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B&C alternator diagnosis

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henry(at)pericynthion.org
Guest

Posted: Sun Oct 28, 2012 4:36 pm Post subject: B&C alternator diagnosis

Dear Bob et al,



I'm the owner but not the builder of a 1979 VariEze equipped with a

starterless O-200 and a B&C alternator (the 12-amp 200G model, I

believe).  I don't have an ammeter in the cockpit.  I do have an LED

bar-graph voltmeter in which I have placed little trust over the past

year or so, since it was showing around 12 volts rather than the

expected 13+.  Perhaps I should have been more trusting.



Last week I had an electrical failure in flight, on a nice day over

familiar terrain.  The first sign of trouble was the backlight

brightness decreasing on my Garmin 480; it subsequently reset itself

and then failed entirely.  I have one magneto and one Lightspeed

electronic ignition, and not much else in the way of electronics in

the cockpit.  Turning off the magneto resulted in rough running -

presumably the EI was trying its best to keep up with the low bus

voltage but didn't have enough juice to fire every time.  Anyway I got

the green light signal from Livermore tower and landed without

incident.  The battery measured 11.7 volts open-circuit.



This weekend I tried to diagnose the problem.  The alternator circuit

breaker seems to be fine.  I removed the regulator (see pics linked

below).  The B&C alternator is a brushless model and only has two

wires coming out of it; I think the regulator is essentially a bridge

rectifier and a linear voltage regulator.  B&C currently seems to sell

a separate "rectifier-type regulator" [1] and "crowbar" overvoltage

protection circuit [2].  I'm not sure if what I have is just the

regulator or a combination of the two.  It looks to be completely

potted in resin except for one adjustment screw.  It has four wires -

red (bus +), black (gnd) and two blue (alternator).



With a multimeter on diode mode I measured 0.55V drop from either blue

wire to the red, as you'd expect with a bridge rectifier.  There was

also 1.2V drop from black to red, again as would be expected.  But it

showed "open circuit" from black to either blue.  Adjusting the screw

(which appeared to turn freely for 20+ revolutions, like one of those

multi-turn pots with the clutch) made no difference.



I plugged the regulator back in to the alternator (but not to the

aircraft bus), started the engine and observed 0.0V output on the red

and black wires.  I disconnected the regulator again, measured the

alternator wires directly and saw around 17V AC.



So - the regulator's bad, right?  It's not just trying to do something

clever in response to an open bus connection?  I just want to be sure

I'm not missing something before I order a new one.

Thanks very much,

Henry



Photos:

Alternator - http://i.imgur.com/nIWgG.jpg

http://i.imgur.com/w8WlE.jpg   http://i.imgur.com/ihwXI.jpg

Regulator - http://i.imgur.com/QXQUr.jpg   http://i.imgur.com/ng9TH.jpg

[1] http://www.bandc.biz/regulator14vhomebuilt.aspx

[2] http://www.bandc.biz/pmovfilterandovprotectionkit14v.aspx

henry(at)pericynthion.org
Guest

Posted: Sun Oct 28, 2012 5:05 pm Post subject: B&C alternator diagnosis

The mystery deepens.  I connected the regulator to the alternator and

hooked the output of the regulator directly to the battery.  Ran the

engine, saw the battery voltage increase from 12.15V (to which I had

previously trickle-charged it) to 12.4V and gradually over a few

minutes up to 12.8V.  I removed the regulator output from the battery

(engine still running) and saw the output voltage from the regulator

rise to 15.0V.  Connected it back to the battery via an ammeter and

saw 3.5A charge current - roughly what I should expect for an engine

idling around 1100 rpm.  Adjusting the regulator's screw while all

this was happening didn't seem to change much.



So now I'm at a loss - it seems to be working again.  Do you think

it's still a good idea to replace the regulator?  The only other thing

I noticed is that one screw terminal on the battery was not tight -

not terribly loose, but I could undo it with just my fingers.  I guess

I will put it all back together with a trusted voltmeter in the

cockpit and go fly in VMC for a while, but I'd love to hear ideas.



