Replacement Capacitor

When ordering a Replacement Capacitor, you want it fast!

All orders less than 50 pieces are shipped USPS First Class or Priority Mail and will arrive 1-3 days from the day of shipment.

All other orders are shipped UPS or FedEx.

Choosing a Replacement Capacitor - Causes of failure

• Is it time to replace your Electric Motor's Start Capacitor?
• How do I know if my Electric Motor's Start Capacitor is bad?
• My motor is slow to start. Is my start capacitor bad?
• Is it time to replace your Motor Run Capacitor?
• Why did my Run Capacitor fail?

• Selection Help

Types of Replacement Capacitors

A motor Start Cap is used to briefly shift phase on a start winding in a single phase electric motor to create an increase increase in torque. Start Capacitors possess a very large capacitance value for their size and voltage rating and as a result are only intended for intermittent duty. It is because of this fact that most start capacitors fail after being left energized too long due to a faulty starting circuit on a motor.

Most electric motor Start Capacitor applications use a rating of 50-1200 uf capacitance and voltages of 110/125, 165, 220/250 and 330 VAC. Case designs are typically round and cast in black phenolic or Bakelite materials. Terminations are usually ¼" push on terminals with 2 terminals per connection post.

A motor Run Capacitor is used to continuously adjust current or phase shift to a motor's windings in an effort to optimise the motors torque and efficiency performance. All motor run capacitors are designed for continuous duty and as a result, have a much lower failure rate than start capacitors.

Most electric motor run capacitor applications use a rating of 2.5-100 uf (microfarrads) capacitance and voltages of 370 or 440 VAC. Case designs are round or oval using most commonly either a steel or aluminum shell and cap. Terminations are usually ¼" push on terminals with 2-4 terminals per connection post.

How are Run Capacitors different from Start Capacitors? Start capacitors give a large capacitance value necessary for motor starting for a very short (seconds long) period of time. They are only intermittent duty and will fail catastrophically if energized too long. Run Capacitors are used for continuous voltage and current control to a motors windings and are therefore continuous duty. They are generally of a much lower capacitance value.

Can Start Capacitors be interchanged with Run Capacitors? Yes and no. In unusual circumstances, a Run Capacitor could be used as a motor Start Capacitor but the values available are much lower than the values usually available for dedicated start capacitors. The capacitance and voltage ratings would have to match the original start capacitor specification. A start capacitor can not ever be used as a run capacitor because it could not handle current continuously (only a couple of seconds).

Capacitor Specifications

The specifications needed for selection a replacement capacitor are:

Voltage of operation or original capacitor voltage. Capacitor Voltage should be at least the voltage that will be seen during operation. A motor being used on a 240 volt supply should use a capacitor rated above 240 volts. Using a capacitor with a rated voltage much higher than what will be seen during operation is an acceptable practice.

Capacitance value (uf, MFD or microfarrads) of original capacitor. This value must be the same as the capacitor being replaced.

Frequency (hz) of operation or original capacitor. Nearly all capacitors will have a 50/60 hz rating. The replacement capacitor must have the frequency in the rating that the motor will be operated on.

Connection terminal style of original capacitor. Most motor capacitors will use a ¼" flag style push on connector. The next question is, "How many terminals per terminal post are needed for the application motor?" Most start capacitor have 2 terminals per post and most run capacitors will have either 3 or 4 terminals per post. Verify that your replacement capacitor selected has at least the number of connection terminals as the original capacitor.

Case Shape and overall size and shape. Nearly all start capacitors have a round case. Round run capacitors are by far the most common, but many motors still use oval designs. Electrically speaking, there is no difference. Fit is the only question here. If space in the mounting box is not limited, the case style does not matter.

Overall size, just like case shape, makes no difference electrically. Select a capacitor that will fit within the space provided.

Choosing a Replacement Capacitor - Causes of Failure

Is it time to replace your Electric Motor's Start Capacitor? Depending on the frequency of starting of a piece of machinery, the relative load during start-up, and the temperature of environment that it is operated in, every motor's start capacitor will eventually have to be replaced.

Is it time to replace your Motor Run Capacitor?

As a general rule of thumb, a motor run capacitor will far out last the same motor's start capacitor. A motor run capacitor will also fail or wear differently, making them slightly more involving when trying to determine if the time has come for replacement. Start capacitors will commonly fail catastrophically, making the decision on when to replace obvious, limiting time spent troubleshooting.

When a motor run capacitor begins to perform outside the allowable range, it is most often indicated by a dropping of the rated capacitance value (the microfarad value has gone down). For most standard motors, a run capacitor will have a "tolerance" specified describing how close to the rated capacitance value that the actual value may be. This will be usually +/- 5% to 10%. For most motors, as long as the actual value is is within the 10% mark of the rated value, you're in good shape. As a run capacitor is used, and the capacitance drops outside of this range, you'll need to look at a replacement.

"Why did my Run Capacitor fail?"

The answer may be simple, but depending on how close to the design life of the run capacitor is, it may also be difficult to nail it down to a single factor.

"How long should my Run Capacitor last?"

The mid point for a good quality aftermarket (didn't come with your motor) run capacitor would be 30,000-60,000 running hours. Factory installed motor run capacitors sometimes have a designed lifespan of much less that this. In highly competitive industries where every part can have a significant impact on cost or where a motor's intended use would likely be intermittent and infrequent, a lower grade of run capacitor may be selected with a design life of as little as 1000 hours. Additionally all of the factors from the section above (run capacitor causes of failure) may dramatically modify the reasonable expected life of a run capacitor.

TEMCo stocks almost every type of Capacitor for Motor application. Common uses include air conditioner capacitor, fan motor capacitor, Single phase starting capacitor, motor run capacitor and many more. Our quality components are used throughout the US and international daily.

Click here for help selecting a motor capacitor. »

TEMCo's industrial power solutions and MG sets are chosen for the most demanding applications, by some of the best and widely known companies in the world. Our quality products are being used throughout the US and internationally every day.

TEMCo's regular customers include: Varian Medical, Applied Materials, Apple Computer, ESPN Networks, NASA, General Motors, American Family Radio, Kaiser Permanente, Nordstrom, BAE Systems, UC Berkeley, Navy Public Works Center, US Army Executive Service, FORD, MIT, Stanford Linear Accelerator (SLAC), Lawrence Livermore National Labs (LLNL), and many thousands more.

All orders less than 50 pieces are shipped USPS First Class or Priority Mail and will arrive 1-3 days from the day of shipment.

All other orders are shipped UPS or FedEx.

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Need help with selecting your Motor Capacitor? See our Motor Capacitor FAQ. click here. »

Need help to Test Capacitor condition? click here »

What is a Starting Capacitor and what they are used for? click here. »

What is a Run Capacitor and what they are used for? click here. »

Need specific Air Conditioner Capacitor selection help? click here. »

How do I select an AC capacitor? click here. »

Where do I buy capacitor replacements for my motor needs? click here. »