Hoval MRHX-02N - User Manual

Questions and Answers

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Ms. Patricia FergusonAug 13, 2025
What to do if Hoval Engine shows error E01?
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  Ryan FloydAug 13, 2025
  If the Hoval Engine displays error code E01, it could be due to several reasons. The belt might be slipping or broken, in which case you should tension or replace it. If an external rotation guard is activated unintentionally, deactivate it by removing the jumper. If the external rotation guard is in use, inspect the magnet, sensor, and holder for any looseness or missing parts, ensuring the sensor is correctly positioned in front of the magnet with a 3-5 mm distance. If the rotor and pulley were accidentally calibrated, redo the calibration process. Lastly, if the motor is too powerful for the rotor's load, exchange the MRHX motor and DRHX controller to match the rotor type; contact Hoval for support.
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Laurie SandersAug 17, 2025
Why does the rotor stop unintentionally in Hoval Engine?
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  Caitlin RosarioAug 17, 2025
  If the Hoval Engine rotor stops unexpectedly, it could be due to a few reasons. The internal rotor guard might be detecting a loose or defective belt, so try tightening or replacing the belt. Alternatively, the internal rotor guard may be incorrectly calibrated, so you might need to recalibrate it. It could also be due to the external rotation guard being activated, even if it's not in use. In this case, refer to fault code E01 for guidance.
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keith71Aug 21, 2025
What does error E06 mean on a Hoval Engine?
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  rmarksAug 21, 2025
  If the Hoval Engine displays error code E06, it could be due to a wobbling belt, potentially caused by incorrect mounting or a damaged rotor. Correct and tension the belt, and check the installation for damage. If springs or dampers are used with the motor bracket, replace them with a fixed motor bracket. If the motor is under-dimensioned, verify the correct size/type of drive equipment is mounted; if correct, maintenance is needed. Also, check the pressure drop, air volumes, and velocity, comparing them to the maximum values in the Hoval handbook. Contact Hoval for support if needed.
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Lauren MillerAug 26, 2025
How to fix Hoval Engine stepper motor/ rotor running in wrong direction?
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  Linda YoungAug 26, 2025
  To correct the direction of the stepper motor/rotor in a Hoval Engine, swap two phase wires in the controller DRHX. Specifically, switch the "V" (black) and "W" (blue) cables to change the motor direction.
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Mark KellerAug 30, 2025
What to do if DRHX cuts out due to an alarm in Hoval MRHX-02N?
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  Leslie AllenAug 30, 2025
  If the Hoval Engine DRHX cuts out due to an alarm, read the active alarms via the display and address the cause of the alarm.
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Kelly GonzalezSep 3, 2025
What does Hoval MRHX-02N error E09 mean?
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  Christopher WalkerSep 3, 2025
  If the Hoval Engine displays error E09, which indicates an internal error between the motor (MOC) and application (AOC), it might be due to an update issue during new software installation. Try reinstalling the firmware. If the error persists after the system has been running for a while, consider replacing the DRHX controller.
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mary00Nov 7, 2025
What to do if the stepper motor is not running in Hoval MRHX-02N?
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  Travis Collins DVMNov 7, 2025
  If the Hoval Engine stepper motor isn't running, start by verifying the voltage supply (230 V AC) to the DRHX terminals "L" and "N", ensuring it matches the rating plate. A constant green light on the LED display indicates proper voltage. Then, check all electrical connections, ensuring they are secure and free of loose threads; use cable shoes for multi-core connections. Also, ensure the DIP switch is correctly set for the selected stepper motor size and speed. If using A/D control, confirm the DRHX receives a start signal via the configured digital input (Din 1, 2, or 3). Verify that DRHX receives an operating signal exceeding 1.1 V on "0-10 V In.". Check for active alarms via the display and resolve the cause. If the motor has stopped 5 times due to overloading, reset the alarm by disco...

