motor trouble shooting
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CHAPTER 2 - Troubleshooting AC MotorsProblem A - Motor won't start or motor accelerates too slowly
A1: Check input power to starter. Is therepower on all lines? (Three-phase motorswon't start on one-phase.) Restore power on all lines
A2: Check starter. Is overload protectiondevice opened? Replace or reset device. Does itopen again when starting?
A3: Is there power on all lines to motor? Repair starter
A4: Is voltage to motor more than 10%below nameplate voltage? Restore proper voltage.
A5: Check motor terminal connections. Areany loose or broken? Repair connections.
A6: May be wrong motor for application. Isstarting load too high? Install Design C or Design Dmotor. Install larger motor.
A7: Is driven machine jammed oroverloaded? Remove jam or overload.
A8: Are misalignments, bad bearings ordamaged components causing excessivefriction in driven machine or powertransmission system?
Repair or replace component.
A9: Are bad bearings, bent shaft, damagedend bells, rubbing fan or rotor or otherproblem causing excessive friction in the
motor?Repair or replace motor.
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A10: Check stator. Are any coils open,shored or grounded? Repair coil or replace motor.
A11: Check commutator. Are any bars orrings broken? Replace rotor.
Problem B - Motor runs noisyB1: Are vibrations and noise from drivenmachine or power transmission system being
transmitted to motor?Locate source of noise andreduce. Isolate motor with belt
drive or elastomeric coupling.
B2: Is a hollow motor foundation acting as asounding board?
Redesign mounting. Coatfoundation underside with sounddampening material.
B3: Check motor mounting. Is it loose? Tighten. Be sure shaft is aligned.
B4: Is motor mounting even and shaftproperly aligned? Shim feet for even mounting andalign shaft.
B5: Is fan hitting or rubbing on stationarypart or is object caught in fan housing?
Repair damaged fan, end bell orpart causing contact. Removetrash from fan housing.
B6: Is air gap nonuniform or rotor rubbing onstator?
Recenter rotor rubbing on wornbearings or relocate pedestalbearings.
B7: Listen to bearings. Are they noisy? Lubricate bearings. If still noisy,replace.
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B8: Is voltage between phases (three-phasemotors) unbalanced? Balance voltages.
B9: Is three-phase motor operating on one-phase? (Won't start on single-phase.) Restore power on three-phases.
Problem C - Motor overheatsC1: Is ambient temperature too high? Reduce ambient, increase
ventilation or install larger motor.
C2: Is motor too small for present operatingconditions? Install larger motor.
C3: Is motor started too frequently? Reduce starting cycle or uselarger motor.
C4: Check external frame. Is it covered with
dirt which acts as insulation and preventsproper cooling?
Wipe, scrape or vacuumaccumulated dirt from frame.
C5: Feel output from air exhaust openings.Is flow light or inconsistent indicating poorventilation?
Remove obstructions or dirtpreventing free circulation of airflow. If needed, clean internal airpassages.
C6: Check input current while driving load. Isit excessive indicating an overload? Go to Step C11.
C7: Is the driven equipment overload? Reduce load or install largermotor.
C8: Are misalignments, bad bearings ordamaged component causing excessivefriction in driven machine or power
Repair or replace badcomponents.
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transmission system?
C9: Are motor bearings dry? Lubricate. Does motor still drawexcessive current?
C10: Are damaged end bells, rubbing fan,bent shaft or rubbing rotor causing excessiveinternal friction? Repair or replace motor.
C11: Are bad bearings causing excessive
friction? Determine cause of bad
bearings (See Problem D).
C12: Check phase voltage. Does it varybetween phases? Restore equal voltage on allphases.
C13: Is voltage more than 10% above or10% below nameplate? Restore proper voltage or installmotor built for the voltage.
C14: Check stator. Are any coils groundedor shorted? Repair coils or replace motor.
Problem D - Motor bearings run hot or noisyD1: Check loading. Is excessive sidepressure, end loading or vibration overloadingbearings?
Reduce overloading.* Installlarger motor.
D2: Is sleeve bearing motor mounted on aslant causing end thrust? Mount horizontally* or install ballbearing motor.
D3: Is bent or misaligned shaft overloading Replace bent shaft or align
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bearings? shaft.*
D4: Is loose or damaged end bell
overloading shaft?Tighten or replace end bell.*
D5: Are bearings dry? Lubricate.*
D6: Is bearing lubricant dirty, contaminatedor of wrong grade? Clean bearings and lubricatewith proper grade*
D7: Remove end bells. Are bearingsmisaligned, worn or damaged? Replace.*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings
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CHAPTER 3 - Troubleshooting DC MotorsProblem E - Motor won't start
E1: Check main input power to controller. Isthere power on the lines? Are contactsclosed? Restore input power.
