Causes of the E.OU Error and Physics of Regenerative Braking
To eliminate the E.OU error (in some sources it is mistakenly searched for as "E.OV") during deceleration, excess energy must be dissipated to an external braking resistor, as the internal capacitance of the frequency inverter's capacitors is unable to absorb large amounts of regenerative power. When the stator supply frequency of an induction motor decreases faster than the actual rotor speed under the influence of inertia, the motor enters generator mode. At this moment, the slip becomes negative, and the direction of active power flow reverses: energy begins to flow from the mechanical load back into the frequency inverter through the freewheeling diodes of the IGBT power bridge. Since standard rectifiers are uncontrolled and unidirectional, this energy accumulates in the DC link capacitors (DC bus), leading to a rapid rise in voltage.
If the DC bus voltage exceeds the critical threshold (typically around 760-800 V for three-phase 380 V grids), the Veichi VFD control system instantly blocks output pulses and generates an E.OU (Overvoltage) alarm. This protects the power capacitors and IGBT modules from electrical breakdown but results in an uncontrolled motor coast-to-stop. This problem is particularly acute when working with high-inertia mechanisms such as exhaust fans, large blowers, centrifuges, as well as in hoisting mechanisms (cranes, elevators, winches) where the potential energy of the load is continuously converted into kinetic energy during lowering.
Braking Resistor Calculation Methodology: Resistance and Power
The braking resistor resistance (Ohm) must never be lower than the minimum allowable value specified in the manual for the specific Veichi model to avoid burning out the built-in braking chopper (IGBT transistor), while its power (W) is calculated based on the Duty Cycle. The choice of resistor resistance determines the maximum current that will flow through the braking transistor (chopper) when it opens. If the resistance is too low, the current will exceed the maximum allowable limit for the transistor, leading to its thermal destruction and a short circuit. If the resistance is too high, the braking current will be insufficient for rapid energy dissipation, and the DC bus voltage will still exceed the limit, triggering the E.OU error again.
The power dissipation of the braking resistor depends on the operating mode of the equipment and the duration of the braking cycle. For calculation, the Duty Cycle (ED) is used, expressed as a percentage of the total duty cycle time. For horizontal loads, such as conveyors, packaging machines, or transfer cars, where braking occurs periodically and lasts for a short time, the Duty Cycle is typically 10-15%. For vertical loads (hoists, crane winches) or high-inertia centrifuges, where the motor operates in generator mode for a long time or even the entire load lowering cycle, the Duty Cycle ranges from 50% to 100%. The formula for calculating the nominal power of the resistor is: P = P_motor * K * Duty_Cycle, where K is the braking efficiency coefficient (usually assumed to be 0.8-1.0).
Examples of Resistor Selection for Veichi AC10 and AC310 Series
To select the braking equipment correctly, always compare the technical specifications of the series: low-power Veichi AC10 VFDs have built-in braking units, whereas heavy high-power AC310 series may require an external braking module (chopper). Let's look at specific engineering examples of equipment selection to resolve the E.OU error issue.
Example 1: A 2.2 kW (380 V) Veichi AC10 frequency inverter operates on a horizontal belt conveyor. For this model, the manufacturer recommends a minimum resistor resistance of 100 Ohm. Since the load is horizontal and the braking time is only 2 seconds every 30 seconds (Duty Cycle around 10%), the resistor power is calculated as: 2200 W * 0.8 * 0.10 = 176 W. In practice, the nearest standard rating with a safety margin is chosen — a 100 Ohm resistor with a power of 250 W or 300 W.
Example 2: An 11 kW (380 V) Veichi AC310 frequency inverter controls a hoisting mechanism (vertical load). The minimum allowable resistance for this model is 16 Ohm. Since the load is lowered for 20 seconds out of a total 40-second duty cycle, the Duty Cycle is 50%. Power calculation: 11000 W * 1.0 * 0.50 = 5500 W. However, considering intense heat radiation and harsh operating conditions, it is recommended to use a resistor bank with a total resistance of 16 Ohm and a total power of at least 1000 W - 2000 W for cyclic modes, or a full resistor cabinet of 5-6 kW for continuous lowering.
