Alternator ON or OFF
Breeza,
I disagree about the chrysler alternator point. Why.. I am not going to digress here in public. Happy to pm you about it tho.
I disagree about the chrysler alternator point. Why.. I am not going to digress here in public. Happy to pm you about it tho.
I'm with you. In the G.O.Ds, I well remember the guy at Hawker DeHavilland, with his little number punches, putting numbers on the said Chrysler alternators one by one, from a bulk buy at the local dealer, and raising a record, then chanting the magic incantation that turned auto parts into "fully approved aviation quality genuine spare parts".
I can probably dig up an old list I has that cross referenced the commercial sources of just about the whole electrical system on most Piper aircraft.
To this day, this is the mechanism whereby ball an roller bearings from CBC or Bearing Services have the CAR 30 holy water sprinkled on them, turning them into "genuine aviation spare parts".
Actually, this can be a trap for young players, as often auto/industrial grade bearings are too close tolerance ---- the OEM spares are actually out of standard tolerance rejects, when they are rejected because the "fit" is sloppy.
Some of you will remember some unfortunate accidents to a particular model of helicopter, because the manufacturer apparently ran out of "approved" bearings for a rotor, and fitted SAE standard bearings. In part, this is the story of the "dot" after the number on said bearings, denoting the out of tolerance rejects that have enough slop for the aeronautical application.
Tootle pip!!
Last edited by LeadSled; 16th Jun 2012 at 13:57.
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I can't understand why you disagree about the Chrysler alternators. I did my Electrical engineering tertiary qualifications in the mid seventies. I have worked on GA aircraft ever since. I own four aircraft. How many Chrysler alternators do you think I have seen recently ?
I work on GA in Aussie, and have done so in many other places about the world.
I have to imagine that there is a stash of aircraft so equipped I have yet to stumble upon.
It has been a long time since I last saw the Chrysler alternator, and I think it would have been on a Cherokee Six. They are just not common like the Prestolite is.
I doubt you are talking from experience but possibly from a secondhand account.
The same as the old generators. They would not have been fitted to many aircraft after the 1960's... we, - the guys that work on the machines just do not see many of them.
I have an Electrical category on my LAME licence so I am not just making this stuff up.
While talk of restamping etc may be a good story it is certainly not prevalent.
The aircraft components are not the same as a car.... normally. Yes I have seen MkIII Zephyr parts fitted by some manufacturers, even Girling brake components... I myself have even fitted toilet seat parts, and that was to a military aircraft. (The seat buffer.)
At the end of the day the machine just has to conform.... checked at each annual review in NZ.
Comparing the average GA aircraft electrical system to that of a car is just not quite accurate. I cannot think of a car, or an aircraft that are the same.
Similar yes, but generally quite a bit different.
That would be why you don't see alternator switches in the average car.
I work on GA in Aussie, and have done so in many other places about the world.
I have to imagine that there is a stash of aircraft so equipped I have yet to stumble upon.
It has been a long time since I last saw the Chrysler alternator, and I think it would have been on a Cherokee Six. They are just not common like the Prestolite is.
I doubt you are talking from experience but possibly from a secondhand account.
The same as the old generators. They would not have been fitted to many aircraft after the 1960's... we, - the guys that work on the machines just do not see many of them.
I have an Electrical category on my LAME licence so I am not just making this stuff up.
While talk of restamping etc may be a good story it is certainly not prevalent.
The aircraft components are not the same as a car.... normally. Yes I have seen MkIII Zephyr parts fitted by some manufacturers, even Girling brake components... I myself have even fitted toilet seat parts, and that was to a military aircraft. (The seat buffer.)
At the end of the day the machine just has to conform.... checked at each annual review in NZ.
Comparing the average GA aircraft electrical system to that of a car is just not quite accurate. I cannot think of a car, or an aircraft that are the same.
Similar yes, but generally quite a bit different.
That would be why you don't see alternator switches in the average car.
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To this day, this is the mechanism whereby ball an roller bearings from CBC or Bearing Services have the CAR 30 holy water sprinkled on them, turning them into "genuine aviation spare parts".
Some of you will remember some unfortunate accidents to a particular model of helicopter, because the manufacturer apparently ran out of "approved" bearings for a rotor, and fitted SAE standard bearings.
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Aircraft are just a machine. Made up of various components. Often in the case of GA aircraft there is nothing too special about them.
Sure many of the components are sourced from the same suppliers as other industries. Bearings, light bulbs, electrical components as mentioned earlier, can be identical. Often they are. It is the next higher assembly that will differ, sooner or later.
