How to Identify Different Types of Motors

To identify different types of motors, start with the nameplate (voltage, phase, frequency, RPM, current, duty), then use visual clues (brushes, capacitor cans, gearboxes, frame), count and trace the leads, perform simple resistance/back-EMF tests, and consider the controller and application. These steps reliably distinguish AC induction and synchronous motors (single- or three-phase), single-phase variants (PSC, capacitor-start, shaded pole), DC brushed, brushless DC/PMSM, stepper, servo, universal, and switched-reluctance motors. Below is a structured guide to make that determination safely and accurately.

Begin with the Nameplate: The Fastest Identifier

The nameplate (or label/engraving) is the single most authoritative source for motor type, ratings, and wiring. Reading it correctly can immediately narrow the options and often provide the exact classification.

• Voltage and phase: “230/460 V, 3 PH, 50/60 Hz” typically indicates a three-phase AC induction or synchronous motor; “12–48 VDC” suggests DC brushed or brushless.
• Frequency and speed: A 50/60 Hz motor with RPM near but below synchronous (e.g., 3450, 1750, 1140) is usually induction (slip below 3600/1800/1200 RPM at 60 Hz). An RPM equal to synchronous (e.g., 3600/1800) implies synchronous or very lightly loaded specialty designs.
• Duty cycle and insulation class: “CONT” (continuous), S1–S9 duty classes, and insulation class (A–H) help confirm general purpose vs. servo/stepper/positioning use.
• Capacitor info: “PSC,” “Capacitor-Start/Run,” or capacitor microfarads on the plate indicates a single-phase induction variant.
• Kv or pole count: “Kv” ratings (e.g., 920 Kv) and “Hall” pinouts imply BLDC; pole count and step angle (e.g., 1.8°) indicate a stepper.
• Standards and codes: NEMA frame sizes (e.g., 56C, 143T), IEC frames (63–225), and encoder part numbers signal industrial AC motors or servomotors.

If the nameplate is intact and legible, it often eliminates guesswork; if not, the following visual and electrical cues will help you classify the motor confidently.

Visual and Mechanical Clues by Motor Type

AC Induction Motor (Squirrel-Cage)

These are the most common industrial and HVAC motors. Their housings, fans, and RPM ratings offer strong clues.

• No brushes or commutator; solid, enclosed rotor (squirrel cage) not visible without disassembly.
• RPM near but below synchronous (e.g., 1725 vs. 1800 RPM at 60 Hz).
• Three-phase units typically have 3, 6, or 9 leads; single-phase variants may have external capacitor cans.
• Robust frame, cooling fan shroud, and NEMA/IEC frame markings.

When you see a heavy frame, slip in RPM, and standard AC ratings, an induction motor is the likely match.

Single-Phase Induction Variants (PSC, Capacitor-Start, Capacitor-Run, Shaded Pole)

Single-phase AC motors are differentiated by their starting method; external components often reveal the subtype.

• PSC (Permanent Split Capacitor): One capacitor can on the housing, smooth quiet operation, modest starting torque.
• Capacitor-Start/Run: Large start capacitor (often in a bulged can) and sometimes a run capacitor; centrifugal switch click on start/stop.
• Shaded Pole: Very small, simple construction, low efficiency and torque, often used in fans and small appliances.
• Split-phase (resistance start): No capacitor; lower starting torque; audible start switch click.

Capacitor presence, size, and any audible start-switch behavior are quick tells for single-phase types.

Three-Phase Synchronous Motor

Synchronous motors turn at exactly synchronous speed and may use permanent magnets or a wound rotor.

• Nameplate RPM equals synchronous (e.g., 1800 at 60 Hz for 4-pole).
• Often paired with a variable-frequency drive (VFD) or field excitation system.
• High power-factor correction capability; may be labeled PMSM (Permanent Magnet Synchronous Motor).

Exact synchronous RPM and PM/wound-rotor references distinguish synchronous units from induction motors.

DC Brushed Motor

These are straightforward to spot thanks to brushes and a commutator.

• Visible brush caps or holders; sparks at commutator under load (if visible).
• Two main terminals; speed proportional to voltage; polarity reverses direction.
• Often paired with a simple DC drive or PWM controller; labeled in VDC and current.

Brush housings and simple two-wire power connections are hallmark features of brushed DC motors.

Brushless DC (BLDC) and PMSM

Externally similar to three-phase AC motors, BLDC/PMSM rely on electronic commutation.

• Three main phase wires plus optional 3–6 small Hall/encoder leads.
• Ratings in VDC, kV (RPM per volt) for hobby/EV; industrial units may state PMSM or require a servo drive/ESC.
• Very smooth, efficient operation; no brushes; often compact for given power.

The combination of three phases, low-voltage DC ratings, and sensor leads points to BLDC/PMSM.

Stepper Motor

Steppers move in discrete steps and have distinctive wiring and mechanical feel.

