alternators and the battery
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alternators and the battery
On a piper warrior/seneca what exactly does the battery power
1. is it used to start the engine?
2. does it power the likes of the radio, gps, turn co-ordinator, lights...
3. does it just provide 12 volt power
4. Is the alternator just there to recharge the battery?
5. When you see a load on the ammeter dial, does this mean that, that amount of amps is being drained from the battery or is that amount of amps being fed into recharge the battery?
6. Can the alternator provide 24 volts and if so what on a piper would be 24 volt and 12 volt?
Many thanks for the help to clear up my understanding of this
1. is it used to start the engine?
2. does it power the likes of the radio, gps, turn co-ordinator, lights...
3. does it just provide 12 volt power
4. Is the alternator just there to recharge the battery?
5. When you see a load on the ammeter dial, does this mean that, that amount of amps is being drained from the battery or is that amount of amps being fed into recharge the battery?
6. Can the alternator provide 24 volts and if so what on a piper would be 24 volt and 12 volt?
Many thanks for the help to clear up my understanding of this
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1) Yep.
2) Kinda. Yes if the engine isn't running, and yes if the alternator has failed!
3) It depends on the battery - different batteries supply different voltages, depends on your aircraft systems. You might also have regulators to give different voltage feeds, and/or have an inverter on a more complex a/c that provides ac power from DC, but unlikely on warrior types.
4) It recharges the battery, and provides power for the systems when the engine is running. Think of the battery as a resevoir.
5) depends on the ammeter and how it is wired. Some are centre zero and show flow in/out of the battery - they will read positive when the battery is charging, and negative when it is draining. Some are showing load on the system and always deflect in a positive sense - it's worth knowing what your usual load is.
6) if it's a 24volt alternator, sure. Depends what it was designed for. That's rather aircraft specific.
Also note that on most aircraft there is some sort of arrangement with the master switch that allows you to switch the alternator / battery on separately.
2) Kinda. Yes if the engine isn't running, and yes if the alternator has failed!
3) It depends on the battery - different batteries supply different voltages, depends on your aircraft systems. You might also have regulators to give different voltage feeds, and/or have an inverter on a more complex a/c that provides ac power from DC, but unlikely on warrior types.
4) It recharges the battery, and provides power for the systems when the engine is running. Think of the battery as a resevoir.
5) depends on the ammeter and how it is wired. Some are centre zero and show flow in/out of the battery - they will read positive when the battery is charging, and negative when it is draining. Some are showing load on the system and always deflect in a positive sense - it's worth knowing what your usual load is.
6) if it's a 24volt alternator, sure. Depends what it was designed for. That's rather aircraft specific.
Also note that on most aircraft there is some sort of arrangement with the master switch that allows you to switch the alternator / battery on separately.
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The battery powers eveything and the alternator charges the battery.
If the aircraft has a 12 volt system the alternator will have to have an output of more than 12 volts to charge the battery, Usually about 14 volts under load. There is an electronic circuit to control the amount of charge.
There are different ways of displaying the load but I think the PA28s I've flown show the alternator output in amps. Others sometimes show charge and discharge. ie the "0" in the middle of the guage.
Some aircraft are 12 volt and others are 24 volt. They will need the correct alternator for the aircraft.
DO.
If the aircraft has a 12 volt system the alternator will have to have an output of more than 12 volts to charge the battery, Usually about 14 volts under load. There is an electronic circuit to control the amount of charge.
There are different ways of displaying the load but I think the PA28s I've flown show the alternator output in amps. Others sometimes show charge and discharge. ie the "0" in the middle of the guage.
Some aircraft are 12 volt and others are 24 volt. They will need the correct alternator for the aircraft.
DO.
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just so im clear
While Im flying and I see on my ammeter lets say 40 amps
1. This is the amount of amps being fed into my Battery by the alternator. If it is zero the alternator is broken
or
2. This is the amount of amps being used by my battery and the alternator will be working in the background toping up the battery
So the battery will power everything and the alternator will just keep recharging the battery??
While Im flying and I see on my ammeter lets say 40 amps
1. This is the amount of amps being fed into my Battery by the alternator. If it is zero the alternator is broken
or
2. This is the amount of amps being used by my battery and the alternator will be working in the background toping up the battery
So the battery will power everything and the alternator will just keep recharging the battery??
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aslan, you might want to take a good look at the description of the electric system of your particular aircraft. This should be in the POH. As others have said, there are several locations where an ammeter can be inserted in the electric system and the exact location differs from airplane to airplane. Furthermore, there are other indicators spread out through the system that you have to keep an eye on, and know what they're supposed to be indicating.
