Is the Alternator Switch an Antique?

[Ironflight]

We are currently working on the switch list for the new RV-3, and I am beginning to think that I am ready to get rid of the alternator field switch. I figure that, at the very least, the idea should be able to generate some ?interesting? discussion?

Here?s the deal. I am quite happy with the ND internally regulated alternators that were, for years, supplied in the FWF kits, and are easily obtained at most auto parts stores. I like the fact that they can be picked up easily in an emergency away from home, and quite frankly, I have never had an airplane alternator (certified or not) last as long ? as long as you operate them the way they were designed. This means that you don?t want to switch them on or off while they are spinning. (I didn?t come up with this little gem of wisdom ? search the archives for alternator posts by GMCJETPILOT). This argument makes sense when you consider the sudden load that can hit the diode/regulator pack if you switch it while the rotor is going full tilt. In automotive use, they don?t have ?pilot? controlled switches, after all.

When I built my -8, I put in a Cessna split master, like many folks did. I brought the alternator on line after engine start. That alternator lasted a few hundred hours before the VR started to ?wander? a bit. I replaced it with a rebuilt unit, decided never to switch it while turning and that was about 800 operational hours ago. We have had similar experience with Louise?s RV-6. The bottom line is that the way the field power is wired is with a circuit breaker and switch in series. If the ONLY time you?re going to switch the alternator off is in a failure condition, then you could easily do that by pulling the breaker. The added benefit is that you are less likely to accidently turn it off without a switch there in a row with the other normally operated switches.

So in summary, I see two good reasons to delete the switch - less chance of accidental activation and the saving of critical panel space (the -3 is a small cockpit). I can?t see any real downside to it.

Relevant thoughts? And no, I am not planning on going with a B&C or PP alternator this time around?.

Paul

 

[Mel]

I agree.

I used to have an "alternator" switch and like you, I switched it on after start. Alternators lasted a few hundred hours. I removed the switch and replaced it with an "Idiot light", and my alternator failure problem went away.

 

[Neal@F14]

Personally, I think the most value in an alternator field switch (or pullable breaker or toggle breaker) with today's modern internally regulated alternators (e.g. the ubiquitous Plane Power lightweight units used in so many RVs) is that if something does wrong with the alternator, you can easily disconnect the juice from the field coil to kill the circuit in an emergency. A simple pullable breaker is probably the cheapest and lightest weight way of accomplishing this.

EDIT: I put a toggle breaker in the RV-8 when it was built and after reading numerous stories of short alternator life, and after my friend lost his new alternator in his new RV-10 after less than 50 hours (regulator shorted and it was overcharging), I've just simply started leaving the alternator field toggle breaker turned on all the time now. My friend with the RV-10 does the same now and has had no more alternator problems either.

Edit #2: And speaking of antiques, my old Cherokee has no separate alternator switch from the factory. When the old fashioned DPDT master switch is turned on, one side of it switches on the field circuit to the alternator before the engine ever turns, and the ancient Chrysler alternator in the plane was been working just fine for more than 2000 hours (it was upgraded from generator to alternator long before the current engine overhaul was ever done and the current engine is now at mid-time). So yep, I agree that having a separate switch plus a pullable breaker for the field circuit is a waste.

 

[Walt]

Externally regulated = Switch is good (my preference)
Internally regulated = No need for a switch, on all the time.

 

[L.Adamson]

The alternator field draws current. If I have the master switch on, to program the GPS, or whatever............I'd prefer to have the alternator field off. I'm not sure how much current it draws, but it's enough to make a noticeable swing on the ammeter.

L.Adamson --- RV6A

 

[Special Delivery]

If you have a Cessna split master... Frame it!

Paul-
Over 10 years on my -8 using a DPDT master switch (master relay/alt field) with a circuit breaker in series on the alt field side. Never a problem and I will be using the same architecture on my -3. I agree with your thinking and my experience suggests that it provides trouble free operation. While I've got you on the line, the photos of you and Louise celebrating the arrival of your Mattituck Red/Gold are PRICELESS!

Edit: -8 =B&C externally regulated / -3 =Plane Power

 

[Neal@F14]

Pullable breakers...