• 4, 6, or 8 leads; sometimes 5-lead unipolar; high holding torque without motion.
• Step angle on label (e.g., 1.8° or 0.9°); NEMA size codes (e.g., NEMA 17, 23).
• “Coggy” feel when turned by hand; pairs of coils with equal resistance.

Multiple leads, equal coil resistances, and step-angle markings identify steppers quickly.

Servo Motor (AC or DC)

“Servo” refers to a motor with feedback for precise control; the internal motor may be BLDC, PMSM, or brushed.

• Encoder or resolver housing and multi-pin feedback connector alongside power leads.
• Manufacturer and drive model pairing (e.g., Sigma, IndraDrive, MR-J); nameplate shows rated torque and speed.
• Often includes a brake and a keyed shaft; compact for torque rating.

Feedback devices and dedicated servo-drive compatibility are the key signals of a servomotor.

Universal Motor

These high-speed motors run on AC or DC and are common in handheld tools and appliances.

• Brushes and commutator present; very high no-load speed; loud operation.
• Series-wound field; simple two-wire AC connection; often lightweight.
• Found in drills, blenders, vacuums, and similar devices.

If it’s small, loud, brush-equipped, and works on AC mains, it’s likely a universal motor.

Switched Reluctance Motor (SRM)

SRMs are robust and efficient but require a special drive; they have salient poles and unique acoustic signatures.

• Multiple heavy leads to distinct phases; no rotor windings or permanent magnets.
• Requires an SR drive; characteristic torque ripple and “growl.”
• Used in some appliances, EVs, and industrial applications.

Absence of magnets/rotor windings combined with a dedicated SR drive indicates an SRM.

Electrical Tests and Measurements

When labels are missing, basic measurements with a multimeter (and, if available, an oscilloscope) can differentiate motor types without disassembly. Always isolate power, discharge capacitors, and follow lockout/tagout procedures where applicable.

• Coil resistance: Identify pairs of equal resistance to find stepper coils or single-phase auxiliary/run windings.
• Insulation test (megger): Confirms winding-to-case integrity; essential for used/unknown motors.
• Back-EMF test: Spin by hand while monitoring phase outputs. Three sinusoidal waveforms suggest PMSM; trapezoidal suggests BLDC; discrete pulses align with steppers.
• Continuity to brushes: Confirms a brushed DC/universal design if brush-to-commutator continuity is present.
• Capacitor verification: Measure capacitance and ESR on external capacitors to identify PSC or capacitor-start/run types.

These quick tests help map windings and commutation style, narrowing motor identity without powering it unsafely.

Lead Count and Wiring Clues

The number, gauge, and grouping of leads provide strong clues, especially when colors or connectors are standardized.

• 2 leads: Often brushed DC or single-phase shaded-pole/split-phase (no external capacitor).
• 3 heavy leads: Three-phase AC induction/synchronous, or BLDC phase leads (look for separate low-voltage sensor cable to distinguish).
• 3 heavy + 3–6 thin leads: BLDC/PMSM with Hall sensors or encoder.
• 4/6/8 leads: Stepper (bipolar/unipolar/series-parallel options) or multi-tap single-phase induction.
• 6 or 9 leads (labeled T1–T9): Reconfigurable three-phase induction motor for delta/wye or dual-voltage.

Lead groupings, especially separated power and feedback connectors, are often definitive for servo-class and BLDC/PMSM motors.

Controller/Drive Pairing as Evidence

The controller used with a motor is a strong indicator of type; many motors will not operate correctly without their specific drive.

• VFD: Typically pairs with three-phase induction or synchronous AC motors.
• ESC (electronic speed controller): Used with BLDC/PMSM; often labeled for Li-ion pack voltages and kV ratings.
• Stepper driver: Current-limited, microstepping drivers pair with stepper motors.
• Servo drive: Matched to motor/encoder models; closed-loop control indicates a servo system.
• Simple DC PWM: Often drives brushed DC motors.

If you know the intended drive, you can usually infer the motor category even before testing or inspection.

A Practical, Quick Classification Checklist

Use this short sequence in the field to classify an unknown motor with minimal tools and time.

1. Check the nameplate for voltage, phase, frequency, RPM, and special labels (PSC, step angle, Kv, PMSM).
2. Count leads and note connectors: separate sensor feedback suggests BLDC/servo.
3. Look for brushes/commutator or external capacitors/switch cans.
4. Measure coil resistances to find pairs and identify steppers or auxiliary windings.
5. Consider the application: high-speed tools (universal), precise positioning (servo/stepper), fans/pumps (induction/PSC).
6. Match with controller type on hand or specified for the system.

Following these steps typically narrows identification to a single motor type without powering the unit.

Common Pitfalls and Cautions

A few frequent mistakes and safety issues can complicate identification or damage equipment.

