Alternator ON or OFF
Joined: Feb 2006
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From: AMONGST BRIGALOW SUCKERS
On bonanzas fitted with the IO520B engine, the alternator is gear driven.
I seem to recall a Beech bloke at a safety seminar warning against EVER (emergency excepted) turning off the alternator at start, and then on with the engine running.
His rationale was that the shock load on the alternator drive when the alternator was suddenly turned on could possibly weaken and shear the undampened alternator drive. This could then cause metal ingress and the broken gear drive components possibly jamming and causing an engine failure.
I seem to recall a Beech bloke at a safety seminar warning against EVER (emergency excepted) turning off the alternator at start, and then on with the engine running.
His rationale was that the shock load on the alternator drive when the alternator was suddenly turned on could possibly weaken and shear the undampened alternator drive. This could then cause metal ingress and the broken gear drive components possibly jamming and causing an engine failure.
Last edited by BEACH KING; 22nd June 2012 at 03:07.
Joined: Jan 2008
Posts: 768
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From: Australia
I should have added one more sentence last post.
Therefore if the load is low simply leave thealternator on all the time, and the comment about the gear driven alternator on Continentals is pertinent and solved by simply leaving the alternator on !!!
Therefore if the load is low simply leave thealternator on all the time, and the comment about the gear driven alternator on Continentals is pertinent and solved by simply leaving the alternator on !!!
Joined: Dec 2004
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From: ChCh NZ
Typical Alternator Regulator
and an Overvolt relay..
Q~~60_12.JPG)
These are examples of components often encountered on GA aircraft.
The Lamar regulator is clearly marked and it can be easily seen what it is all about. They are often found on Piper singles, and throughout the range at that.
The overvolt unit can be seen on Cessna's and even some Islanders.
They are not precision devices, - the operating points (voltages) can be somewhat variable and indeed the Lamar depicted is adjustable.
Joined: Jul 2007
Posts: 6,864
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From: in the classroom of life
Creamie, how small do you reckon those things are today, besides those built in to modern avionics already 
Tank engine, Beachie is not talking with forked tongue. He is one cleaver chap
Tank engine, Beachie is not talking with forked tongue. He is one cleaver chap
Joined: Jan 2008
Posts: 768
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From: Australia
Today is still Transistor Technology, just packaged somewhat more discretely, it is how my super fund makes my living, and justifies my B eng .
I really love the way you all disparage simple Physicswhich are the heart of aviation and the way it records its progress.
C'mon Creamiesay something profound about how the Law is protecting us all.
I really love the way you all disparage simple Physicswhich are the heart of aviation and the way it records its progress.
C'mon Creamiesay something profound about how the Law is protecting us all.
Joined: Oct 2010
Posts: 2,055
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From: Styx Houseboat Park.
This CP- eh?.
T28D -C'mon Creamie say something profound about how the Law is protecting us all.
We are, of course kind to a brother 'amateur' pilot: (as clearly this is) but then again, you have to ask – would you (considering it's track record) put you and yours in these hands?. Short answer NO. The rest I leave up to your discretion.
Refer to it's previous posts related to aerodynamics, engines, electrics etc. etc.
His imagined (friends) AKA CASA cohorts (and Brothers in exile), can they really provide the answers it truly seeks?; ask any professional pilot in Australia about CASA flying/ on line operatational abilities (under privilege of course) – they will, in no uncertain terms give an answer, under OATH during 'in camera' testimony.
Not usually one to give advice, but; – CP ; in my tribe, it is considered that more knowledge can be gained with mouth firmly closed and ears open; than in any other way.
Only a country boy's opinion of course: - M'lud.
Last edited by Kharon; 26th June 2012 at 14:00.
Joined: Jul 2007
Posts: 6,864
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From: in the classroom of life
T28D, as I suggested above, I reckon most of that protection is now concealed in an area the size of of a key on a keyboard including a relay, SSR of course.
The modern surface mount board
Can you imagine the cost of building an old radio, say early 60's King today. An SL40 s cheap!!
Jaba sane? If he was he would not be here
The modern surface mount board
Can you imagine the cost of building an old radio, say early 60's King today. An SL40 s cheap!!
Jaba sane? If he was he would not be here
Joined: Jun 2003
Posts: 471
Likes: 1
From: Australia
The placard that is mentioned and queried in this thread is a result of CASA AD/Gen/37 amdt 3 of 9/2000.As a result of this the warning must be in place on all aircraft that fall within the AD scope.
