"Larry Dighera" wrote in message
...
On Mon, 18 Jul 2005 12:57:42 GMT, "Lakeview Bill"
wrote in
::

On an aircraft with separate "battery" and "alternator" switches, should
you
turn on BAT and leave ALT off during engine start, or should you turn them
both on prior to start?

A little bit of the "why" on this would be nice also...



Of course, you should follow the starting procedure stated in the POH.
That usually has you turning on the alternator field winding after the
engine starts. Energizing the field winding causes about a 5 ampere
current draw. That five amps is better used for turning the starter
motor until the alternator is able to spin fast enough to produce
useable electrical output current.


1. Does not the starter circuitry include a "contactor" solenoid that pulls
off the power to most everything else during the time that the starter is
engaged?

2. The generic 1976 C172 POH, Section 7 says "Normally, both sides of the
master switch should be used simultaneously". So that's how I start a 1976
172. I am sure another POH may recommend something else.

3. How does pulling the BAT half of the master during engine-running,
reconcile with the caution about pulling battery power on a boat/automobile?
( There ...boats/cars..., isolating the battery from the alternator while
running, is said to cause the alternator to blow diodes and fail. )