Another thought... if I was wiring up the RV-8 all over again, I think this time I'd probably choose the cheaper, lighter, more compact Klixon pull breakers instead of the expensive, heavy Tyco units we bought. Probably could've saved a couple pounds of weight... but at the time those heavy duty Tyco breakers looked rugged and cool, like they belonged in a military aircraft.

 

[Kevin Horton]

I see no reason to have a separate alternator switch. I've got a three position Battery Master/Alternator switch on my RV-8. The mid position is Battery Master ON and Alternator OFF. But, there is no practical need for that mid position, as I can kill the alternator if needed by pulling the field CB. My GPS is on an Essential Bus that can be powered by a toggle switch, so I don't need to throw the Battery Master to program the GPS.

Go with the simple, light and cheap solution. Ditch the alternator switch.

 

[Ironflight]

It's always nice to get a consensus that confirms my own opinion!

I always use pullable breakers (Yes, the Klixon's are light and compact, and I love 'em) because it gives me more control, especially in a Technically Advanced Airplane where I frequently power cycle components when doing maintenance and software updates. Since they rarely (if ever) get cycled in flight, I can save the weight and failure modes of a switch, and use the breaker for this occasional function.

I am going to do the same thing with the alternator switch - the breaker will serve the function just fine.

Paul

(And yes Ernie, I still walk out to just look at the engine every day....)

 

[miyu1975]

I am quite happy with the ND internally regulated alternators that were, for years, supplied in the FWF kits, and are easily obtained at most auto parts stores.

I am interested in these alternators, which brand and auto parts store can they be found?

 

[Dave Cole]

Paul-
Over 10 years on my -8 using a DPDT master switch (master relay/alt field) with a circuit breaker in series on the alt field side. Never a problem and I will be using the same architecture on my -3. I agree with your thinking and my experience suggests that it provides trouble free operation. snip...

I have my -7 set up set up this way, too. The DPDT master switch...wired OFF-BAT-ALT...allows me to connect the battery to the main bus prior to engine start without energizing the alternator field. This is useful for powering up the avionics for updates, or to turn on the lights for pre-flight.

I have a Plane Power alternator with internal over-voltage protection, so the master switch is not need to de-energize the alternator field, and I don't intend to use it that way. If necessary, I also have the option of pulling the alternator field circuit breaker.

 

[Bill Wightman]

Be aware: many of these automotive combined alternator/regulator units don't have any over voltage protection. If the internal regulator fails, the consequences might not be good.

 

[Mike S]

I am quite happy with the ND internally regulated alternators that were, for years, supplied in the FWF kits, and are easily obtained at most auto parts stores.

I am interested in these alternators, which brand and auto parts store can they be found?

ND is the brand, Nippon Denso. They are the ubiquitous alternator for Japanese autos.

Most any auto part store will have them, I happen to be partial to NAPA.

Not sure of the model number, but I suspect it will appear soon.

 

[Ironflight]

Be aware: many of these automotive combined alternator/regulator units don't have any over voltage protection. If the internal regulator fails, the consequences might not be good.

Correct - which is why you can (and should) install overvoltage protection in your system pretty easily.

Of course, I haven't seen a lot of '87 Suzuki Samurais with blown electrical systems due to overvoltage either....

Paul

 

[hevansrv7a]

just a bit of contrary data

I started with the ND that came with the FWF kit. I have a Cessna master switch. I NEVER switched the field off or on while it was turning. I had repeated failures after very few hours. I switched to PlanePower.

I have no opinion about the need for the field switch, but my failures were not, IMHO, caused by switching while turning.

I suspect there is a lot of variation in quality control in those auto-parts sourced alternators. BTW, Bosch makes one to the same physical dimensions as the ND.

 

[RV6_flyer]

AeroElectric Connection

The EXPERT on aircraft electrics is Bob Nuckolls at the AeroElectric Connection. I may make my living as an Electrical Engineer but Bob's thinking on aircraft electrics is almost exactly the same as mine. There are some differences but he is much better in putting his thoughts in writing than I can. You will not go wrong following his recommendations.

Yes I would leave the Alternator Switch out of my next airplane but there would be a pull type circuit breaker on the field.

