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Strobes - Light Plane Maintenance Article

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nuckollsr(at)cox.net
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Posted: Fri Aug 24, 2007 5:42 am Post subject: Strobes - Light Plane Maintenance Article

At 05:52 PM 8/23/2007 -0700, you wrote:



 	  Quote: 	
		  

<mwcreek(at)frontiernet.net>

The Sept 2007 edition of LPM has an article on strobe lights.  I'm curious

as to how accurate the following excerpt is:



"A strobe power supply that has been left "off" for long periods - weeks or

months - is subject to eventual failure because the electrolytic capacitors

used in the device will loose polarity formation.  As a rule, a strobe that

has been inactive for one year can be considered eligible for sudden

failure"



I have two Areoflash power supplies that were purchased new six months ago

and have since been waiting for final installation.  Do I need to "exercise"

this strobe system to keep it from going bad?


	


   There have been some excellent responses to this

   so I'll offer only the following:



   Articles like this are a disservice to the community

   because they are non-quantified. I.e., no data followed

   with logical deductions which lead to repeatable experiments

   (recipes for success). This topic has been raised many

   times over the years on the various aviation forums. On

   one occasion in years past, I scrounged around in my

   junk box for a high voltage electrolytic capacitor that I

   KNEW had not been powered up for decades.



   I connected it to a supply equal to it's rated voltage

   (450 volts if I recall correctly). On initial power up,

   the capacitor did what every capacitor does . . . draw

   whatever current the source will deliver until equilibrium

   is achieved. After several seconds, the capacitor's

   "draw" was measured in a hand-full of milliamps and

   after a minute, charging was essentially complete

   and "leakage" was under 1 mA. After ten minutes,

   leakage dropped to about 100 microamps.



   I then did a measurement of apparent capacity. The

   device was within 10% of rated value. I left the

   capacitor connected to the power supply for several

   days and measured apparent capacity again. It's

   increase was so tiny as to make measurement

   problematic.



   Bottom line: In days of yore when capacitor

   technology and fabrication techniques were in a

   relative state of infancy, the devices were indeed

   subject to deleterious effects of long term,

   dormant storage.



   But "modern" capacitors (meaning those built in

   the last 20 or so years) have exhibited great strides

   in operating performance and service life. Here's

   an exemplar article on the topic:



http://www.aeroelectric.com/articles/Long_Term_Stability_Aluminum_Electrolytics.pdf



   This article addresses an expected elevation of

   leakage currents in the first few minutes of a long

   term storage but that, "no damage to the capacitor

   is to be expected".



   This article is consistent with my own experience

   and in particular, with an experiment conducted on

   the bench. If anyone has data from an experiment arguing

   with the foregoing deductions, it would be interesting

   and useful for us to examine it for new understanding.



   Bob . . .

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echristley(at)nc.rr.com
Guest

Posted: Fri Aug 24, 2007 6:56 am Post subject: Strobes - Light Plane Maintenance Article

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		  

   This article is consistent with my own experience

   and in particular, with an experiment conducted on

   the bench. If anyone has data from an experiment arguing

   with the foregoing deductions, it would be interesting

   and useful for us to examine it for new understanding.



  


	


The electrolytics I have had to replace have been cheap ones in consumer 

products that experience continuous elevated temperatures.  Computer 

motherboards and stereo equipment stored in closed cabinets, for the 

most part.  This is consistent with the article Bob presented.  Cheap 

caps could be expected to possibly include more defect producing 

contaminants, and the article makes note that high heat tends to be 

detrimental.



-A strobe power supply may or may not be stored in a way to control 

temperature.  Ambient temps have exceeded the 25C that the article 

suggest for weeks now here in NC.  If it were buried in a wing stored in 

the rafters of a hanger, the temps could be much higher still. Could 

that be the nexus of the problem?



-If the strobe is using cheap caps...well, I'd just be upset about that one.

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nuckollsr(at)cox.net
Guest

Posted: Mon Aug 27, 2007 9:57 am Post subject: Strobes - Light Plane Maintenance Article

At 09:23 AM 8/27/2007 -0500, you wrote:



 	  Quote: 	
		  I called Wheelen when I had a "new in the box"  twenty year old power supply.

I was told three volts for an hour, then six, nine, twelve. Each for one 

hour. That was three years ago, still works fine.

Kevin Boddicker

Tri Q 200 N7868B 63.5  hours

Luana, IA.

On Aug 27, 2007, at 8:06 AM, John McMahon wrote:



>Just an additional comment.. In the Whelan strobe installation manual it 

>cautions you not to apply full voltage to a power supply that has not 

>been charged for a long time,  such as on initial installation.   If I 

>remember correctly it says to start by applying half power initially.  I 

>am on the road so cannot look it up until the end of the month, maybe 

>someone else can confirm my recollection.


	


     It never hurts to do a 'reforming' exercise on a strobe

     supply that has been in storage for a long period of time.

     What is not known . . . and will never be known without some

     judicious data gathering and analysis is whether or not

     the device really benefits from this exercise. It's doubtful

     that any of the big dogs in the strobe business will come

     forward with real data . . . it's pretty hard to find capacitors

     that have been in storage for 20+ years.



     The 'reforming' routine has been a standard fixture in

     the installation manuals for 40 years. Some folks still

     recommend avionics master switches for radios. But when asked

     to supports the validity of the exercise with simple-ideas

     and repeatable-experiments, the standard response is "that's

     the way we've always done it."



     If anyone is worried about it, by all means do the extended

     spool-up exercise.



     Bob . . .



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

        ( "Physics is like sex: sure, it may   )

        ( give some practical results, but     )

        ( that's not why we do it."            )

        (                                      )

        (                 Richard P. Feynman   )

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

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue Aug 28, 2007 6:48 am Post subject: Re: Strobes - Light Plane Maintenance Article

Check--http://industrial.rell.com/pdfs/IPG_AN_appguide.pdf



Excerpt from above: 



"Aluminum electrolytic capacitors stored for more than 5 to

10 years may have increased levels of DC leakage current.

Check if DCL meets application requirements before placing

in service. Recondition high DCL units by applying

rated voltage through 1,000 ohm resistor for 30 minutes.

Shelf life is a measure of how the capacitors will withstand

storage for long times especially at high temperature. To

test shelf life place the capacitors in an oven set to the

shelf-life test temperature –0 +3 °C for the shelf-life test

period. Upon completion of the test stabilize the capacitors

at 25 °C for 24 h or more. Apply the rated voltage for 30

minutes, then verify the post test limits. Unless otherwise

specified the capacitance, DCL and ESR will meet initial

requirements."

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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