This engineering reference provides additional technical background for concepts commonly used with Electromen motor controllers and related products. It is intended to support system design, product selection, commissioning and parameter adjustment.
The equations and examples below describe general engineering principles. Always refer to the product-specific datasheet and user manual for actual electrical ratings, limits, parameters and available functions.
Electrical DC power can be estimated from voltage and current:
P = V × I
where:
P = electrical power [W]
V = voltage [V]
I = current [A]
Example: A motor operating at 24V and 5A receives approximately:
P = 24V × 5A = 120W
Actual mechanical output power is lower because losses occur in the motor, controller and mechanical system.
For a DC or BLDC motor, torque is approximately proportional to motor current within the normal operating range:
T = kT × I
where:
T = motor torque [Nm]
kT = motor torque constant [Nm/A]
I = motor current [A]
For this reason, the current limit of a motor controller can also be used as an effective torque limit.
Continuous current is the current that the controller can supply continuously under specified thermal conditions. Peak current is a higher current that is permitted only for a limited time.
The available continuous current depends strongly on cooling, ambient temperature, installation and PCB or enclosure thermal conditions.
The supply voltage must remain within the operating range specified for the controller. The actual voltage can vary due to power supply regulation, wiring losses, load changes and regenerative braking.
Ripple is the AC variation superimposed on a DC supply voltage. Excessive ripple can cause incorrect operation, increased heating or overvoltage and undervoltage conditions.
The peak voltage, not only the average voltage, must remain within the permitted voltage range of the controller.
A rotating motor generates a voltage called back electromotive force (Back EMF). It increases approximately in proportion to motor speed:
E = kE × ω
where:
E = Back EMF [V]
kE = motor voltage constant
ω = angular velocity [rad/s]
A simplified motor voltage equation is:
V = E + I × R
where R represents motor winding resistance.
As motor speed increases, Back EMF increases and less voltage remains available for producing motor current and torque.
Angular velocity and rotational speed are related by:
ω = 2 × π × n / 60
where:
ω = angular velocity [rad/s]
n = rotational speed [rpm]
Electromen motor controllers use PWM switching to regulate the effective voltage and power delivered to the motor.
A simplified relationship is:
VAVG ≈ D × VDC
where:
VAVG = average motor voltage
D = PWM duty cycle, 0...1
VDC = DC supply voltage
For example, with a 24V supply and 50% duty cycle:
VAVG ≈ 0.5 × 24V = 12V
The actual motor current depends on motor inductance, Back EMF, winding resistance, PWM frequency and mechanical load.
A four-quadrant motor controller can produce motor torque in both directions and can also provide electrical braking in both directions.
| Quadrant | Speed | Torque | Operation |
|---|---|---|---|
| Q1 | Forward | Forward | Forward motoring |
| Q2 | Forward | Reverse | Forward braking |
| Q3 | Reverse | Reverse | Reverse motoring |
| Q4 | Reverse | Forward | Reverse braking |
Four-quadrant operation is particularly useful in applications requiring frequent direction changes, controlled deceleration or regenerative braking.
A rotating mechanical system stores kinetic energy:
EK = 1/2 × J × ω2
where:
EK = kinetic energy [J]
J = total rotational inertia [kgm2]
ω = angular velocity [rad/s]
During regenerative braking, part of this mechanical energy is converted back into electrical energy.
When a suitable battery is used as the DC supply, regenerative energy can normally be returned to the battery, provided that the battery and its charging system can accept the returned current.
Many standard DC power supplies cannot absorb reverse energy. In this case, regenerative braking causes the DC bus voltage to rise.
A braking resistor can be used to dissipate the excess energy as heat.
Instantaneous resistor power can be estimated from:
P = V2 / R
where:
P = resistor power [W]
V = voltage across resistor [V]
R = resistance [Ω]
For example, at 30V with a 10Ω braking resistor:
P = 302 / 10 = 90W
This is instantaneous power. The required resistor rating also depends on braking duration, repetition rate, duty cycle and thermal capacity.
For repeated braking cycles, resistor selection should be based on energy as well as peak power:
E = P × t
where:
E = energy [J]
P = power [W]
t = braking time [s]
Current limiting restricts the maximum motor current without necessarily stopping the motor.
Because motor torque is approximately proportional to current:
Current Limit → Torque Limit
The current limit should be selected according to the motor, controller, mechanical system and required application torque.