• Assuming three heavy leads always mean AC induction; BLDC phases can look identical—check for sensors and DC ratings.
• Powering single-phase motors without the proper capacitor/start circuit can cause overheating or failure to start.
• Confusing servo motors with generic AC motors; servos require matched drives and feedback connections.
• Ignoring insulation integrity; test before energizing an unknown or stored motor.
• Overlooking dual-voltage reconfiguration on 6/9-lead motors; miswiring can damage windings.

Take a moment to verify wiring schemes and drive compatibility; it can prevent dangerous faults and costly damage.

Summary

Identifying a motor is a systematic process: read the nameplate, examine physical features, count and trace leads, perform simple electrical tests, and consider the controller and application. These steps separate AC induction from synchronous, single-phase variants from three-phase, and distinguish DC brushed, BLDC/PMSM, stepper, servo, universal, and switched-reluctance motors. With careful observation and basic measurements, you can classify most motors confidently and select the correct wiring and drive for safe operation.

How to identify types of motors?

To determine your engine, locate your vehicle’s Vehicle Identification Number (VIN), usually found on the dashboard or driver’s side doorjamb, and decode it using an online VIN decoder. The eighth character of the VIN often specifies the engine type. You can also check the engine under-hood label for the engine size and family or look for specific casting or stamped numbers on the engine block itself. 
Using the VIN

1. Find your VIN: Opens in new tabLook for the 17-character VIN on the front of your dashboard or on the driver’s side door pillar or door jamb. 
2. Use a VIN decoder: Opens in new tabEnter the VIN into a free online VIN decoder from sites like AutoZone.com or Edmunds. 
3. Identify the engine code: Opens in new tabThe VIN decoder will provide details about your vehicle, including the engine type, often indicated by the eighth digit of the VIN. 

Checking Under the Hood

1. Open the hood: Release the hood from inside the vehicle. 
2. Locate the engine decal: Look for a white sticker on the radiator support or timing cover, which usually contains the engine size, engine family, and emissions information. 

Using Engine Stamped Numbers 

1. Inspect the engine block: Opens in new tabOn older vehicles, you may find casting or stamped numbers on the engine block.
2. Decode the numbers: Opens in new tabThese numbers can indicate the engine’s year of manufacture, the factory where it was assembled, and the specific engine model. You can use websites or resources to find out what these numbers mean.

Other Methods

• Owner’s manual: The engine information, including the engine code, is typically found on a vehicle identification sticker in the owner’s manual or service booklet. 
• Vehicle registration or insurance documents: These documents often list the VIN and the corresponding engine details. 
• Consult a professional: If you’re unsure, a professional mechanic or the vehicle’s manufacturer can provide detailed engine information. 

What is S1, S2, S3, and S4 in motor?

Duty Types (Duty Cycles)
The continuous load is referred to as S1 Duty Cycle. Electric motors can be used at various Duty Cycles, short-term or intermittent (S2, S3, S4, etc.). A higher power output may be achieved whilst used at short-term or intermittent duty.

What are the four main types of motors?

In this article, we will cover four common types of electric automobile motors, explaining their respective features and highlights.

• Permanent Magnet Synchronous Motor (PMSM)
• Induction Motor (Asynchronous Motor)
• Switched Reluctance Motor (SRM)
• Brushless DC Motor (BLDC)
• Electric Motors for Vehicles from Power Motor.

How to tell the difference between AC and DC motor?

You can tell the difference between an AC and a DC motor by examining its construction and identifying its power source. DC motors typically have brushes and a commutator, which is a segmented ring connected to the rotor that handles current reversal. In contrast, AC motors do not have brushes or a commutator, and the power is supplied through the stationary stator windings, which creates a rotating magnetic field that turns the rotor. 
This video explains the key differences between AC and DC motors: 1mElectrical lecturesYouTube · Nov 7, 2023
Key Construction Differences 

• Brushes and Commutator: Opens in new tabLook for carbon brushes and a segmented commutator ring on the rotor of a DC motor. These are absent in AC motors, making them simpler in construction and more reliable. 
• Rotor vs. Stator Winding: Opens in new tabIn DC motors, the armature (windings) is typically on the rotor, which receives current through the brushes. In AC motors, the stator windings generate the magnetic field, and the rotor (often a “squirrel cage” design) rotates due to electromagnetic induction from this rotating field. 

Power Source and Terminals

• Power Source: Opens in new tabAC motors run on alternating current, which periodically reverses direction, while DC motors run on direct current, flowing in one constant direction, often supplied by batteries. 
• Input Terminals: Opens in new tabDC motors usually have two terminals (positive and negative), whereas AC motors, especially three-phase ones, have three terminals. 

This video visually shows the differences between AC and DC motors: 59sEarth BondhonYouTube · Jan 19, 2023
Other Clues

• Speed Control: AC motor speed is controlled by changing the frequency of the power supply, often using a Variable Frequency Drive (VFD). DC motor speed is controlled by adjusting the voltage or current to the armature windings. 
• Labeling: Check the nameplate or label on the motor. It will often indicate the type of motor, its power source (AC or DC), and other technical specifications.