Thanks,

Henry



On Sun, Oct 28, 2012 at 5:34 PM, Henry Hallam <henry(at)pericynthion.org> wrote:

 	  Quote: 	
		   



 Dear Bob et al,



 I'm the owner but not the builder of a 1979 VariEze equipped with a

 starterless O-200 and a B&C alternator (the 12-amp 200G model, I

 believe).  I don't have an ammeter in the cockpit.  I do have an LED

 bar-graph voltmeter in which I have placed little trust over the past

 year or so, since it was showing around 12 volts rather than the

 expected 13+.  Perhaps I should have been more trusting.



 Last week I had an electrical failure in flight, on a nice day over

 familiar terrain.  The first sign of trouble was the backlight

 brightness decreasing on my Garmin 480; it subsequently reset itself

 and then failed entirely.  I have one magneto and one Lightspeed

 electronic ignition, and not much else in the way of electronics in

 the cockpit.  Turning off the magneto resulted in rough running -

 presumably the EI was trying its best to keep up with the low bus

 voltage but didn't have enough juice to fire every time.  Anyway I got

 the green light signal from Livermore tower and landed without

 incident.  The battery measured 11.7 volts open-circuit.



 This weekend I tried to diagnose the problem.  The alternator circuit

 breaker seems to be fine.  I removed the regulator (see pics linked

 below).  The B&C alternator is a brushless model and only has two

 wires coming out of it; I think the regulator is essentially a bridge

 rectifier and a linear voltage regulator.  B&C currently seems to sell

 a separate "rectifier-type regulator" [1] and "crowbar" overvoltage

 protection circuit [2].  I'm not sure if what I have is just the

 regulator or a combination of the two.  It looks to be completely

 potted in resin except for one adjustment screw.  It has four wires -

 red (bus +), black (gnd) and two blue (alternator).



 With a multimeter on diode mode I measured 0.55V drop from either blue

 wire to the red, as you'd expect with a bridge rectifier.  There was

 also 1.2V drop from black to red, again as would be expected.  But it

 showed "open circuit" from black to either blue.  Adjusting the screw

 (which appeared to turn freely for 20+ revolutions, like one of those

 multi-turn pots with the clutch) made no difference.



 I plugged the regulator back in to the alternator (but not to the

 aircraft bus), started the engine and observed 0.0V output on the red

 and black wires.  I disconnected the regulator again, measured the

 alternator wires directly and saw around 17V AC.



 So - the regulator's bad, right?  It's not just trying to do something

 clever in response to an open bus connection?  I just want to be sure

 I'm not missing something before I order a new one.

 Thanks very much,

 Henry



 Photos:

 Alternator - http://i.imgur.com/nIWgG.jpg

 http://i.imgur.com/w8WlE.jpg   http://i.imgur.com/ihwXI.jpg

 Regulator - http://i.imgur.com/QXQUr.jpg   http://i.imgur.com/ng9TH.jpg

 [1] http://www.bandc.biz/regulator14vhomebuilt.aspx

 [2] http://www.bandc.biz/pmovfilterandovprotectionkit14v.aspx

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 29, 2012 8:34 am Post subject: B&C alternator diagnosis

 	  Quote: 	
		  Adjusting the regulator's screw while all

this was happening didn't seem to change much.


	


    This alternator output is too small to be set

    reliably at combinations of low rpm and significant

    load.



 	  Quote: 	
		  So now I'm at a loss - it seems to be working again.  Do you think

it's still a good idea to replace the regulator?  The only other thing

I noticed is that one screw terminal on the battery was not tight -

not terribly loose, but I could undo it with just my fingers.  I guess

I will put it all back together with a trusted voltmeter in the

cockpit and go fly in VMC for a while, but I'd love to hear ideas.