E2: Check controller. Is the overloadprotective device open? Reset or replace device. Does itopen again when starting motor?
E3: Check controller. Is there voltageavailable at output terminals?
Check controller for openstarting resistor, broken leadsand connections or othermalfunctions. Repair.
E4: Set the controller for full speed. Is thevoltage for field or armature circuits too low?
Check voltage from powersource. Correct if too low. Checkcontroller for malfunction.Repair.
E5: Check for weak or non-existent field. Ismotor field open? Has one field coil shorted?
Repair broken leads orconnections. Rewind or replaceopen or shorted coil.
E6: Check for open armature circuit. Isvoltage at motor armature terminals zerowhen starting?
Repair damaged armaturecircuit.
E7: Is driven machine jammed oroverloaded? Remove jam or overload orinstall larger motor.
E8: Are misalignments, bad bearings or worncomponents causing excessive friction indriven machine or power transmissionsystem?
Correct misalignment or repair orreplace worn component.
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E9: Are bad bearings, bent shaft, rubbing fanor rotor, damaged end bells, or othermechanical problems causing excessivefriction in motor?
Repair or replace damagedmotor components or install new
motor
Problem F - Motor starts but stops and reverses directionF1: Check polarity of power source. Did itreverse? Determine why power supplyreversed polarity and repair.
F2: Shunt and series field may be buckingeach other. To check and correct:Reconnect the shunt or series field to correctpolarity. Connect armature for desiredrotation direction. Try fields separately todetermine rotation direction and connect soboth give the same rotation.
Problem G - Motor runs but overload protective device trips too often.G1: Is motor too small for load? Haveloading conditions changed? Reduce load or install largermotor.
G2: Check controller. Is overload device set
too low for application?Increase overload setting.NEVER exceed safe limits
specified by codes or equipmentmaker.
G3: Is motor overheating? See Problem H.
Problem H - Motor overheats
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H1: Is ambient temperature too high? Reduce ambient, increaseventilation or install larger motor.
H2: Check external frame. Is it covered withlayer of dirt which acts as insulation andprevents proper cooling?
Wipe, scrape or vacuumaccumulated dirt from frame.
H3: Feel output from air exhaust openings.Is flow light or inconsistent indicating poorventilation?
Remove obstructions or dirtpreventing free of air flow. Ifneeded, clean internal airpassages.
H4: High load speed consumes extrahorsepower overloading motor. Is motoroperating above normal speed? See Problem J.
H5: Check for overload. See Steps E7 thru E9.
Problem I - Motor runs too slowly.I1: Is motor overloaded? See Steps E7 thru E9.
I2: Is the field resistance too low? Add proper resistance.
I3: Check for shorts in armature or betweencommutator bars. Are armature coils orwedges burned? Are any commutator barsburned?
Replace or replace coils or bars.
I4: Check brush holders. Are brushes setahead of neutral? Reset brushes to neutral.
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I5: Voltage to armature too low. Setcontroller for full speed. Is voltage at output
terminals below nameplate voltage?Check power source outputvoltage. Raise if too low. Checkcontroller for malfunction.
Repair.
I6: DC motors may run 20% slower on lightloads when they don't heat up. Is motoroperating cold?
Increase load or reduceventilation to increase heating.Install new motor.
Problem J - Motor runs too fast.J1: Is driven load too light allowing motor torun fast? Increase load or install smallermotor.
J2: Check for a weak field per Steps J3through J6.
J3: Are shunt or series coils reversed? Reconnect reversed coils forproper polarity.
J4: Is there excessive resistance in shuntfield circuit? Remove excessive resistance.
J5: Is excessive heat causing higherresistance in shunt field circuit? Increase ventilation or correctother cause of overheating.
J6: No field causes unbalanced shunt motorto race. Is field circuit open? Repair broken lead orconnection. Replace open coil.
J7: Set controller for full speed. Is voltage atoutput terminals of controller abovenameplate voltage?
Reduce output voltage. Checkcontroller for malfunction.Repair.
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J8: Check brush holders. Are brushes setbehind neutral? Reset brushes to neutral.
Problem K - Motor runs noisyK1: Are vibrations and noise from drivenmachine or power transmission system beingtransmitted to motor?
Locate source of noise andreduce. Isolate motor with beltdrive or elastomeric coupling.
K2: Is a hollow motor foundation acting as asounding board?
Redesign mounting. Coatfoundation underside with sounddampening material.
