FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
A technician is selecting a solid-state device to convert 28-volt DC battery power into 115-volt, 400 Hz AC power for cockpit instruments during an emergency electrical configuration. Compared to a rotary inverter, what is the main advantage of a static inverter for this application?
- AIt can supply significantly more electrical power than a rotary inverter of the same weight
- BIt automatically regulates output frequency without requiring a stable DC input voltage
- CIt produces a purer sine wave output at any load condition
- DIt has no moving parts, resulting in less maintenance and longer service life
Show answer & explanationAnswer & explanation
Correct answer: D. It has no moving parts, resulting in less maintenance and longer service life
A static inverter uses solid-state oscillator and transformer circuitry with no rotating parts, unlike a rotary inverter which uses a DC motor driving an AC generator. This eliminates brushes and bearings, reducing maintenance and increasing reliability.
Why the other options are wrong
- A. Static inverters are typically used for lower power applications, not higher capacity.
- B. Static inverters still require a regulated/stable DC input for accurate frequency output.
- C. Rotary inverters can also produce clean sine waves; this is not the defining advantage.
Static Inverter
A solid-state device that converts DC to AC using transistor oscillator and transformer circuitry, with no moving parts, unlike a rotary inverter which uses a motor-generator set.
- No moving parts — reduced maintenance vs rotary inverter
- Used to supply AC power for instruments from DC battery bus
- Rotary inverters use a DC motor driving an AC generator
Memory trick: Static stands still — no spinning parts to wear out.