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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Wed Jul 05, 2006 10:03 am Post subject: Alternator failure thoughts

On Jul 5, 2006, at 10:23 AM, PWilson wrote:



 	  Quote: 	
		   I would appreciate an explanation of for all the diodes.


	


Well, as I said in my earlier post, there are two diodes for each leg  

in the stator. You may find some alternators that have diodes in  

parallel to carry more current. That would lead to there being 12  

diodes in some cases. (Diodes do not parallel well as one diode of a  

parallel pair will hog more of the current.)



Nippon Denso adds two more diodes going to the center tap of the wye  

which will help the alternator keep going if one of the stator  

windings happens to fail open.



If there are more diodes over and above the (basically) six output  

diodes then they are there to provide power to the internal  

regulator. The most typical system I have seen has three extra diodes  

to provide the power to the regulator. Nippon Denso just gets its  

regulator power from the B-lead. This means that whenever the battery  

is connected to the alternator the alternator is using some amount of  

battery power but the full power to the field is not switched on (it  

would kill the battery in a couple of hours) until power is applied  

to the 'I' lead. This is generally not a problem for an aircraft  

application as the battery is disconnected from the alternator when  

the battery master contactor is switched off.



In most other alternators there is no way for current to flow from  

the battery to the regulator. You either have to provide start-up  

power for the regulator through the ignition ('I') or idiot-lamp  

('L') terminals, or you have to spin the alternator fast enough that  

the residual magnetism in the armature will generate enough to get  

the internal regulator to start sending some on to the field.



Does that help?



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

Jerry Cochran

Joined: 10 Jan 2006
Posts: 111
Location: Wilsonville, OR

Posted: Wed Jul 05, 2006 10:39 am Post subject: Alternator failure thoughts

Charlie, IIRC you are an automotive technician so I am curious... In your  years in that industry, how many alternators did you see fail mechanically  enough to toss parts and pieces around? Before I retired 8 years ago, I owned a  shop with 4 busy mechanics, many  alternator failures we saw, but  I don't recall one that destroyed itself that way. We saw a few that seized and  destroyed the belt, but that's about it. 

 Jerry Cochran

  	  Quote: 	
		  From:    Charlie Kuss <chaztuna(at)adelphia.net>

Subject: Re: AeroElectric-List:    Alternator failure thoughts

 	  Quote: 	
		  snipped

I have seen a number    of alternator failures on cars, boats, and

airplanes. Some were pretty    simple, no-brainer failures and some were

"HOLY S--T" failures. I    thought I would toss in here the ways I can

see alternators failing    (and have failed) and then address the failures.

Here are the    failure modes I have see so far (feel free to add to

this    list):

1. Straight electrical failures:

            a. regulator failed -- no output

            b. brushes failed -- no output

            c. output diode failure -- whine and reduced    output

         d. diode trio failure -- no    output

         e. regulator failed -- runaway    output (destroys battery and 

 anything

else attached to the    bus)

snipped

Brian,

  I'd like to expand on item C of the    list above

Output diodes comprise the rectifier. (converts AC current    to 

DC)  For the purposes of the alternators we use, the rectifier is    

comprised of 6 diodes. These diodes can fail in two modes, open or    

short.  Failing open (diode blows apart) is the more common failure    

mode. In this mode, each diode that fails will reduce the 

alternator's    output by 1/6th.

  Diodes that fail shorted are more insidious. Often,    the pilot will 

not notice a decrease in performance. However, he/she will    generally 

notice an increase in noise (generally on the radios) This is    because 

1/6th of the alternator's output is now bleeding through as AC    

current. The ship's electrical system is designed for DC current. The    

one item which really can not tolerate AC current is the battery. Any    

time an alternator fails, it is best to do a postmortem, to determine    

the cause.

  Shorted rectifier diodes which are not repaired    promptly, will soon 

destroy the battery's storage capacity. This damage to    the battery 

may not be noticed, without conducting a battery output test.    This is 

important if you subscribe to Bob N's ideas regarding battery only    

emergency operations.

Charlie Kuss

pwmac(at)sisna.com
Guest

Posted: Wed Jul 05, 2006 11:30 am Post subject: Alternator failure thoughts

Thanks Brian it helps

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



At 11:57 AM 7/5/2006, you wrote:

 	  Quote: 	
		  



On Jul 5, 2006, at 10:23 AM, PWilson wrote:



>I would appreciate an explanation of for all the diodes.



Well, as I said in my earlier post, there are two diodes for each leg

in the stator. You may find some alternators that have diodes in

parallel to carry more current. That would lead to there being 12

diodes in some cases. (Diodes do not parallel well as one diode of a

parallel pair will hog more of the current.)