The OJ Electronics Stepper motor system, comprising MRHX stepper motors and DRHX control units, is designed for regulating the speed of rotary heat exchangers in air handling units (AHUs). This manual specifically details the setup of the Hoval drive system in RHE applications, with the DRHX control unit pre-programmed with a Hoval custom UDF file.

Function Description

The DRHX controller regulates the speed of a rotary heat exchanger by controlling an MRHX stepper motor. The system is designed for analogue control (0-10V) by default, but can also be controlled via Modbus or OJ's DRHX PC – Tool. Key digital inputs (DI) include DI1 for rotor rotation, DI2 for enabling an external rotor guard, and DI3 for receiving a signal from an external rotor guard. The system features built-in stepper motor protection and an EMC filter.

A "Start function" automatically provides higher current to the motor during start-up (10 seconds at 150% of rated current). A "Purging function" (cleaning) automatically activates when the stepper motor has been stopped for 10 minutes, causing the shaft to rotate 10 times at low speed before stopping. A "Holding torque" (brake function) is activated when the motor has no operating signal, preventing the rotor from rotating due to airflow or starting by itself.

The system includes built-in protection mechanisms:

If the internal temperature of the DRHX exceeds 95°C, the unit reduces current to the stepper motor to lower heat generation.
Current limitation protects the stepper motor and cables, preventing the supply of more current than rated.
Short-circuit protection is provided for phase-phase short-circuits on the DRHX connector terminals (U, V, W) and for DRHX control inputs.

Rotation monitoring is crucial due to the mechanical connection between the stepper motor and rotor via a belt. The DRHX controller triggers a "rotor guard" alarm (E01) if the motor is no longer turning the rotor due to lack of tension or a damaged belt. The system offers both internal and external rotor monitoring. The internal rotor guard, which is the factory setting, monitors rotor rotation by measuring the electrical signal from the motor every 10 seconds. If five consecutive failed detections occur within one hour, an E01 alarm is triggered. This internal monitor operates automatically at motor speeds above 25 rpm. If an external rotor guard (3-wire sensor) is connected to the digital input ports (GND, +12V, DI3) and a jumper is placed between terminals 11 and 12, the internal rotor guard is automatically deactivated. The external sensor requires a distance of 3-5 mm from the magnet.

Important Technical Specifications

Control Unit (DRHX-1055 MAD5 / DRHX-1220 MAD5):

Max Torque: 2 Nm (DRHX-1055 MAD5), 4 Nm (DRHX-1220 MAD5), 8 Nm (DRHX-1220 MAD5 for MRHX-08N, with a note that 8 Nm torque is at max. 250 motor rpm, but only max. 5 Nm torque at max. 400 motor rpm).
Input Signal: 0-10V.
Output Rpm 50Hz: 150/170/200/400 rpm (depending on configuration).
Voltage Input 50/60Hz: 1x230V AC.
Motor Voltage: 3x0-200V AC.
Rated Current: 0.6A (DRHX-1055 MAD5), 2.4A (DRHX-1220 MAD5).
Class of Protection: IP54.
Weight: 0.9 kg.

Motor (MRHX-3P0xN-03C5):

Weight: 2.4 kg (MRHX-02N), 3.5 kg (MRHX-04N), 5 kg (MRHX-08N).
Shaft Ø: 12 mm.
Motor Power: 0.055 kW (MRHX-02N), 0.110 kW (MRHX-04N), 0.220 kW (MRHX-08N).

Electrical Connections:

Power Supply: 230V AC, +/-10%.
Control Terminals: Max. wire dimension 0.75 mm².
PE Wire Recommendation: 20 mm longer than other wires for safety.
Motor Cable: Factory-connected, not allowed to be replaced or shortened.
Digital Relay Output: Potential-free relay with changeover switch. Max. load 2A/30V DC/24V AC. Factory-configured as an alarm relay.

