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  • New item   -191.27€Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40
    New item   -191.27€Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40 1
    New item   -191.27€Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40 2
    New item   -191.27€Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40 3
    New item   -191.27€Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40 4

    Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40

    Code: STRS4-25L40
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  • Product description

    Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40

    STRS4-25L40 – Sentera Controls transformer speed controller for three-phase 400 VAC fan and pump motors up to 2.5 A, with TK terminals for motor thermal protection. 5 steps, sinusoidal output voltage, automatic restart after power failure.

    Key idea:
    STR-4 functionality plus motor protection: the motor thermal contacts are connected to the TK terminals, so an overheated motor will not go unnoticed. After a power failure the controller restarts by itself.
    What it is for STRS4-25L40:
    This model is intended for medium-power fans (up to 2.5 A) – duct fans in offices, classrooms, retail premises or 2–3 smaller fans together.
    Max. motor current
    2.5 A
    Control
    5-position rotary switch
    Motor protection
    TK terminals
    Supply / protection
    3×400 VAC + N; IP54

    Operating principle

    The controller is wall-mounted. The 3×400 VAC supply is connected to R, S, T and N, the motor – to U, V, W, the motor thermal contacts – to the TK terminals, and the unregulated 230 VAC output (L1) can supply a damper actuator.

    The controller is based on an autotransformer with several taps (steps). When the knob is turned, the motor is switched to another tap, so the output voltage changes in steps rather than steplessly. Regulated output voltages of the L40 version: 0 – 130 – 180 – 230 – 300 – 400 VAC; of the L50 version (14 A model) – 0 – 170 – 220 – 260 – 300 – 400 VAC (the 130 VAC tap is present but not connected). Position 0 – motor off.

    The output voltage is SINUSOIDAL – without phase cutting as in electronic controllers. Therefore the motor runs quietly even at low speed, does not heat up due to higher harmonics and does not interfere with other equipment. This is the solution for motors that hum or buzz when controlled by an electronic controller.

    The TK terminals are intended for motor thermal protection – the thermal contacts built into the motor windings are connected to them. When power is lost and restored, the controller restarts automatically, so ventilation resumes without human intervention. Engineer's note: reducing the voltage of an AC induction motor increases slip, so energy savings are lower than with an EC fan or a frequency inverter. The strength of a transformer controller is reliability, quietness and simplicity, not maximum efficiency.

    Benefits STRS4-25L40?
    Quiet three-phase fan control with motor thermal protection and automatic restart after power failure – without additional relays.

    Technical specifications

    Product type Transformer three-phase fan motor speed controller with TK
    Manufacturer / code Sentera Controls / STRS4-25L40
    Series STRS4 (1.2 / 1.5 / 2.5 / 4 / 6 / 8 / 11 / 14 A)
    Supply voltage 3×400 VAC, 50–60 Hz, with neutral (R, S, T, N)
    Max. motor current 2.5 A
    Regulated output (U, V, W) 0 – 130 – 180 – 230 – 300 – 400 VAC (positions 0–5), sinusoidal voltage
    Unregulated output (L1) 230 VAC, 2 A, 50–60 Hz
    Motor protection TK terminals for motor thermal contacts
    Restart after a power failure Automatic
    Control 5-position rotary switch with OFF position
    Indication Blue LED – device switched on
    Housing Metal, powder-coated RAL 7035
    Protection class IP54 (EN 60529), for indoor use only
    Operating environment -20…+35 °C, 5–95 % rH non-condensing
    Dimensions A 300 / B 325 / C 185 / D 255 / E 255 mm (letter meanings – according to the datasheet drawing)
    Packaging (L × W × H) 340×310×200 mm
    Weight 13 kg (net)
    Compliance LVD 2014/35/EU, EMC 2014/30/EU (EN 61326), WEEE 2012/19/EU, RoHS 2011/65/EU

    Manufacturer documentation

    ✔ Recommended by Elektrotechnikos sprendimai

    Original manufacturer documentation – technical data, wiring diagrams and installation instructions.

    Main functions

    • TK terminals – the motor thermal contacts are connected to the controller – protection against overheating.
    • Automatic restart – after a power failure ventilation resumes by itself.
    • 5 speed steps – one of five voltages or off is selected with the knob.
    • Sinusoidal output voltage – quiet motor operation at all steps.
    • Unregulated 230 VAC output (2 A) – for a damper actuator or indication.

    Where is it used?