I have a switch for wing strobes and a switch for tail strobe. I would leave the tail strobe switch out on the next build also. It would be replaced with a pull type circuit breaker. The reason for this switch being left out is that it acts a a tattle-tale that the master is on after shut down and also as a warning that the prop is going to start turning at start up.

 

[elippse]

Typical alternator field current is about 4A; you definitely don't want to have it on if you have your master on for any period of time. I've never seen this post about alternator failures or short life due to switching the field on while the engine is running. If their is an effect it is probably due to immediately applying the field voltage when the alternator is working into a load. Doing something like that will definitely cause a big mechanical jerk to the alternator and its belt drive. I guess the reason I have no problem with this on my plane is that I designed and built my own regulator with OVP and it is not connected directly to the buss but is instead connected to the alternator-side of the alternator breaker. The reason for this is to prevent a big transient if the alternator breaker happens to open up and then is switched back in.

 

[Special Delivery]

Check this out!

This just appeared on Antique Road Show and was valued as PRICELESS!

 

[Mike S]

You know, by some definitions, I am an antique

Perhaps the thread should ask if the alt switch is "obsolete" instead??

 

[Physics Flyer]

A Lesson Learned???

My previously used alternator with internal regulator failed after about 20 hours of my Phase I testing of my RV-6A. The only glitch I had in testing was possibly a result of my misuse of the Alt.Field switch as mentioned in this thread. After replacing the diodes my repair man recommended I replace the switch with an idiot light and use the pull-type breaker to shut down the system if necessary. I think I would eliminate that switch if I were redoing the wiring after reading this thread and reviewing my experience with friends.

The only instruction I ever recall getting from a CFI in reviews was many years ago when I was told to leave the alternator switch off to reduce the load on the battery at start, then turn it on. I have never had any CFI correct me or say anything about my use of that switch. I suspect they have never been properly instructed either. I hope I have learned a useful lesson here and will share it with friends. Long live those alternators!!!

 

[Mike S]

Welcome to VAF!!!!

after about 20 hours of my Phase I testing of my RV-6A.

Bob, welcome to VAF.

You built and tested an RV, and a pre pre-punched kit at that, without ever being a member of VAF?????!!!

I did not think that was possible

Good to have you aboard, how about some photos of the plane, and a bit more info on you, and the plane?

Enjoy

 

[molson309]

600 hours on a B&C alternator with a field switch that is always turned on after engine start. No problems. My Rocket also has an alternator field switch, and I definitely prefer it that way.

I think the admonition about turning on/off alternators is mostly about pulling the CB (if you have one) on the "B" (load) lead of the alternator. THAT will definitely stress the diode pack. I do not see any reason why turning off/on the field while the alternator is turning would be injurious to the alternator. In fact, old style regulators - and some newer ones - regulate the alternator output by rapidly turning the field on and off!

Most alternators draw 4-5A field current if energized while not turning. Having the alternator ON while trying to start the engine works against you in two ways: The current being drawn by the field means there is less to deliver to the starter, and the mechanical drag of the energized alternator requires extra starter torque to overcome. That's overcome by having an alternator field switch and leaving it off until the engine is running.

Mark Olson N407V RV-7A ~ 600 hrs
N16XV F1 Rocket ~45 hours

 

[AlexPeterson]

Junk the switch

1200+ hours on my internally regulated ND 40 amp. Only time I've ever used my 3 position switch in the middle position (master on, alt off) was one time when I started the plane with it that way to test that I had wired it correctly.

BTW, I should get many more hours on that alternator, as I bought a spare to keep at the hangar!

 

[Ironflight]

BTW, I should get many more hours on that alternator, as I bought a spare to keep at the hangar!

I call those "Voodoo Spares", and keep them around for various components, just to ward off failures.....

 

[apkp777]

I installed the Cessna style switch as I was originally concerned about whether or not my battery was going to be strong enough to start my engine on cold Wisconsin days (about half the year). Those of you who have flown Piper products know all about saving as much juice as you can. And the dreaded urha, urha, urh, ur, u...

Now, I realize that the battery is sufficient. The only time I think I would use the field switch is if my battery was drained a bit. Of course, in that rare occasion, I could just pull the field breaker.

My start procedure is to fire up my EFIS using it's back up battery, master/field on, fire away. The only load on the battery is the alternator field, P-mags and the starter.

