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Fwd: AC voltage at aircraft bus at approx. 1000rpm

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flyadive(at)gmail.com
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Posted: Thu Feb 04, 2010 2:48 pm Post subject: Fwd: AC voltage at aircraft bus at approx. 1000rpm

Keith & Gary:

  

 Looking at your picture ... In the lower right corner the screen reads 0.2 V/Div.

 That means between EACH large Tic it is 0.2 V.

 SO ... Your Peak reading is about (again looking at the picture) 0.24 Volts and the Peak to Peak (P-P) is 0.28 Volts.

 As for what is acceptable... That may be determined by the manufacture or the FAA.  I do not know.  BUT!  When I do a very simple but ACCURATE test using a DMM (Digital Multi Meter) I look for 0.4 to 0.5 V AC at the BATTERY to determine if a diode is bad.

   

 For the little voltage you are seeing I would put a 0.001 uF Ceramic Cap in parallel with a 50,000 uF (or more) Electrolytic Cap and the NEG side of the Cap goes to GROUND, POS side to POS Battery

  

 AND/OR - Put a large electrolytic Cap from the 'S' terminal of the VR to Ground.  

  

 If you have that little noise (0.48 V P-P) the caps will remove it.

  

 Barry

 



 

 On Thu, Feb 4, 2010 at 2:48 PM, <teamgrumman(at)aol.com (teamgrumman(at)aol.com)> wrote:

 [quote]Here is the ripple on a PP alternator.  Even with a Zeftronics regulator and a Garmin audio panel, the noise comes through.

 

 

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flyadive(at)gmail.com
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Posted: Fri Feb 05, 2010 5:40 am Post subject: Fwd: AC voltage at aircraft bus at approx. 1000rpm

I agree.  It should work correctly.

  

 Couldn't you think of a better analogy ... Say ... Like taking a shower with an raincoat on.

  

 Because if the glove don't fit you must acquit.

  

 Barry

 On Thu, Feb 4, 2010 at 10:55 PM, <teamgrumman(at)aol.com (teamgrumman(at)aol.com)> wrote:

 [quote]The whole point is not to patch together something that should work without a "FIX."  It says right on the alternator and the associated paperwork that no noise filter is required.    



 It's kind of like wearing a glove when you buy a pen that leaks.



 

   

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flyadive(at)gmail.com
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Posted: Fri Feb 05, 2010 5:44 am Post subject: Fwd: AC voltage at aircraft bus at approx. 1000rpm

Gary:

  

 You are correct, the time base should be opened up to define the type of wave and see if there is a identifiable frequency.

  

 We could start a thread on how to use an O-Scope?

 f = 1/T

 T- 1/f ...

 So 60 Hz would have a time base of 0.01666

  

 Hey!  Pretty good picture of the scope and wave form.

  

 Barry

 On Thu, Feb 4, 2010 at 11:50 PM, Gil Alexander <gilalex(at)earthlink.net (gilalex(at)earthlink.net)> wrote:

 [quote] Gary,



At 5 mS/div on the scope... could you be seeing some 60 Hz pickup? - which would be just over 3 divisions.



Is the noise frequency proportional to RPM?



How long was the ground lead to your probe?

 

gil A   

 

At 08:55 PM 2/4/2010, teamgrumman(at)aol.com (teamgrumman(at)aol.com) wrote:

 [quote]The whole point is not to patch together something that should work without a "FIX."  It says right on the alternator and the associated paperwork that no noise filter is required.   

 

It's kind of like wearing a glove when you buy a pen that leaks.



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flyadive(at)gmail.com
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Posted: Fri Feb 05, 2010 12:24 pm Post subject: Fwd: AC voltage at aircraft bus at approx. 1000rpm

Gary:

  

 The noise going away with the Master OFF is normal.  With the Master OFF there is NO voltage being supplied to the Alternator Field, there for NO output from the Alt.

  

 I am not sure what you are referring to when you say: "The ground lead was long enough to reach the O-scope."  Which ground lead, the scope's?

  

 I would LQQK at the GROUND of the VR.  Start by making a SHORT but HEAVY gage wire with alligator clips to function as a ground and hook it to the VR and see if the noise diminishes or goes away.

  

 Also check the ENGINE GROUND, the BATTERY GROUND and of course the ALT GROUND.

  

 Going back to your O-Scope run a shielded or twisted pair of wires to the scope.  Set the scope to monitor a 60 Hz noise and see if the frequency changes with RPM.  If it does there is a HUGE change there is a bad diode or diode connection in the ALT.

   

 If as you say CONTROLLERS are also hearing the NOISE then the noise is coming in on the B+ line and reflects back to the two items mentioned above - GROUND and/or Diode.

  

 Barry



To: teamgrumman-list(at)matronics.com (teamgrumman-list(at)matronics.com); teamgrumman-list(at)matronics.com (teamgrumman-list(at)matronics.com)

 Sent: Thu, Feb 4, 2010 8:50 pm

Subject: Re: Fwd: AC voltage at aircraft bus at approx. 1000rpm

  [quote]     Gary,



At 5 mS/div on the scope... could you be seeing some 60 Hz pickup? - which would be just over 3 divisions.



Is the noise frequency proportional to RPM?



How long was the ground lead to your probe?

 

gil A

At 08:55 PM 2/4/2010, teamgrumman(at)aol.com (teamgrumman(at)aol.com) wrote:

 [quote]The whole point is not to patch together something that should work without a "FIX."  It says right on the alternator and the associated paperwork that no noise filter is required.   

 

It's kind of like wearing a glove when you buy a pen that leaks.



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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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