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Update: Strange alternator behavior at Startup

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nuckollsr(at)cox.net
Guest

Posted: Mon Feb 27, 2006 10:31 am Post subject: Update: Strange alternator behavior at Startup

At 07:08 AM 2/27/2006 -0500, you wrote:



 	  Quote: 	
		  

<mstewart(at)iss.net>



Update:

Was up north this weekend and was able to do a good test in the cold.

Temp was 10F and I cranked her up.

Set immediate idle at 800rpm. No charge. Sat ther for 10 seconds or so.

Went to 1100rpm for about 5 seconds. And Wallah, charging.

Back to 700rpm for 10 seconds. Still Charging.

Down to 350rpm for 10 seconds and still charging.


	


   This MAY be an on-purpose feature built into your

   alternator. My little romp through the data sheet on the

   MC33092A regulator chip offered some insights into

   the thinking of at least these chip designers. Don't

   know that the MC33092A found its way into your alternator

   but it's a sure bet that any designer of a new chip who

   is worth his salt has studied the market. The time delay

   function offered in the MC33092A combined with the low/high

   RPM transition switch may well have been included in your

   alternator.



   Don't jerk it out yet. It just might be performing

   exactly as the designers intended.



   Bob . . .

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mstewart(at)iss.net
Guest

Posted: Mon Feb 27, 2006 12:27 pm Post subject: Update: Strange alternator behavior at Startup

Just as a reminder,

This behavior does not exist when OAT is above 40F OR is it is an

already warm engine. 



On that same cold day Saturday, I started the warm engine at 400rpm and

it was charging immediately. There was no need to raise the rpm. Its

definitely temperature related.

Mike

--

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nuckollsr(at)cox.net
Guest

Posted: Mon Feb 27, 2006 2:50 pm Post subject: Update: Strange alternator behavior at Startup

At 01:46 PM 2/27/2006 -0700, you wrote:



 	  Quote: 	
		  



Hey everybody (especially Bob),



I've been sitting around thinking about how to make circuits more

complicated than they need to be (grin)...  Here's an idea for turning off

an IR alternator with the end goal of not causing damage due to load dump.

  It definitely adds parts count, and doesn't address over voltage nuisance

trips.  The idea depends on the alternator using the sense lead as a

reference voltage input for the regulator.  One of the schematics that I

looked at for an IR chip supported such behavior...



So, here's the idea.  Actuating the 'off' position of the alternator

switch would actually connect a pumped ic regulator (LM1577 or similar)

output to the sense lead of the IR alternator at a voltage higher than

alternator output voltage.  Say bump it up by 2Volts or so.  This would

signal to the IR that the alternator output current needs to be reduced in

order to return to regulated voltage (in effect re-regulating, or fooling

the IR).  After 1 sec or so, the alternator disconnect relay is then

opened, safely disconnecting the unit from the bus - no load-dump.

Turning the alternator switch back 'on' boots the circuit, closes the

alternator disconnect relay, and disconnects the pump regulator from the

sense lead circuit.



I can work up a schematic if this sounds interesting..


	


    Your solution pre-supposes that we have access to an

    internal sense lead and that the builder is willing/

    able to add that lead at installation. Your premise is

    sound. Anything you can do to fool a normally working

    regulator into an orderly shut down would do the trick.



    The approach I have in mind requires no modifications

    to an alternator . . . it would even work with the so-called

    one-wire alternators that don't have a control-wire.



    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       >

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brian

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

Posted: Mon Feb 27, 2006 5:19 pm Post subject: Update: Strange alternator behavior at Startup

Robert L. Nuckolls, III Startup wrote:

 	  Quote: 	
		  > Set immediate idle at 800rpm. No charge. Sat ther for 10 seconds or so.

> Went to 1100rpm for about 5 seconds. And Wallah, charging.

> Back to 700rpm for 10 seconds. Still Charging.

> Down to 350rpm for 10 seconds and still charging.

 ...

    Don't jerk it out yet. It just might be performing

    exactly as the designers intended.

This is actually normal behavior for a self-exciting alternator if you

don't hook up the ignition terminal or the idiot light. There is no

source of power to provide any field excitation so excitation comes from

the residual magnetic field in the armature. Eventually you get it

spinning fast enough that there is enough output from the stator to

begin to excite the regulator and the field. The result is that the

alternator begins to bootstrap, i.e. a little current gets to the field

which slightly increases the output which causes a little more current

to get to the field, until the alternator has enough output to fully

turn on the regulator and the field.

-- 

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-Exupery

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_________________
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

mstewart(at)iss.net
Guest

Posted: Tue Feb 28, 2006 4:07 am Post subject: Update: Strange alternator behavior at Startup

Oh.

Well that is very interesting Brian. Could it be that my IGN wire is

dead? 