 

[Alan Carroll]

I installed the Cessna style switch as I was originally concerned about whether or not my battery was going to be strong enough to start my engine on cold Wisconsin days (about half the year). Those of you who have flown Piper products know all about saving as much juice as you can. And the dreaded urha, urha, urh, ur, u...

Now, I realize that the battery is sufficient. The only time I think I would use the field switch is if my battery was drained a bit. Of course, in that rare occasion, I could just pull the field breaker.

Ditto. I installed the Cessna master switch, and have always started with both sides turned ON (including cold weather), with no problems. I think the whole point of the split switch was to use both halves simultaneously. For example, the following comes from the 1980 Information Manual for the 172RG:

Normally, both sides of the master switch should be used simultaneously; however, the BAT side of the switch could be turned ON separately to check equipment while on the ground.

Personally I do find it convenient to be able to turn on the battery side of the switch while on the ground. I actually kind of like the Cessna switch because it is red and different from all the other switches. Using a single switch for battery plus alternator (with pull breaker) also seems fine, although I guess I don't quite see why such a configuration would necessarily be better. Is because a toggle switch might last longer?

 

[Fred.Stucklen]

Split Master/3 pos switch, might be better....

Ok guys, here's an electrical question for you to ponder. I'm Assuming that you do not have a field switch, just an alternator field circut breaker.. You start the engine normally, but sometime, while the engine is running (maybe in flight) you have the need to shut off the master (maybe due to an electrical fire!). What causes the alternator to stop putting out power?
In this case, the battery has been disconected from the main power bus. Because it was never shut off, the alternator starts to supply it's own field current trough the regulator as it has never shut down. (this might be unstable as the buss has lost the battery capacitence to make if more stable). Your main electrical bus is still hot! You electrical fire continues to burn until you pull the breaker in the field circut.......
So to stop the alternator from supplying energy to the fire, you have to shut off the master AND pull the field breaker (IF you remember in the heat -pun intended - of the moment)....
I would rather have just one function to perform to eliminate my main buss power.... The split master or three position switch does that....

 

[Ironflight]

You make a good point Fred - the split master will get both the battery and the alternator with one movement. I guess that would make this topic a choice between a split master or not. So many planes (at least one of ours) have already made the choice of going with a separate switch for the alternator that we've already accepted that it is an Emergency Checklist item to get the alternator switch (or breaker) for an electrical short.

The three-position switch to me invites starting the engine and then powering up the alternator - fine for the externally-regulated units designed for that, but strong empirical evidence suggests that's a good way to shorten the life of the internal regulator.

Paul

 

[JonJay]

What about your poor wingies?

I have a switch for wing strobes and a switch for tail strobe. I would leave the tail strobe switch out on the next build also. It would be replaced with a pull type circuit breaker. The reason for this switch being left out is that it acts a a tattle-tale that the master is on after shut down and also as a warning that the prop is going to start turning at start up.

You still need to kill your tail strobe for the guy behind you in close trail.

 

[jferraro17]

My start procedure is to fire up my EFIS using it's back up battery, master/field on, fire away. The only load on the battery is the alternator field, P-mags and the starter.

Tony,

Do you then turn on an Avionics Master to pick up the EFIS load (and subsequent radios, etc.?)

Electrical idiot--
Joe

 

[nomocom]

electrical fire

electrical fire continues to burn until you pull the breaker in the field circut.......
So to stop the alternator from supplying energy to the fire, you have to shut off the master AND pull the field breaker (IF you remember in the heat -pun intended - of the moment)....
I would rather have just one function to perform to eliminate my main buss power.... The split master or three position switch does that....

Well...when the smoke doesn't stop, you'll remember the field breaker

That is a good point Fred. I have an airplane so equiped, and very infrequently I've shut the master off with the engine running and it does take a few seconds to remember why everything is still lit up. I do get used to the electrons coming and going with the master switch position, but isn't always so.

 

[apkp777]

Tony,

Do you then turn on an Avionics Master to pick up the EFIS load (and subsequent radios, etc.?)

Electrical idiot--
Joe

Joe,

Yes, I have a single Avionics switch which powers up everything on my panel. All my avionics are wired through an AvMaster Relay (http://www.aircraftspruce.com/catalog/avpages/avionicsMaster.php).