Nippon Denso adds two more diodes going to the center tap of the wye

which will help the alternator keep going if one of the stator

windings happens to fail open.



If there are more diodes over and above the (basically) six output

diodes then they are there to provide power to the internal

regulator. The most typical system I have seen has three extra diodes

to provide the power to the regulator. Nippon Denso just gets its

regulator power from the B-lead. This means that whenever the battery

is connected to the alternator the alternator is using some amount of

battery power but the full power to the field is not switched on (it

would kill the battery in a couple of hours) until power is applied

to the 'I' lead. This is generally not a problem for an aircraft

application as the battery is disconnected from the alternator when

the battery master contactor is switched off.



In most other alternators there is no way for current to flow from

the battery to the regulator. You either have to provide start-up

power for the regulator through the ignition ('I') or idiot-lamp

('L') terminals, or you have to spin the alternator fast enough that

the residual magnetism in the armature will generate enough to get

the internal regulator to start sending some on to the field.



Does that help?



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

brinker(at)cox-internet.c
Guest

Posted: Wed Jul 05, 2006 12:07 pm Post subject: Alternator failure thoughts

          I have run  a auto salvage business for 20 years and I cannot recall ever seeing or hearing  of an exploded alternator. I have seen many of them seized up as you mention. It  is hard to say how many I've sold (several thousand I would guess)  And I  have never heard of any damage to an auto engine resulting from an alternator  seize. I would guess most auto engines will cruise somewhere between 2000 and  3000 rpms which would put it close to what an airplane engine is run. But  on a long drive I would guess the alternator would see 4000 and above rpm's in  an automobile many times while downshifting to pass, going uphill, accelerating  from stop etc, which in an airplane the max will normally be around 2700 rpm.   Accually the alt itself would see a much higher rpm possibly twice or more  that of the engine rpm's since the crank pulley is generally at least twice the  circumference of the alt pulley on an auto engine and probably around 3  times difference on the airplane crank vs. alt pulley. Which would make the alt  rpm's much higher than an auto if the same sized alt pulley. Taking into  consideration the higher rpm's of the auto engine the alt maximum seen rpm's  difference between the aircraft and auto alt's would be somewhere close I  would think, especially if the airplane alt pulley was larger. I am not  saying that an alt seizing cannot explode or damage an engine but I would think  it very rare. My observations are deffinately not scientific but I should think  a good indicator of the rarity.

  

 Randy

 [quote]   ---

frank.hinde(at)hp.com
Guest

Posted: Wed Jul 05, 2006 12:41 pm Post subject: Alternator failure thoughts

The standard large pully  on  lyc is around 9.5 inches so the alt speed does get up there even at a  cruise of around 2400 RPM.

 Mind you if the alt  seized I'm sure it would simply vapourise the belt. Can't imaging the belt will  absorb more than 30HP without breaking.  Hard to see it stopping an  engine....At leats I hope not...

  

 Frank



   From: owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of  Brinker

Sent: Wednesday, July 05, 2006 1:06 PM

To:  aeroelectric-list(at)matronics.com

Subject: Re: Re:  Alternator failure thoughts 

 

           I have run  a auto salvage business for 20 years and I cannot recall ever seeing or hearing  of an exploded alternator. I have seen many of them seized up as you mention. It  is hard to say how many I've sold (several thousand I would guess)  And I  have never heard of any damage to an auto engine resulting from an alternator  seize. I would guess most auto engines will cruise somewhere between 2000 and  3000 rpms which would put it close to what an airplane engine is run. But  on a long drive I would guess the alternator would see 4000 and above rpm's in  an automobile many times while downshifting to pass, going uphill, accelerating  from stop etc, which in an airplane the max will normally be around 2700 rpm.   Accually the alt itself would see a much higher rpm possibly twice or more  that of the engine rpm's since the crank pulley is generally at least twice the  circumference of the alt pulley on an auto engine and probably around 3  times difference on the airplane crank vs. alt pulley. Which would make the alt  rpm's much higher than an auto if the same sized alt pulley. Taking into  consideration the higher rpm's of the auto engine the alt maximum seen rpm's  difference between the aircraft and auto alt's would be somewhere close I  would think, especially if the airplane alt pulley was larger. I am not  saying that an alt seizing cannot explode or damage an engine but I would think  it very rare. My observations are deffinately not scientific but I should think  a good indicator of the rarity.

  

 Randy

 [quote]   ---

chaztuna(at)adelphia.net
Guest

Posted: Wed Jul 05, 2006 1:17 pm Post subject: Alternator failure thoughts

---- Jerry2DT(at)aol.com wrote: 

 	  Quote: 	
		    

 Charlie, IIRC you are an automotive technician so I am curious... In your  

 years in that industry, how many alternators did you see fail mechanically  

 enough to toss parts and pieces around? Before I retired 8 years ago, I owned a  

 shop with 4 busy mechanics, many  alternator failures we saw, but  I don't 

 recall one that destroyed itself that way. We saw a few that seized and  destroyed 

 the belt, but that's about it. 

