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Start Capacitor

Start Capacitor


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What is a Start Capacitor?

Designed for momentary use, the start capacitor is what lets a motor start up instantly instead of taking a long time to come up to speed before it can be used. It stays energized long enough to rapidly bring the motor to 3/4 of its full speed and is then taken out of the circuit. It will briefly increase motor starting torque and allow a motor to be cycled on and off rapidly, but is not meant to be used for more than a few seconds.



What exactly does it do?

Single phase motors will commonly have both a start and run capacitor. The difference between the two is that the start capacitor has a much higher ability to store charge, also known as its capacitance rating, for its size than that of the run capacitor. Essentially, the start cap gives the motor a bolt of energy in order to get it up and running, while the run capacitor keeps the motor going after the start capacitor shuts down.



How do I select the correct Start Capacitor?

Most electric motor start capacitors will come with similar specs.


  • Voltage – 110/125, 165, 220/250 or 330 VAC
  • Frequency – 50 or 60 Hz
  • Capacitance – 50 to 1200 uf

It is important to note that when choosing a replacement capacitor, you should always select one with the same capacitance and frequency as the original. In terms of voltage, you can choose a new capacitor with a voltage that is higher or lower than the original but it must still be higher than the operational voltage of the motor for it to work. The start capacitor can usually be identified by their black phenolic or plastic case and a recessed top where the connections are located.


What else should I know about Start Capacitors before I buy one?

Since a start capacitor is designed to give a quick burst of energy, it can sometimes burn out. There are two easily identifiable signs that the start capacitor is not functioning normally: if your motor is either not turning on at all, or is slow to start.


If the motor is simply slow to start, your start capacitor may have lost its capacitance rating due to wear and age. It is also possible in this case that you may have other issues with your motor unrelated to the capacitor, but replacing a start capacitor is relatively cheap, so it is a good place to start.


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.



Working Start Capacitor Failed Start Capacitor

On the left is a working start capacitor. The image on the right shows a start capacitor that has failed.


What's the difference between a start and a run capacitor?

Viewour video tutorial video to learn more about start vs. run capacitors.



Start Capacitor Troubleshooting

When a motor is first turned on, it will immediately come to life, running at full capacity in mere seconds. But how many people even know that they have the start capacitor to thank for it? TEMCo now offers start caps for all of your needs.


Learn how to replace a start capacitor in a single phase motor and the differences between start and run capacitors.





Start Capacitor Product Selection

ViewTEMCo's selection of start capacitors below.


Specifications: Round, ¼" terminals, 50/60 Hz

Start Capacitor Special Volume Discount
Start Capacitor Shipping

Round Start Cap, 165V, ¼" Flag Terminal, 50/60 Hz

Capacitance
Value
1 Piece 5 Piece 10 Piece
124-149 SC0092
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SC0093
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SC0094
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189-227 SC0095
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SC0096
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SC0097
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400-480 SC0098
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SC0099
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SC0100
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Round Start Cap, 330V, ¼" Flag Terminal, 50/60 Hz

Capacitance
Value
1 Piece 5 Piece 10 Piece
88-106 SC0101
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SC0102
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SC0103
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135-162 SC0104
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SC0105
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SC0106
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Capacitor for Motor Help