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Dumb electrical question

azonic75

Well Known Member
If it is "bad" to run an alternator without a battery, what happens when you turn the master off in an "emergency"? Obviously if you are on fire it is a non issue but what if that is the mechanism by which you "load shed", what is the consequence (assuming for whatever reason the alternator was still generating power)?

In the Aeroelectric schematics with "essential" or "endurance" busses if you turn off the master and "engage" the essential buss isn't this exactly what happens?

What about if you master contactor failed?
 
It's better to turn the alternator off before the battery. If you don't have a nice big fat battery in there to act as a buffer between the alternator and your expensive electronics, you might get some voltage spikes that can damage things.

Many of the "split" switches make it impossible to have the alternator on without the battery. I have 3 position toggle: off - battery - battery&alternator

There has been some discussion about if it's possible to turn off some alternators once they are started - this can apparently happen to some alternators, so probably best to test that you have an alternator that can be turned off if this is a concern. The most popular alternators can be turned off without problem, but generally it seems to be recommended by the alternator guys at PP/Hartzell to have the alternator off during starting, and then turn it on when the engine is running and leave it on until the engine is shut down cleanly.
 
This thread might answer part of your questions:
http://www.matronics.com/digest/dig...=html&Chapter=2012-09-13&Archive=AeroElectric
My PC680 battery failed open while flying. I did not realize it until closing the throttle to land when electrical loads shut off. Looking at the EFIS data later, the bus voltage was unstable but not enough to cause any problems.
The aircraft electrical system is powered by the alternator, not by the battery.
If the battery is disconnected, the alternator doesn't know it, so it keeps working.
 
It's better to turn the alternator off before the battery.

The most popular alternators can be turned off without problem, but generally it seems to be recommended by the alternator guys at PP/Hartzell to have the alternator off during starting, and then turn it on when the engine is running and leave it on until the engine is shut down cleanly.

I hope I'm not doing it wrong, but I turn on the alternator AFTER starting and before lights and avionics. When shutting down I switch off all electrical loads, then the alternator, then mixture to idle/cutoff, and when the engine stops I then switch off the ignitions and the master.
 
thanks

This thread might answer part of your questions:
http://www.matronics.com/digest/dig...=html&Chapter=2012-09-13&Archive=AeroElectric
My PC680 battery failed open while flying. I did not realize it until closing the throttle to land when electrical loads shut off. Looking at the EFIS data later, the bus voltage was unstable but not enough to cause any problems.
The aircraft electrical system is powered by the alternator, not by the battery.
If the battery is disconnected, the alternator doesn't know it, so it keeps working.

I think your direct experience answers the question. Perhaps the story that running an alternator "without a battery" results in some catastrophic and/or expensive event is exaggerated.
 
I hope I'm not doing it wrong, but I turn on the alternator AFTER starting and before lights and avionics. When shutting down I switch off all electrical loads, then the alternator, then mixture to idle/cutoff, and when the engine stops I then switch off the ignitions and the master.

Long ago in a galaxy …..
There used to be a lot of premature alternator failures. The “accepted theory” was the standard automotive type alternators in common use didn’t like to be turned on or off while the engine was running. It was recommended to enable the alternator before start and turn it off after shut down.
I had an early failure. Replaced the alternator with the same automotive type and adopted the above procedure. Haven’t had an issue since.

I think there is more at play here, type of alternator, brand, etc….. so, take it for what it’s worth.
 
I also will add that most alternators use simple rectifiers with no, or little, filtering. I wouldn’t want to run on alternator alone as a practice. The battery is an excellent filter.
That said, I think electronics in general are more robust today than they used to be and probably tolerate a lot more abuse than in the past.
 
Long ago in a galaxy …..
There used to be a lot of premature alternator failures. The “accepted theory” was the standard automotive type alternators in common use didn’t like to be turned on or off while the engine was running. It was recommended to enable the alternator before start and turn it off after shut down.
.

Yes, I've heard that theory. The idea was that turning on the alternator after engine start induced a "shock load" on the gears and bearings. I even heard a corollary, that it was okay with a belt driven alternator (the belt would stretch a bit to dissipate any shock) but not okay with a gear driven unit.