I-Trip is an overcurrent shutdown function. A simplified operating condition is:
I > ILIMIT for longer than tTRIP
When this condition is fulfilled, the controller stops motor operation and enters a fault state.
Current limiting and I-Trip should not be confused: current limiting controls the current, while I-Trip protects the system by shutting down after an excessive current condition persists.
Motor winding losses increase approximately with the square of current:
PCU = I2 × R
Doubling the current therefore produces approximately four times the resistive winding loss if resistance remains unchanged.
This is one reason why correct current limit adjustment is important even when the motor appears mechanically capable of producing more torque.
Hall sensors provide information about the electrical rotor position of a BLDC motor. A typical sensored BLDC motor uses three Hall signals: A, B and C.
The controller uses these signals to determine the correct phase commutation sequence.
In six-step 120° commutation, the power stage switches the motor phases according to six electrical rotor states per electrical revolution.
The relationship between mechanical and electrical rotation depends on the number of motor pole pairs:
Electrical revolutions = Mechanical revolutions × Pole pairs
With six Hall states per electrical revolution, the theoretical Hall-based position resolution is:
Positions per mechanical revolution = 6 × Pole pairs
| Pole Pairs | Hall Positions / Revolution |
|---|---|
| 1 | 6 |
| 2 | 12 |
| 4 | 24 |
| 7 | 42 |
A gearbox can increase the effective positioning resolution at the output shaft. A simplified relationship is:
Output positions/revolution = Motor feedback positions/revolution × Gear ratio
For example, a motor providing 42 Hall positions per motor revolution combined with a 100:1 gearbox gives theoretically:
42 × 100 = 4200 positions/output revolution
Practical positioning accuracy is also affected by gearbox backlash, mechanical elasticity, friction and controller tuning.
The basic positioning error is:
Position Error = Target Position − Actual Position
The controller uses this error to determine the required direction and drive level.
Dead zone defines an acceptable error around the requested position:
|Target − Actual| ≤ Dead Zone
Inside this range, corrective motor movement is normally not required.
A smaller dead zone can improve theoretical positioning accuracy but may cause hunting or oscillation if the mechanical system has backlash, friction or elasticity.
The braking area defines how far before the target position the controller starts reducing speed.
Too large a braking area can make positioning unnecessarily slow. Too small a braking area can cause overshoot and corrective reverse movement.
Load compensation provides additional drive at low speed or close to the target position. It can help overcome static friction and mechanical load.
Excessive load compensation can cause unstable movement or oscillation.
Incremental feedback provides movement information but does not inherently provide an absolute mechanical position after power-up.
Homing moves the mechanism to a known reference position and resets the internal position counter.
A learning routine can extend the homing process by moving between mechanical limits and measuring the available travel.
A typical sequence is:
The full range represents the measured or configured mechanical travel:
Full Range = PositionMAX − PositionMIN
Typical analog control ranges include 0–5V and 0–10V. The controller converts the analog voltage into a digital internal value.
A 10-bit analog-to-digital converter provides:
210 = 1024 levels
The theoretical step size over a 0–10V range is approximately:
10V / 1023 ≈ 9.8mV per step
Digital resolution should not be interpreted directly as total system accuracy. Noise, component tolerances and mechanical characteristics also affect practical accuracy.
A limited input range can be scaled to represent the full required command range:
Normalized Value = (VIN − VMIN) / (VMAX − VMIN)
This allows signals such as 0.4–5.0V to be mapped to the required operating range.
A current signal can be converted to voltage using a resistor:
V = I × R
For example, a 20mA signal through a 220Ω resistor produces:
V = 0.020A × 220Ω = 4.4V
The start ramp controls how quickly motor speed or output increases after a start command.
A longer ramp reduces acceleration, current peaks and mechanical shock.
The stop ramp controls how quickly motor speed is reduced.
A very short stop ramp can generate high braking current and high regenerative energy. This is particularly important with high-inertia loads.
The torque required to accelerate a rotating load is related to inertia:
T = J × α
where:
T = acceleration torque [Nm]
J = total rotational inertia [kgm2]
α = angular acceleration [rad/s2]
Higher inertia or faster acceleration therefore requires higher motor torque and typically higher motor current.
Rotational mechanical power is:
P = T × ω
where:
P = mechanical power [W]
T = torque [Nm]
ω = angular velocity [rad/s]
Using rotational speed in rpm:
P = T × 2 × π × n / 60
Example: 2Nm torque at 1000rpm:
P ≈ 2 × 2 × π × 1000 / 60 ≈ 209W
Power semiconductor conduction losses can be approximated by:
PLOSS ≈ I2 × RDS(on)
Actual controller losses also include switching losses, PCB losses, gate-drive losses and other electronic losses.
