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Wikipedia

Motor capacitor

January 01, 1970

Not to be confused with Punch capacitor.

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]

A typical motor start capacitor

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 edit

 
Simple capacitor-start single-phase motor circuit diagram.[3]: 12  Note that starting capacitor is connected in series with auxiliary winding just like in LC circuit.
 
Capacitor motor with a speed limiting governor device.

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]

Run capacitors edit

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]

Dual run capacitors edit

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]

Labeling edit

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).

Failure modes edit

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:

  • S0 – no protection;
  • S1, S2 – fail open-circuit or short-circuit;
  • S3 – fail open-circuit only.[8]

Safety issues edit

Heat edit

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]

Toxic edit

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]

References edit

  1. ^ a b c d e f g LA.gov, Louisiana. "Capacitor Sizing Dilemmas (motor capacitors)". LA.gov. Retrieved 2012-01-29.
  2. ^ a b c d e f JustTheRightAir (Sep 2008). . justtherightair.com. Archived from the original on 2008-07-12. Retrieved 2008-09-24.
  3. ^ a b Emadi, Ali (2018). Energy-efficient electric motors (3rd ed. rev. and expanded ed.). [Boca Raton]. ISBN 978-1-4200-3081-5. OCLC 1083013923.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ^ Alternating Current Machines. Firewall Media. 2024-02-19. ISBN 978-81-7008-222-4.
  5. ^ a b c Motor start and motor run capacitors; capacitorguide.com
  6. ^ This link only shows irrelevant types (July 2018) do they even exist? Allied electronics, Aluminium Electrolytic, Quick connect
  7. ^ Regal-Beloit. (PDF). GE Capacitors. Archived from the original (PDF) on 2011-10-26. Retrieved 2011-09-04.
  8. ^ "MotorCap DM AC Film Capacitors for Motor Run Applications" (PDF). Epcos AC, Munich, Germany. Retrieved 2012-04-22.
  9. ^ a b "CPSC, Firms Announce Recall of Infinity and Lifestyle Spas" U.S. CPSC, Washington, DC, CPSC.gov, 2003-12-09, webpage: CP7 2013-01-08 at the Wayback Machine.
  10. ^ Dan Bench. "Identification, Management, and Proper Disposal of PCB-Containing Electrical Equipment used in Mines" (PDF). U.S. Environmental Protection Agency.

Calculate your kvar requirement for your motor : Calculate kvar for motor

External links edit

January 01, 1970
motor, capacitor, confused, with, punch, capacitor, motor, capacitor, electrical, capacitor, that, alters, current, more, windings, single, phase, alternating, current, induction, motor, create, rotating, magnetic, field, citation, needed, there, common, types. Not to be confused with Punch capacitor 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 A typical motor start capacitor 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 Contents 1 Start capacitors 2 Run capacitors 3 Dual run capacitors 4 Labeling 5 Failure modes 6 Safety issues 6 1 Heat 6 2 Toxic 7 References 8 External linksStart capacitors edit nbsp Simple capacitor start single phase motor circuit diagram 3 12 Note that starting capacitor is connected in series with auxiliary winding just like in LC circuit nbsp Capacitor motor with a speed limiting governor device 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 mF with four major voltage classifications 125 V 165 V 250 V and 330 V 1 Start capacitors above 20 mF 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 Run capacitors editSome 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 mF 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 Dual run capacitors editA 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 mF such as 40 plus 5 mF 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 Labeling editThe units of capacitance are labeled in microfarads mF 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 Failure modes editThis section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed December 2019 Learn how and when to remove this message 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 S0 no protection S1 S2 fail open circuit or short circuit S3 fail open circuit only 8 Safety issues editHeat edit 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 Toxic edit 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 References edit a b c d e f g LA gov Louisiana Capacitor Sizing Dilemmas motor capacitors LA gov Retrieved 2012 01 29 a b c d e f JustTheRightAir Sep 2008 Round Dual Run Capacitors justtherightair com Archived from the original on 2008 07 12 Retrieved 2008 09 24 a b Emadi Ali 2018 Energy efficient electric motors 3rd ed rev and expanded ed Boca Raton ISBN 978 1 4200 3081 5 OCLC 1083013923 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link Alternating Current Machines Firewall Media 2024 02 19 ISBN 978 81 7008 222 4 a b c Motor start and motor run capacitors capacitorguide com This link only shows irrelevant types July 2018 do they even exist Allied electronics Aluminium Electrolytic Quick connect Regal Beloit AC Capacitors for Motor Run Applications PDF GE Capacitors Archived from the original PDF on 2011 10 26 Retrieved 2011 09 04 MotorCap DM AC Film Capacitors for Motor Run Applications PDF Epcos AC Munich Germany Retrieved 2012 04 22 a b CPSC Firms Announce Recall of Infinity and Lifestyle Spas U S CPSC Washington DC CPSC gov 2003 12 09 webpage CP7 Archived 2013 01 08 at the Wayback Machine Dan Bench Identification Management and Proper Disposal of PCB Containing Electrical Equipment used in Mines PDF U S Environmental Protection Agency Calculate your kvar requirement for your motor Calculate kvar for motorExternal links editThis article uses bare URLs which are uninformative and vulnerable to link rot Please consider converting them to full citations to ensure the article remains verifiable and maintains a consistent citation style Several templates and tools are available to assist in formatting such as reFill documentation and Citation bot documentation April 2023 Learn how and when to remove this message http highperformancehvac com run start capacitors hvac motors 1 http www capacitorformotor com motor capacitor html http www wikihow com Check a Start Capacitor http electronics stackexchange com questions 101408 what is the purpose of the motor run capacitor https www epa gov sites production files documents pcbidmgmt pdf Retrieved from https en wikipedia org w index php title Motor capacitor amp oldid 1224189719, wikipedia, wiki, book, books, library,

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