It clearly states on page 2 of the AD that "The reason for this directive is to ensure that the aircraft battery does not become flat in flight resulting in a generator not being able to produce power when selected on."
The term generator in CASA speak also refers to any electrical producing unit and includes alternators.The lack of auto excitation on an alternator has already been referred to by a number of posters.
This is different and really has nothing to do with why an alternator would be selected off prior to start.The only bearing that this AD would have on the original question is that if the gen/alt is left on then the chance of flattening the battery accidentally is removed.
In many Cessnas at least, when ground power is applied a number of circuits are not powered by the GP, particularly avionics.
Wunwing
It clearly states on page 2 of the AD that "The reason for this directive is to ensure that the aircraft battery does not become flat in flight resulting in a generator not being able to produce power when selected on."
The term generator in CASA speak also refers to any electrical producing unit and includes alternators.The lack of auto excitation on an alternator has already been referred to by a number of posters.
This is different and really has nothing to do with why an alternator would be selected off prior to start.The only bearing that this AD would have on the original question is that if the gen/alt is left on then the chance of flattening the battery accidentally is removed.
In many Cessnas at least, when ground power is applied a number of circuits are not powered by the GP, particularly avionics.
Wunwing
Last edited by Wunwing; 27th June 2012 at 07:55.
Joined: Jul 2005
Posts: 264
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From: australia
We seem to diverge from the original post.
"Many moons ago I was taught to only switch on the BATT side of the dual switches (on the Cessna's) and in the after start procedure then switch on the alternator to check that it is working in the correct sense.
Is their any merit in this system rather than switching on both at the same time prior to starting and then checking the alternator output. Maybe an engineer can shed some light if there is a technical issue at work here."
My response was to indicate that if you are out in the boondocks in a 182 with an almost flat battery, for whatever reason, you may increase the possibly of getting a start if you turn the alternator off before starting, and back on after starting of course.
This is a response from the school of hard knocks and may help someone some day.
"Many moons ago I was taught to only switch on the BATT side of the dual switches (on the Cessna's) and in the after start procedure then switch on the alternator to check that it is working in the correct sense.
Is their any merit in this system rather than switching on both at the same time prior to starting and then checking the alternator output. Maybe an engineer can shed some light if there is a technical issue at work here."
My response was to indicate that if you are out in the boondocks in a 182 with an almost flat battery, for whatever reason, you may increase the possibly of getting a start if you turn the alternator off before starting, and back on after starting of course.
This is a response from the school of hard knocks and may help someone some day.
Joined: Jun 2003
Posts: 471
Likes: 1
From: Australia
The problem with checking an alternator after start is that the traditional instrument on aircraft for the generating system is an ammeter.With an alternator the ammeter alone is of little use. A voltmeter is much better and that is why cars and trucks have had voltmeters as standard for a long while.
On 12 volts the normal alternator output should be 13.9 to 14.5 volts. The higher the voltage output the greater load that it is handling. So a high voltage continuously may indicate a battery problem.However a low alternator amp output doesn't neccessarily indicate that the battery is happy.
Generators on the other hand tell all via an ammeter.
Its a mystery as to why aircraft which use similar alternators to automotive stick to ammeters.
Wunwing
On 12 volts the normal alternator output should be 13.9 to 14.5 volts. The higher the voltage output the greater load that it is handling. So a high voltage continuously may indicate a battery problem.However a low alternator amp output doesn't neccessarily indicate that the battery is happy.
Generators on the other hand tell all via an ammeter.
Its a mystery as to why aircraft which use similar alternators to automotive stick to ammeters.
Wunwing
Joined: Dec 2004
Posts: 402
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From: ChCh NZ
To answer Flywatchers question.
Firstly if the battery is suspected of being flat, indeed marginal for a start, then there is one switch you would not operate.
Sure load share as much as you can with the pre-start routine. Alternator and avionics master off.
Now this is where you need to know your aircraft... the one switch I would not be touching is the starter !
That can make life very difficult, indeed possibly a show stopper.
I will have to generalise as we can't cover all aircraft or engine types..
On something like a Lycoming O-320 and up to O-540's you may get a satisfactory swing start.
Once the starter has been operated a failed start will mean the Bendix will remain engaged.
Many Pilots have no idea how to swing start an engine safely, or correctly. Swinging a prop with the Bendix engaged makes the job so much more difficult, - indeed next to impossible on the bigger engines.
I am not even happy swinging a Tomahawk with the starter Bendix engaged.
