In this article, we are going to see how we can identify that motor run capacitors of electric motor needs replacement?
There are three cases of bad capacitors.
Bad motor run capacitors – capacitor is weak or completely failed
Bad capacitor – Weak or completely failed capacitor
Visible damage to any type of capacitor. For example, the case is swollen or cracked, visible leaks or corrosion occur.
Bad start capacitor
If the electric motor is ringing without starting, or if you have trouble starting but it works when depressed (like rotating fan blades – watch out for a cut finger), you may have a bad START cap.
If the engine is ringing, does not start, and the thermal overload switch does not fire, the START cap may be bad.
Bad Motor Run Capacitors
If the electric motor draws a large amount of current while driving, the motor run capacitors may be defective. There are other reasons, such as bad motor bearings or motor overload.
In short, it can be difficult to start a failed motor, but replacing the cover is very cheap compared to replacing the motor, so often the technician will try to use a new starting cover first, and then replace it. Check if the motor life can be extended before.
NOTE: If your STARTING or RUN capacitors are swollen, burnt, punctured, or leaking oil, it means it’s got a bullet and needs to be replaced.
Examples of capacitor damage
Torn or swollen capacitors:
A “catastrophic capacitor failure” of the motor run capacitors is one whose starting capacitor “explodes” or explodes.
This occurs when the starting capacitor is left connected for too long. Probably because the engine’s centrifugal switch did not disconnect the starter cap circuit when it should.
CAUTION: Exposing the capacitor to a voltage much higher than the rated input voltages can cause the capacitor to explode.
Ulcerated or swollen capacitors:
This capacitor malfunction is similar to a blown capacitor, but less dramatic, but then again, if you see a bulging, bulging, blowing, or exploding orifice in the capacitor, the cap is failing. , it must be replaced.
Hidden internal damage:
The capacitance of the starting capacitor is simply shown as the capacitance loss that occurs due to aging or “wear” over time. An electrical test of the capacitor may reveal this failure.
How to choose a replacement motor capacitor – 4 ways
The best option when replacing a starting capacitor or a start/running capacitor is to match the equipment in the system. This means paying attention to the data printed on your existing capacitors – if they are legible and matched.
We know that this is not the motor run capacitors because it only has two terminals.
How to match replacement capacitors to electric motors
Replacement motor capacitor matching options include:
- Check the original capacitor for matching voltage and capacitance, uF or microfarad ratings.
- Find and record all markings on the capacitor.
- Normally you will see a rating in microfarads like 25uF on the capacitor in the image above, and the red circle in the image above will also see a voltage range rating like 370VAC (maximum voltage) rating.
- Take the capacitor or the entire electric motor to a motor repair shop or local electrical supplier
- If the markings on the capacitor are visible, they can be matched. If the capacitor tags are illegible, the electrical supplier or motor builder will recommend starting, running or fused capacitors based on the motor’s data tag information.
What if the capacitor is missing or has no visible markings?
If you have the engine make and model (serial number preferred), you can also get the exact OEM part number. Please contact the engine manufacturer. They can provide exact OEM capacitor spare parts numbers or specifications.
Check the engine type, engine part number, and data card specifications, and use the Replacement Engine Parts or OEM Parts Catalog.
If the reader has no marks on the capacitor at all, the electricity supplier will want to know the technical details about what the capacitor is for. It can be found on the engine data card provided by the cover.
Typical pool/spa motor capacitor: Some pool pumps use a motor that gets the starting impulse from the starting capacitor.
For example, a typical above-ground swimming pool, hot tub or spa drive
The starting capacitor is rated at around 50-400 MFD and 125 or 250 VAC. Also, for the same motor, the running capacitor is rated at around 15-50 MFD and 370 VAC.
Capacitor value limits – microfarads
Select the replacement motor run capacitors with a capacitance value in µF (microfarads), typically expressed in a range such as 30°F to 50°F, to match the original capacitor and/or the electric motor data mark.
Limitations of choice on capacitor voltage ratings
The capacitor voltage rating indicates the maximum nominal voltage at which the capacitor is designed to operate.
There is no harm in using a capacitor with an undervoltage. For example, if your car engine uses a capacitor rated at 370VAC, you can replace it with a 370V or 440VAC capacitor. 440VAC capacitors last longer.
However, there is no harm in using a higher rated cap (440) where a lower rated cap (370) was originally installed, as these voltage ratings are simply the highest voltages the capacitor can handle.
The operating capacitor shall not be subject to more than 10% of the nominal rating and the starting capacitor shall not be subjected to more than 30% of the nominal rating.
Note: the voltage seen by the capacitor is not the line voltage, but the higher voltage generated in the starting winding (often called the back EMF or the back EMF). For a typical 230V motor, the output voltage can be up to 400V and is determined by the starting characteristics of the winding, compressor speed and applied voltage.
Select capacitors based on electric motor type, motor power, motor rating Kw or kilowatts, or frequency (Hz).
Most capacitors are rated 50/60 Hz, which means that the capacitor can operate at a frequency or Hz. However, do not use only 50 Hz parameter caps in 60 Hz circuits. vice versa.
If you can’t find the data showing the make, model, and specs of your motor, and you don’t have tags or even an actual old run/running capacitor for your electric motor, choosing a capacitor based on your motor’s power will help you find that the right pitch can come in. effort and application.
If we don’t have this data, we are stuck. Take the motor to an electric motor repair professional and you may find the signs you missed.
What if the engine has no data tag? Approximate operating capacitor value
If your engine has no visible markings or data marks, double-check first. Some electric motors, such as oil-burning motors, have data sealed in the metal case of the motor itself. The data may be there, but it is only visible under good lighting.
Electric motor start capacitors typically range from 50 to 1200 degrees Fahrenheit, are rated for voltages of 110/125, 165, 220/250 or 330 VAC, and are rated to operate at 50 Hz or 60 Hz.
Most capacitors use 1/4″ flat blade terminal connectors with two terminals per shaft. An operating capacitor may have 3 to 4 terminals per pole. Most starting capacitors wear round housings, but some are oval in design. The shape does not affect the function of the capacitor, but the shape of the capacitor can affect its ability to fit into the location of the original capacitor or the condition of the device or motor.