DC Motor Symbol
Definition: The DC Motor symbol represents a direct-current electric motor — drawn as a circle containing the letter M (and often an equals sign = to denote DC) — that converts direct-current electrical energy into mechanical rotation, with a positive supply terminal (+) and a negative return terminal (−); DC motors are designated M in schematics and are standardised under IEC 60617-06 and ANSI Y32.2 / IEEE 315.
Also known as: DC motor symbol, direct current motor symbol, M symbol schematic, motor symbol circuit diagram, electric motor symbol, brush motor symbol.
What the DC Motor symbol means
The DC Motor symbol in a circuit diagram indicates that the component converts direct-current electrical power into mechanical torque and rotational speed. The symbol's circle represents the motor housing and rotor assembly as a single functional block, with a + terminal (positive supply) and a − terminal (negative return) protruding from the circle. Reversing the polarity of the supply across the two terminals reverses the direction of motor rotation, a property that is fundamental to reversing and H-bridge drive circuits. The annotation M alone indicates a generic motor; adding an equals sign (= or ≡) inside or beside the circle specifies it as a DC motor in IEC convention.
DC Motor symbols appear in schematic diagrams of robotics, automotive systems, industrial drives, and consumer electronics wherever a controlled rotational actuator is needed. In control-circuit schematics, the motor symbol is usually accompanied by its rated voltage and power (e.g. 12 V / 30 W) written as a reference next to the designator label M1. Additional symbols — such as an armature winding symbol inside the circle or a separate field-winding symbol — may be added to represent separately-excited, series-wound, or shunt-wound DC motor configurations in more detailed schematics.
How to identify the DC Motor symbol
The DC Motor symbol is a circle of uniform diameter with a capital letter M printed at its centre. A horizontal line (the positive terminal, +) extends from the left side of the circle and a second horizontal line (the negative terminal, −) extends from the right side of the circle, though the exact exit direction varies by draughting convention. In IEC 60617 practice, the equals sign (=) or two short horizontal lines may appear inside or below the M to explicitly denote DC as opposed to AC. Some schematics place a small arrow inside the circle to indicate rotation direction. The circle-with-M glyph is distinctly different from the transformer, inductor, or relay coil symbols, and its uniform circular outline makes it easily identifiable on any schematic.
Function in a circuit
A DC motor converts direct-current electrical energy into mechanical rotational energy through the interaction of a magnetic field and current-carrying conductors in the motor's armature. When DC voltage is applied across the + and − terminals, current flows through the armature windings, generating a force (torque) on the rotor by the Lorentz principle, causing it to spin. Speed is proportional to applied voltage; torque is proportional to armature current. DC motors are well-suited to variable-speed applications because their speed can be precisely controlled by varying the supply voltage or by using pulse-width modulation (PWM) to adjust average voltage — both techniques are straightforward to implement with solid-state motor driver ICs.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-06 (rotating machines and transformers section) defines the general motor symbol as a circle with M. The DC motor is distinguished by adding the equals sign (=) or a DC annotation inside or adjacent to the circle. The terminal designator letters are per IEC 60034 (rotating electrical machines): terminal 1 (positive) and terminal 2 (negative) for a two-terminal brush DC motor. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (R1989) / IEEE 315-1975, section 4.15, uses the same circle-with-M convention for a motor. DC is indicated by labelling the terminals + and − or by a DC annotation. The designator M is consistent with IEC usage. |
| Key difference | IEC 60617 and ANSI Y32.2 / IEEE 315 use essentially the same circle-with-M glyph for a DC motor. The IEC version more rigorously requires the equals sign (=) inside the circle to explicitly denote DC operation; ANSI drawings more commonly rely on terminal polarity labelling (+ and −) or a 'DC' text annotation. Functionally and visually the two are nearly identical. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Common DC motor voltage ratings: 3.3 V, 5 V, 6 V, 9 V, 12 V, 24 V, 48 V. Power range: 0.1 W (micro motors) to tens of kilowatts (industrial DC drives). Speed range: typically 1,000 RPM–30,000 RPM depending on design. Stall current: 2–10 × rated running current. Brushless DC (BLDC) motors operate at the same voltage ranges but require a three-phase drive; their schematic symbol includes three AC-phase terminals and is annotated BLDC or M~ instead of M=.