  

 Jerry Cochran

snipped
	




Jerry,

 I, like you, own an auto repair shop. I have never in 30+ years seen an automobile alternator "explode". It just doesn't  happen. What did happen, back in the days when cars mounted alternators like is done on light aircraft, was that the adjuster bracket cracked and broke.  The alternator then starts bouncing around. If the driver didn't shut the engine down fairly soon, it would attempt to depart the engine. On most light aircraft, the normal operating noises would preclude any chance of you hearing this situation in time to do anything about it.

 You have two brackets, the pivot bracket and the adjuster bracket. The adjuster bracket is the long arm with the slotted hole in it. These brackets broke with some regularity back before the use of large cast mounting and tensioning pulleys.

 They would break for one of two reasons. 



#1   The brackets were under designed for the load. I think that the bracket supplied by Vans Aircraft is marginal here. (I'm building an RV-8A, so that's my reference point with experimental aircarft)

#2  Due to carelessness or poor workmanship during an alternator replacement, a mechanic omitted some of the retaining hardware for the alternator or it's brackets.



 Most common was loosing the large "fender" (think AN970) washer between the adjuster bolt and the slotted hole in the adjuster bracket. This would concentrate the vibratory stresses around the hex head of the bolt at the adjuster bracket. The adjuster bracket is weak due to the adjustment slot machined (or broached) into it. The purpose of the fender washer was to spread the stress over an area large enough to absorb it, and to reinforce this less than steller mount design.

 I also have a background in aerospace machine assembly. I was taught that any metal surface less than 1/4" thick should have a flat washer installed between the bolts (or nut) and the surface it bore down on (in this case the bracket)

 Another rule of thumb is that all brackets should be triangulated. By this I mean that they should have 3 mounting points. Two points should attach to the engine and one to the alternator. 

 Many aviation (and decades old cars) did not meet either of these engineering rules of thumb. Most RV alternator adjusting brackets have this failing. The adjustment bracket mounts to the engine with only one fastener and to the alternator with one fastener. Compound the problem with the following agrivating conditions.

#1    The 4 cylinder Lycoming's reputation to mimic a wet dog during start up and shut down.

#2   An adjustment slot that is much longer than necessary to do the job. 



So you have 3 conditions which are trying to destroy your adjustment bracket. I suggest to the listers that they ensure that their alternator mounting system is stout enough to do the job. Also take care when installing and removing the mounting hardware to it.



Charlie Kuss

brinker(at)cox-internet.c
Guest

Posted: Wed Jul 05, 2006 2:25 pm Post subject: Alternator failure thoughts

            Thanks for that info. I have a loose IO-540 flywheel that measures 9 3/4" I  measured it to the outside, Lyc. may get their measurement from down in the  groove. That spurred me to check some automobile measurements (I have aprox. 150  or so engines on my engine rack from anything from a chevy v-8 to a 4cyl  foreign) It was interesting to see the varying sizes on the crankshaft pulley's,  they ranged from aprox. 4 1/2" to 8". Of course many of them had double and  triple pulley system, so not sure which one would have been the alt. pulley.  Although the largest 8" was a single crank pulley system off of a 99 Plymouth  Breeze ( I am 99% sure it was a single pulley system, I found no indications of  any other pulleys that may have been bolted to it).

            I  also went thru my alternator racks and got various different pulley  measurements. They ranged from aprox. 2 1/4" to 2 7/8" although I am almost  certain I have seen some over 3" in diameter in the past but just not on the  rack at this time.

          Keep in mind  these measurements we're all outside pulley measurements. I did not even try to  figure the diameter where the belt accually rides. I would guess the shoulder  measurements we're anywhere from 1/8" to 1/4" on the serpintine types and  probably around 1/2" deep for the v-belt type. 

          So from my perspective, there are some auto's that approach the Lyc. flywheel  size so the alt. rpm's difference would not be extremely far apart and some of  the auto alt's would probably surpass the airplane alt. rpm speed ( although  most do not ) while in an acceleration. But even if only say 10% of the auto  alt's would exceed the airplanes rpm's even only 10% of the time that would be I  believe a significant enough number to say that if it we're a real world problem  with them exploding we would have seen at least one. 

           Nope not  exactly scientific data but I hope this may give some perspective. Of course I  thru in some Randy rambling logic for free. Sorry for the rant.

