A motor capacitor [1] [2] is an electrical capacitor that alters the current to one or more windings of a single-phase alternating-current induction motor to create a rotating magnetic field.[ citation needed ] There are two common types of motor capacitors, start capacitor and run capacitor (including a dual run capacitor). [2]
Motor capacitors are used with single-phase electric motors [3] : 11 that are in turn used to drive air conditioners, hot tub/jacuzzi spa pumps, powered gates, large fans or forced-air heat furnaces for example. [1] A "dual run capacitor" is used in some air conditioner compressor units, to boost both the fan and compressor motors. [1] Permanent-split capacitor (PSC) motors use a motor capacitor that is not disconnected from the motor. [4]
Start capacitors briefly increase motor starting torque and allow a motor to be cycled on and off rapidly. A start capacitor stays in the circuit long enough to rapidly bring the motor up to a predetermined speed, which is usually about 75% of the full speed, and is then taken out of the circuit, often by a centrifugal switch that releases at that speed. Afterward the motor works more efficiently with a run capacitor. [1] [5]
Start capacitors usually have ratings above 70 μF, with four major voltage classifications: 125 V, 165 V, 250 V, and 330 V. [1]
Start capacitors above 20 μF are always non-polarized aluminium electrolytic capacitors [6] with non solid electrolyte and therefore they are only applicable for the short motor starting time.
The motor will not work properly if the centrifugal switch is broken. If the switch is always open, the start capacitor is not part of the circuit, so the motor does not start. If the switch is always closed, the start capacitor is always in the circuit, so the motor windings will likely burn out. If a motor does not start, the capacitor is far more likely the problem than the switch.[ citation needed ]
Some single-phase AC electric motors require a "run capacitor" to energize the second-phase winding (auxiliary coil) to create a rotating magnetic field while the motor is running. [5]
Run capacitors are designed for continuous duty while the motor is powered, which is why electrolytic capacitors are avoided, and low-loss polymer capacitors are used. Run capacitors are mostly polypropylene film capacitors (historically: metallised paper capacitors) and are energized the entire time the motor is running. [1] Run capacitors are rated in a range of 1.5 to 100 μF, with volt classifications of 250, 370 and 440 V. [1]
If a wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor. This causes the rotor to hesitate at the uneven spots, resulting in irregular rotation, especially under load. This hesitation can cause the motor to become noisy, increase energy consumption, cause performance to drop and the motor to overheat. [5]
A dual run capacitor supports two electric motors, with both a fan motor and a compressor motor. It saves space by combining two physical capacitors into one case. The dual capacitor has three terminals, labeled C for common, FAN, and HERM for hermetically-sealed compressor.
Dual capacitors come in a variety of sizes, depending on the capacitance (measured in microfarads, μF), such as 40 plus 5 μF, and also on the voltage. A 440-volt capacitor can be used in place of a 370-volt, but not a 370-volt in place of a 440-volt. [2] The capacitance must remain within 5% of its original value. [2] Round cylinder-shaped dual run capacitors are commonly used for air conditioning, to help in the starting of the compressor and the condenser fan motor. [2] An oval dual run capacitor could be used instead of a round capacitor; in either case the mounting strap needs to fit the shape used. [2]
The units of capacitance are labeled in microfarads (μF). Older capacitors may be labeled with the obsolete terms "mfd" or "MFD", which can be ambiguous but are, especially in this context, used for microfarad as well (a millifarad is 1000 microfarads and not usually seen on motors).
This section needs additional citations for verification .(December 2019) |
A faulty run capacitor often becomes swollen, with the sides or ends bowed or bulged out further than usual; it can then be clear to see that the capacitor has failed, because it is swollen or even blown apart causing the capacitor's electrolyte to leak out. Some capacitors have a "pressure-sensitive interrupter" design that causes them to fail before internal pressures can cause serious injury. One such design causes the top of the capacitor to expand and break internal wiring. [7]
Over many years of use the capacitance of the capacitor drops; this is known as a "weak capacitor". As a result, the motor may fail to start or to run at full power.
When a motor is running during a lightning strike on the power grid, the run capacitor may be damaged or weakened by a voltage spike, thus requiring replacement.
IEC/EN 60252-1 2011 specifies the following levels of protection for motor run capacitors:
A motor capacitor which is a component of a hot tub circulating pump can overheat if defective. [9] This poses a fire hazard, and the U.S. Consumer Product Safety Commission (CPSC) has received more than 100 reports of incidents of overheating of the motor capacitor, with some fires started. [9]
Motor capacitors manufactured before 1978 likely contain polychlorinated biphenyls (PCBs). These are extremely toxic and persistent chemicals with many long-lasting negative human and wildlife health effects. Capacitors were required to be labeled in the U.S. with "No PCBs" or similar language. Capacitors without these labels are suspect.
PCB containing capacitors must be replaced and disposed by consulting local environmental authorities. If these capacitors leak or fail, PCBs can be released into the environment and will very likely result in extremely expensive environmental cleanups, and potentially, lawsuits. There are extensive toxicological reports on PCBs in the research community. U.S. EPA has much information on the correct way to test and manage these toxic chemicals in older capacitors. [10]
A Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891. It is used to produce high-voltage, low-current, high-frequency alternating-current electricity. Tesla experimented with a number of different configurations consisting of two, or sometimes three, coupled resonant electric circuits.