	


     The regulator can be accurately adjusted ONLY

     with a fully charged battery, very light sytem

     loads (suggest 2A or less) and SIGNIFICANT rpm,

     like something 2000 or better.



     The alternator is exceedingly robust . . . very

     unlikely to fail. The rectifier/regulator has

     a very low parts count, is potted for mechanical

     ruggedness and is vulnerable to few stresses OTHER

     than overheat.



     If it has a history of good performance (Not accurately

     known without an accurate voltmeter) what appears to

     be a transient failure may have been a poor connection

     that got 'cured' as a product of removal and replacement.



     If it were my airplane, I'd fit it with a voltmeter of

     trustworthy accuracy. Also, a low voltage warning

     light so that future failures are not a surprise.



     Find out where the system voltage stabilizes under light

     load after some sustained operations . . . say just before

     descent to land on your next trip. Make little tweeks

     of the potentiometer setting based on these observations.

     Shoot for 14.2 but settle for 14.0 to 14.5.



     The successful resolution starts with trustworthy

     measurement and observation.  Where's your rectifier/

     regulator mounted? Where does it tie into the electrical

     system? Do you have a wiring diagram for this airplane

     that can be scanned/shared?

   Bob . . .

henry(at)pericynthion.org
Guest

Posted: Mon Oct 29, 2012 7:02 pm Post subject: B&C alternator diagnosis

On Mon, Oct 29, 2012 at 9:33 AM, Robert L. Nuckolls, III

<nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



> Adjusting the regulator's screw while all

> this was happening didn't seem to change much.

    This alternator output is too small to be set

    reliably at combinations of low rpm and significant

    load.


	


Thanks for the insights!  I also found this doc on B&C's site:

http://www.bandc.biz/pdfs/sd8trbreva.pdf that agrees with everything

you've said.



 	  Quote: 	
		       The successful resolution starts with trustworthy

     measurement and observation.  Where's your rectifier/

     regulator mounted? Where does it tie into the electrical

     system? Do you have a wiring diagram for this airplane

     that can be scanned/shared?

   Bob . . .


	


I will definitely be fitting a reliable voltmeter and warning light.

Unfortunately I don't have a wiring diagram, though I'm working on

putting one together from my own notes taken during maintenance and

upgrades.  My rectifier/regulator is mounted on the engine side of the

firewall, in what I think is a relatively cool location (on the high

pressure side of the updraft cooling system).  The positive output

goes via a 14 AWG wire to a 10-amp CB on the instrument panel and from

there to the positive battery terminal (battery in the nose of the

canard-pusher airplane).  The negative output goes to a general ground

terminal on the engine mount frame and from there via a similar 14 AWG

wire to the negative battery terminal.  The instrument power bus is

connected to the battery terminals by another set of wires, and

there's a third set for the electronic ignition.

Any reason not to tune the regulator voltage setpoint on the bench

with a constant-current bench supply on the blue wires and my airplane

battery on the red+black?



Thanks again for the advice.

Henry

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 30, 2012 5:17 am Post subject: B&C alternator diagnosis

 	  Quote: 	
		  I will definitely be fitting a reliable voltmeter and warning light.

Unfortunately I don't have a wiring diagram, though I'm working on

putting one together from my own notes taken during maintenance and

upgrades.  My rectifier/regulator is mounted on the engine side of the

firewall, in what I think is a relatively cool location (on the high

pressure side of the updraft cooling system).


	




    Good



 	  Quote: 	
		  The positive output

goes via a 14 AWG wire to a 10-amp CB on the instrument panel and from

there to the positive battery terminal (battery in the nose of the

canard-pusher airplane).


	




    Does your airplane have a starter? If so, where

    is the starter contactor located?



 	  Quote: 	
		  The negative output goes to a general ground

terminal on the engine mount frame and from there via a similar 14 AWG

wire to the negative battery terminal.


	


    Hmmmm . . . I deduce that there is no starter

    and the 14AWG ground is the only conductor between

    the crankcase and the battery(-)?



