and heat generated by the motor will increase, and if the capacitor's capacitabce is small, the motor's torque will decrease.

That's right. There are some other things you should confirm about the capacitor though. Do you know what they are?

Eh! Is there something else to check? The specification list in the catalog only listed the capacitor capacitance (μF), so I thought I could use it as long as the capacitance was the same, but is that not the case?

To be honest, it is better to use the same capacitor that is included with the motor, but if you have no choice but to use a capacitor other than the one that was included with the motor, you need to use a capacitor with the same rated voltage as well as capacitance. Using a capacitor that exceeds the rated voltage may cause damage to the capacitor and lead to heat generation and fire.

Rated voltage? Is that the same as the motor's power supply voltage?

No, it's not. Listen very carefully. Single-Phase power motors use a capacitor to create a phase-difference power supply to rotate the motor. In this case, the phase difference voltage would add voltage of about 1.5 to 2 times the power supply voltage between the capacitor terminals.

That's no good. That would destroy the customer's capacitor. What should we do? I will contact the customer immediately.

The capacitor that is originally attached with the motor is selected to ensure the best performance of the motor, so the customer can use it with confidence. The product names of the attached capacitors are also listed in the general catalog (see figure below). If the capacitor is lost, damaged, or needed for maintenance after purchasing the motor, be sure to let them know that we also sell capacitors only.

I understand. I will keep the rated voltage in mind from now on.

We also get a lot of questions relating to capacitors like "I wired the motor according to the connection diagram, but the motor won't start. But when I turned the shaft by hand, it started moving in the direction I turned." Vex, can you answer why that is?

Eh? I'm not sure.

In such cases, I ask them to check if there is poor contact or disconnection in the capacitor section, and as a way of finding that out, I ask them to measure the terminal voltage of the capacitor to see if it is at least 1.5 times the motor power supply voltage. If it doesn't increase 1.5 times or more, there is possibility that the capacitor is not working properly.

I see!

We also sometimes receive inquiries like, "Do I need a capacitor to use a motor that rotates in one direction?" In such case, please tell them that capacitors are always required for setting the starting torque and rotation direction.

Capacitors are surprisingly hard-working, aren't they?

For single-phase power motors, capacitors are indispensable.

Yes! I'll also do my best to be indispensable to my customers!