  

 Rambling Randy

  

  

 ---

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Wed Jul 05, 2006 3:18 pm Post subject: Alternator failure thoughts

On Jul 5, 2006, at 4:36 PM, Hinde, Frank George (Corvallis) wrote:



 	  Quote: 	
		   The standard large pully on  lyc is around 9.5 inches so the alt  

 speed does get up there even at a cruise of around 2400 RPM.

 Mind you if the alt seized I'm sure it would simply vapourise the  

 belt. Can't imaging the belt will absorb more than 30HP without  

 breaking.  Hard to see it stopping an engine....At leats I hope  

 not...


	


I think it more likely that the mounting ears could break and the  

alternator could find itself bouncing around in the cowling. I don't  

think it will turn into a grenade but who knows.



Brian Lloyd                         361 Catterline Way

brianl at lloyd dot com             Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



"Five percent of the people think.

  Ten percent of the people think they think.

  Eighty-five percent of the people would rather die than think."

        ---Thomas A. Edison





Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

chaztuna(at)adelphia.net
Guest

Posted: Thu Jul 06, 2006 5:35 am Post subject: Alternator failure thoughts

Frank

  All cars except Honda products, spin their alternators in the opposite direction than Lycomings. Air is supposed to be sucked into the alternator (longitudinally) at both the front and rear (fans at both ends) and expelled through the grates in the center of the case (radially). Correct fan rotation aids in cooling, as incoming air from the cowl is going into the front of the alternator. Also, cooling shrouds on the rear of the alternator are more effective. All that said, Bob N says that using an ND off of a Toyota or other vehicle won't greatly affect the cooling of the unit. The air will simply be drawn in from the center and expelled out the ends.

 Charlie Kuss



 

  	  Quote: 	
		   Not sure i understand this "backwards turning" deal. Frome what i can see  the internal fan alternators appear to have simply radial fan blades that simply throw air out thru the sides of the alt. Therby presumably sucking air in from both front and back.

  

 Adding a cool air supply to the regulator should therefore augment the existing fan. I am thinking of doing a similar thing by riveting something similar to the stamped rear cover of my Autozone Toyota Camry special.

  

 Cetainly couldn't hurt

  

 Frank

 

  From: owner-aeroelectric-list-server(at)matronics.com [ mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of John Burnaby

 Sent: Wednesday, July 05, 2006 8:55 AM

 To: aeroelectric-list(at)matronics.com

 Subject: Re: Alternator failure thoughts

 

 I'm not flying yet, but my 60 A ND ER alternator (of undetermined auto application) has been modified by removing the stamped steel vented rear cover and replacing it with a fiberglass closed cover with a stub to accept a blast tube to force air over the diode plate, as an attempt to compensate for a backward turning alt fan. Aside from buying a B&C or Plane Power unit, is there a better way? Is this likely to have a positive effect?

  

 John

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 06, 2006 5:42 am Post subject: Alternator failure thoughts

At 08:55 AM 7/5/2006 -0700, you wrote:



 	  Quote: 	
		  I'm not flying yet, but my 60 A ND ER alternator (of undetermined auto 

application) has been modified by removing the stamped steel vented rear 

cover and replacing it with a fiberglass closed cover with a stub to 

accept a blast tube to force air over the diode plate, as an attempt to 

compensate for a backward turning alt fan. Aside from buying a B&C or 

Plane Power unit, is there a better way? Is this likely to have a positive 

effect?



John


	


    Positive, forced air cooling of an alternator is never a bad thing

    to do. The question that has always plagued the OBAM aircraft

    community continues to be: "Is cooling necessary?"



    Until we mount an effort to gather meaningful temperature data

    internal to the alternator under various electrical loads and

    flight conditions (hot-day, Vx climb), etc.



    From the viewpoint of regulators who have blessed an

    electrical load analysis based on what the alternator's nameplate

    ratings, now they want to see if installation

    issues (drive ratios and cooling) will produce the power

    your load analysis claims.



    We know that very few OBAM aircraft will ever need all of

    the alternator's nameplate power. We also know that cooling

    effectiveness of air movement under the cowl can be strongly

    influenced by changes in baffling, cowl geometry, accessory

    locations, belt ratios, etc.



    The bright side of all this uncertainty is that few alternators

    fail in OBAM aircraft for reasons obviously attributable to

    heat . . . nonetheless, when some poor builder is on his

    third in a string of alternator failures, cooling is one

    of several things to be explored. The standard approach is to

    add some form of blast cooling and hope the next alternator

    survives.



    In the past half-dozen or so seminars, I've offered to help

    any interested builder in crafting a test plan and then

    providing them with the data acquisition system that would

    let us investigate alternator cooling issues on their

    airplane. The same activity would work toward development of

    a testing model and an article that might encourage others

    to add further test data to the library. So far, no takers.