I have the IGN with voltage applied before cranking (I think. I have not

checked it since initial install) and I have an idiot light installed

which does work as expected. I will check that IGN wire next time I have

the cowl off to verify it is supplying power before cranking. Based on

your note below, it is quite possible the IGN wire is doing nothing.

Wonder why temperature is at play though.



Ill check it and report back.

Thanks

Mike

Do not archive



--

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brian

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

Posted: Tue Feb 28, 2006 7:24 am Post subject: Update: Strange alternator behavior at Startup

Stewart, Michael (ISS Atlanta) wrote:

 	  Quote: 	
		   

 

 Oh.

 Well that is very interesting Brian. Could it be that my IGN wire is

 dead? 


	


Could be.



 	  Quote: 	
		   I have the IGN with voltage applied before cranking (I think. I have not

 checked it since initial install) and I have an idiot light installed

 which does work as expected. I will check that IGN wire next time I have

 the cowl off to verify it is supplying power before cranking. Based on

 your note below, it is quite possible the IGN wire is doing nothing.


	


Some older regulators get their initial excitation through the idiot

light circuit. If the alternator has no output the regulator draws

current through the idiot light causing most of the current to flow

through the field which starts the bootstrap ball rolling. If the

alternator has an ignition terminal then that terminal is used to

provide the initial field current to bootstrap the alternator.



And every IR alternator is different. If you want the details, you need

to find out how your particular alternator works. It is just that I have

worked with a fair number (cars, boats, gen-sets, and airplanes) and

what I wrote above has been generally true for these devices.



The Delco truck alternator I had on my CJ6A had nothing connected to the

idiot light circuit or the IGN lead and used to require that I get up to

around 2000 RPM (2300 RPM was red-line) before it would self-excite.

After that it would be fine even at idle. I ended up selling the

airplane before I got around to fixing that problem.



 	  Quote: 	
		   Wonder why temperature is at play though.


	


Just a wild guess but most silicon devices have a negative temperature

coefficient. The drop across a cold diode is greater than the drop

across a warm diode. This could change the required voltage from the

alternator requiring it to turn faster to self-excite.



But this latter comment is pure speculation on my part with nothing to

back it up so is not worth much.



[quote] Ill check it and report back.

 Thanks

 Mike

 Do not archive

 

 

 

 --

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klehman(at)albedo.net
Guest

Posted: Tue Feb 28, 2006 1:19 pm Post subject: Update: Strange alternator behavior at Startup

Michael

If it makes you feel better I have some IGN wire sleuthing to do as well 

although it is not near the top of my to do list at the moment.

My brand new mini ND IR alternator (100211-1680) draws 3.3 amp field 

current through the B-lead any time the OV contactor is closed with the 

engine not running. The IGN terminal is simultaneously energised so my 

next test is to see if this still happens with the IGN wire 

disconnected. If so then it is shopping time for another regulator but 

of course on mine it is difficult to get at that wire to test it. I 

thought most of these things were smart enough to not energise the field 

until the rotor was turning but maybe not. Or perhaps it is just annoyed 

because I'm not allowing it to draw its normal 4 ma of standby current 

that it would draw from the battery if I wasn't using an OV contactor  

 It charges and regulates perfectly when the engine is running.

Ken

Brian Lloyd wrote:

 	  Quote: 	

Stewart, Michael (ISS Atlanta) wrote:

>

>

>Oh.

>Well that is very interesting Brian. Could it be that my IGN wire is

>dead? 

>    

>

Could be.

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nuckollsr(at)cox.net
Guest

Posted: Wed Mar 01, 2006 6:35 am Post subject: Update: Strange alternator behavior at Startup

At 10:49 PM 2/28/2006 -0500, you wrote:



 	  Quote: 	
		  



In a message dated 2/28/2006 8:02:43 P.M. Central Standard Time,

mstewart(at)iss.net writes:



So it  would seem that it needs that initial rpm to get the juices

flowing in the  cold.

I can live with that.

Thanks to whom ever it was that suggested  an initial burst of RPM to get

her going. Worked

Best,

Mike

Do not  archive



Good Evening Mike,



Do you really want to give it that short burst of power?



Personally, I like to warm up the engine at as low an RPM as possible

consistent with adequate oil pressure and any need for the crankshaft to 

throw  the

oil against the innards of the engine. I do not know what engine you have,

but I would not give it a burst above any RPM that I wanted to use for 

warm up

purposes.



Isn't that the whole idea behind doing a warm up?


	


    Absolutely.  The behavior noted is NOT what we would

    generally consider acceptable . . . the "work around"

    described is functional but it's almost a certainty

    that this alternator is either deprived of some accommodation

    that allows it to come up normally at ramp idle -OR-

    has a design feature that makes it a poor choice for

    use on aircraft.



    Bob . . .

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