Lenze 3A2956 7812.2 E SO 7800 Series Transistor DC Motor Controller
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Product Information
The Lenze 3A2956 (Type 7812.2 E SO) is a transistorized DC speed controller from the Lenze 7800 Series, engineered for closed-loop speed regulation of industrial DC motors. Operating from a three-phase AC mains supply rated between 380 V AC and 415 V AC, this compact drive module supplies a continuous armature current of 12 A with an output voltage rating up to 270 V DC. Utilizing a pulse-width modulated transistor output switching stage combined with closed-loop DC tachometer generator feedback, the unit maintains high dynamic response and precise speed stability across variable load conditions in processing and material handling applications.
Field connection and integration rely on physical terminal points supporting a 0 to +/-10 V DC analog setpoint signal, controller enable and pulse inhibit command inputs, and tachometer feedback connections. Putting a replacement module into service does not require programming software or handheld terminal devices, as drive setup is accomplished entirely through hardware potentiometers and jumper links located on the module. Commissioning engineers calibrate key operational characteristics—including maximum motor speed, armature current limits, acceleration and deceleration ramp times, and IxR voltage compensation—directly on the board to align output behavior with the driven machinery.
Operational diagnostics are facilitated by front-panel LED indicators that display controller readiness, output suppression, and active fault states. Supplementary test points on the circuit board allow technicians to evaluate armature voltage and current signals directly using a multimeter or oscilloscope. If persistent overcurrent or hardware faults occur during operation, board-level power component failures cannot be serviced in the field, making a tested replacement or repair service through ABC Industrial Parts the standard solution for returning equipment to active service.
Technical Specifications
| Manufacturer | Lenze |
| Part Number | 3A2956 |
| Model / Type | 7812.2 E SO |
| Product Family | 7800 Series |
| Component Type | DC Motor Controller |
| Supply Voltage Range | 380 V AC to 415 V AC (3-Phase) |
| Rated Armature Current | 12 A Continuous |
| Maximum Output Voltage | 270 V DC |
| Control Method | Transistor Switching DC Speed Regulator |
| Setpoint Input Signal | 0 to +/-10 V DC Analog |
| Speed Feedback | DC Tachometer Generator |
Programming and Configuration
The Lenze 7812.2 E SO DC speed controller operates entirely on analog hardware control principles, eliminating the need for software installations, fieldbus parameter files, or digital programming cables. Drive calibration is executed manually using dedicated trimpots and jumper configurations accessible on the unit.
Commissioning involves setting physical potentiometers to match the electrical and dynamic requirements of the attached DC motor. Key adjustable parameters include maximum motor speed, current limit protection, acceleration and deceleration ramp rates, and IxR compensation to maintain steady motor torque at low speeds under changing mechanical loads.
Communication and System Integration
System integration is achieved through standard control wiring terminated at the module's connection terminals. The unit accepts a 0 to +/-10 V DC analog setpoint signal, making it fully compatible with traditional PLC analog output cards and manual setpoint potentiometers.
In addition to setpoint references, control terminals accommodate enable and pulse inhibit signals for starting and stopping drive output, as well as dedicated inputs for a DC tachometer generator. The module mounts directly into standard Lenze 7800 series control racks and enclosure panel assemblies.
Diagnostics and Status Indication
Real-time operational feedback is provided by three status LEDs located on the front panel of the drive. These indicators allow maintenance staff to quickly identify normal operating conditions, active output inhibits, or trip states caused by electrical or thermal faults.
For detailed signal troubleshooting, the module includes dedicated circuit board test points. Technicians can connect an oscilloscope or multimeter to these points to measure DC armature voltage and current dynamics during operation or current limit trip conditions.
Status LED Indicators
| LED | Color/Status | Meaning |
|---|---|---|
| Betrieb / Ready | Green - Solid | Power supply and operating status normal |
| Impulssperre / Pulse Inhibit | Yellow - Solid | Controller output disabled |
| Störung / Fault | Red - Solid | Overcurrent, overtemperature, or internal hardware error |
Replacement and Spare Part Considerations
When installing a replacement Lenze 3A2956 module into an existing panel, care must be taken to match the hardware settings of the original drive. Because settings are managed by physical potentiometers and jumpers, technicians should record the trimpot positions for speed, current limits, ramp times, and IxR compensation on the faulty unit prior to removal.
Before applying power to the replacement unit, verify that mains supply voltages fall within the 380 V AC to 415 V AC range and that tachometer generator polarity is correctly wired. Correct tachometer wiring ensures stable closed-loop feedback control without run-away conditions upon startup.
Frequently Asked Questions
What programming software is required to commission the Lenze 3A2956 drive?
No programming software or digital handheld terminal is required. Commissioning is performed entirely via front-accessible physical potentiometers and jumper settings.
What are the power supply requirements for the Lenze 7812.2 E SO?
The module requires a three-phase AC mains supply rated between 380 V AC and 415 V AC, delivering up to 270 V DC armature voltage at a continuous current rating of 12 A.
What motor speed feedback device is compatible with this unit?
The 7812.2 E SO utilizes direct closed-loop feedback from a DC tachometer generator connected to its dedicated feedback terminals.
What do the front-panel LEDs indicate?
The green LED (Betrieb / Ready) indicates normal power and operating status, the yellow LED (Impulssperre / Pulse Inhibit) indicates that output is disabled, and the red LED (Störung / Fault) indicates an overcurrent, overtemperature, or internal hardware fault.
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Disclaimer:
We are not an authorised distributor of Lenze.
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