    It occurs to me that recent discussions on alternator

    "failures" may have suffered from a lack of definition for

    the word. As a professional in TC aviation I've come to understand

    that failures come in three broad classes: (1) failure due to

    lack of due-diligence in observance of manufacturer's instructions.

    (2) failure to meet design goals for operating performance.

    (3) failure to meet reasonable (or guaranteed) expectations for

    service life. In the TC aircraft world, "failure" is applied

    to those devices that required replacement or disassembly for

    refurbishment/upgrading.



    The perception of value for service life is a BIG driver

    in the supplier/consumer relationship. I recall a conversation

    with one of our hangar renters at 1K1 who was telling me that

    TBO on his ultra-light engine was about 300 hours! 2000 hour, TC

    engine drivers sitting on the porch with us were aghast.

    I remember thinking that was about 6 years of average flying.

    He quickly followed up that he was already on his "second engine"

    having overhauled it on a Saturday afternoon for $600 worth of

    parts.  Hmmmm $2/hr for parts. 6 hours labor. Not a "bad"

    return on investment as long as the device wears in an orderly

    manner such that the owner can choose when to do replacement

    or refurbishment based on inspection.



    When looking over the various postings on the 'net concerning

    ANY product, one needs to sort out discussions for relevance

    against your working definition of failure and a host of other

    issues. These include user understanding for both the

    basic physics of the system augmented with skill of the

    writers of installation instructions. One can find a great

    deal of discussion about a lot of products where root cause

    of the discussion is NOT a failure of the product but

    a customer service issue. This is where the manufacturer

    has an opportunity to excel. One can have the best-we-know-

    how-to-do product and still gather less-than-stellar reviews

    if the customer doesn't get whatever support is necessary

    for satisfactory installation and operation.



    I can cite you a great example of how a once admired

    supplier to RAC has crapped in their mess kit by failing

    to go the extra mile with customer support. A product I

    designed for them 25 years ago has been replaced under

    warranty in the field at a cost of $millions$. It didn't take

    much investigation to find that installation and trouble-shooting

    instructions were poor. The supplier's attitude is that

    "The parts go out of here meeting all quality assurance

    requirements. We've done everything we signed up to do."



    Nonetheless, hundreds of no-fault-found units get replaced for

    lack of understanding. As far as purchasing is concerned,

    the computer records don't lie. They see losses against that

    part in $millions$, the project group thinks the supplier

    is incompetent, the users just shrug it off as the high cost

    of owning an airplane and the supplier says "we did what

    we signed up to do." The thing that really irks me

    personally is the fact that my name is on all the drawings

    that define how the thing is built and few persons who

    pick those drawings up see the big picture and understand

    why there is so much grief. The easy and common thing to

    do is curse those "ivory tower" engineers . . .  My momma

    told me that I would be judged by the company I keep.

    Took me 40 years to understand what she was talking about.



    The supplier is now on the (at)!#(at)-list and not likely

    to get new business from that project group. The recipes

    for success call for much more than the elegant design.

    You need to be prepared to support your product from

    cradle to grave whether problems are your fault or not.

    Failure to do so can severely damage a perfectly good

    reputation for really stupid reasons that start with

    ignorance of the supporting simple-ideas.



    Bob . . .

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Thu Jul 06, 2006 6:12 am Post subject: Alternator failure thoughts

On Jul 6, 2006, at 9:40 AM, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 At 08:55 AM 7/5/2006 -0700, you wrote:



> I'm not flying yet, but my 60 A ND ER alternator (of undetermined  

> auto application) has been modified by removing the stamped steel  

> vented rear cover and replacing it with a fiberglass closed cover  

> with a stub to accept a blast tube to force air over the diode  

> plate, as an attempt to compensate for a backward turning alt fan.  

> Aside from buying a B&C or Plane Power unit, is there a better  

> way? Is this likely to have a positive effect?

>

> John



    Positive, forced air cooling of an alternator is never a bad thing

    to do. The question that has always plagued the OBAM aircraft

    community continues to be: "Is cooling necessary?"



    Until we mount an effort to gather meaningful temperature data

    internal to the alternator under various electrical loads and

    flight conditions (hot-day, Vx climb), etc.


	


That might not be too hard to do. Interesting thing is that the  

Balmar alternator controllers include a temp sensor for the  

alternator. If the alternator gets too hot the controller reduces  

alternator output. They just bolt a thermistor to the alternator case  

much like we do with a CHT sensor. That shouldn't be hard to craft at  

all.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

frank.hinde(at)hp.com
Guest

Posted: Thu Jul 06, 2006 6:44 am Post subject: Alternator failure thoughts

Like I said i have not pulled and alt apart to see what it  has but radial fans come in three forms...Simple spade blades, forward curved  centrifugal and backards curved centrifugal.

