From T6b Naval manual:
A dedicated permanent magnet alternator (PMA), mounted on the reduction gearbox, powers the PMU. The PMA supplies 32 VAC, which the PMU converts to DC. The PMU automatically switches to the 28 VDC battery bus when propeller RPM drops below 40-50% NP, or when the PMA fails.
- What does the PMA really do? From looking online I only found that in other engines the PMA is good to convert mechanical energy into electrical not sure if this is the case for the PT6 engine.
- I think it has to be with the startup process, not sure. During the startup the aircraft its connected to an Electrical Power source if battery is low but the engine does not require any gear accessory connection, only electrical power. I have seen how big jet engines need an accessory gear connection go turn the compressor, how does this PT6 engine actually starts? Im guessing electrical power somehow moves the compressor shaft?
- The PT6-68 engine has an Starter/Generator that acts as an starter and then a generator, which is aft the accessory gear box. Is this related to the PMA? Does the starter somehow moves the compressor shaft?
- I couldn’t find much in The P&W manual, its in the link below. Thank u in advance https://mikeklochcfi.files.wordpress.com/2018/08/training-pt6a-60-series.pdf