I have no idea how much of this is fact, vs fiction.
 
Battery or no battery, that is the ?

This was from B&C last year. We can decide if relevant. Maybe other producers power generators are ok.

=========================================

Thank you for contacting us with that good question.

In general terms, yes – there would need to be a battery in the circuit for an Alternator to function properly. In the scenario you’ve suggested, Alternator output would likely continue for a time, but the bus voltage would be less stable and the power quality would be diminished. Should a large bus load be removed during this condition, a voltage surge would likely result (due to the lack of a battery); and should this voltage excursion

exceed 16.0V (approximately), that would cause the Regulator OV protection to shut down field excitation to the Alternator … with no means remaining to re-establish it given the absence of the battery.

I hope the above makes sense and is helpful. If you have any other questions, or if I can be of help to you in any other way, please do not hesitate to contact me.

Kind Regards,

“TJ” Jenkins
B&C Specialty Products
 
This thread might answer part of your questions:
http://www.matronics.com/digest/dig...=html&Chapter=2012-09-13&Archive=AeroElectric………….
The aircraft electrical system is powered by the alternator, not by the battery.
If the battery is disconnected, the alternator doesn't know it, so it keeps working.

Very risky if not dangerous approach. A safer way of thinking (and more appropriate IMO) = the electrical is powered by the battery. The alt charges the battery.

The voltage may remain steady/system may stay on line initially with no battery. Change of load from radio xmition, flap motor energize, etc. could easily cause enough of a voltage swing to trip it off line. You may get away with it once, twice, whatever. It’s good until it isn’t.
 
Electrical loads always draw current from the source that has the highest voltage. The alternator puts out a higher voltage than the battery.
I never recommended flying with the master switch off. Just saying that if the battery contactor fails while flying, the pilot might not realize it.
Read what Bob Nuckolls says in post number 3 of this thread:
http://www.matronics.com/digest/dig...=html&Chapter=2012-09-13&Archive=AeroElectric


You missed the point or I wasn't clear enough. I stated "it's a safer way of thinking." No one will argue that current flows from the highest potential source. Having your VR rely on the system's capacitance (not battery) alone is a recipe for disaster. The battery doesn't have to be in series, just there. More will point to experience where their flight wasn't severely, negatively impacted from a "failed" battery. The butterfly effect looms largely over that scenario.

It's a Monday so I'll really step in it. People like to defend their choices here.

From a safety standpoint, I'll take a two battery/one alt system over a two alt/one battery system any day. This assumes of course that both are designed and maintained appropriately. Have fun with is one.
 
Side note. The concept that the battery is a “filter” is not correct. The battery is a “surge volume” to provide changes in demand, either adding or taking loads off.

The battery only knows DC. If you have AC ripple (or RF for that matter) that noise will just float on top of the DC. Alternator whin is example.

Carl
 
Operation of the ALT/ BAT switches

Turning the BAT-switch ON will supply bus Voltage to the voltage regulator SENSE input.
Turning the ALT-switch ON will supply a current (amps) to the alternator field winding and then to engine GND.
The field current ranges from 0-4 A, where 0 A = no charging and 4 A = full battery charge current.
If the engine/ alternator is not running, the bus voltage is the same as battery voltage. This will result in a field current of 4 A because voltage regulator is set to 14,5 V.

When starting the engine one would want all amps go to the starter and no
mechanical load on the alternator.
As I understand it this is the reason why one would start the engine with
BAT-switch ON and ALT-switch OFF.

Good luck
 

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Side note. The concept that the battery is a “filter” is not correct. The battery is a “surge volume” to provide changes in demand, either adding or taking loads off.

The battery only knows DC. If you have AC ripple (or RF for that matter) that noise will just float on top of the DC. Alternator whin is example.

Carl

“Filter” as a generic term has been used to describe the interaction between alternator/battery circuits since, well, they where invented and used together.
Doesn’t really take away from the discussion.
Call it a surge protector, spike reducer, or whatever you want…..
 
It's a Monday so I'll really step in it. People like to defend their choices here.

From a safety standpoint, I'll take a two battery/one alt system over a two alt/one battery system any day. This assumes of course that both are designed and maintained appropriately. Have fun with is one.