  

 I would bet the fan is a rudimentary backwards curved  design. Either way the fan will still flow air in the correct direction but not  as efficiently...I.e its still a centrifugal fan that sucks air into the middle  and throw radially outwards.

  

 I have never personally done this but my suspicion was just  confirmed by one of my techs here in the office.

  

 Bottom line is then running backwards will equate to less  cooling flow but is this an issue...Without instrumentation its impossible to  tell.

  

 Frank

  

  



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of  Charlie Kuss

Sent: Thursday, July 06, 2006 6:33 AM

To:  aeroelectric-list(at)matronics.com

Subject: RE: AeroElectric-List:  Alternator failure thoughts

 

Frank

 All cars except Honda products, spin  their alternators in the opposite direction than Lycomings. Air is supposed to  be sucked into the alternator (longitudinally) at both the front and rear (fans  at both ends) and expelled through the grates in the center of the case  (radially). Correct fan rotation aids in cooling, as incoming air from the cowl  is going into the front of the alternator. Also, cooling shrouds on the rear of  the alternator are more effective. All that said, Bob N says that using an ND  off of a Toyota or other vehicle won't greatly affect the cooling of the unit.  The air will simply be drawn in from the center and expelled out the  ends.

Charlie Kuss

  	  Quote: 	
		  Not sure    i understand this "backwards turning" deal. Frome what i can see  the    internal fan alternators appear to have simply radial fan blades that simply    throw air out thru the sides of the alt. Therby presumably sucking air in from    both front and back.

 

Adding a cool air supply to the regulator should    therefore augment the existing fan. I am thinking of doing a similar thing by    riveting something similar to the stamped rear cover of my Autozone Toyota    Camry special.

 

Cetainly couldn't hurt

 

Frank



      From:    owner-aeroelectric-list-server(at)matronics.com [    mailto:owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)] On Behalf Of    John Burnaby

Sent: Wednesday, July 05, 2006 8:55    AM

To: aeroelectric-list(at)matronics.com

Subject: Re:    Alternator failure thoughts



I'm not flying yet, but my 60 A ND ER    alternator (of undetermined auto application) has been modified by removing    the stamped steel vented rear cover and replacing it with a fiberglass closed    cover with a stub to accept a blast tube to force air over the diode plate, as    an attempt to compensate for a backward turning alt fan. Aside from buying a    B&C or Plane Power unit, is there a better way? Is this likely to have a    positive effect?

 

John

chaztuna(at)adelphia.net
Guest

Posted: Thu Jul 06, 2006 10:17 am Post subject: Alternator failure thoughts

Frank

 Thank you for correcting my misguided notion that running these fans backwards would reverse the direction of air flow.

Charlie Kuss

---- "Hinde wrote: 

 	  Quote: 	
		   Like I said i have not pulled and alt apart to see what it has but

 radial fans come in three forms...Simple spade blades, forward curved

 centrifugal and backards curved centrifugal.

  

 I would bet the fan is a rudimentary backwards curved design. Either way

 the fan will still flow air in the correct direction but not as

 efficiently...I.e its still a centrifugal fan that sucks air into the

 middle and throw radially outwards.

  

 I have never personally done this but my suspicion was just confirmed by

 one of my techs here in the office.

  

 Bottom line is then running backwards will equate to less cooling flow

 but is this an issue...Without instrumentation its impossible to tell.

  

 Frank

  

  

 

 ________________________________

 

 [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of

 Charlie Kuss

 Sent: Thursday, July 06, 2006 6:33 AM

 

 

 Frank

  All cars except Honda products, spin their alternators in the opposite

 direction than Lycomings. Air is supposed to be sucked into the

 alternator (longitudinally) at both the front and rear (fans at both

 ends) and expelled through the grates in the center of the case

 (radially). Correct fan rotation aids in cooling, as incoming air from

 the cowl is going into the front of the alternator. Also, cooling

 shrouds on the rear of the alternator are more effective. All that said,

 Bob N says that using an ND off of a Toyota or other vehicle won't

 greatly affect the cooling of the unit. The air will simply be drawn in

 from the center and expelled out the ends.

 Charlie Kuss

 

 

 

 

 	Not sure i understand this "backwards turning" deal. Frome what

 i can see  the internal fan alternators appear to have simply radial fan

 blades that simply throw air out thru the sides of the alt. Therby

 presumably sucking air in from both front and back.

 	 

 	Adding a cool air supply to the regulator should therefore

 augment the existing fan. I am thinking of doing a similar thing by

 riveting something similar to the stamped rear cover of my Autozone

 Toyota Camry special.