 

[GOEZ]

Ok guys, here's an electrical question for you to ponder. I'm Assuming that you do not have a field switch, just an alternator field circut breaker.. You start the engine normally, but sometime, while the engine is running (maybe in flight) you have the need to shut off the master (maybe due to an electrical fire!). What causes the alternator to stop putting out power?

This is the exact question that I faced when designing my power distribution. For the master switch, I originally planned on using a single pole toggle switch to supply the ground for the master contactor. By simply changing this switch to a double pole it could also supply a make / break circuit for the alternator similar to the standard alternator switch. Thus when the master is switched off the alternator is also automatically turned off. Seems to still work fine for me after 70 hours or so with no issues. If I was doing this again, I'd choose to not install the separate alternator switch.

 

[Danny King]

Field switch

Paul,
I will agree with your logic as long as you run the wire from the field circuit breaker to the voltage regulator, thought the other half of the Master switch. (DPDT)

If you need to kill all the power, the master switch will do that in a single action. As you know, switching off the master switch alone will not affect main bus power, as long as the voltage regulator is being powered from alternator output on the main bus. You would also have to pull the field breaker for VR.

I wired the Doll with a separate field switch, but then rooted the field wire to the other half of the Master switch before it connected to the VR. I put a red cover on the Master switch, and it will kill all power in a single action except the keep alive circuit which is fused at the battery.

In defense of a separate field switch, I was flying over to Jay Pratt's hanger on a cold morning, and the cheap voltage regulator from Van's stuck on full output. The main buss voltage went to 19.5. I reached over and switched off the field switch, and buss voltage dropped to battery voltage. I continued on the battery to Jay's, and later flew back to home base on the battery to make repairs. Thanks B&C!

 

[Christopher Murphy]

alt field control

Bob, welcome to VAF.

You built and tested an RV, and a pre pre-punched kit at that, without ever being a member of VAF?????!!!

I did not think that was possible

Good to have you aboard, how about some photos of the plane, and a bit more info on you, and the plane?

Enjoy

I find Mikes quote very humurous. How many guys built airplanes before there was even an internet.! How did we do it?

How many light twins are started first and then the field energized?

Chris M

 

[vlittle]

You still need to kill your tail strobe for the guy behind you in close trail.

Jon, we've learned to use all of our strobes in formation flight. Our training has allowed us to grow accustomed to them. Annoying at first, but you get used to it.

It's amazing how many other aircraft never see a formation flight of RVs, even with all of our lights and strobes on. Nevertheless, everything helps.

Vern

 

[Bill Dicus]

Alternator switch

This is great info - thank you all! I have a 3-position switch like Kevin (Stein said this is used in DC-9's). Guess it can stay, since the battery-master position could be used for programming EFIS's etc with no current draw from the alt field. It'll be in the "alternator on" position from before start until after shutdown as a result of this thread. To think I had considered ditching the Van's alternator for a Plane Power! These posts could save folks a lot of money as well as the inconvenience, time and effort that go along with a failure of the alternator. Again, many thanks.

 

[molson309]

I still find it hard to believe that turning on the field after the alternator is turning has anything to do with failures of any kind. I submit that people that have experienced alternator failures would have had them occur regardless of their use of the field switch.

I would like to hear a rationale on how the regulator "knows" the difference between a spinning field coil and a stationary one, and how this influences the life of the regulator or other parts of the alternator. The field coil of an alternator is nothing more than a electromagnet that can be rotated.

I find an alternator field switch convenient and useful, and would not be without one.

Mark Olson N407V RV-7A
N16XV F1-EVO Rocket

 

[Brantel]

PP sez that the stuff about the field circuit being turned on and off after startup is hogwash....They say it does not matter if you do or if you don't.

I turn mine on after start and off after shutdown with the master. I have done this since day one on my plane and it has not had any issues so far. It is still very young though at 90hrs. It has a PP alternator.

I have a master off-battery-alternator toggle switch setup. I mostly put this switch in as a way to turn on the master without powering up the alt field which eats battery power!!! I suppose I could have used the field breaker for that but I don't like using breakers for switches.