The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units (SI), equivalent to 1 coulomb per volt (C/V). It is named after the English physicist Michael Faraday (1791–1867). In SI base units 1 F = 1 kg−1⋅m−2⋅s4⋅A2.
Capacitance is the capability of a material object or device to store electric charge. It is measured by the charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related notions of capacitance: self capacitance and mutual capacitance. An object that can be electrically charged exhibits self capacitance, for which the electric potential is measured between the object and ground. Mutual capacitance is measured between two components, and is particularly important in the operation of the capacitor, an elementary linear electronic component designed to add capacitance to an electric circuit.
A photoflash capacitor is a high-voltage electrolytic capacitor used in camera flashes and in solid-state laser power supplies. Their usual purpose is to briefly power a flash lamp, used to illuminate a photographic subject or optically pump a laser rod. As flash tubes require very high current for a very short time to operate, photoflash capacitors are designed to supply high discharge current pulses without excessive internal heating.
An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. Because of their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance-voltage (CV) product per unit volume than ceramic capacitors or film capacitors, and so can have large capacitance values. There are three families of electrolytic capacitor: aluminium electrolytic capacitors, tantalum electrolytic capacitors, and niobium electrolytic capacitors.
An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements. A datasheet for an electronic component is a technical document that provides detailed information about the component's specifications, characteristics, and performance. Discrete circuits are made of individual electronic components that only perform one function each which are known as discrete components, although strictly the term discrete component refers to a component with semiconductor material such as individual transistors.
Capacitors are manufactured in many styles, forms, dimensions, and from a large variety of materials. They all contain at least two electrical conductors, called plates, separated by an insulating layer (dielectric). Capacitors are widely used as parts of electrical circuits in many common electrical devices.
In electronics, a decoupling capacitor is a capacitor used to decouple one part of a circuit from another. Noise caused by other circuit elements is shunted through the capacitor, reducing its effect on the rest of the circuit. For higher frequencies, an alternative name is bypass capacitor as it is used to bypass the power supply or other high-impedance component of a circuit.
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term still encountered in a few compound names, such as the condenser microphone. It is a passive electronic component with two terminals.
A capacitance meter is a piece of electronic test equipment used to measure capacitance, mainly of discrete capacitors. Depending on the sophistication of the meter, it may display the capacitance only, or it may also measure a number of other parameters such as leakage, equivalent series resistance (ESR), and inductance. For most purposes and in most cases the capacitor must be disconnected from circuit; ESR can usually be measured in circuit.
A ceramic capacitor is a fixed-value capacitor where the ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material defines the electrical behavior and therefore applications. Ceramic capacitors are divided into two application classes:
Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose. Capacitors allow only AC signals to pass when they are charged blocking DC signals. The main components of filters are capacitors. Capacitors have the ability to connect one circuit segment to another. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits.
A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of porous tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as a cathode. Because of its very thin and relatively high permittivity dielectric layer, the tantalum capacitor distinguishes itself from other conventional and electrolytic capacitors in having high capacitance per volume and lower weight.
The gyrator–capacitor model - sometimes also the capacitor-permeance model - is a lumped-element model for magnetic circuits, that can be used in place of the more common resistance–reluctance model. The model makes permeance elements analogous to electrical capacitance rather than electrical resistance. Windings are represented as gyrators, interfacing between the electrical circuit and the magnetic model.
An ESR meter is a two-terminal electronic measuring instrument designed and used primarily to measure the equivalent series resistance (ESR) of real capacitors; usually without the need to disconnect the capacitor from the circuit it is connected to. Other types of meters used for routine servicing, including normal capacitance meters, cannot be used to measure a capacitor's ESR, although combined meters are available that measure both ESR and out-of-circuit capacitance. A standard (DC) milliohmmeter or multimeter cannot be used to measure ESR, because a steady direct current cannot be passed through the capacitor. Most ESR meters can also be used to measure non-inductive low-value resistances, whether or not associated with a capacitor; this leads to several additional applications described below.
A polymer capacitor, or more accurately a polymer electrolytic capacitor, is an electrolytic capacitor (e-cap) with a solid conductive polymer electrolyte. There are four different types:
Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called film caps as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometimes combined with paper as carrier of the electrodes.
A capacitive power supply or capacitive dropper is a type of power supply that uses the capacitive reactance of a capacitor to reduce higher AC mains voltage to a lower DC voltage.
Aluminum electrolytic capacitors are (usually) polarized electrolytic capacitors whose anode electrode (+) is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminum oxide by anodization that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer, serving in principle as the second electrode (cathode) (-) of the capacitor. A second aluminum foil called "cathode foil" contacts the electrolyte and serves as the electrical connection to the negative terminal of the capacitor.
A niobium electrolytic capacitor is an electrolytic capacitor whose anode (+) is made of passivated niobium metal or niobium monoxide, on which an insulating niobium pentoxide layer acts as a dielectric. A solid electrolyte on the surface of the oxide layer serves as the capacitor's cathode (−).
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