 	 

 	Cetainly couldn't hurt

 	 

 	Frank

 	

 	

 ________________________________

 

 	From: owner-aeroelectric-list-server(at)matronics.com [

 mailto:owner-aeroelectric-list-server(at)matronics.com

 <mailto:owner-aeroelectric-list-server(at)matronics.com> ] On Behalf Of

 John Burnaby

 	Sent: Wednesday, July 05, 2006 8:55 AM

 	To: aeroelectric-list(at)matronics.com

 	Subject: Re: Alternator failure thoughts

 	

 	I'm not flying yet, but my 60 A ND ER alternator (of

 undetermined auto application) has been modified by removing the stamped

 steel vented rear cover and replacing it with a fiberglass closed cover

 with a stub to accept a blast tube to force air over the diode plate, as

 an attempt to compensate for a backward turning alt fan. Aside from

 buying a B&C or Plane Power unit, is there a better way? Is this likely

 to have a positive effect?

 	 

 	John

chaztuna(at)adelphia.net
Guest

Posted: Thu Jul 06, 2006 2:20 pm Post subject: Alternator failure thoughts

snipped



 	  Quote: 	
		   >John

 

     Positive, forced air cooling of an alternator is never a bad thing

     to do. The question that has always plagued the OBAM aircraft

     community continues to be: "Is cooling necessary?"

 

     Until we mount an effort to gather meaningful temperature data

     internal to the alternator under various electrical loads and

     flight conditions (hot-day, Vx climb), etc.

snipped
	


 	  Quote: 	
		   

     We know that very few OBAM aircraft will ever need all of

     the alternator's nameplate power. We also know that cooling

     effectiveness of air movement under the cowl can be strongly

     influenced by changes in baffling, cowl geometry, accessory

     locations, belt ratios, etc.

snipped
	


 	  Quote: 	
		       In the past half-dozen or so seminars, I've offered to help

     any interested builder in crafting a test plan and then

     providing them with the data acquisition system that would

     let us investigate alternator cooling issues on their

     airplane. The same activity would work toward development of

     a testing model and an article that might encourage others

     to add further test data to the library. So far, no takers.

snipped
	


 	  Quote: 	
		       Bob . . .


	


Bob,

 Where would you suggest mounting a thermister on an alternator to monitor temperature?

Charlie Kuss

chaztuna(at)adelphia.net
Guest

Posted: Thu Jul 06, 2006 6:40 pm Post subject: Alternator failure thoughts

At 06:57 AM 7/5/2006, you wrote:

  	  Quote: 	
		  In a message dated 7/4/2006 9:25:44 PM Eastern Standard Time, chaztuna(at)adelphia.net writes:

   For the purposes of the alternators we use, the rectifier is  

  comprised of 6 diodes. These diodes can fail in two modes, open or  

  short.  Failing open (diode blows apart) is the more common  

  failure mode. In this mode, each diode that fails will reduce the  

  alternator's output by 1/6th.

  Charlie,



  Charlie:

  

 Why 6 diodes?  Half wave rectification only requires 2 diodes.  And Full wave reverification only requires 4 diodes.  So why 6 and how are they hooked up?

  

 Barry

 "Chop'd Liver" 	


 Barry,

  The ND alternators actually DO have 8 diodes. 6 of these rectify the AC current from the 3 windings of the stator into DC current. The main function of the other two diodes is to prevent the battery from discharging back into the alternator when the engine is not running. You have to remember that a DC motor and a generator are very similar. You apply current into a motor to create mechanical motion. With a generator (or alternator in this case) you apply mechanical motion and a magnetic field to create electrical current.

  If either of these two isolation diodes were to fail short, the battery would discharge into the alternator. The alternator would act like a seized motor.  The input current from the battery can not turn over the engine, via the alternator's pulley and drive belt.

  Have you ever had a vehicle which operated OK when driven daily. Yet, if allowed to sit unused for a number of days, the vehicle would have a dead battery? Shorted isolation diodes in the alternator are one possible cause of this situation.

 Charlie Kuss

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 06, 2006 7:02 pm Post subject: Alternator failure thoughts

At 03:19 PM 7/6/2006 -0700, you wrote:



 	  Quote: 	
		  



snipped



 > >John

 >

 >     Positive, forced air cooling of an alternator is never a bad thing

 >     to do. The question that has always plagued the OBAM aircraft

 >     community continues to be: "Is cooling necessary?"