 

[DGlaeser]

Caveat on IR alternators

Many (most ??) of the automotive IR alternators do NOT turn off when you remove power from the excitation wire - it's not a real field control wire. Once they are excited, they remain internally excited even if power is removed from the excitation wire. So, no real need for a switch. If you install a breaker or fuse on that wire you can still pull it for maintenance to remove whatever drain it has.

The IR may well have OVP, but that's typically an unknown. Since you don't have absolute control of the field, the only way to have external OV protection is to put a contactor on the output wire and have the OVP circuit control that. (Insert the AeroElectric alternator 'discussion' here )

I'd just install an auto IR alternator, no alternator switch, breaker on the output wire and go fly

 

[Ironflight]

Just to keep the discussion centered folks, I was NOT talking/asking about Plane power or B&C alternators. Different designs, different operating criteria. I would wire and operate them EXACTLY as the instructions tell you to do, since that is how they were designed.

The Internally regulated ND's were designed to be turned on with the main power, and turned off when the vehicle is shut off, so why not use them that way? The question about twins where you switch the alternator on after start is irrelevant - there are no RV twins, and the certified light twins do not use the ND alternators - again, use them as designed.

As far as the switch in series with the circuit breaker - I am still not convinced that the switch buys you anything except saving an extra second if you have to power things down with a short. If you subscribe to the theory that reducing parts count increases reliability, the breaker should be good enough - as long as you religiously follow your Emergency Procedures (I put a red ring around my alternator field switch). I don't want to belittle that argument BTW, it is a good one - but it is a choice between two "risks", and different folks can choose differently based on their experience.

Paul

 

[JAT]

Paul,

First you say you do and then you don't, then you say you will and then you won't, you're undecided now, so what am I gonna do? Say, that would make a good song! Am I back to the original Cessna switch where I turn both on and off at the same time? When the dust settles Paul, just tell me what you have finally decided to do. That will do me just fine and I will follow your lead, as usual!

Thanks, as usual!

Jim

 

[Fred.Stucklen]

Split Master or three position toggle

Well...when the smoke doesn't stop, you'll remember the field breaker

That is a good point Fred. I have an airplane so equiped, and very infrequently I've shut the master off with the engine running and it does take a few seconds to remember why everything is still lit up. I do get used to the electrons coming and going with the master switch position, but isn't always so.

Another point to ponder. Lets say one were to utilize the split master or three position master switch design. Lets also consider the auto alternator that can not be turned off by interrupting the field circuit. (This does not include Plane Power as it CAN be switched off.)
If the alternator can not be switched off by the pilot, opening the master contactor will only disconnect the battery from the main buss. It will NOT disconnect the alternator, thereby allowing it to continue to supply power to a fault on the main buss (i.e., the fire won't go out!). The pilot now has to pull the alternator output breaker to "put out the fire".....
To complicate matters even more, if this non-field controllable alternator were to somehow fail with an over voltage failure mode, you've just fried all you expensive electronics, even if the pilot could shut the master off and pull the alternator output breaker.....
There's a good safety related reason why all the spam cans had master switches that shut off the alternator output.....

Consider this: You're 20 miles off the coast of North Carolina (over the Atlantic), IFR, North bound to New England. Everything seems to be going just fine, until your passenger comments "Do you smell smo... " Click goes the master, shutting down the whole electrical system, before the comment can be finished. You turn left, direct to Charletton, NC, and start tuning off all electronics, then enable the master again. You see low voltage, not alternator output, are able to raise ATC on a radio (but other equipment seems to also be ON),and land uneventfully. Trouble shooting the failure indicates that the field circuit has "Burned Up", shorting out several other wires in the harness in the process. Yet,from the onset of the first wiff of smoke , to the time everything was disabled, was less than a second... (I'm not going into the stupid reason an electrical engineer allowed this to happen in the first place....)
If the pilot had hesitated any longer, there would have been a bonna fida fire while in flight, especially if he had to take the time to think about what additional steps weere required to shut down the alternator output if the alternator wasn't controllable......

 

[Ironflight]

So Fred, if I understand your argument, you are essentially arguing against the ND alternator, not the concept of using the circuit breaker on the field as a switch - is that correct?