After all, you have three major components that can have current flowing between them: the alternator, the battery and the rest of the electric system (and this all could be split over several buses, to be precise). If you only have one ammeter, it could theoretically be placed in at least three locations. So with a single ammeter you will never be able to get a full picture of what your electric system is doing. You will always need to combine this with, for instance, the low voltage light or the alternator failure indicator to understand what's going on.
In the POH of the PA-28-161 Cadet (issued Sep 9, 1988), I found the following:
So if everything is correct then in the cruise the 40 amps consumed by the electric system is totally supplied by the alternator since the battery is, and remains, full. (Although the PA28 POH suggests that keeping the battery topped off will consume about 2A anyway.)
But more likely what you will actually see is that right after starting the current is higher than 40 amps. The excess is used to top off the battery, which was drained during pre-engine-start actions and the engine start itself. After a few minutes the battery is topped off and the current drops to 40.
After all, you have three major components that can have current flowing between them: the alternator, the battery and the rest of the electric system (and this all could be split over several buses, to be precise). If you only have one ammeter, it could theoretically be placed in at least three locations. So with a single ammeter you will never be able to get a full picture of what your electric system is doing. You will always need to combine this with, for instance, the low voltage light or the alternator failure indicator to understand what's going on.
In the POH of the PA-28-161 Cadet (issued Sep 9, 1988), I found the following:
As installed, the ammeter does not show battery discharge; rather, it indicates the electrical load on the alternator in amperes. With all the electrical equipment off and the battery master and alternator switches on, the ammeter will indicate the charging rate of the battery. As each electrical unit is switched on, the ammeter will indicate the total ampere draw of all units including the battery.
But more likely what you will actually see is that right after starting the current is higher than 40 amps. The excess is used to top off the battery, which was drained during pre-engine-start actions and the engine start itself. After a few minutes the battery is topped off and the current drops to 40.
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Lots of great information here, it's covered the subject pretty well.
One of the simplest descriptions of the two different ways an ammeter can be wired, can be found part way into the Electronics International instructions , which are here:
http://www.buy-ei.com/Information/OI...II%20VA-1A.pdf
One of the simplest descriptions of the two different ways an ammeter can be wired, can be found part way into the Electronics International instructions , which are here:
http://www.buy-ei.com/Information/OI...II%20VA-1A.pdf
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The battery powers eveything and the alternator charges the battery.
The battery is purely for emergency power and starting the engine.
Its the TYPE of ammeter that is important not its position
There are two types, the charge/discharge type and the load type.
The charge/discharge type will remain centered so long as the system output can meet the system demand. Beyond this point the needle will indicate a discharge and use of battery power.
The load type of ammeter will begin near zero and rise as more electrical load is put online. The voltage warning light will indicate if the load requirement is beyond the alternator's ability to produce. The load meter reflects the actual electrical load as it is turned on. A load ammeter at zero or discharge is saying that you are using battery power.
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Pull what said:
Nonsense! True one would normally use the charge/discharge type of ammeter when locating it between the master solenoid and the busbar (typically Cessna), and the loadmeter type of ammeter if locating it between the alternator and the busbar (typically Piper), but it is the POSITION of the ammeter that determines the nature of the information that is being provided to the pilot, NOT the TYPE of ammeter.
To understand the purpose of the ammeter instrument and interpret it accordingly, the pilot HAS to understand where in the electrical system it is located. Agreed, the type of instrument is a clue, but I've flown older aeroplanes where the instrument has been replaced with the wrong type and it is by no means the definitive answer!
Its the TYPE of ammeter that is important not its position
To understand the purpose of the ammeter instrument and interpret it accordingly, the pilot HAS to understand where in the electrical system it is located. Agreed, the type of instrument is a clue, but I've flown older aeroplanes where the instrument has been replaced with the wrong type and it is by no means the definitive answer!
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In fact, what you will see if you look at the innards of both types of ammeters, is that they are constructed similarly. A coil through which runs a current, which creates a magnetic field, and a little magnet connected to the spring-loaded needle reacting to that field. (Or the magnet is fixed and the coil connected to the spring-loaded needle - the effect is the same.) Plus a shunt to handle the majority of the amps. The difference between both types is simply the position of the needle when there is zero current.
Ammeter - Wikipedia, the free encyclopedia
In a pinch you could probably swap one type for the other and still get more-or-less meaningful results. If you know how they work that is, and where they're place in the electric system. And if the needle doesn't deflect beyond the scale.
And that would definitely not be an approved solution of course.