The boat outboard motor hydraulic pump on a Piper Arrow has to be different somewhere. Indeed we can soon see that not many marine products use Mil Spec 5606 fluid.. maybe that could be an important difference. Same with brake components. I guess what may often look identical may just have some important subtle differences, - the changed part number may indicate different seals have been fitted.
The electrical system on some GA aircraft does use identical components to those fitted to other vehicles. The electrons are the same so yes, - it may be common to see inter-changeability with the component. The overall system may well be different.... as I believe they are.
Cars simply do not require an alternator field switch. They may not have an Overvolt relay added to the circuitry either.
That said, many automotive electronic regulators worked much better on the Cherokees and the Islanders than the OEM products... remember electronics changed a lot during the 70's.
The regulator generally just varies field current in response to alternator output voltage (bus) when all said and done. I am sure many here would have experienced the fluctuating needle movement in some of the original Piper ammeters (loadmeters).
I don't recall the R22 transmission.
I do know much (too much !!) about the R22 drive train failure of the one out of Nelson seven years ago. It was the owner who demanded an incorrect Dash number part be fitted. Saved him a Dollar but cost him his life.
Some guys really do have that mentality...
Sure many of the components are sourced from the same suppliers as other industries. Bearings, light bulbs, electrical components as mentioned earlier, can be identical. Often they are. It is the next higher assembly that will differ, sooner or later.
The boat outboard motor hydraulic pump on a Piper Arrow has to be different somewhere. Indeed we can soon see that not many marine products use Mil Spec 5606 fluid.. maybe that could be an important difference. Same with brake components. I guess what may often look identical may just have some important subtle differences, - the changed part number may indicate different seals have been fitted.
The electrical system on some GA aircraft does use identical components to those fitted to other vehicles. The electrons are the same so yes, - it may be common to see inter-changeability with the component. The overall system may well be different.... as I believe they are.
Cars simply do not require an alternator field switch. They may not have an Overvolt relay added to the circuitry either.
That said, many automotive electronic regulators worked much better on the Cherokees and the Islanders than the OEM products... remember electronics changed a lot during the 70's.
The regulator generally just varies field current in response to alternator output voltage (bus) when all said and done. I am sure many here would have experienced the fluctuating needle movement in some of the original Piper ammeters (loadmeters).
I don't recall the R22 transmission.
I do know much (too much !!) about the R22 drive train failure of the one out of Nelson seven years ago. It was the owner who demanded an incorrect Dash number part be fitted. Saved him a Dollar but cost him his life.
Some guys really do have that mentality...
Blackhand,
I am, in fact, referring to Australian accidents re. helo. not the NZ case, to which you refer.
As to the original manufacturers of bearings supplied by CBC, Bearing Services or other engineering supply houses, I have sat and watched (awaiting delivery) as a felt pen was used to "inscribe" the Part No. on the bearing box, and the release note (on invoice) raised, by the CAR 30 "supplier". The actual bearings never left the box.
That CAR 30 magic is a valuable quantity, a $15 or so bearing was magically turned into a $139 bearing, by said holy water.
Quite frankly, very few organizations would have the equipment to dimensionally test a ball or roller bearing, outside of the OEM.
Tootle pip!!
I am, in fact, referring to Australian accidents re. helo. not the NZ case, to which you refer.
As to the original manufacturers of bearings supplied by CBC, Bearing Services or other engineering supply houses, I have sat and watched (awaiting delivery) as a felt pen was used to "inscribe" the Part No. on the bearing box, and the release note (on invoice) raised, by the CAR 30 "supplier". The actual bearings never left the box.
That CAR 30 magic is a valuable quantity, a $15 or so bearing was magically turned into a $139 bearing, by said holy water.
Quite frankly, very few organizations would have the equipment to dimensionally test a ball or roller bearing, outside of the OEM.
Tootle pip!!
Last edited by LeadSled; 17th Jun 2012 at 04:01.
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Possible reasons for the recommendation to switch of the alternator field for ground power starts.
1 . Voltage transients created when switching between GPU and battery potentially damaging diodes in alternator (think jumper leads and computers in cars).
2. GPU not appreciating being 'charged' by aircraft alternator.
I doubt an alternator would be turned fast enough during cranking to generate any power.
1 . Voltage transients created when switching between GPU and battery potentially damaging diodes in alternator (think jumper leads and computers in cars).
2. GPU not appreciating being 'charged' by aircraft alternator.
I doubt an alternator would be turned fast enough during cranking to generate any power.
Lumps
I have a feeling this may be another thread out there but I've never had two LAME / old timer pilot s agree on: why do many POHs say DO NOT TURN ALTERNATOR ON IN FLIGHT?