DIP Switch Settings:

DIP 1-2: Motor size (1Nm, 2Nm, 4Nm, 8Nm).
DIP 3-4: Motor rpm (Speed 1 400 rpm, Speed 2 200 rpm, Speed 3 170 rpm, Speed 4 150 rpm).
Incorrect DIP switch settings can lead to reduced performance or overload.

Usage Features

Installation:

Control Unit: Must be positioned for free airflow around cooling fins, installed vertically and on a slope (max. 45° gradient) for optimal cooling. Cable glands must not point upwards to prevent water ingress. Attach using at least 3 screw holes. Avoid direct sunlight.
Motor: Must be mounted on a fixed motor bracket, firmly attached to the chassis of the rotary heat exchanger or AHU. Do not use vibration dampers or springs.
Potential Equalization: Crucial to prevent electrical interference. Control unit and motor must be fixed with metallic screws into the casing. If not factory-mounted, use lugs and a 10 mm² equalization conductor attached to the DRHX alu-profile and between the stepper motor and AHU chassis.

Operation:

Test Button: Located inside the controller, used for test functions.
- Running Test for RHE: Press and hold the test button. The controller enters test mode, display shows "tSt", LED is orange. Motor rotates at 100 rpm. Release button to stop. Belt must be mounted.
- Pulley Calibration Test: Used for internal rotor guard calibration. Turn off DRHX, remove belt. Power up, briefly press test button (<1 sec). LED shines orange, display shows "tSt". Motor accelerates to 100 rpm. Internal rotor guard function starts, motor accelerates at short intervals for 1 minute. If motor stops and restarts, calibration is correct. If motor continues to run, recalibration is needed (press and hold test button until LED flashes orange, then release). Mount belt after calibration.
Display: Shows current status (stepper motor speed, rotor speed, torque, fault codes, purging function, test function, hold function, stop mode).
LED Indicator: Provides status feedback (OFF, Green ON, Flashing green, Red ON, Flashing red, Orange ON, Flashing orange).

Troubleshooting:

Rotation Direction: If rotor rotation is wrong, swap the "V" (black) and "W" (blue) cables to change motor direction.
Alarm Codes: Displayed on the unit. "Critical" alarms stop the motor; "Non-critical" alarms reduce performance. Alarms are automatically reset if the situation passes or if power is disconnected for >60 seconds.
Common Alarms:
- E01: Alarm from rotor guard (belt slipping/broken, external guard activated incorrectly, sensor/magnet loose, incorrect calibration).
- E02/E03: Excessive/insufficient supply voltage.
- E04: Increased power to motor (short-circuiting cable/connector/motor).
- E05: Excessive internal temperature (>95°C).
- E06: Blocked motor (rotor load too high, wobbling belt, springs/dampers used, undersized motor).
- E07: No valid RS-485 interface communication.
- E08: Phase fault on stepper motor power supply.
- E09: Internal hardware error.

Maintenance Features

Safety First: Always disconnect mains voltage and wait approximately 3 minutes before opening the DRHX cover to allow capacitors to discharge.
Cable Glands: Use factory-fitted PG9 cable glands for power and stepper motor cables. Re-tighten to ensure ingress protection. Unused glands should be replaced with blank glands/plugs.
Cleaning: The purging function helps clean the system automatically.
No On-Site Repair: DRHX control units and MRHX motors cannot be repaired on site. Contact Hoval for support if defective.
Pre-Installation Check: If the product is damaged during transportation, it must be checked and repaired by OJ Electronics A/S before installation and energization.
Firmware Update: Internal errors (E09) might be resolved by re-installing firmware.
Belt Maintenance: Regular checks for belt tension and condition are essential to prevent E01 alarms.
Sensor/Magnet Check: For external rotor guards, ensure the magnet/sensor/holder is secure and correctly positioned.

Hoval MRHX-02N Specifications

General

Brand	Hoval
Model	MRHX-02N
Category	Engine
Language	English