The maximum continuous output current depends on the controller's ability to transfer heat to the surrounding environment.
Cooling can be improved by:
RS-485 uses differential signalling. Information is determined from the voltage difference between the two bus conductors rather than their voltage relative to ground.
This provides good noise immunity and makes RS-485 suitable for industrial environments.
Long RS-485 lines should normally be terminated at the physical ends of the bus using the termination resistance specified for the system.
Incorrect termination, excessive cable length, poor topology or incorrect wiring can cause communication errors.
Modbus RTU is a serial communication protocol commonly used with RS-485. Each device on the bus has a unique Modbus address.
A Modbus RTU message contains:
Address | Function | Data | CRC
The CRC is used to detect transmission errors.
Devices on the same RS-485 network must use compatible communication settings, including:
In open-loop control, the controller applies an output according to the command without continuously correcting it from measured motor speed or position.
Actual speed can therefore change when load or supply voltage changes.
Closed-loop control compares the requested value with measured feedback:
Error = Setpoint − Feedback
The controller adjusts its output to reduce this error.
Closed-loop control can provide improved speed regulation, positioning accuracy and disturbance compensation.
Backlash is free mechanical movement between components when direction changes. It directly reduces achievable positioning accuracy.
Static friction is the force or torque required to initiate movement. It can be higher than the friction present after motion has started.
This is particularly important in low-speed positioning systems.
Belts, couplings, shafts, gears and mechanical structures can deform under load. Stored elastic energy can cause overshoot or oscillation during positioning.
Inertia describes resistance to a change in rotational speed. High-inertia systems require more torque for acceleration and can return significant energy during deceleration.
Resolution is the smallest change that the feedback or command system can theoretically distinguish.
Accuracy describes how closely the actual mechanical position corresponds to the requested position.
Resolution and accuracy are not the same.
Practical positioning accuracy can be affected by:
PWM motor controllers generate fast voltage and current transitions. Correct installation is therefore important for electromagnetic compatibility.
Typical installation considerations include:
Electromen motor controllers are components intended to be integrated into a complete machine or system. EMC performance of the final installation depends on the complete system, wiring, power supply, motor, enclosure and installation.
| Protection | Purpose |
|---|---|
| Current Limit | Limits motor current and available torque. |
| I-Trip | Stops operation after excessive current persists for the configured time. |
| Overtemperature | Protects the controller against excessive internal temperature. |
| Overvoltage | Protects against excessive DC supply voltage. |
| Undervoltage | Prevents incorrect operation when supply voltage is too low. |
| External Fuse | Protects supply wiring and system against excessive fault current. |
When selecting a motor controller, the following parameters should be considered together:
The motor nominal current alone is not sufficient for selecting a controller. Starting, acceleration, braking and temporary overload conditions can require significantly higher current than steady-state operation.
| Quantity | Relationship | Meaning |
|---|---|---|
| Electrical power | P = V × I | Electrical input or output power |
| Motor torque | T = kT × I | Torque is approximately proportional to current |
| Back EMF | E = kE × ω | Generated motor voltage increases with speed |
| Mechanical power | P = T × ω | Mechanical shaft power |
| Acceleration torque | T = J × α | Torque required to accelerate inertia |
| Rotational energy | E = 1/2 × J × ω2 | Energy stored in rotating mass |
| Resistor power | P = V2 / R | Instantaneous braking resistor power |
| Copper loss | P = I2 × R | Resistive heating in motor windings and conductors |
| Angular velocity | ω = 2 × π × n / 60 | Conversion from rpm to rad/s |
| Current-to-voltage conversion | V = I × R | Conversion of analog current signal using a resistor |
The information in this Engineering Reference Appendix describes general electrical, mechanical and control principles related to Electromen products. It does not replace product-specific technical documentation.
Electrical ratings, current limits, protection thresholds, parameter numbers, I/O functions, braking resistor values and communication settings vary between products. Always verify the requirements from the datasheet and user manual of the specific Electromen product before designing, installing or commissioning the system.
Electromen products are components intended for integration into a complete machine or system. The system designer or integrator is responsible for ensuring that the complete installation meets the applicable electrical, EMC, safety and machine requirements.
