Motor-Start Capacitors vs Motor-Run Capacitors
When working with single-phase electric motors, it is important to understand the difference between motor-start capacitors and motor-run capacitors. They are both capacitors, but they have fundamental differences in purpose, design, and operational characteristics, making them non-interchangeable. At its most basic level, a capacitor is a device used to store energy in an electrical charge. So, what sets motor-start capacitors apart from motor-run capacitors, and how do these differences impact their roles in a motor’s operation?
Motor-Start Capacitors: These are designed for short-term use to provide a high burst of energy required to start a motor. They typically have a higher capacitance value compared to motor-run caps and are not built to handle continuous current flow. Motor-start caps normally have a range of rated capacitance compared to a specific rating that run-caps have. Using a motor-start capacitor in place of a motor-run capacitor would result in overheating and potential failure since it cannot withstand prolonged operation.
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Motor-Run Capacitors: These are built for continuous use and are designed to improve the efficiency and power factor of a motor during its operation. They have lower capacitance values and are constructed to endure sustained electrical loads. Substituting a motor-run capacitor with a motor-start capacitor would compromise the motor’s performance and longevity, as the start capacitor’s higher capacitance could disrupt normal operation and damage the motor over time.
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Below is an example from ElectricalA2Z of a single phase induction motor (with a wiring diagram) that has a capacitor in the start winding and a capacitor in the run winding.
Summary: Motor-start capacitors are designed to provide an initial boost of electrical energy to help the motor overcome inertia and begin turning. They are typically rated for short-term use and are disconnected from the circuit once the motor reaches a certain speed. In contrast, motor-run capacitors remain connected to the circuit during operation, providing continuous support for efficient motor performance.