 	  Quote: 	
		     The instrument power bus is

connected to the battery terminals by another set of wires, and

there's a third set for the electronic ignition.


	


    Hmmmm . . . battery terminal used as a power distribution

    point. Is there a battery switch?



 	  Quote: 	
		  Any reason not to tune the regulator voltage setpoint on the bench

with a constant-current bench supply on the blue wires and my airplane

battery on the red+black?


	


    Yes, this is a crude form of switchmode regulator.

    Not of the inductor-stored energy variety, but a

    duty cycle switched series regulator with SCR's

    that get triggered in a variable position along

    each half-cycle of the incoming waveform.



    It must be adjusted under operating conditions that

    mimic the as-installed condition on the airplane.

    Here's a schematic of an exemplar rectifier/regulator

    for a PM alternator:



http://tinyurl.com/94585zs



    When we crafted installation instructions for that

    regulator/alternator combination on a no-starter

    airplane years ago, I brought ac power to the

    battery area on a twisted pair. The R-R was mounted

    close to the battery so that series resistance in the

    sense-lines shared with power-delivery lines did

    not become significant impedances in the control

    loop.



    Later drawings published by B&C dropped that

    configuration. That's been so long ago that I

    don't recall if I had any conversation with them

    about the change. I cannot prove that the old

    configuration was demonstrably 'better' but it

    was crafted with consideration for deleterious

    effects of unnecessary resistance in sense

    feeders shared with power feeders.



    Don't know if it's an option for you but you

    might consider using the 14AWG pair coming

    forward as AC power feeders and move the R-R

    to the forward space shared with the battery.

   Bob . . .

henry(at)pericynthion.org
Guest

Posted: Tue Oct 30, 2012 9:23 am Post subject: B&C alternator diagnosis

On Tue, Oct 30, 2012 at 6:11 AM, Robert L. Nuckolls, III

<nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	
		  > The positive output

> goes via a 14 AWG wire to a 10-amp CB on the instrument panel and from

> there to the positive battery terminal (battery in the nose of the

> canard-pusher airplane).



    Does your airplane have a starter? If so, where

    is the starter contactor located?




	


No starter.



 	  Quote: 	
		  

> The negative output goes to a general ground

> terminal on the engine mount frame and from there via a similar 14 AWG

> wire to the negative battery terminal.

    Hmmmm . . . I deduce that there is no starter

    and the 14AWG ground is the only conductor between

    the crankcase and the battery(-)?


	


Yes, except there are probably some other (skinnier) ground paths due

to engine sensors and the electronic ignition.  The main ground

conductor might be 12 AWG rather than 14, I'll check tomorrow.



 	  Quote: 	
		  >   The instrument power bus is

> connected to the battery terminals by another set of wires, and

> there's a third set for the electronic ignition.

    Hmmmm . . . battery terminal used as a power distribution

    point. Is there a battery switch?


	


There's a switch labeled "battery" that supplies the instrument bus

(with individual CBs after that for each instrument).  Is this

arrangement a bad idea?



 	  Quote: 	
		  

> Any reason not to tune the regulator voltage setpoint on the bench

> with a constant-current bench supply on the blue wires and my airplane

> battery on the red+black?

    Yes, this is a crude form of switchmode regulator.

    Not of the inductor-stored energy variety, but a

    duty cycle switched series regulator with SCR's

    that get triggered in a variable position along

    each half-cycle of the incoming waveform.



    It must be adjusted under operating conditions that

    mimic the as-installed condition on the airplane.

    Here's a schematic of an exemplar rectifier/regulator

    for a PM alternator:



 http://tinyurl.com/94585zs


	


Makes sense, thanks!



 	  Quote: 	
		  

    When we crafted installation instructions for that

    regulator/alternator combination on a no-starter

    airplane years ago, I brought ac power to the

    battery area on a twisted pair. The R-R was mounted

    close to the battery so that series resistance in the

    sense-lines shared with power-delivery lines did

    not become significant impedances in the control

    loop.