I have a feeling this may be another thread out there but I've never had two LAME / old timer pilot s agree on: why do many POHs say DO NOT TURN ALTERNATOR ON IN FLIGHT?
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MakeItHappenCaptain - yes that's what I was referring to. I remember when learning to fly asking what the purpose of this placard is (not in POHs I apologise, it was a while a go and I can't remember where exactly I saw it). Except for the obvious eventual depletion of the battery - my instructor said it was more to do with if you turned the alternator ON in flight - then proceeded to draw on the blackboard the waves of alternating current sprouting something about turning it on with the engine spinning at say 2200rpm would create a large spike in current that would pop your relay/regulator whathaveyou.
We all prefer an explanation of any kind rather than no explanation at all, just wondering if anyone could back this instructor up. He was a good'n
We all prefer an explanation of any kind rather than no explanation at all, just wondering if anyone could back this instructor up. He was a good'n
So why is Australia still the only country, in this age of comprehensive flight manuals, applying placards that came from the days when flight manuals came off a typewriter and were (agreeably) woefully written.
I deliver new aircraft from a factory overseas and that is the only item that is requred to be added to make the aircraft airworthy in Australia. Bit of a joke, unfortunately.
I deliver new aircraft from a factory overseas and that is the only item that is requred to be added to make the aircraft airworthy in Australia. Bit of a joke, unfortunately.
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Exactly BH.
As we know it would be generalising to say all GA aircraft are the same, they are far from it.
Something like a Cherokee has no control of the alternator apart from the switching, and control, of the field voltage.
ie, no voltage on the field winding means no output... this is what the Alt switch does. The alternator switch does not control the high current output from the alternator through a contactor... most installations don't have such a beast.
The Overvoltage relay, sometimes contained within the regulator, does the same. It just turns off the field voltage which in turn kills the alternator output.
Some salient features of a typical GA electrical system.
The battery contactor is controlled by placing an EARTH at the control, via the Master Switch.
The alternator switch controls the FIELD voltage on the alternator circuit.
There is often no protection on the Alternator output, it does not go to the bus via a fuse or CB.... more likely through an ammeter shunt though.
As mentioned in the previous post, - the battery must have sufficient voltage to operate the Master Contactor and then also be sufficient to provide alternator field.
Turning the Alternator switch off in flight may not necessarily guarantee it will come online again.
Some charging systems can be a little fragile and can do something akin to PIO when the alternator field 'chases' the bus voltage. This could be more likely at higher rpm. Basically a series of high voltage surges as the regulator struggles to come to terms with a very active and lively alternator output voltage. I have experienced the Overvolt relay operating and killing the alternator whenever it the alternator was switched on.
If it persists then the obvious thing to do is bring the engine back to idle before trying again. Switching (shedding) some electrical load may be required also.
EDIT.. Sometimes load may need to be applied, especially if the battery is at a high state of charge already. With very little load on the system, a fully charged battery and a high output voltage from the spun up alternator the bus voltage can very easily rise a few points. An Overvolt relay set at say 14.2 volts could easily trip and open the field. (End Edit).
Although the term alternator implies they are an AC device they are not in a typical aircraft installation. The output is DC as the diode pack is self contained in the rear of the alternator.
Now a completely different subject..
The Ignition switch is independent of the charging circuit.
It does do a number of functions though, some of which are not always understood.
The Ign switch places an earth on the relevant magneto, via the P lead, to turn the mag off.
The switch also takes bus voltage and applies it to the start contactor when the switch is in the 'Start' position. At this position there is also other switching which normally applies an Earth to the right magneto. This is via an external link screwed across the terminals.
The link can be opened if the intention is to have both mags live during the start... if for example the engine has two impulse couplings fitted.
Normally only half the spark plugs are firing during a typical piston engine start. Often the top plug on one bank and the bottom on the other.
So it can be seen that while the switch is held on 'Start' it could be that the engine may only be firing on a couple of cylinders... if the bottom plugs are fouled or flooded.
That is why they will often pick-up when the switch is released.
As we know it would be generalising to say all GA aircraft are the same, they are far from it.
Something like a Cherokee has no control of the alternator apart from the switching, and control, of the field voltage.
ie, no voltage on the field winding means no output... this is what the Alt switch does. The alternator switch does not control the high current output from the alternator through a contactor... most installations don't have such a beast.
The Overvoltage relay, sometimes contained within the regulator, does the same. It just turns off the field voltage which in turn kills the alternator output.
Some salient features of a typical GA electrical system.
The battery contactor is controlled by placing an EARTH at the control, via the Master Switch.
The alternator switch controls the FIELD voltage on the alternator circuit.