Configuring Veichi Frequency Inverter Parameters
After physically connecting the resistor to the P+ and PB terminals, it is mandatory to activate the dynamic braking function in the Veichi VFD parameters and configure the deceleration time to avoid premature protection triggering. Simply connecting the resistor is not enough if the software settings have automatic voltage limiting functions enabled, which interfere with the normal operation of the braking chopper.
For correct system operation, follow these steps in the frequency inverter programming menu:
- Locate parameter F10.11 (DC-bus overvoltage suppression) and set its function digit to 0 (disabled). If this function is enabled, the VFD will automatically extend the braking time in an attempt to reduce the DC bus voltage, making a fast stop at the set time impossible.
- Check parameter F10.12 (bus overvoltage suppression point). For a three-phase 380 V grid (T3), the factory overvoltage point is about 820 V DC. When this voltage is reached, the built-in IGBT chopper opens and begins passing current through the resistor.
- Configure parameter F01.23 (deceleration time 1) according to the process requirements. Thanks to the installed resistor, you can safely reduce this time severalfold without the risk of triggering an E.OU fault.
- Monitor the current DC bus voltage status using monitoring parameter U0.02 during test runs under maximum load.
Comparison Table for Resistor Selection Across Different Load Types
Use the ready-made table values for quick design of electric drive systems, adjusting the resistor power depending on the actual operating mode of the equipment. Below are the recommended parameters for popular Veichi frequency inverter models to help avoid design errors.
| VFD Power (kW) | Veichi Model | Recommended Resistance (Ohm) | Power (Horizontal Load, ED 10%) | Power (Vertical Load, ED 50-100%) |
|---|---|---|---|---|
| 0.75 kW | AC10-S2-R75G | 150 Ohm | 80 W | 400 W |
| 1.5 kW | AC10-T3-1R5G | 150 Ohm | 150 W | 750 W |
| 2.2 kW | AC10-T3-2R2G | 100 Ohm | 250 W | 1100 W |
| 5.5 kW | AC310-T3-5R5G | 40 Ohm | 500 W | 2700 W |
| 11 kW | AC310-T3-011G | 16 Ohm | 1000 W | 5500 W |
| 15 kW | AC310-T3-015G | 16 Ohm | 1500 W | 7500 W |
Steps for Safe Installation and Connection
Mount braking resistors exclusively on metal, non-combustible surfaces in well-ventilated areas of the control cabinet, as their temperature can exceed 150 degrees Celsius during active braking. Failure to follow installation rules can lead to overheating of adjacent components, melting of cable insulation, or even fire.
To ensure long-term and safe operation of the equipment, follow this installation algorithm:
- Completely de-energize the frequency inverter and wait at least 10 minutes for the discharge resistors to reduce the voltage on the power capacitors to a safe level (verify the absence of voltage on the P+ and P- terminals using a voltmeter).
- Check the actual resistance of the braking resistor with a multimeter before installation to ensure there are no manufacturing defects or transport damage.
- Connect the resistor terminals to the P+ and PB terminals on the Veichi VFD chassis. It is strictly forbidden to connect the resistor to the PE grounding terminals, COM or GND control terminals, or directly to the negative potential bus P- without an external braking module.
- Use only heat-resistant copper cable of the appropriate cross-section with reliable insulation for connection, as the wires will be in a high-temperature zone.
- Be sure to ground the metal chassis of the braking resistor by connecting it to the general grounding loop of the electrical installation.
If you need a high-quality specific category of frequency inverters or professional assistance in calculating braking systems, please contact our store specialists. We will help you select the optimal Veichi equipment for any process tasks.
