C172SP engine start with battery switch only?

[Robert Winn]

Rented a C172SP (Made in 1999) on 04/10/04 and was told to start the engine
with the battery side of the master switch only on, then turn on the
alternator side after the engine was running. I was told that this was a
new recommendation for all C172SP's. Can someone tell me where to find the
text of this recommendation?

Thanks in advance,

Robert Winn

[Peter Clark]

On Sun, 11 Apr 2004 16:21:45 -0500, "Robert Winn"
> wrote:

>Rented a C172SP (Made in 1999) on 04/10/04 and was told to start the engine
>with the battery side of the master switch only on, then turn on the
>alternator side after the engine was running. I was told that this was a
>new recommendation for all C172SP's. Can someone tell me where to find the
>text of this recommendation?

It was included in a service bulletin from Cessna regarding some
faulty ACU's in (insert large number of serial numbers here).
SB04-24-01A, Mar 1 04. The temporary start procedure (alternator side
of master off) to be removed from POH once the replacement unit is
installed.

P

[Mark Klebanoff]

On Sun, 11 Apr 2004 22:20:51 UTC, Peter Clark
> wrote:


> It was included in a service bulletin from Cessna regarding some
> faulty ACU's in (insert large number of serial numbers here).
> SB04-24-01A, Mar 1 04. The temporary start procedure (alternator side
> of master off) to be removed from POH once the replacement unit is
> installed.
>
> P

I've read that we should start all airplanes with a split master
switch that way. Turning on the alternater half of the master
energizes the field windings of the alternator, which just wastes
battery power and heats up the alternator. I've been starting planes
that way for many years now. Once the engire starts I bring the
alternator on line by turning on both halves of the mater switch.
Every Cherokee, Cessna and Bonanza I've been in has a split master,
but as I recall the Mooney 201 and 231's I've flown do not-- it's
either everything on or nothing on.

[Bob Gardner]

It's common sense, when you think about it. With both halves of the switch
ON, the alternator field windings are connected across the battery, creating
a drain in addition to that drawn by the starter...and the alternator can't
make electricity until the engine is rotating anyway. So why keep that load
across the battery? Turn off the alternator side, directing all battery
voltage to the starter, and only then put the alternator field windings into
play.

Bob Gardner

"Robert Winn" > wrote in message
...
> Rented a C172SP (Made in 1999) on 04/10/04 and was told to start the
engine
> with the battery side of the master switch only on, then turn on the
> alternator side after the engine was running. I was told that this was a
> new recommendation for all C172SP's. Can someone tell me where to find
the
> text of this recommendation?
>
> Thanks in advance,
>
> Robert Winn
>
>

[Roger Long]

By watching the ammeter as you do this, you can verify the charging system
function and confirm that the starter relay has not hung up which can turn
the starter into a generator at higher RPM's and fry parts of the electrical
system and avionics. It also makes for easier starts in cold weather for
the reasons the other posters mention.

When you start you should see negative ammeter deflection and any alternator
warning lights should come on. After the engine is running. bring the
alternator on line and the ammeter should switch over to positive deflection
and taper back to zero within about a minute. The alternator warning lights
should go out. After you have done this a few times in a plane, you'll be
able to spot any change in charging system function quiet easily.

You can even get an insight into battery condition. If you've drained it by
having lights on for your preflight, running flaps ups and down, etc. You'll
see a larger ammeter deflection. If you see that deflection without a
reason, it may mean something is going south in the charging system.

The only reason I have heard not to do this all the time is that the
alternator has a sudden load thrown on it. This may be an issue for
alternators directly driven by expensive gear trains but I think the belt
driven ones have a pretty good shock absorber in the belt.
--
Roger Long

Robert Winn > wrote in message
...
> Rented a C172SP (Made in 1999) on 04/10/04 and was told to start the
engine
> with the battery side of the master switch only on, then turn on the
> alternator side after the engine was running. I was told that this was a
> new recommendation for all C172SP's. Can someone tell me where to find
the
> text of this recommendation?
>
> Thanks in advance,
>
> Robert Winn
>
>

[Peter Duniho]

"Bob Gardner" > wrote in message
news:_tkec.120289$K91.333719@attbi_s02...
> It's common sense, when you think about it. With both halves of the switch
> ON, the alternator field windings are connected across the battery,
creating
> a drain in addition to that drawn by the starter

It's worse than that, too. Not only is the battery being used to energize
the alternator field circuit, but having that circuit energized creates drag
on the engine, making the starter work harder.

Pete

[C J Campbell]

"Robert Winn" > wrote in message
...
> Rented a C172SP (Made in 1999) on 04/10/04 and was told to start the
engine
> with the battery side of the master switch only on, then turn on the
> alternator side after the engine was running. I was told that this was a
> new recommendation for all C172SP's. Can someone tell me where to find
the
> text of this recommendation?
>
> Thanks in advance,

This was a service bulletin that applies to Cessna piston singles having to
do with the alternator field breaker popping. Until this SB is fully
complied with you are supposed to start the engine this way. The SB came
with a temporary yellow page that is inserted into the "Normal Procedures"
checklist in the POH, but no revision for the separate checklist.

Mike Pickett tells me that you should only use the battery side of the
switch anyway, especially when using external power. He says starting the
engine on external power with the alternator switch on was what caused my
alternator to burn out several months ago.

[David Brooks]

"Peter Duniho" > wrote in message
...
> "Bob Gardner" > wrote in message
> news:_tkec.120289$K91.333719@attbi_s02...
> > It's common sense, when you think about it. With both halves of the
switch
> > ON, the alternator field windings are connected across the battery,
> creating
> > a drain in addition to that drawn by the starter
>
> It's worse than that, too. Not only is the battery being used to energize
> the alternator field circuit, but having that circuit energized creates
drag
> on the engine, making the starter work harder.

It makes sense to me, too, but I've always been told to follow the
procedures in the POH. My 172 POH's don't contemplate the split switch
start. Also, I'm concerned that if I change my routine now, I'll be taking
off with a rapidly draining battery one day.

Having said that, I split the switch to do the flaps and lights check early
in the pre-flight.

-- David Brooks

[Roger Long]

Check in the section on operations in cold weather. It will probably refer
to the split switch start there. If you can do it cold weather, and they
don't give a maximum temperature at which it is "permissible" you are in
compliance with the POH.

Of course, if you fly your (at least older) Cessna in strict compliance with
the POH, you'll screw up your engine.

--
Roger Long
David Brooks > wrote in message
...
>
> "Peter Duniho" > wrote in message
> ...
> > "Bob Gardner" > wrote in message
> > news:_tkec.120289$K91.333719@attbi_s02...
> > > It's common sense, when you think about it. With both halves of the
> switch
> > > ON, the alternator field windings are connected across the battery,
> > creating
> > > a drain in addition to that drawn by the starter
> >
> > It's worse than that, too. Not only is the battery being used to
energize
> > the alternator field circuit, but having that circuit energized creates
> drag
> > on the engine, making the starter work harder.
>
> It makes sense to me, too, but I've always been told to follow the
> procedures in the POH. My 172 POH's don't contemplate the split switch
> start. Also, I'm concerned that if I change my routine now, I'll be taking
> off with a rapidly draining battery one day.
>
> Having said that, I split the switch to do the flaps and lights check
early
> in the pre-flight.
>
> -- David Brooks
>
>