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PM alternator capacitors . . .

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nuckolls.bob(at)aeroelect
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Posted: Tue Aug 19, 2014 6:54 am Post subject: PM alternator capacitors . . .

 The legacy 22,000 uF capacitor installation on PM alternators  is of limited utility for smoothing the output from  PM alternator rectifier/regulators.  Peek at the bus with  a 'scope and do a capacitor-connected/disconnected comparison  for confirmation. A casual observation with a 'scope will  not produce much confidence that the capacitor is doing  anything useful in the time domain. See:  http://tinyurl.com/n5yd3vw

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

  I was asked about the significance of the data cited above . . . and I beg your indulgence . . . it's not immediately obvious.

  I've re-posted the data package and encircled the pertinent data points: RMS and peak-to-peak voltage numbers cited at the edge of the 'scope screen.

  These Pk-Pk values speak to the greatest voltage excursions detected in the displayed plot . . . you can have some pretty high numbers here if the wave form shows even the shortest of 'spikes' . . . pk-to-pk numbers are not terribly significant in these plots. RMS speaks to the ENERGY in the noise.

  Note that for ALL conditions measured, there are no gross variations in measured noise configurations of capacitor size and whether or not a battery is on line. All measured values were well under those we are told to expect on the legacy 704/160 realm of DC power systems.

  Publication of this data is not intended to say that there is no value for including a capacitor . . . but the published narratives don't speak to any rationale other than noise mitigation. It may be that some clever designer perceived an improvement in performance for something other than noise. If so, I'm unaware of it.

  Bob . . .     [quote][b]

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jwd3ca(at)gmail.com
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Posted: Wed Aug 20, 2014 12:20 pm Post subject: PM alternator capacitors . . .

Interesting. I see you say "[b]Publication of this data is not intended to say that there is no value for including a capacitor . [/b]So, in laymen's terms, does this mean that you will amend your wiring diagrams that include a 22,000 uF capicitor, such as Z20L? Can/should we remove installed caps from our systems? Does/can that large cap have *adverse* effects? Thanks, Bob, as always.

 

On 19 August 2014 10:53, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  	  Quote: 	
		      The legacy 22,000 uF capacitor installation on PM alternators  is of limited utility for smoothing the output from  PM alternator rectifier/regulators.  Peek at the bus with  a 'scope and do a capacitor-connected/disconnected comparison  for confirmation. A casual observation with a 'scope will  not produce much confidence that the capacitor is doing  anything useful in the time domain. See:  http://tinyurl.com/n5yd3vw

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

  I was asked about the significance of the data cited above . . . and I beg your indulgence . . . it's not immediately obvious.

  I've re-posted the data package and encircled the pertinent data points: RMS and peak-to-peak voltage numbers cited at the edge of the 'scope screen.

  These Pk-Pk values speak to the greatest voltage excursions detected in the displayed plot . . . you can have some pretty high numbers here if the wave form shows even the shortest of 'spikes' . . . pk-to-pk numbers are not terribly significant in these plots. RMS speaks to the ENERGY in the noise.

  Note that for ALL conditions measured, there are no gross variations in measured noise configurations of capacitor size and whether or not a battery is on line. All measured values were well under those we are told to expect on the legacy 704/160 realm of DC power systems.

  Publication of this data is not intended to say that there is no value for including a capacitor . . . but the published narratives don't speak to any rationale other than noise mitigation. It may be that some clever designer perceived an improvement in performance for something other than noise. If so, I'm unaware of it.

  Bob . . .      	  Quote: 	
		  



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-- 

Regards,  J.

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

J. Davis,   

email: jwd3ca at gmail dot com

*NIX consulting, Medical Imaging research programming

 

- Zenith STOL CH750 C-FJNJ: Jab 3300, Whilrwind GA prop, AeroCarb

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- former C-IGGY CH701 owner/builder

- see these and more at http://cleco.ca

 



 

  [quote][b]

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nuckolls.bob(at)aeroelect
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Posted: Sat Aug 23, 2014 6:40 am Post subject: PM alternator capacitors . . .

At 03:17 PM 8/20/2014, you wrote:

  	  Quote: 	
		  Interesting. I see you say "   Publication of this data is not intended to  say that there is no value for including a  capacitor .  So, in laymen's terms, does this mean that you will amend your wiring diagrams that include a 22,000 uF capicitor, such as Z20L? Can/should we remove installed caps from our systems? Does/can that large cap have *adverse* effects? Thanks, Bob, as always. 	


     Haven't decided. I must acknowledge a level

     of risk for removing a component that really

     DID have some value at some point in time.



     But without seeing the numbers and understanding

     the idea behind the capacitor's original

     inclusion, I'm not prepared to offer any

     blanket opinion. But it will be the topic of

     a future study wherein there is a high probability

     of discovery of the capacitor's no-value-added

     existence.



     I'm aware of no potential for adverse effects

     so don't rush out and remove any that are already

     installed . . . 



 

 

   Bob . . .     [quote][b]

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