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  • New item   -44.32€Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50
    New item   -44.32€Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50 1
    New item   -44.32€Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50 2

    Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50

    Code: ATR-4-25L50
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  • Product description

    Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50

    ATR-4-25L50 – Sentera Controls three-phase 400 VAC autotransformer for fan speed control, up to 2.5 A. The secondary winding has taps at 130, 170, 220, 260, 300 and 400 VAC; designed for installation in a control panel.

    Key idea:
    An open (IP20) autotransformer without enclosure or switch – a component for control panel builders: the required voltage is selected by wiring or an external selector switch, and the motor receives a sinusoidal voltage.
    What it is for ATR-4-25L50:
    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. current
    2.5 A
    Taps
    0 / 130 / 170 / 220 / 260 / 300 / 400 VAC
    Primary voltage
    3×400 VAC ±10 %, 50–60 Hz
    Protection
    IP20, for control panel installation

    Operating principle

    The autotransformer is fixed with sturdy brackets to the control panel mounting plate. The 3×400 VAC supply is connected to L1, L2, L3, the motor – to U, V, W, earth – to PE. Connection via screw terminals.

    The autotransformer reduces the primary winding voltage in steps. The secondary winding has taps at 0, 130, 170, 220, 260, 300 and 400 VAC – the fan speed is set by selecting a tap. Control is in steps, not stepless.

    The output voltage is SINUSOIDAL, so the motor runs quietly even at low speed, without electronic hum. This also suits motors that buzz with an electronic controller.

    Insulation class F (155 °C), dielectric strength 2500 VAC. The device operates quietly and is well protected against corrosion. Engineer's note: reducing the voltage of an AC asynchronous motor increases slip, so less energy is saved than with an EC fan or frequency inverter. The strength of a transformer speed controller is reliability, quietness and simplicity, not maximum efficiency.

    Benefits ATR-4-25L50?
    A compact and lighter solution than a wall-mounted controller when speed control has to be integrated into an electrical or automation control panel.

    Technical specifications

    Product type Three-phase autotransformer for fan speed control
    Manufacturer / code Sentera Controls / ATR-4-25L50
    Series ATR-4 (1.5 / 2.5 / 4 / 6 / 8 / 11 / 14 A)
    Primary voltage 3×400 VAC ±10 %, 50–60 Hz (L1, L2, L3)
    Rated max. current 2.5 A
    Secondary winding taps (U, V, W) 0 / 130 / 170 / 220 / 260 / 300 / 400 VAC
    Insulation class 155 / F
    Construction class II
    Dielectric strength 2500 VAC
    Connection Screw terminals; PE terminal
    Installation Sturdy brackets for fixing to the control panel mounting plate
    Protection class IP20 (EN 60529), for indoor use only
    Operating environment Max. +35 °C, < 90 % rH non-condensing
    Dimensions A 108 / B 100 / C 112 / D 90 / E 75 mm (letter meanings – according to the datasheet drawing)
    Weight 3.6 kg (net)
    Compliance LVD 2014/35/EU, EMC 2014/30/EU, 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

    • 7 output voltages – 0, 130, 170, 220, 260, 300 and 400 VAC – speed is selected by tap.
    • Sinusoidal output voltage – quiet motor operation at all steps.
    • Screw terminals – fast and reliable connection in the control panel.
    • Sturdy mounting brackets – simple fixing to the control panel mounting plate.
    • Class F insulation – durability and reliability.

    Where is it used?

    • Electrical and automation control panels with fan control
    • Ventilation unit manufacturers (OEM)
    • Industrial ventilation systems with three-phase motors
    • Systems where the motor voltage needs to be reduced to a constant level

    On-demand operation

    For the panel builder.
    Compact IP20 component with brackets and screw terminals.
    For the automation engineer.
    Taps can be switched by contactors or relays – a multi-speed mode is created according to the controller logic.
    For the ventilation installer.
    A simple way to set a constant reduced fan speed.

    Application guide: how it is used in practice

    Typical ATR-4-25L50 applications:

    Site What is connected Result Installer's note
    Control panel with a constant reduced speed Motor → selected tap The fan always runs at the required speed Select the tap according to the required air volume
    Multi-speed control from a controller Contactors / relays between the taps and the motor Speed is switched by automation Ensure mutual interlocking – only one tap at a time
    Ventilation unit manufacturing (OEM) Autotransformer in the equipment's electrical control panel Compact speed control without a separate wall-mounted controller IP20 – only in a closed control panel
    A motor that hums with an electronic controller Autotransformer instead of an electronic controller Quiet operation at low speed Check that the motor is suitable for voltage control

    How to select the controller current

    Rated current of the motor(s) Recommended model
    up to 1.5 A ATR-4-15L50 (1.5 A)
    1.5–2.5 A ATR-4-25L50 (2.5 A) ← this model
    2.5–4 A ATR-4-40L50 (4 A)
    4–6 A ATR-4-60L50 (6 A)
    6–8 A ATR-4-80L50 (8 A)
    8–11 A ATR-4110L50 (11 A)
    11–14 A ATR-4140L50 (14 A)
    Rule: autotransformer rated current ≥ motor rated current (see the motor nameplate). When connecting several fans – motors of the same type – add up their rated currents.
    When to choose another solution: for wall mounting with a knob and IP54 enclosure – STR-4 series; with TK terminals – STRS4; with NO/NC and alarm – STRA4 or STTA4; for 0-10 VDC control – STVS4.

    Pros

    • 7 output voltages 0–400 VAC
    • Sinusoidal output voltage
    • Compact, installed in a control panel
    • Screw terminals, sturdy brackets
    • Insulation class F

    Cons / limitations

    • IP20 only – an enclosed control panel is required
    • No switch, indication, TK or protection – these must be provided in the control panel diagram
    • Step (not stepless) control
    • Operating temperature up to +35 °C, indoor use only
    • Not suitable for EC fans

    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).
    • Install only in a closed control panel – protection class IP20.
    • The motor rated current must not exceed 2.5 A; select protective devices according to the control panel design.
    • When switching taps, ensure that two taps are never connected at the same time.
    • Ensure control panel ventilation – ambient temperature up to +35 °C.

    Quick selection guide

    2.5 A
    3×400 VAC
    Autotransformer
    IP20
    For control panels
    Suitable when you need:
    • speed control of a three-phase fan up to 2.5 A in a control panel;
    • for OEM ventilation units;
    • quiet motor operation without electronics.
    Check before use:
    • the motor rated current and whether it is voltage-controllable;
    • whether there will be an enclosed control panel (IP20);
    • how the taps will be switched and which protective devices will be used.
    Important reminder: ATR-4-25L50 – a control panel component, not a finished wall-mounted controller.

    FAQ

    How does it differ from STR-4?
    ATR-4 – open autotransformer (IP20) for a control panel, without enclosure or switch; STR-4 – wall-mounted IP54 controller with a 5-position switch.
    What voltages can be obtained?
    0, 130, 170, 220, 260, 300 and 400 VAC.
    Can it be wall-mounted?
    Protection class IP20, so it is installed in a closed control panel.
    How do I switch the speeds?
    By selecting the tap via wiring or external contactors / a selector switch.
    Is it suitable for EC fans?
    No, only for voltage-controllable AC motors.

    Three-phase autotransformer for fan speed control | Sentera Controls | ATR-4-25L50

    Sentera ATR-4-25L50 – three-phase 400 VAC autotransformer for fan speed control up to 2.5 A, taps 130-170-220-260-300-400 VAC, sinusoidal voltage, IP20, for control panel mounting.

    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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