SPO-9

Aircraft static converter SPO-9

SPO-9 is an aircraft single-phase static converter used in onboard electrical power supply systems. It converts DC power from the aircraft network into single-phase AC power for low-power consumers. The unit is used mainly where navigation equipment, sensors or small avionics circuits require a stable 36 V / 400 Hz supply. SPO-9 is an electronic converter, not a rotary machine, so it has no motor, generator, brushes or rotating parts.

Power conversion through SPO-9

In operation, SPO-9 receives 27 V DC from the aircraft electrical system and forms a rectangular single-phase AC output. Voltage conversion is performed by transistors operating in switching mode. The converter can also operate from a reduced emergency supply level, depending on the aircraft circuit. Because the output is rectangular rather than sinusoidal, the connected equipment must be approved for this type of supply. It should not be treated as a universal replacement for any 36 V / 400 Hz source without checking the load requirements.

SPO-9 in navigation and sensor circuits

SPO-9 is used in pilot-navigation equipment and aircraft systems that need low-power AC supply. Typical consumers may include navigation instruments, sensors, signal units and small control circuits. The converter is found on Mi-8 family helicopters, including Mi-8MTV-1 and Mi-171 versions, and on Ka-32 helicopters. The exact circuit depends on the helicopter modification and installed avionics set. For replacement, the aircraft electrical diagram and equipment list should be checked together with the marking on the converter.

Static design of the SPO-9 converter

The static design is one of the main differences between SPO-9 and older electromechanical converters. Since there are no rotating parts, there is no brush wear, collector maintenance or mechanical noise typical for motor-generator units. Inspection is still required, but it is focused on connectors, electronic components, housing condition, overheating marks and output parameters under load. If the connected equipment does not receive correct voltage, the fault may be in the converter, input line, load circuit or wiring.

Identification and ordering of SPO-9

Before ordering SPO-9, the unit marking should be compared with the aircraft parts catalog, electrical system documentation or installed equipment list. Similar converters may differ by output power, waveform, supply tolerance and approved application. For correct selection, provide the aircraft type, installed converter marking, required output voltage, connected equipment and a photo of the data plate if available. The product is also known under alternative designations SPO-9 and СПО-9.

Product Type: Aircraft single-phase static converter
Function: Conversion of DC power into single-phase AC power
Application / Where Used: Low-power navigation equipment, sensors and onboard electrical consumers
System / Installation Area: Aircraft electrical power supply system / pilot-navigation equipment circuits
Compatible Aircraft / Equipment: Mi-8 family helicopters, Mi-8MTV-1, Mi-171, Ka-32
Input Voltage: 27 V DC +10%; emergency mode 22 ±2 V
Output Voltage: 36 ±5 V AC, rectangular waveform
Number of Output Phases: 1
Output Frequency: 400 Hz ±2%
Output Signal Form: Rectangular
Conversion Principle: Transistor switching mode
Maximum Output Power: 8 VA with active-reactive load, cos φ = 0.7, at rated supply voltage
Current Consumption: Not more than 0.75 A at 22 V supply voltage and 8 VA output power
Weight: 0.9 kg
Dimensions: 200 × 88 × 67 mm
Technical Documentation: Aircraft electrical system documentation, parts catalog, product passport and operating documentation

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