	


Interesting.  It's great to get insight from the designer.



 	  Quote: 	
		  

    Later drawings published by B&C dropped that

    configuration. That's been so long ago that I

    don't recall if I had any conversation with them

    about the change. I cannot prove that the old

    configuration was demonstrably 'better' but it

    was crafted with consideration for deleterious

    effects of unnecessary resistance in sense

    feeders shared with power feeders.



    Don't know if it's an option for you but you

    might consider using the 14AWG pair coming

    forward as AC power feeders and move the R-R

    to the forward space shared with the battery.




	


I'll look into it - I agree that sounds like a better arrangement

feedback-wise, but I don't think the existing wire run I have is a

twisted pair, so I'd be a bit concerned about EMI emissions from that

long of a run of chopped AC.  I'll see how much trouble a new wire run

would be.  If I had the time it could be a fun project to design my

own switching regulator with separate sense lines...  for that matter,

do you know why these brushless alternator designs didn't use three

phases like a modern BLDC motor?



Thanks again

Henry

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 30, 2012 1:30 pm Post subject: B&C alternator diagnosis

 	  Quote: 	
		  

 I'll look into it - I agree that sounds like a better arrangement

 feedback-wise, but I don't think the existing wire run I have is a

 twisted pair, so I'd be a bit concerned about EMI emissions from that

 long of a run of chopped AC. 	


   I've not had an opportunity to run a PM alternator in

   the lab . . . so the twisted pair was simple a prophylactic

   derived from common sense. In any case, I doubt that

   EMI products go very high in frequency. Given that ADF

   is gone (taking am radio with it), the probability

   for real interference is small. It would be a relatively

   easy experiment. See if you can use the existing 14AWG

   pair as an AC power feeder and then fly it.



  	  Quote: 	
		    I'll see how much trouble a new wire run would be. 	


   Many moons ago, I was able to use an existing wire as

   a pull-tape to run in a new instrumentation wire . . .

   a shielded trio. The bundles between firewall and the nose

   section were not tightly tied.



   You might see if tugging on the 14AWG produces any

   significant motion at non-scary forces.



  	  Quote: 	
		    If I had the time it could be a fun project to design my

 own switching regulator with separate sense lines... 	


   Yeah, I have such a design somewhere. I'll see if I

   can dig it out. The design is a buck-regulator scaled

   to run off the un-regulated, full wave rectified DC

   out of the alternator. I looked at that product about

   20 years ago but some new kids on the block might

   re-open the door. Consider this:



   A full wave rectifier on the firewall and local

   capacitor would get you unregulated, HV dc. I don't

   recall now what the open circuit AC votlage is for

   your alternator at cruise . . . you might get a measurement

   at some known ramp RPM from which we can extrapolate

   the higher rpm value.  Use a rectifier and filter capacitor

   with a light load, say 100 ohms across it. Measure the resulting

   DC at some handy RPM.



   If max DC is below 28, then this regulator might have

   promise:

 

  http://tinyurl.com/8fm6reh



   Given that you do not have a starter, there may not

   be a good reason to keep a battery on board . . .

   or the battery could be scaled down to deal with

   only with taxi rpm situations. These regulators provide

   constant, clean output as long as the input is

   high enough. You might even consider two regulators.

   They're light and smaller than a battery. One could

   be a standby. It's exceedingly unlikely that you would

   ever loose the alternator.



   Food for thought.



  for that matter,

  	  Quote: 	
		  do you know why these brushless alternator designs didn't use three

 phases like a modern BLDC motor? 	


   You could do that . . .  here's an interesting

   motor

 [img]cid:.0[/img]

 [img]cid:.0[/img]



    BEMF of 6v/krpm says you'll get about 24 volts at

    4000 pad drive speeds. The winding resistances are

    low. It seems that you would get 10A plus out of this

    motor back-driven as a PM, 3-phase alternator. 



