Start Auxiliary Bus on 690 series

[Roberto Serrano]

What is purpose of the start auxiliary bus on the electrical system on the Commanders 690 A/B series.

[donv]

We really need Barry Lane to answer this one... even though I was flying a 690A this summer.

[donv]

After looking at my FlightSafety manual, I believe the purpose is to prevent 48 volts from going into the electrical system during a series start. During a parallel start, power goes from the #1 battery through the start auxiliary bus and powers the left side of the aircraft, while power from the #2 battery powers the right side.

In a series start, the start over voltage relay opens and only the #2 battery is powering the distribution busses, through the start bus and the diode protecting the start aux bus.

The JetProps (840/980/900/1000) have a simplified system where the batteries don't have to go through the start bus to power the distribution busses in normal operation.

[Roberto Serrano]

Thanks appreciate your time !!

[donv]

When they developed the JetProp series (840/980/900/1000), they really took a hard look at the systems. The 690B is an evolution from where they were with the 680 series, with things tacked on here and there and everywhere... the JetProps took a clean look, and really simplified and improved a lot of stuff.