There is often no protection on the Alternator output, it does not go to the bus via a fuse or CB.... more likely through an ammeter shunt though.
As mentioned in the previous post, - the battery must have sufficient voltage to operate the Master Contactor and then also be sufficient to provide alternator field.
Turning the Alternator switch off in flight may not necessarily guarantee it will come online again.
Some charging systems can be a little fragile and can do something akin to PIO when the alternator field 'chases' the bus voltage. This could be more likely at higher rpm. Basically a series of high voltage surges as the regulator struggles to come to terms with a very active and lively alternator output voltage. I have experienced the Overvolt relay operating and killing the alternator whenever it the alternator was switched on.
If it persists then the obvious thing to do is bring the engine back to idle before trying again. Switching (shedding) some electrical load may be required also.
EDIT.. Sometimes load may need to be applied, especially if the battery is at a high state of charge already. With very little load on the system, a fully charged battery and a high output voltage from the spun up alternator the bus voltage can very easily rise a few points. An Overvolt relay set at say 14.2 volts could easily trip and open the field. (End Edit).
Although the term alternator implies they are an AC device they are not in a typical aircraft installation. The output is DC as the diode pack is self contained in the rear of the alternator.
Now a completely different subject..
The Ignition switch is independent of the charging circuit.
It does do a number of functions though, some of which are not always understood.
The Ign switch places an earth on the relevant magneto, via the P lead, to turn the mag off.
The switch also takes bus voltage and applies it to the start contactor when the switch is in the 'Start' position. At this position there is also other switching which normally applies an Earth to the right magneto. This is via an external link screwed across the terminals.
The link can be opened if the intention is to have both mags live during the start... if for example the engine has two impulse couplings fitted.
Normally only half the spark plugs are firing during a typical piston engine start. Often the top plug on one bank and the bottom on the other.
So it can be seen that while the switch is held on 'Start' it could be that the engine may only be firing on a couple of cylinders... if the bottom plugs are fouled or flooded.
That is why they will often pick-up when the switch is released.
Last edited by baron_beeza; 22nd Jun 2012 at 00:20.
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MIHC
The UK CAA had/has an AD whereby the starter circuit has to be either through a seperate switch or have an indication when the starter is operating.
The Islander has the External power switch to confuse pilots but it is common to see lights added to Cherokees. A Starter Operating lamp.
The placard you speak of is new to me but could be a CASA AD or other certification requirement. Some of those things can take a while to rewrite or sort out.
Often the original incident that prompted the requirement was years ago... but so catastrophic that no-one is prepared to change back from the status quo.
Has anyone put it to CASA ?
The UK CAA had/has an AD whereby the starter circuit has to be either through a seperate switch or have an indication when the starter is operating.
The Islander has the External power switch to confuse pilots but it is common to see lights added to Cherokees. A Starter Operating lamp.
The placard you speak of is new to me but could be a CASA AD or other certification requirement. Some of those things can take a while to rewrite or sort out.
Often the original incident that prompted the requirement was years ago... but so catastrophic that no-one is prepared to change back from the status quo.
Has anyone put it to CASA ?
Possible reasons for the recommendation to switch of the alternator field for ground power starts.
1 . Voltage transients created when switching between GPU and battery potentially damaging diodes in alternator (think jumper leads and computers in cars).
2. GPU not appreciating being 'charged' by aircraft alternator.
1 . Voltage transients created when switching between GPU and battery potentially damaging diodes in alternator (think jumper leads and computers in cars).
2. GPU not appreciating being 'charged' by aircraft alternator.
It is the master switch and any avionics switches that needs to be switched off during connection and disconnection of the ground power supply to prevent sparking and damage to the aircraft electrical system.
If a GPU battery start is attempted with the master switch in the on position the battery may be connected in parallel and drag the power of the GPU down to its level. That is if you try to start with external power because of a low aircraft battery and leave the master switch on you may experience very low crank rate due the system being dragged down to the lower level of the depleted battery. In cold conditions they state you can use the GPU battery in parallel with a charged aircraft battery to prolong cranking time.
The Piper variants I'm familiar with have checklists that require confirmation of the master switch in the on position before start. Piper refers to the combination split Bat/Alternator swith as the Master switch in most cases unless seperate alternator switches are fitted. Master switch on refers to both battery and alternator on in the split switch situation. After start the checklists call for a simple check of alternator output.
The alternator off switch is provided to switch it off if it fails to prevent drain of battery charge attempting to excite the dead alternator.
As far as load on start the actual cranking of the engine and accessories would far outweigh any load from the alternator itself. Switch on and off the alternator after start to see how much power it drains from the running engine, there will not be much.