Yup, it's Monday so I'll do the same and jump in. I think just the opposite (Unless of course you have full EI, in which case you pretty much have to have two batteries.). I'll take a backup alternator any day. In over 2000 hours I've already had three alternator related failures (never the B&C alternator itself), and no battery failures. It would be an interesting poll to see how many folks have had battery failures v.s. alternator failures....

Apart from master solenoid failures, which generally occur on energizing (Contact corrosion, wear), not random drop off during flight, loss of a battery seems far, far less likely than alternator failures. Alternators have many ways to fail - to start with, they could be a Plane Power (joke!), brush wear, broken field wire from engine vibration, broken belt, diode failure to mention a few. By comparison, batteries are far more robust wrt sudden failures. So with one alternator and two batteries, with an (more likely) alternator failure you can just fly a bit longer due to the additional battery charge, and if its a backup battery that may not even add up to much. With a battery failure, ok, you could just keep going, possibly having to switch things around accordingly.

With two alternators (one the backup), with the far likelier alternator failure than battery failure, you can keep going with the backup. Done that, all the way from Teterboro to Chicago. And with a (highly unlikely) battery loss, apart from the issue of not knowing and dropping the alternator due to a sudden substantial load change, you also keep going.

That brings us to the issue of detecting a battery dropping out and in most cases going undetected. I dealt with that with a sensitive battery ground strap current direction detector. The battery ground side cable should always have at least a small amount of current flowing down toward ground. Flowing upward means the battery is not charging or discharging in excess of alternator output plus loads, and no current means the battery is failed/disconnected. The current sensor looks for that positive current to frame ground, and if it is negative signals a charging/alternator failure and if it is zero, a battery failure. And in the worst case fly home with the battery backed up Garmin G5 and handheld!
 
interesting argument. Yes batteries fail but my experience (which counts for nothing) has been an internal short/bad cell versus an open. I assume you're talking about something without a BMS (different pile to step in with equally passionate followers here). In the aforementioned case, wattage becomes unusable work (heat) and the system is again forced to operate on its hairy edge (getting awfully close to third pile; need for Ammeter, voltage meter, both). In either case, the VR/protection circuit is probably the tripping point if not weak point IMO.

BTW. I'll have a B&C main with a Monkworkz as a BU and two AGMs. I actually need the weight up front; plus, I've installed EFI/EI; a forth pile. Is it Friday yet?
 
Aero Electric Connection Chapter 17

Very risky if not dangerous approach. A safer way of thinking (and more appropriate IMO) = the electrical is powered by the battery. The alt charges the battery.

The voltage may remain steady/system may stay on line initially with no battery. Change of load from radio xmition, flap motor energize, etc. could easily cause enough of a voltage swing to trip it off line. You may get away with it once, twice, whatever. It’s good until it isn’t.

This was from Robert's book. We can design as we please. For me using a battery system with a BMS that is at least theoretically possible to switch off and an electrical dependent engine I'll use 2.
 

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I'm a little late to the party, but just to bring a little real world application into all this debate about electrical theory;

What situation or failure mode could you conceivably find yourself where you would want to turn off the battery master and leave the alternator online?

I can't think of a single scenario where that would make sense. I guess I should throw a disclaimer out there and say I'm a little fuzzy on the wiring of exotic electrically dependent airplanes, but other than that (maybe?) It' s not even physically possible to do that in most airplanes.
 
Alternator performance with failed battery contactor

I have some notes from VAF and AEL re alternator performance with failed battery contactor.

Sounds like the excerpt from the Aeroelectric Connection book in post 18 refers to a former time technologically speaking.

Seems like Monkworkz changes the landscape for those with both main and vacuum pad alternators (Monkworkz calls the latter a generator because it is permanent magnet) because the Monkworkz will start and run without a battery and it puts out 30A from 1,800 and up Lycoming rpm (15A at 1,000 rpm).
.
 
Need battery

B&C is willing to document that their alternators need a battery in-line as of a few months ago, recent and good enough for me not to give it a try. (See previous posts)
 
I have some notes from VAF and AEL re alternator performance with failed battery contactor.