Ammeter - Wikipedia, the free encyclopedia
In a pinch you could probably swap one type for the other and still get more-or-less meaningful results. If you know how they work that is, and where they're place in the electric system. And if the needle doesn't deflect beyond the scale.
And that would definitely not be an approved solution of course.
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OK then put it another way its important to know which type of ammeter you have-so its position isnt important!
In the Charge/Discharge Meter configuration, the ammeter is directly in series with the battery.
In the Load type configuration, the ammeter is in series with the alternator.
The 'innards' of both instruments are the same, it's the scale and the information thats different!
In the Charge/Discharge Meter configuration, the ammeter is directly in series with the battery.
In the Load type configuration, the ammeter is in series with the alternator.
The 'innards' of both instruments are the same, it's the scale and the information thats different!
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The battery dosn't power anything when the alternator and rectifier are online.
The battery is purely for emergency power and starting the engine.
The battery is purely for emergency power and starting the engine.
The airplane is equipped with a 28-volt, direct-current electrical system. The system uses a battery, located aft of the rear cabin wall as the source of electrical energy and a belt-driven 60 amp alternator to maintain the battery's state of charge
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Put it another way, the alternator is the main source of power to the aircraft systems after engine start, not the battery.
Basic PPL aircraft general and principles of flight exam question!
Basic PPL aircraft general and principles of flight exam question!
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Well, trying to deliniate whether it is the alternator or battery which provides the electrical power to the aircraft systems is kinda' like trying to determine if the propeller pulls into a low pressure area, or pushes against a higher pressure area, to propel the aircraft. The right answer is it's either and both.
Without an alternator/generator, a battery is a wonderful source of electricity for a finite period. Without a battery, an alternator is a troublesome source of electricity for a much longer period of time. They work in harmony, each doing their own rather different job. Ammeters are basically the same as to how they work, be it center zero, or end of scale zero, the means of operation is the same. If you wire an end of scale zero ammeter differently, it will indicate backward off the scale.
So why does the referenced Cessna POH say that the alternator maintains the battery's state of charge? because the aircraft load is constantly discharging it otherwise! If you flick on the landing light, with the nav lights on, and operate electric flaps or an electric hydraulic system, you will momentarily exceed the capacity of the alternator. Do you pop the breaker? No, 'cause the battery takes the load for that time. When you turn final, and pull the power to idle, with the landing light on, you can be assured that the battery is powering everything, and will continue to do so, until you add power, because at idle, the alternator is doing very little. Indeed, this condition is very hard on alternator trives, for reasons a little beyond the scope of this post. My habit is to turn off the alternator side of the master switch when landing at night, to ease the load on the alternator drive. My battery is very useful at that time. Of course, a bit of ammeter monitored ground high idle afterword, brinngs the battery back up to where it should be.
So, the subject can be argued either way, but the bottom line, is the battery should be treated and respected as the source of electricity for the aircraft, with the alternator charging it. If I thought that the battery were no longer providing, or able to provide power in flight, I would most likely turn off everything electrical - certainly all avionics.
For the discussion about the position of the ammeter in the circuit, I again refer posters to the EI document I linked earlier. If you wanted the perfect indication of the function of the electrical system, you would actually use two ammeters, each connected in the circuit in a differnt place. The EI dcoument makes it very clear as to why.
Disagreed.
The battery, in addition to the foregoing, acts as a giant capacitor in a way, absorbing and returning power to the system as needed. Without it, you have problems.
Pilot DAR
Without an alternator/generator, a battery is a wonderful source of electricity for a finite period. Without a battery, an alternator is a troublesome source of electricity for a much longer period of time. They work in harmony, each doing their own rather different job. Ammeters are basically the same as to how they work, be it center zero, or end of scale zero, the means of operation is the same. If you wire an end of scale zero ammeter differently, it will indicate backward off the scale.
So why does the referenced Cessna POH say that the alternator maintains the battery's state of charge? because the aircraft load is constantly discharging it otherwise! If you flick on the landing light, with the nav lights on, and operate electric flaps or an electric hydraulic system, you will momentarily exceed the capacity of the alternator. Do you pop the breaker? No, 'cause the battery takes the load for that time. When you turn final, and pull the power to idle, with the landing light on, you can be assured that the battery is powering everything, and will continue to do so, until you add power, because at idle, the alternator is doing very little. Indeed, this condition is very hard on alternator trives, for reasons a little beyond the scope of this post. My habit is to turn off the alternator side of the master switch when landing at night, to ease the load on the alternator drive. My battery is very useful at that time. Of course, a bit of ammeter monitored ground high idle afterword, brinngs the battery back up to where it should be.