Last edited by 43Inches; 20th Jun 2012 at 08:14.
Switch on and off the alternator after start to see how much power it drains from the running engine, there will not be much.
Even if every system is switched off after start in the aircraft I fly, the battery will charge quite vigorously when the alternator is on. If I leave or switch the alternator off after start, the battery won’t charge. Is the difference in the on/off current measurements the drain of the alternator?
The Ign switch places an earth on the relevant magneto, via the P lead, to turn the mag off.
The switch also takes bus voltage and applies it to the start contactor when the switch is in the 'Start' position. At this position there is also other switching which normally applies an Earth to the right magneto. This is via an external link screwed across the terminals.
The link can be opened if the intention is to have both mags live during the start... if for example the engine has two impulse couplings fitted.
Normally only half the spark plugs are firing during a typical piston engine start. Often the top plug on one bank and the bottom on the other.
So it can be seen that while the switch is held on 'Start' it could be that the engine may only be firing on a couple of cylinders... if the bottom plugs are fouled or flooded.
That is why they will often pick-up when the switch is released.
The switch also takes bus voltage and applies it to the start contactor when the switch is in the 'Start' position. At this position there is also other switching which normally applies an Earth to the right magneto. This is via an external link screwed across the terminals.
The link can be opened if the intention is to have both mags live during the start... if for example the engine has two impulse couplings fitted.
Normally only half the spark plugs are firing during a typical piston engine start. Often the top plug on one bank and the bottom on the other.
So it can be seen that while the switch is held on 'Start' it could be that the engine may only be firing on a couple of cylinders... if the bottom plugs are fouled or flooded.
That is why they will often pick-up when the switch is released.
I’ve looked at the circuit diagrams for ostensibly identical aircraft. Some have 2 impulse coupling-fitted magnetos, some only 1, some have retard breakers, some have ‘shower of sparks’ and other start-assistance technology fitted to only one magneto, and some to both. 4 different ignition switch wiring and shorting link arrangements, despite the switches themselves being the same, the airframes being the same and the engine (aside from ignition systems) being the same.
Be careful: all systems on ostensibly identical aircraft may not be the same.
Errrmmmm….how do I work out what the alternator itself drains,
from switching it on and off?
Even if every system is switched off after start in the aircraft I fly, the
battery will charge quite vigorously when the alternator is on. If I leave or
switch the alternator off after start, the battery won’t charge.
from switching it on and off?
Even if every system is switched off after start in the aircraft I fly, the
battery will charge quite vigorously when the alternator is on. If I leave or
switch the alternator off after start, the battery won’t charge.
I was only stating a test where you could see how little engine power the loaded alternator uses at low engine rpm.
The power required to excite the alternator is very minimal so even if it was drawing some charge during start it would be of absolutely no consequence. The reason it needs to be considered after an alternator failure in flight is that you are minimising to essential power only, cutting any non-essential systems no matter how small.
Last edited by 43Inches; 20th Jun 2012 at 10:57.
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Be careful: all systems on ostensibly identical aircraft may not be the same
I did tend to try and state that I was generalising as there is a huge variety of GA aircraft.
Probably all the moreso now as new generation training aircraft are starting to appear.
I know of a Tomahawk with twin impulse couplings, Slickstart on the left mag, and with the ignition switch link opened.
An otherwise identical sister aircraft has the more conventional single impulse.
Going back to charging and electrical systems, - one has the PEP (Ext Pwr) socket and the other does not so quite a difference there also.
I think those two aircraft would be a good graphical example of how the AFM may not accurately reflect the installation on that particular machine.
Many pilots would possibly be unaware of the differences, especially on a training aircraft.
I am not a big fan of turning the alternator off and on as a check after start-up. I would not allow it on my own aircraft, - preferring the landing light to be operated instead. I monitor bus voltage during flight with the Pilot III displaying supply voltage. Some aircraft, like the Tomahawk, also have an Alt Inop light.
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That is why they will often pick-up when the switch is released.
Recent problem with shower of sparks had this as a symptom.
Had me nonplussed for a while, same vibrator services both engines and was making appropriate noises.
Worked it out in the end - hint push button starter switch
Last edited by blackhand; 21st Jun 2012 at 21:21. Reason: syntax
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Simple Math, engine at 2300 rpm alternator at max output say 100 amps at 28 volts = 2800 watts
2800 watts / 746 watts/ hp = ~ 3.5 hp needed from the engine to power the alternator plus some mechanical load, friction, windage.
So alternator load is hardly a factor.
2800 watts / 746 watts/ hp = ~ 3.5 hp needed from the engine to power the alternator plus some mechanical load, friction, windage.
So alternator load is hardly a factor.