Sounds like the excerpt from the Aeroelectric Connection book in post 18 refers to a former time technologically speaking.

Seems like Monkworkz changes the landscape for those with both main and vacuum pad alternators (Monkworkz calls the latter a generator because it is permanent magnet) because the Monkworkz will start and run without a battery and it puts out 30A from 1,800 and up Lycoming rpm (15A at 1,000 rpm).
.

B&C is willing to document that their alternators need a battery in-line as of a few months ago, recent and good enough for me not to give it a try. (See previous posts)

To me (ME not EE), it seems like some are blurring the line between alt self-excitation and a VR being able to keep the system within limits without battery capacitance available to dampen current fluctuations.

At a minimum, test your system under load excursions with the battery contactors open. If it fails to keep the alt on-line, then you know for sure. If it passes? It means it passed that day under those conditions. I'll state again, the butterfly effect has as large looms large over such a situation. I see no reason not to trust the component OEM here; but, it's EAB. Do what you want. Stay safe.
 
This not a dumb question.

First (sincere question) do you know how an alternator works. An alternator needs excitation power to run. More on that later. Do you know the difference between an externally regulated alternator or internally regulated one. What KIND of alternator do you have. Is it a "single wire" car alternator, typically a Nippon Denso (or clone of one). How is it wired into electrical system?

The excitation power (dc power to rotor field winding) is typically through the Alternator to BATTERY "B-lead", a heavy wire to handle amperage and charge the battery. But it works both ways. It gives excitation power to the alternator and tells the alternator if the bus voltage is below or above set voltage of the VR. It will adjust the power going to the alternators winding to increase or decrease the output to maintain voltage for a given load or demand.

In cars that B-lead is often direct to battery with no switch but typically has a fuse or fusible link. The DOWN side is the regulator even when car is off, engine not turning will drain a small amount of power to keep the computer alive (IVR has an IC chip). That is where the small SINGLE WIRE comes in. That is the GO TO SLEEP or WAKE UP logic wire. It does not carry much power, it is more of a signal to tell the VR IC chip to go into standby or sleep. Sometimes there is another second small wire. It is open or grounded to turn on a low voltage light. This low volt sense is in the alternator voltage regulator. The voltage regulator is complex with an IC chip to do the voltage regulation, protect from low or high voltage, protect the alternator, make it sleep with engine not running, come on when RPM is high enough, provide low volt warning..... However if you do not wire it and operate it properly you can fry it. You wire and operate as designed and keep it cool (from exhaust radiant heat using a heat shield and add a blast tube to regulator cooling fins) it will run reliably like it does in a car with no input from driver or pilot. Meaning no alternator switch is "needed".

In your car (and as these alternators were designed), you turn off the ENGINE (ignition) and electrical / battery power to the car at one time. HOWEVER the alternator is still getting power direct from the B-lead. It is not switched. As the RPM drops the alternator is still drops off line per voltage regulator IC logic. BUT it stays awake for a period of time ready if you start the car. It will stay awake for a programed time depending on the VR, 5 seconds, 15 seconds, 60 seconds. The specs are available based on voltage regulator (VR) part number spec sheet; At the end of this stay awake time it goes to sleep because that single small wire was turned off with ignition key to off, removing power from the stay awake/sleep wire. The alternator regulator IC chip logic shuts the alternator off to keep from draining battery. This is why if you car battery goes dead due to parasitic drain while not driving you have to wait 5 mins to let all the computers go to sleep. The problem is opening a door may turn some of them back on. The drain to power the IVR IC chip is small if it is not exciting the windings, which it should not even with power to the sleep/wake wire.

LIKE A CAR A SEPERATE ALTERNATOR SWITCH IS NOT NEEDED. iT IS AUTOMATIC. If you engine is running full tilt in flight and you turn off the power to the alternator stay awake wire and turn it back on... YOU CAN FRY THE REGULATOR. It was not made to switch the alternator off and on while making power. This goes down into a can of worms about OV protection. These "single wire" alternators rarely have OV if wired and operated properly. The IC has OV protection in it. However if you start to monkey and control the STAY AWAKE/SLEEP power YOU MAY (not always) KILL THE VOLTAGRE REGULATOR and possibly cause an OV condition. Most of the time it will just die and stay dead... I am for some way to switch the sleep/wake control via a pull able CB.