So, the subject can be argued either way, but the bottom line, is the battery should be treated and respected as the source of electricity for the aircraft, with the alternator charging it. If I thought that the battery were no longer providing, or able to provide power in flight, I would most likely turn off everything electrical - certainly all avionics.
For the discussion about the position of the ammeter in the circuit, I again refer posters to the EI document I linked earlier. If you wanted the perfect indication of the function of the electrical system, you would actually use two ammeters, each connected in the circuit in a differnt place. The EI dcoument makes it very clear as to why.
The battery dosn't power anything when the alternator and rectifier are online.
The battery is purely for emergency power and starting the engine.
The battery is purely for emergency power and starting the engine.
The battery, in addition to the foregoing, acts as a giant capacitor in a way, absorbing and returning power to the system as needed. Without it, you have problems.
Pilot DAR
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Pilot DAR has it right.
There is a lot of "terminology" splitting hairs here, the sort of thing which the exam writers love
An alternator, with its voltage regulator, is a constant voltage power supply.
Unfortunately, while (with a sophisticated voltage regulator) it could work by itself, most current implementations do rely on the presence of a battery for stability and a smooth output voltage. The alternator generates a 3-phase output which even when full-wave rectified still has a lot of ripple on it and would play havoc with a lot of avionics, if the battery was disconnected.
If the alternator, or its rectifier, or its voltage regulator, fails then you are running from the battery until it goes flat.
Unless the voltage regulator fails into a short in which case the thing will run until the battery overcharges
The only alternator system I know of which can run with a smooth output without a battery is the GAMI Supplenator but that does't "exist" yet.
There is a lot of "terminology" splitting hairs here, the sort of thing which the exam writers love
An alternator, with its voltage regulator, is a constant voltage power supply.
Unfortunately, while (with a sophisticated voltage regulator) it could work by itself, most current implementations do rely on the presence of a battery for stability and a smooth output voltage. The alternator generates a 3-phase output which even when full-wave rectified still has a lot of ripple on it and would play havoc with a lot of avionics, if the battery was disconnected.
If the alternator, or its rectifier, or its voltage regulator, fails then you are running from the battery until it goes flat.
Unless the voltage regulator fails into a short in which case the thing will run until the battery overcharges
The only alternator system I know of which can run with a smooth output without a battery is the GAMI Supplenator but that does't "exist" yet.
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Yep IO has got it in one line:
Practically that is the reality, and dont forget it. I have had two alternators fail in flight and landed before the battery went flat but I am in no doubt it would have gone flat. I had an alternator fail in my Caterham a little while back and sure enough the battery went flat and the car stopped - of course at least the aircraft engine will keep running unless it is a Thielert. 
If the alternator, or its rectifier, or its voltage regulator, fails then you are running from the battery until it goes flat.
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That's why in the UK there is/was a requirement to fit a low volt light to warn of an alternator failure. I know of someone flying an N reg with no such system, finding out that his alternator had failed only because his handheld GPS (connected to cigar lighter) went dead. The flight manual should also contain an estimate as to how long the battery would last with only the essentials running. Again a UK requirement.
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It is IMHO completely unacceptable for an aircraft engine to simply stop as a result of an electrical failure elsewhere.
Alternators do pack up, and batteries definitely go flat.
I don't know why Thielert did not fit a second little alternator just for the engine. That's why GAMI developed their "supplenator" - to power the FADEC system. These little alternators have been around for years, and some are STCs for stuff like Bonanzas, IIRC.
Alternators do pack up, and batteries definitely go flat.
I don't know why Thielert did not fit a second little alternator just for the engine. That's why GAMI developed their "supplenator" - to power the FADEC system. These little alternators have been around for years, and some are STCs for stuff like Bonanzas, IIRC.
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Has anyone mentioned yet that the magnetos provide an independent electrical supply to the spark plugs? The engine will not stop as a result of alternator/rectifier failure or battery flatness.
Electric flaps, undercart, avionics, coffee machine etc, will not work but the engine will continue to run.
Yes, newer designs are doing away with the old fashioned mags & they will fail when electrical systems go pop. Good thing, bad thing?
Electric flaps, undercart, avionics, coffee machine etc, will not work but the engine will continue to run.
Yes, newer designs are doing away with the old fashioned mags & they will fail when electrical systems go pop. Good thing, bad thing?
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Indeed, that's why serious engines have a permanent magnet alternator (PMA) fitted. A PMA is just about the simplest electrical machine you can design (and thus one of the most reliable). It has but one moving part and a very crude, inefficient but reliable control system. Why Thielert did not fit one is beyond me too.