100% New Mitsubishi Programmable Logic Controller PLC FR-A840-00126-2-60 3.7KW

Mitsubishi FR-A840-00126-2-60 | FREQROL FR-A800 Series 3.7kW 400V Variable Frequency Drive — 9A, 0.2–590Hz, Advanced Vector Control, RS-485, Conformal Coating, IP20, 260×150×140mm

Overview

The Mitsubishi FR-A840-00126-2-60 is a 3.7kW, 400V class variable frequency drive from the FREQROL FR-A800 series — Mitsubishi's top-tier general-purpose inverter range.

The FR-A800 is positioned above the FR-E700 and FR-D700 families in Mitsubishi's drive portfolio, bringing advanced vector control, wide-range process network integration, and built-in functional safety into a standard VFD package. 

The 3.7kW/9A unit is among the most commonly specified frame sizes in the A840 line — large enough to drive pumps, fans, and conveyor motors that dominate industrial HVAC and material handling, compact enough to fit comfortably in a standard control panel.

This particular variant carries two important suffix designations.

The "-2" indicates conformal coating applied to the drive's internal PCBs — a factory-applied protective lacquer that seals the circuit board surfaces against moisture, humidity cycling, condensation, and corrosive airborne contaminants.

In applications near coastal environments, in food processing facilities with regular wash-down cycles, in chemical plants with airborne vapours, or in outdoor panel enclosures subject to temperature cycling and condensation, conformal coating significantly extends drive PCB life. 

The "-60" suffix designates the CA terminal type — a 0–20mA current analogue input configuration in addition to the standard 0–10V voltage reference input.

Key Specifications

FR-A800 Control Methods — Selecting the Right Mode

The FR-A840's real sensorless vector control (the default for most applications) does not require an encoder on the motor shaft. It uses the drive's internal current and voltage measurement — continuously computing a real-time model of the motor's rotor flux and torque — to maintain accurate speed and torque control across the full speed range.

The result: stable speed regulation from a few Hz up to the maximum output frequency, with good low-speed torque that makes sensorless vector the correct choice for variable-torque loads like fans and pumps, and for constant-torque loads like conveyors and compressors where the load is predictable and an encoder is not worth the installation cost.

When an encoder is installed on the motor shaft and connected to the drive's optional encoder feedback card, the FR-A840 switches to full closed-loop vector control. Speed regulation tightens dramatically — typically to ±0.01% compared to ±0.2% for sensorless — and the speed control range extends to 1:1500.

This configuration is used for precise tension control in winding applications, coordinated web-speed synchronisation in printing and converting, and machine tool spindle drives where speed accuracy across the full torque range matters.

V/f control (constant voltage-to-frequency ratio) is the simplest and most universal mode — appropriate for multi-motor applications (one drive, multiple motors in parallel), for very long motor cables where the vector control model cannot accurately account for cable impedance, and for retrofitting legacy equipment where the motor data is unknown.

0.2 to 590Hz Output — The Extended Frequency Range

Most general-purpose inverters target a 0–400Hz output range. The FR-A840's 590Hz upper limit serves a specific engineering need: high-speed motor applications where the motor's rated frequency is above 60Hz.

High-frequency induction motors in grinding spindles, dental drills, centrifugal separators, and air-bearing spindles operate at 200Hz, 400Hz, or higher nominal frequencies — requiring a drive that can supply the necessary output frequency without limiting the motor's maximum speed.

At 590Hz output, the FR-A840 can drive motors running at up to 30,000–40,000 RPM depending on the motor's pole count — territory typically reserved for specialised high-speed drives, achieved here in the FR-A800's standard catalogue product.

Network Integration and RS-485

The FR-A840's built-in RS-485 port supports Modbus RTU communication — the most widely implemented serial communication protocol in industrial drives and instrumentation.

Using the standard Modbus register map published by Mitsubishi in the FR-A800 communication manual, a PLC, SCADA system, or building management controller can read actual speed, current, torque, and fault history from the drive and write speed setpoints, run/stop commands, and parameter updates — all over a single RS-485 twisted-pair cable running at up to 19.2kbps.