These alternators are TOTALLY different from older externally regulated alternators where you CONTROLLED the power to the VR and thus the excitation directly. The modern alternators have power to the IVR and thus excitation is available to the alternator to make power. You can not shut them down while running. They will do that for you if you have OV or Low V.

If you want to ADD external pilot control or automated OV protection on a internally regulated alternator there are many ways to do it.... It is not necessary in my opinion. The most common is put the B-Lead on the back side of the master relay not direct to battery like a car. So now we are leaving the car bus system. The next thing is run the B-lead through a FUSE or CB. Cars use fuses. However ADD a CROW BAR. It is an OV sensor that will SHORT the fuse to ground and blow the fuse. The alternator will not be happy, but if it were misbehaving it would be automatically isolated.

Plane Power and B&C take stock ND alternators and modify them and charge a mint. KEEP IN MIND a Genuine ND alternator is high quality as is but harder to come by. Most of the stuff on the market are cheap clones (but some are OK) or they are rebuilt and sold at auto part stores. That is the advantage of going with a stock car alternator. If you are flying on a trip and alternator dies you can go to auto parts store across the street from airport and get one cheap.

FIND OUT WHAT ALTERNATOR YOU HAVE. If stock car ND (Nippon Denso, popular because they are small and light) then follow my suggestions you will be OK. If you have a separate alternator switch and it is powered and unpowered with master you don't need it. If it is independent of master and you can turn it on and off, be carful. You will should turn BAT then ALT to on in that order to power up, then start engine. To shut down, cut mixture, shut engine down, then turn ALT and BAT in that order (but it does not really matter if engine is shut down.

The most simple way to wire is have the IVR wire to master buss and alternator on the switch side of master relay. AS long as battery master is ON before start you are good, Shutting down as long as you KILL engine before turning master off you are good.

Pilots, builders who have problems with IVR car alternators are turning the power OFF and back ON while flying to SEE WHAT HAPPENS. Don't do that. It is all electronically controlled, automatic, digital stuff going on in the VR IC chip. As long as you keep it semi cool with heat shield and blast tube it will last a long time like it does in a car. If it does fail it is almost always PASSIVE and just shuts down. No action required by pilot but land and replace voltage regulator or whole alternator. It could be brushes. Even the expensive Plane Power and B&C fail all the time... trust me.

There are so many ways to wire these alternators, some ways not so good. However it is how you operate it and how it is wired. If it is PLANE POWER or B&C or other modified expensive "aircraft" alternator (warmed over ND alternator clones) with "modified" internal VR* or wired for external VR follow their instructions. These alternators have issues as well, but if you install and operate them as designed they will be OK... So will stock car ND alternators. As far as Aeroelectric he has a very strong dogmatic opinions of how things shall be. His super redundant systems get very complexed to install and operate. That is fine. Do as you like but keep it light and simple. If you need redundant electrical systems you can add a second battery charged from a single ND IVR alternator. You can put a OV disconnect to isolate the back up battery. I did that running a DC to DC battery charger. If that charger were to **** out I still have battery reserves, or I could switch the essential DC bus to main bus manually. BTW most (not all) electronics have their own OV protection and run from 10-30 volts. Old avionics had no power filter and the first thing it hit were semi conductors rated for 18 volts...

BTW you can go in and gut the ND IVR and take out the magic IC chip and run a FIELD WIRE direct an external voltage regulator. I recommend the Transpo 12V Remote Voltage Regulator VR1200. This will give you direct access to the alternators field and thus ultimate control of shutting the alternator down without an IC chip doing it for you. It is an option. But how reliable are IC and transistors? Very if you don't cook them. They have operating limits 100C and can survive more. So don't run your exhaust pipe 2 inches from the back of the alternator.
 
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Thanks for the very thoughtful reply

I’m using an externally regulated Band C alternator. The thing that prompted my question was simply thinking about what would happen in the albeit unusual circumstance of master contractor failing in flight (equivalent to turning off the master). It seems the general conclusion is “hopefully you don’t have to find out”!
 
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