    • Three-phase fans with thermal contacts (TK)
    • Production, storage, agricultural buildings
    • Continuously running ventilation systems
    • Three-phase voltage-controllable pumps

    On-demand operation

    For the electrician.
    The TK circuit is connected directly to the controller – no separate protection relay is needed.
    For the ventilation installer.
    After a power failure the system recovers by itself – fewer call-outs.
    For the building owner.
    The motor is protected against overheating; operation is quiet.

    Application guide: how it is used in practice

    Typical STRS4-25L40 applications:

    Site What is connected Result Installer's note
    Fan with thermal contacts Motor TK wires → TK terminals The motor is protected against overheating If the motor has no TK – follow the installation instructions regarding the TK circuit
    Site with occasional power failures Standard supply R, S, T, N When voltage returns, the fan restarts by itself Important for remote or rarely visited sites
    Fan with damper Damper actuator 230 VAC → L1 The damper opens together with the fan L1 load – up to 2 A
    Noise-sensitive environment A motor that hums with an electronic controller Quiet operation at all steps Choose the step according to the required air volume

    How to select the controller current

    Rated current of the motor(s) Recommended model
    up to 1.2 A STRS4-12L40 (1.2 A)
    1.2–1.5 A STRS4-15L40 (1.5 A)
    1.5–2.5 A STRS4-25L40 (2.5 A) ← this model
    2.5–4 A STRS4-40L40 (4 A)
    4–6 A STRS4-60L40 (6 A)
    6–8 A STRS4-80L40 (8 A)
    8–11 A STRS4110L40 (11 A)
    11–14 A STRS4140L50 (14 A)
    Rule: controller max. current ≥ motor rated current (see the motor nameplate). When connecting several fans – motors of the same type – add up their rated currents. Choose a margin if the motor current is close to the model's limit or the fan often runs at the maximum step.
    When to choose another solution: without TK – STR-4; with remote on (NO/NC) and alarm output – STRA4 or STTA4; for control by a 0-10 VDC signal – STVS4; for two speeds – SC2A4 or ST2R4; for a 3×230 VAC network – STR-3.

    Pros

    • TK terminals for motor thermal protection
    • Automatic restart after a power failure
    • Sinusoidal output voltage
    • Unregulated 230 VAC output (2 A)
    • Metal IP54 enclosure

    Cons / limitations

    • No remote switch-on inputs and no alarm output – STRA4 / STTA4 for that
    • Step (not stepless) control – the speed is selected from fixed voltages
    • Heavy weight and large dimensions compared with electronic controllers
    • Indoor use only, operating temperature up to +35 °C
    • Not suitable for EC fans and motors controlled by a frequency inverter

    Safety and installation notes

    • Installation and connection must be carried out by a qualified electrician with the power disconnected.
    • Always connect the protective earth (PE).
    • Check that the motor is suitable for voltage control and that its rated current does not exceed 2.5 A.
    • The supply requires a neutral (N).
    • Connect the TK circuit according to the diagram in the installation manual.
    • The device is heavy – fix it to a load-bearing wall or structure using suitable fixings.
    • For indoor use only (-20…+35 °C, non-condensing); leave space for cooling.

    Quick selection guide

    2.5 A
    3×400 VAC
    TK
    5 steps
    IP54
    Suitable when you need:
    • control of a three-phase fan with TK up to 2.5 A;
    • sites where automatic restart after power failure is important;
    • quiet motor operation.
    Check before use:
    • the motor rated current and whether it is voltage-controllable;
    • whether the motor has thermal contacts (TK);
    • the installation location (13 kg, up to +35 °C).
    Important reminder: STRS4-25L40 does not control EC fans and has no alarm output.

    FAQ

    What are the TK terminals for?
    The motor thermal contacts are connected to them – protection against motor overheating.
    Will the controller restart after a power failure?
    Yes, the datasheet specifies automatic restart.
    What voltages does the motor receive?
    0, 130, 180, 230, 300 and 400 VAC.
    How does it differ from STR-4?
    STRS4 has TK terminals and automatic restart.
    Can it be controlled by a remote contact?
    No, the STRA4 and STTA4 series with NO/NC inputs are intended for that.

    Transformer three-phase fan motor speed controller with TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | STRS4-25L40

    Sentera STRS4-25L40 – transformer speed controller for three-phase fans up to 2.5 A with TK terminals, 3×400 VAC, 5 steps, sinusoidal voltage, automatic restart after power failure, IP54.

    Illustrative image may have been created using AI. The appearance of the product may differ slightly from the image shown. Please refer to the technical specification.

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