So on certain aircraft and you think you may have a marginal battery the best thing to do would be to break out the cellphone and ring the LAME. Leave ALL switches in the aircraft off..
Don't even hit the starter, Alternator switched off or not.
Now back to the question about where to have the switches during a normal start..
I would be reading the POH and listening just a little to the instructor. If there is any difference then it would be time to quiz the instructor a little more about it.
Firstly if the battery is suspected of being flat, indeed marginal for a start, then there is one switch you would not operate.
Sure load share as much as you can with the pre-start routine. Alternator and avionics master off.
Now this is where you need to know your aircraft... the one switch I would not be touching is the starter !
That can make life very difficult, indeed possibly a show stopper.
I will have to generalise as we can't cover all aircraft or engine types..
On something like a Lycoming O-320 and up to O-540's you may get a satisfactory swing start.
Once the starter has been operated a failed start will mean the Bendix will remain engaged.
Many Pilots have no idea how to swing start an engine safely, or correctly. Swinging a prop with the Bendix engaged makes the job so much more difficult, - indeed next to impossible on the bigger engines.
I am not even happy swinging a Tomahawk with the starter Bendix engaged.
So on certain aircraft and you think you may have a marginal battery the best thing to do would be to break out the cellphone and ring the LAME. Leave ALL switches in the aircraft off..
Don't even hit the starter, Alternator switched off or not.
Now back to the question about where to have the switches during a normal start..
I would be reading the POH and listening just a little to the instructor. If there is any difference then it would be time to quiz the instructor a little more about it.
Joined: Nov 2000
Posts: 3,080
Likes: 6
From: Salt Lake City Utah
Now this is where you need to know your aircraft... we can't cover all aircraft or engine types..
Surely there’s one rule that can be applied to every situation, so instructors can just parrot that rule.
Joined: Jun 2010
Posts: 203
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From: TinselTown
I wish knew how to do quotes....
but thanks wunwing for: "The placard that is mentioned and queried in this thread is a result of CASA AD/Gen/37 amdt 3 of 9/2000"
Seems so obvious it would hardly need placarding! Like 'do not turn magnetos off in flight'
Seems so obvious it would hardly need placarding! Like 'do not turn magnetos off in flight'
Joined: Apr 2008
Posts: 935
Likes: 1
From: Australia
Beeza Says...
Firstly if the battery is suspected of being flat, indeed marginal for a start, then there is one switch you would not operate.
(trimmed)
Now this is where you need to know your aircraft... the one switch I would not be touching is the starter !
That can make life very difficult, indeed possibly a show stopper.
(trimmed)
.
Once the starter has been operated a failed start will mean the Bendix will remain engaged.
(trimmed)
Now this is where you need to know your aircraft... the one switch I would not be touching is the starter !
That can make life very difficult, indeed possibly a show stopper.
(trimmed)
.
Once the starter has been operated a failed start will mean the Bendix will remain engaged.
How many pilots/car drivers have you seen attempting an MB start where it struggles through the compression, or even worse tapping the starter button until it finally gives up and goes through the compression? I bet not one of these people realise just how much damage they are doing to the starters internals, and potentially to the battery itself.
LAME's bank accounts love these dopes.
Many Pilots have no idea how to swing start an engine safely
So on certain aircraft and you think you may have a marginal battery the best thing to do would be to break out the cellphone and ring the LAME. Leave ALL switches in the aircraft off..
Don't even hit the starter, Alternator switched off or not.
Don't even hit the starter, Alternator switched off or not.
Now back to the question about where to have the switches during a normal start..
I would be reading the POH and listening just a little to the instructor. If there is any difference then it would be time to quiz the instructor a little more about it.
I would be reading the POH and listening just a little to the instructor. If there is any difference then it would be time to quiz the instructor a little more about it.
then kick back with a beer to enjoy the fireworks. Then check what I learned with a LAME. We had a conversation about this very thread at the aeroclub on sunday, and I thought now was an oppurtune time to recheck my thoughts....so opened my travel-air manual to x-check my recollections of the procedures and why.
The Be95, has 2 big arse ALT FAIL lamps set high on the coaming. In the pre-start, you use the Test button to make sure they light up. To keep it simple...
.....Master on.
Alt on
Alt warning lamp should illuminate.
Light the fire
Alt lamp should extinguish
Check amp metre, once it falls to its lowest point, light 2nd fire.
Doing it this way shows that the failure warning circuit is working as advertised.
If you start it with the alternator off, the fail lamp will never show you if the warning system is working.
Enjoy!
Cheers little ears!
Jas