    It would cost you about $200 to put your hands on one

    to play with.



  http://tinyurl.com/95jny8c



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 31, 2012 7:32 am Post subject: B&C alternator diagnosis

At 07:14 PM 10/30/2012, you wrote:

  	  Quote: 	
		  Bob,

 This is fairly common in the RC industry.

 See  http://mysite.verizon.net/vze49gsg 

 Raja may be interested in building the rectifiers. 

  	


   Yeah, those little RC BLDC motors are amazing products.

   I've got a couple here that have been played with a bit.

   A few years ago, I was asked to proposed a table-top

   demonstrator for quantifying both brushed and

   brushless DC motor performance. Never got a response

   back on my proposal. But it was an opportunity to

   sample what was out there.



   I've considered studying their application in a wind-driven

   power source for ultra-lights and antiques. But that's

   a project WAAAAaaayyy back on the burners!



 

 

   Bob . . .    [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Wed Oct 31, 2012 10:02 am Post subject: Re: B&C alternator diagnosis

 	  Quote: 	
		  do you know why these brushless alternator designs didn't use three 

phases like a modern BLDC motor? 	


This is pure speculation on my part; so correct me if wrong.

If the coils of a single phase alternator were rewired to make a 3 phase alternator, then voltage output would be only 1/3 of the single phase voltage.  In order for a 3 phase alternator to have the same voltage output as a single phase alternator, it would have to have two more windings of the same size.  Then it would weigh more and cost more.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 31, 2012 12:11 pm Post subject: B&C alternator diagnosis

At 01:02 PM 10/31/2012, you wrote:


 > do you know why these brushless alternator designs didn't use three

 > phases like a modern BLDC motor?



This is pure speculation on my part; so correct me if wrong.

If the coils of a single phase alternator were rewired to make a 3 

phase alternator, then voltage output would be only 1/3 of the single 

phase voltage.  In order for a 3 phase alternator to have the same 

voltage output as a single phase alternator, it would have to have 

two more windings of the same size.  Then it would weigh more and cost more.

Joe



--------

Joe Gores



    The power output from an AC device is roughly proportional

    to the weight of the active magnetic material (core), magnetic

    strength and speed (rpm). I'm recalling from memory now but

    back when I was winding my own transformers, a 1 pound core

    was good for about 60 watts at 60 Hz. The same weight of core

    in a 400 Hz system was good for 6.5 times that power . . .

    400 watts. This assumes similar levels of magnetic flux

    that can be carried in the core without saturation or

    increases losses at higher frequencies.



    An automotive alternator is already crafted as a 3-phase

    device. The configuration requires that pole-pairs on the

    rotating magnet come in some multiple of 3 (usually

    6 pairs but can be more on larger machines).



    The output voltage of any given widing is proportional

    to speed x flux value x number of turns. When you 'rewind'

    to get more voltage, it generally has to be done with

    smaller wire . . . the winding window in the core is fixed.



    The practical power output is not a linear function because

    of heating effects of I-squared x R in the wires and the

    windings ability to reject heat into the core and end turns.

    There's not a great deal to be gained in power by going from

    single to three-phase . . . it's that weight,flux,speed thing.



    The BIG toe-stubber is pole piece configuration. The magnets

    glued to the inside of the popular PM alternator shells (or

    wound-field machines) are already optimized for their as-

    manufactured condition. It takes more than a 'rewinding'

    to morph from single to 3-phase configuration. But assuming

    all other things are held the same, the watts-per-pound-per-

    velocity will be the same for both configurations.



    The BIG advantage of 3-phase is the smoother output with

    simple full-wave rectification . . . about 5% ripple as

    compared to 100% ripple for single-phase. But if the designer

    sets out to do a clean piece of paper, 3-phase design it

    will be only moderately more expensive. The power can be

    a little better because the windings share duties . . . i.e.

    there is never a time when current goes to zero in more than

    one winding.



    Bob . . .



   Bob . . .

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