Starter Capacitor FAQ
Having trouble with your motor? If your motor is slowing down or simply not turning on anymore, it might just need a new starter capacitor. TEMCo is the place for all of your starter capacitor needs!
Get Factory level pricing! Most models of Starter Capacitor stocked for Same Day Shipment.
What is a Starter Capacitor?
Starter capacitors are what let a motor start up instantly instead of taking minutes to warm up before it can be used. The start capacitor quickly brings the motor to 3/4 of full speed and then is disconnected. Starter capacitors are designed to be used for only a few seconds.
Single phase motors have both a run and a starter capacitor. The starter capacitor has a much higher capacitance rating, or ability to store charge, for its size than the run capacitor does. The starter capacitor is what initially starts the motor, while the run capacitor is what keeps the motor going.
How do I select the correct Starter Capacitor for my needs?
The majority of starter capacitors will come with specs in the same range:
- Voltage – 110/125, 165, 220/250 or 330 VAC
- Frequency – 50 or 60 Hz
- Capacitance – 50 to 1200 uf
When replacing a starter capacitor, the same capacitance and frequency as the original capacitor must be used. You can choose a new capacitor with a voltage that is in the range of the operational voltage of the motor; a capacitor will have a marked voltage indicating peak voltage acceptable. Starter capacitors will have either a black plastic or phenolic case, thought this will not have any bearing on how well the capacitor will work. The starter capacitor will also have a recessed top where the connections are located.
How do I replace a start capacitor in my single phase motor?
View our video tutorial below for an in-depth explanation on how to troubleshoot start capacitor problems your single phase motor.
What is a Bleed-Down Resistor?
View our video tutorial below to learn about start capacitor resistor applications.
What else should I know about Starter Capacitors before I buy one?
Due to the quick burst of energy the starter capacitor is designed to produce, burn outs can sometimes occur. If your motor is either not turning on at all, or is slow to start, these are two easily identifiable signs that the starter capacitor is not functioning normally. In the event that the motor is simply slower than usual, overuse and age may have caused your starter capacitor to lose its capacitance rating. It is possible, though, that you may have other issues with your motor that have nothing to do with the capacitor. Due to the relative ease and low cost of replacing a starter capacitor it is a good place to start, as it may solve your problem with little hassle.
The starter capacitor may, in some cases, overheat and/or rupture. One cause of this may be overvoltage, where a sudden surge of voltage will cause a buildup of pressure. In other cases, as relays open and close, electric sparks can cause the contacts to stick together. This is known as a sticking relay, and it can lead to failure if the starting circuit is left energized too long, as starter capacitors are not meant to be used for more than a few seconds. This is a problem that may lead to complete failure, where the top of the starter capacitor will pop off and the insides may be partially or fully ejected. Another cause of overheating can be the mechanical devices that cycle often, such as air compressors. Starter capacitors that cycle above 20 starts, or cycles per hour, may be subject to overheating. If any of these do occur and damage the capacitor, simply replace it.
In more serious cases, the motor's starting circuit might be engaged too long for the intermittent duty rating of the start capacitor. The top of the start capacitor may become dislodged, and the insides may, in some cases, be partially or fully ejected. If start capacitors are left energized too long due to a faulty starting circuit on a motor they can overheat. Similarly, but not quite as dramatic, a start capacitor may just exhibit a ruptured pressure relief blister. If any of these do occur, and damage the capacitor, it must simply be replaced.
On the left is a working starter capacitor. The image on the right shows a starter capacitor that has failed.
What's the difference between a start and a run capacitor?
View our video tutorial video to learn more about start vs. run capacitors.