65W Isolating Transformer

The 65W Isolating Transformer is a single‑phase, fully encapsulated transformer designed for AGL series circuits with higher power demands. With a secondary rating of 65W, it is used where increased light output is required — typically for high‑intensity runway edge lights on CAT II/III precision approaches, approach lighting systems with extended barrettes, and modern LED fixtures that consume more power than traditional 45W halogen lamps.

The 65W transformer provides the same galvanic isolation and constant‑current transfer as lower‑power variants, but with a larger core, heavier windings, and enhanced thermal capacity to handle the increased power dissipation. It is fully interchangeable with 45W transformers in terms of primary and secondary connections, allowing flexible upgrades or replacements in the field.

The 65W isolating transformer exists for fixtures that need more light output than the standard 45W rating provides — high-intensity runway edge lights supporting CAT II/III precision approaches, extended approach lighting barrettes, and LED fixtures that draw more power than their halogen predecessors. Its purpose is unchanged from the standard transformer: isolate the fixture electrically from the series loop while stepping the shared current down to the voltage that specific lamp needs.

Being interchangeable with 45W units in terms of primary and secondary connections matters operationally, because it means a field crew can upgrade a fixture's power rating without redesigning the loop's wiring, keeping the transition to higher-intensity lighting straightforward rather than requiring a circuit-wide overhaul.

The 65W isolating transformer is deployed in high‑intensity AGL applications, including:

• High‑Intensity Runway Edge Lights: CAT II/III precision approach runways requiring maximum luminous intensity (≥10,000 cd).
• Approach Lighting Systems (ALS): High‑intensity barrettes, crossbars, and sequenced flashing lights in ALSF‑1 and ALSF‑2 configurations.
• High‑Intensity LED Fixtures: Modern LED runway edge lights and centreline lights that draw more power than halogen equivalents while delivering superior efficiency and life.
• Runway End Identifier Lights (REIL): High‑intensity flashing lights at runway thresholds.
• Obstruction Lighting: Medium‑ and high‑intensity obstruction lights on tall structures (e.g., chimneys, transmission towers).
• Taxiway Centreline Lights: High‑intensity taxiway centreline lights on major taxiways, especially in low‑visibility conditions.

The transformer is installed in handholes, pits, or direct‑buried enclosures, using standard L‑823 primary connectors and secondary cabling. Its higher power rating makes it a critical component for airfields with demanding operational requirements.

Serving high-intensity CAT II/III fixtures, the 65W transformer is installed in a handhole or pit adjacent to the fixture, sized with enough internal clearance for the extra heat it dissipates compared with lower-wattage units. The primary is spliced into the series loop with a standard L-823 connector, and the secondary is run to the fixture using cabling sized for the higher secondary current draw. Where it feeds high-intensity LED retrofits that draw more power than the halogen fixtures they replace, the same enclosure and cable route can typically be reused, provided the pit has adequate ventilation for the transformer's duty cycle.

The 65W transformer operates on the same electromagnetic induction principle as other isolating transformers. The primary winding is connected in series with the 6.6A constant‑current loop. The primary current induces a secondary voltage in the secondary winding, typically 9.85V (for a 65W lamp at 6.6A, V = P/I = 65W/6.6A ≈ 9.85V) or 12V/24V for other configurations. The secondary supplies power to the fixture.

Specific design features for the 65W variant include:

• Larger Core and Windings: The core cross‑section is increased to handle higher flux density, and windings use thicker copper wire to reduce losses and handle the higher current.
• Enhanced Thermal Management: The 65W power level generates more heat, requiring improved thermal conductivity in the encapsulation and often a larger form factor for better heat dissipation.
• Optimised Turns Ratio: Typically designed for a secondary voltage around 9.85V at 6.6A, providing the required power to the lamp while maintaining the efficiency of the primary‑secondary coupling.
• Excellent Voltage Regulation: Maintains secondary voltage within ±5% over the full dimming range (2.8A to 6.6A), ensuring consistent light output across all brightness steps.
• Robust Short‑Circuit Protection: The leakage impedance limits secondary fault currents, protecting the loop and preventing CCR tripping during fault conditions.

The 65W transformer occupies the same position in the control chain as any other isolating transformer: an Airfield Lighting Control and Monitoring System (ALCMS) selects the required brightness step based on prevailing RVR, ATC instruction, or pilot-controlled lighting input, and the CCR regulates the whole loop to the corresponding fixed current (2.8A–6.6A, 5-step). The transformer has no addressable identity of its own — it converts whatever current the loop is carrying at that moment into roughly 9.85V, or 12V/24V for other configurations, and cannot be commanded independently of the rest of the loop. This wattage typically feeds a higher-intensity fixture than the 45W tier, such as a higher-output edge or approach light, so a fault here is detected the same way as elsewhere on the circuit: a CCR-monitored voltage rise flags increased loop impedance without distinguishing an open-circuit lamp from a failed transformer, and sectionalised field testing narrows the fault to the specific fixture position.

The 65W unit is built the same way as the rest of the potted range, sized up to carry a heavier winding: the primary and secondary windings around a laminated core are enclosed in a moulded outer shell, vacuum-impregnated, and back-filled with epoxy or polyurethane resin so no internal cavity is left for moisture to collect in. The encapsulation itself is what delivers the IP68, submersible rating — there is no gasket or lid to maintain. Winding insulation is specified to Class F or Class H depending on the manufacturer, and the complete unit typically weighs 4.0–6.5 kg, heavier than the 45W tier it commonly complements on higher-intensity CAT II/III fixtures. Leads terminate in sealed L-823 splice connectors rated for direct burial and continuous immersion, and the unit sits in its own base can beside the fixture it feeds, held in place by the surrounding backfill rather than mechanical fasteners.