K3: Check motor mounting. Is it loose? Tighten. Be sure shaft is aligned.
K4: Is motor mounting even and shaftproperly aligned? Shim feet for even mounting andalign shaft.
K5: Is fan hitting or rubbing on stationarypart or is object caught in fan housing?
Repair damaged fan, end bell orpart causing contact. Removetrash from fan housing.
K6: Is air gap nonuniform or armature rotorrubbing on pole pieces?
Tighten loose pole piece.Recenter armature by replacingworn bearings or relocatingpedestal bearings.
K7: Listen to bearings. Are they noisy? Lubricate bearings. If still noisy,replace.
K8: Are bearings noisy or running hot? See Problem L.
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K9: Are the brushes developing high or lowfrequency chatter? See Problem M.
Problem L - Motor bearings run hot or noisyL1: Check loading. Is excessive sidepressure, end loading or vibration overloadingbearings?
Reduce overloading.* Installlarge motor.
L2: Is sleeve bearing motor mounted on aslant causing end thrust? Mount horizontally* or install ballbearing motor.
L3: Is bent or misaligned shaft overloadingbearings? Replace bent shaft or alignshaft.*
L4: Is loose or damaged end belloverloading shaft? Tighten or replace end bell.*
L5: Are bearings dry? Lubricate.*
L6: Is bearing lubricant dirty, contaminatedor of wrong grade?
Clean bearings and lubricate
with proper grade.*
L7: Remove end bells. Are bearingsmisaligned, worn or damaged? Replace.*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings.
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Problem M - Brushes sparking excessively; may be accompanied by brushchatter
and/or excessive wear and chipping.
M1: Is motor overloaded? Reduce overload or install largermotor.
M2: Is vibration from driven machine ormotor present? Locate source of vibration andreduce.
M3: Check brushes and brush holders. Arebrushes worn too short? Replace brushes.
M4: Does each brush fit commutator asindicated by polished surface over entirebrush face. Refit brushes to commutator.
M5: Are brushes hanging up in holders? Clean brushes and holders.Remove rough surfaces thatcause extra friction.
M6: Are brush springs broken or is springpressure too light?
Replace spring or increasepressure. Be sure pressure isequal on all brushes.
M7: Is spring pressure to high? (May alsocause brush chipping) Reduce pressure or replace withlighter spring.
M8: Are brush holders set off neutral? (Mayalso cause brush chipping) Reset holders at neutral.
M9: Are brushes set a wrong angle? (Mayalso cause brush chipping)
Reset holders for brush anglerecommended by motormanufacturer.
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M10: Is brush holder set for more than 1/8"clearance above commutator? (May alsocause brush chipping) Reset holder for 1/8" clearance.
M11: Chipping brushes may also indicatewrong brush material. Are brushes too weakfor duty?
Consult motor manufacturer forrecommendations.
M12: Check commutator. Is commutatorsurface under brushes polished brown color? Normal condition. Go toStep M18.
M13: Is commutator surface black (generallycaused by sparking)?
Check for overloads, low springtension, poorly undercut mica,loose commutator bars, etc.Correct sparking. Dresscommutator.
M14: Is there thick film on commutator - mayappear black? Use more abrasive brushes.
M15: Is commutator surface bright andbrassy looking?
If humidity is below 2 grams percu. ft., increase humidityORreduce spring pressure, use lowfriction brushes or use lessabrasive brushes.
M16: Is commutator surface contaminatedfrom paint spray, oil or chemical fumes? Isthere excessive moisture in air?
Clean commutator and brushesand protect motor fromcontamination. Install motor withproper enclosure to protectcommutator.
M17: Is commutator streaked or grooved
under one or more brushes?Be sure all brushes same grade.Replace if some are too
abrasive. Check for faulty shuntconnections causing unbalanced
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load; repair.
M18: Is commutator rough or eccentric? Grind commutator roundUndercut mica
M19: Is mica above bar surface? Undercut mica.
M20: Are some commutator bars too high,too low or loose?
Replace commutator or tightenV-ring bolts to tensionrecommended by manufacturerand grind commutator.
M21: Are there flat or burned spots oncommutator bars caused by unbalanced loadin armature circuit?
Balanced load. Grindcommutator.
M22: Is conductive film carbon dust orcopper flaking causing shorts between
armature bars?Undercut mica.
M23: Are there any shorts or opens inarmature circuits? Locate and repair.
M24: Are there any grounds, shorts oropens in the field wiring circuits? Locate and repair.
M25: Are connections to brush holder pooror broken? Locate and repair.
M26: Is the interpole current weak or the airgap too great? Increase interpole current orreduce gap.
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