Certainly that is a valid topic for discussion - not the question I asked of course, but one that would be worthy of it's own thread. realistically, if we are depending on the human to turn off the Master switch at the smell of smoke, we can also rely on him or her to pull the field breaker - there is more time lost in going "what's that smell?" than in operating two "switches".

 

[DGlaeser]

Not to worry . . .

There won't be any passengers to smell the smoke in an RV-3

But to Fred's point, the field breaker won't do anything - you need a breaker on the alternator output.

 

[L.Adamson]

My airplane still has the contactor relay from the day's of the Bob K. over voltage setup. The device that trips the breaker (which disconnects the contactor) has been removed from the circuit. I left the contactor in, as I have no desire to re-wire the alternator B-lead.

However, this contactor is energized by the alt-switch. If the alt-switch or master switch is turned off, that heavy wire from the alternator is disconnected at the firewall. Could be a good thing..........or just extra weight.

These day's my alternator is a Plane Power.

L.Adamson --- RV6A

 

[Chino Tom]

Ok guys, here's an electrical question for you to ponder. I'm Assuming that you do not have a field switch, just an alternator field circut breaker.. You start the engine normally, but sometime, while the engine is running (maybe in flight) you have the need to shut off the master (maybe due to an electrical fire!). What causes the alternator to stop putting out power?
In this case, the battery has been disconected from the main power bus. Because it was never shut off, the alternator starts to supply it's own field current trough the regulator as it has never shut down. (this might be unstable as the buss has lost the battery capacitence to make if more stable). Your main electrical bus is still hot! You electrical fire continues to burn until you pull the breaker in the field circut.......
So to stop the alternator from supplying energy to the fire, you have to shut off the master AND pull the field breaker (IF you remember in the heat -pun intended - of the moment)....
I would rather have just one function to perform to eliminate my main buss power.... The split master or three position switch does that....

I set my system up so this won't happen. My alternator field CB/switch
get its power from the main bus. When the master is turned off the alternator
field power is shut down. I also have a constant current relay
between the B power from the alternator and the main bus which is also
controlled by the Alternator field CB/Switch. I believe once you have excited
the field, and the alternator is spinning, turning off the field doesn't guarantee
that the alternator will quit producing power. Thus the reason for the
constant current relay. With the master switch on, turning on the Alt field
supplies current to the field and closes (allows power to pass through, I always confuse myself
with open or closed) the constant current relay. Of course
as posted by Paul, a simple Circuit breaker would accomplish the same
thing.

 

[Walt]

One of the reasons I prefer the externally regulated B&C is the positive shutdown of the of the Alt with the master switch (OFF-BAT-ALT).

With the Alt switch off, you shut off the regulator (which supplies field current) so the alternator WILL positively shut down.

 

[Ron Lee]

I think I have a goal for 2011. Understand what is being said here.

I have a master rocker switch and an alternator (Field) rocker switch. Due to an indication of higher than normal output voltage, I removed the 14684 type ND alternator and had it tested by an AI who does build engines. It is working around 14.2 volts.

Initial startup on the test stand shows zero alternator output. Energize the field and it outputs 14.2 volts. Remove the jumper and it cuts the alternator output.

This appears to be inconsistent with other comments made. I will test it more tomorrow after reading these posts, but for now I will install my backup alternator and see what happens.

I am pondering adding over voltage protection.

 

[DGlaeser]

Cool!

I think I have a goal for 2011. Understand what is being said here.
I have a master rocker switch and an alternator (Field) rocker switch. Due to an indication of higher than normal output voltage, I removed the 14684 type ND alternator and had it tested by an AI who does build engines. It is working around 14.2 volts.
Initial startup on the test stand shows zero alternator output. Energize the field and it outputs 14.2 volts. Remove the jumper and it cuts the alternator output.
This appears to be inconsistent with other comments made. I will test it more tomorrow after reading these posts, but for now I will install my backup alternator and see what happens.
I am pondering adding over voltage protection.

Not inconsistent, just not always the case. I also have an IR alternator which works that way (chosen because it has that feature). With that control, adding OV protection is easy and straightforward. I did because I have no idea whether the IR has OVP built-in or not. To me it's worth $$ to protect $$$$$ in radios.