 >

 >     Until we mount an effort to gather meaningful temperature data

 >     internal to the alternator under various electrical loads and

 >     flight conditions (hot-day, Vx climb), etc.

snipped

 >

 >     We know that very few OBAM aircraft will ever need all of

 >     the alternator's nameplate power. We also know that cooling

 >     effectiveness of air movement under the cowl can be strongly

 >     influenced by changes in baffling, cowl geometry, accessory

 >     locations, belt ratios, etc.

snipped

 >     In the past half-dozen or so seminars, I've offered to help

 >     any interested builder in crafting a test plan and then

 >     providing them with the data acquisition system that would

 >     let us investigate alternator cooling issues on their

 >     airplane. The same activity would work toward development of

 >     a testing model and an article that might encourage others

 >     to add further test data to the library. So far, no takers.

snipped

 >     Bob . . .



Bob,

  Where would you suggest mounting a thermister on an alternator to 

 monitor temperature?

Charlie Kuss


	


   If we were doing the typical full-up temperature survey on an

   alternator in flight, a thermocouple would be attached to:



   front bearing casting

   rear bearing casting

   diode commoning-plate/heat-sink(s)

    . . . and finally a thermocouple wedged into

   a stator winding slot.



   The DAS would record all thermocouples in the

   alternator + temperature of incoming cooling

   air, oat and probably one cht slot. This would

   be a total of 8 or 9 devices. Temperatures would

   be recorded about once every 2 seconds. I'd also

   consider adding a couple of absolute pressure

   transducers for Palt and Ptotal.



   We would also record alternator load (I have some

   precision servoed hall-effect sensors that are easy

   to install over the b-lead). If this were a certification

   effort, we'd have to install a load bank to load the

   machine to nameplate rated output. However, getting

   three sets of data at min, max and some intermediate

   load generated by your on-board systems is generally

   sufficient to extrapolate max load conditions with

   fair accuracy.



   Lots of hardware but stuff I keep in inventory

   (my shop is the last of the 'skunk werks' left at

   RAC). The laptop is a klunky ol' dos machine

   running a Power Basic utility that queries two

   A/D converters modules and writes comma-delimited

   text files to disk that can be easily sucked into

   Excel for plotting and analysis.



   It's easy to set in the right seat, start recording

   process and forget it until after shutdown. Just

   keep a time of day log of flight conditions to be

   achieved as part of a test plan.



   You game? We could make some real history here and

   actually KNOW something about a typical OBAM alternator

   installation.



   Bob . . .

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Thu Jul 06, 2006 7:27 pm Post subject: Alternator failure thoughts

On Jul 6, 2006, at 11:01 PM, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		     If we were doing the typical full-up temperature survey on an

   alternator in flight, a thermocouple would be attached to:



   front bearing casting

   rear bearing casting

   diode commoning-plate/heat-sink(s)

    . . . and finally a thermocouple wedged into

   a stator winding slot.


	


You know, the marine and RV alternator guys have solved these  

problems. I bet they have some good data.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

nuckollsr(at)cox.net
Guest

Posted: Fri Jul 07, 2006 4:38 am Post subject: Alternator failure thoughts

At 11:24 PM 7/6/2006 -0400, you wrote:



 	  Quote: 	
		  



On Jul 6, 2006, at 11:01 PM, Robert L. Nuckolls, III wrote:



>   If we were doing the typical full-up temperature survey on an

>   alternator in flight, a thermocouple would be attached to:

>

>   front bearing casting

>   rear bearing casting

>   diode commoning-plate/heat-sink(s)

>    . . . and finally a thermocouple wedged into

>   a stator winding slot.



You know, the marine and RV alternator guys have solved these

problems. I bet they have some good data.


	




   Don't understand "problem" . . . the goal is to confirm

   the influence of the installation in a particular airplane.

   If you have an off-the-shelf alternator in hand, the hardware

   has already been crafted to meet design goals that are generally

   confirmed independently of the installation.



   A typical installation study for the purpose of acquiring

   a TC or STC involves looking at the same points of interest

   as-installed as the manufacturer of the alternator looked

   at during their laboratory qual testing and making sure that

   installed stresses are not alarmingly greater than those

   encountered during qualification.



   People have killed perfectly good hardware by not understanding

   and accommodating it's limits in a new installation.



        Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Jul 07, 2006 5:50 am Post subject: Alternator failure thoughts

On Jul 7, 2006, at 8:37 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		  > You know, the marine and RV alternator guys have solved these

> problems. I bet they have some good data.

   Don't understand "problem" . . . the goal is to confirm

   the influence of the installation in a particular airplane.

Perhaps problem is not the right word. Knowing maximum safe operating  

temperature, temp rise with load, etc., would help someone plan their  

installation better than just bolting it in there an hoping it works.

 	  Quote: 	
		     People have killed perfectly good hardware by not understanding

   and accommodating it's limits in a new installation.

Right. And what are those limits and how can we mitigate?

OTOH, most alternators work just fine so maybe just ignoring the few  

failures is acceptable.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

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