E2 Unit 19 Compressor Relays and Capacitors.ppt

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E2 Motors and Motor Starting#2 Compressor Relays and Capacitors

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Single Phase Compressor StartingSingle phase compressors have a start winding and a run winding

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Split Phase Compressor MotorRUN WINDINGRSTART WINDINGSC

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Starting a Split Phase CompressorPower must first go to both the run winding and the start winding

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Split-Phase Compressor Motor Starting LINERUN WINDINGSTART WINDINGCRPower is needed for the motor to runPower is also needed to startOnce started, the start windings are removed from the circuit

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Start RelaysA relay is used to energize the start winding The same relay is also used to take the start winding out of the circuit The next slide is a diagram of where start components are located in a compressor motor circuit

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Diagram of Compressor Start ComponentsCRSNL1For the motor to run, power is needed to Common and RunFor the motor to start, power is needed to the Start terminal.Add torque with a Start CapacitorAfter start up, A Start Relay opens the circuitSTART RELAY

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Types of Compressor StartingRSIR: Resistance start, induction run Uses a start relay only CSIR: Capacitor start, induction run Uses a start relay and start capacitor CSCR: Capacitor start, capacitor run Uses a start relay and both start and run capacitors

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Two Types of Starting RelaysCurrent Relays Potential Relays

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Current and Potential Relay

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Current RelaysUsed on compressors under one horsepower Switch contacts are normally open (NO) Relay coil energized by high starting current

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Current Relay

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Motor Amp Draw on Start up Current relays respond to amp draw Relay contacts close on high starting current Relay contacts open as amperage drops60A 40A 20A 0A 20% 40% 60% 80% 100%Motor SpeedLRAStart UpRLAAmperage DrawMotors draw high amps (LRA) on start up.Amperage drops as speed increases.

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Starting with a Current RelayCurrent relays are used on refrigeration systems with fixed metering devices When system pressures are equalized only a relay is needed to start the compressor

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Split Phase Motor with Current Relay LINERUN WINDINGSTART WINDINGSCRMSCURRENT RELAYLPOWER ON1- High starting amps energize relay coil, close contacts2- Line voltage goes to start windings3- Motor speed increases, amperage decreases, relay coil allows contacts to open4- Start Winding drops out5- Motor continues to run, drawing normal currentOriginal Diagram from Copeland Handbook

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How a Current Relay WorksThe drawing on the next slide shows how the start winding is energized, then how it is taken out of the circuit

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Current Relay21MSJumper wirePower InAlso used to connect optional start capacitorRelay CoilTo Main (Run) TerminalTo Start Terminal

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Energize Start and Run WindingsVoltage ready for Start WindingPower to Main (RUN) WindingVoltage through coilHigh starting current increases coil magnetismPlunger is pulled upContacts closePower to Start Winding

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Start winding de-energizedNo voltage to Start WindingPower to Main (RUN) WindingPower to Start WindingAs motor speed increases, amperage fallsPlunger fallsPlate falls, contacts openCompressor continues running

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Adding a Start CapacitorA refrigeration system with a TEV requires more starting torque Adding a start capacitor in series with the start winding is all that is needed

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Capacitor Start Induction Run Motor (CSIR) LINERUN WINDINGSTART WINDINGSCRMSCURRENT RELAYLSTART CAPACITOR

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Start CapacitorsThey provide more phase shift to the start winding Start capacitors are designed to be in the circuit for only a few seconds A resistor quickly bleeds off capacitor charge to prevent excessive arcing across the relay contacts Note: Always replace capacitors with the same microfarad rating (MFD or µF) and equal (or greater) volt amp capacity (VAC)

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Start CapacitorBleed Resistor 15,000 Ohms

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Terminal box on a small compressorA current relay plugs into the start and run terminals The external overload is mounted inside the terminal box

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Current Relay and Overload

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Current Relay and Overload

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Last Updated: 8th March 2018

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