Beyond Modbus, the FR-A800 supports optional network communication boards for CC-Link (A8CON-CCL), PROFIBUS-DP (A8CON-PBT), DeviceNet (A8CON-DNT), and EtherNet/IP (A8CON-EIP) — the same A8CON option cards share a slot across the FR-A800 frame range, so the communication option chosen for a 3.7kW unit is architecturally identical to that used on a 55kW unit in the same system.

FAQ

Q1: What is conformal coating, and when is it necessary for the FR-A840?

Conformal coating is a factory-applied thin polymer film on the drive's internal PCBs that seals circuit board traces, solder joints, and components against moisture, humidity, and light chemical contamination.

Without it, repeated humidity cycling (condensation forming and evaporating on PCB surfaces) causes electrochemical migration — gradual growth of conductive dendrites between traces that eventually causes short circuits.

Conformal coating is specified for drives installed in outdoor enclosures, coastal environments, food processing or pharmaceutical facilities with high humidity or wash-down operations, and chemical processing environments with airborne acids or alkalis.

For standard climate-controlled indoor industrial panel installations, the non-coated variant is adequate.

Q2: What is the difference between Normal Duty (ND), Light Duty (LD), and Heavy Duty (HD) ratings?

These designate the overload tolerance the drive can handle continuously. ND (Normal Duty) at 9A supports 150% overload for 60 seconds — appropriate for fans, pumps, and moderate conveyor loads with short starting peaks.

HD (Heavy Duty) rates the same drive at 6A continuous with 200% overload for 60 seconds — for cranes, hoists, extruders, and applications with prolonged heavy starting loads.

LD (Light Duty) operates at 11.5A with reduced overload tolerance, allowing the drive to power a slightly larger motor for low-overload applications like fans and centrifugal pumps. 

Select ND for most general applications; HD when the driven machine requires sustained overloads during starting or load peaks.

Q3: What motor data parameters need to be entered for sensorless vector control to function correctly?

The FR-A840 requires the motor's rated power (kW), rated voltage, rated current, rated frequency, and number of poles as a minimum parameter set.

For best performance, the drive should also be given the motor's no-load current and primary resistance (R1) — either entered from the motor nameplate or measured automatically using the FR-A800's auto-tuning function (offline tuning with the motor stationary).

Auto-tuning takes approximately 30–60 seconds per motor and generates an accurate motor model. 

After tuning, sensorless vector control accuracy is maximised — especially important for speed control below 10Hz, where an inaccurately modelled motor can be unstable.

Q4: How is the drive reset after a fault, and what fault history is available?

The FR-A840 retains a fault history log of the most recent eight fault events, accessible through the operator panel (FR-DU08 or FR-LU08) or via Modbus registers. Each entry records the fault code and the drive's operational parameters at the time of fault (output frequency, current, voltage, temperature).

To reset the drive after a fault: clear the trip condition that caused the fault (e.g., restore correct supply voltage for overvoltage, reduce load for overcurrent), then send a reset command via the control terminal (RES terminal on input card) or via the operator panel's STOP/RESET key.

Fault history is useful for distinguishing one-time transient trips from recurring systematic faults that need engineering investigation.

Q5: Can the FR-A840-00126-2-60 be used for constant torque applications such as conveyors and compressors?

Yes. The FR-A840 in Normal Duty (ND) configuration handles constant torque loads up to the rated 9A continuous current — appropriate for constant-torque machines whose starting current does not exceed the 150% overload capacity for more than 60 seconds.

For heavy constant-torque applications with difficult starting characteristics (loaded conveyors starting against a full belt, reciprocating compressors with check valves), the HD rating (6A continuous / 200% overload) provides more sustained overload headroom.

Select ND for most conveyors and light compressors; HD when the starting torque requirement consistently approaches or exceeds 150% of rated.