Where the DC Motor symbol is used
- Robotics and mechatronics — 6 V or 12 V DC motors driving wheels, arms, and gripper mechanisms via H-bridge driver ICs
- Automotive systems — 12 V DC motors for window lifts, windshield wipers, seat adjustment, and HVAC blower fans
- Consumer electronics — 5 V DC motors in printers, optical disc drives, and camera auto-focus mechanisms
- Industrial DC drives — 24 V to 500 V DC motors for conveyor belts, hoists, and CNC axis drives with regenerative braking
- Toys and hobby electronics — small DC motors in RC vehicles and motorised toys, driven by MOSFET or relay H-bridge circuits
- Battery-powered tools — 18 V to 40 V DC brushed or brushless motors in cordless drills, saws, and garden tools
- Model railway control — 12 V DC motors with variable-voltage speed control via PWM throttle controllers
Example
In an Arduino-driven tank robot schematic, two DC Motor symbols labelled M1 (left track) and M2 (right track) each show a circle with M= glyph; each motor's + terminal connects to one output pin of an L298N dual H-bridge IC, and each − terminal connects to the H-bridge's opposite output, allowing the microcontroller to independently control forward, reverse, and differential steering by changing the PWM duty cycle and polarity applied to each motor symbol.
Key facts
- The DC Motor symbol is a circle containing the letter M; an equals sign (=) inside or beside the circle explicitly identifies the motor as DC in IEC 60617 practice.
- A DC motor symbol has two terminals: + (positive supply, pin id 'pos') and − (negative return, pin id 'neg'); reversing polarity reverses rotation direction.
- The standard designator letter for a motor is M, per both IEC 60617 and ANSI Y32.2 / IEEE 315; individual motors are indexed M1, M2, etc.
- DC motor speed is approximately proportional to terminal voltage; torque is approximately proportional to armature current — making DC motors well-suited to PWM-based speed control.
- Common DC motor supply voltages used in schematics are 5 V, 12 V, and 24 V; the rated voltage and power are written alongside the M designator label.
- An H-bridge circuit (four switches forming an H around the motor) is the standard schematic topology for reversible DC motor control and is referenced alongside the motor symbol in drive-circuit drawings.
- Brushless DC motors (BLDC) use a different symbol: a circle with M and three winding terminals labelled U, V, W, reflecting the three-phase drive requirement.
- Stall current of a DC motor (the current drawn when the shaft is held stationary) can be 5–10 times the running current; this value is critical for sizing fuses and motor driver ICs shown elsewhere in the schematic.
Diagrams that use this symbol
- ignition diagram
- diagram what wires go to the starter solenoid
- ignition switch diagram
- ignition switch wiring diagram
- vehicle wiring diagrams
- car wiring diagram
- starter diagram
- starter motor diagram
Frequently asked questions
What does the DC motor symbol look like?
The DC motor symbol is a circle with the letter M at its centre. In IEC 60617 schematics, an equals sign (=) or two short parallel lines appear inside or below the M to indicate DC operation. Two terminal lines extend from the circle: one labelled + (positive) and one labelled − (negative). The circle is drawn at a consistent size relative to other symbols on the schematic.
What does the DC motor symbol mean in a circuit diagram?
The DC motor symbol means a direct-current electric motor is present at that point in the circuit — a component that converts DC electrical power into mechanical rotation. The + and − terminals indicate polarity: the positive terminal receives the higher supply voltage, and current flows through the motor to the negative terminal, driving the rotor to spin.
What is the designator letter for a DC motor?
The standard designator letter for a motor is M, per IEC 60617 and ANSI Y32.2 / IEEE 315. DC motors are labelled M1, M2, etc. in schematics. 'DC' or an equals sign annotation distinguishes them from AC motors (which may be labelled M~ in IEC convention).
What is the difference between the IEC and ANSI DC motor symbol?
Both IEC 60617 and ANSI Y32.2 / IEEE 315 use a circle with M for a motor. The IEC standard adds an equals sign (=) inside the circle to specifically denote a DC motor. ANSI drawings typically indicate DC by labelling terminals + and − or by adding a 'DC' text annotation rather than a symbol modifier. The two conventions are functionally equivalent.
How do I reverse a DC motor in a circuit diagram?
To reverse a DC motor's direction, the polarity across the + and − terminals must be swapped — i.e. the previously positive terminal is connected to the lower potential and vice versa. In schematics this is achieved with an H-bridge circuit (four switches arranged in an H around the motor symbol) or a DPDT relay, both of which are drawn surrounding the motor symbol on the schematic.
What is the difference between a DC motor symbol and a brushless DC motor symbol?
A brushed DC motor symbol is a circle with M= and two terminals (+ and −). A brushless DC (BLDC) motor symbol is a circle with M and three terminals labelled U, V, W (or 1, 2, 3) representing the three stator phases. The three terminals reflect the requirement for a three-phase electronic commutation drive, rather than the simple two-wire polarity input of a brushed DC motor.
What voltage and power values are written next to a DC motor symbol?
The rated supply voltage (e.g. 12 V DC or 24 V DC) and rated power (e.g. 30 W) are written alongside the M1 designator label on the schematic. The rated current (A) and rated speed (RPM) may also be annotated. These values are sourced from the motor's datasheet and are essential for sizing the motor driver IC, fuse, and power supply shown in the same circuit.
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