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Alternator Question - Redux

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kearney

Joined: 20 Sep 2008
Posts: 563

Posted: Mon Aug 14, 2017 10:05 am Post subject: Alternator Question - Redux

Bob



Thank you for your comments and explanations they were most helpful. 



I have started another thread just so things aren't too cluttered. I would like to a follow up questions just to make sure I understand things so please forgive me if it seems repetitive. 



To clarify I was wondering what would happen if the Bat/Alt Master Switch failed completely. Would this not immediately remove all power to the main bus on the Z12? If so, how would the aux alternator field be energized if located on the main bus?



Cheers



Les

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donvansanten(at)gmail.com
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Posted: Mon Aug 14, 2017 10:37 am Post subject: Alternator Question - Redux

Les,I added a PC 310 battery through a 40 amp relay to my main bus on the Z12. It is switched by the switch that fed my e bus. I no longer have the e bus but still have dual power feeds to the main bus.

On Aug 14, 2017 11:13 AM, "kearney" <kearney(at)shaw.ca (kearney(at)shaw.ca)> wrote: 	  Quote: 	
		  --> AeroElectric-List message posted by: "kearney" <kearney(at)shaw.ca (kearney(at)shaw.ca)>

 

 Bob

 

 Thank you for your comments and explanations they were most helpful.

 

 I have started another thread just so things aren't too cluttered. I would like to a follow up questions just to make sure I understand things so please forgive me if it seems repetitive.

 

 To clarify I was wondering what would happen if the Bat/Alt Master Switch failed completely. Would this not immediately remove all power to the main bus on the Z12? If so, how would the aux alternator field be energized if located on the main bus?

 

 Cheers

 

 Les

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=471857#471857

 

 

 

 

 

 

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nuckolls.bob(at)aeroelect
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Posted: Mon Aug 14, 2017 11:17 am Post subject: Alternator Question - Redux

At 01:05 PM 8/14/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "kearney" <kearney(at)shaw.ca>



 Bob



 Thank you for your comments and explanations they were most helpful. 



 I have started another thread just so things aren't too cluttered. I would like to a follow up questions just to make sure I understand things so please forgive me if it seems repetitive. 



 To clarify I was wondering what would happen if the Bat/Alt Master Switch failed completely. Would this not immediately remove all power to the main bus on the Z12? If so, how would the aux alternator field be energized if located on the main bus? 	


   But how does it fail completely?  Get one of these

   switches, choose any combinations of force/tools

   you choose to disassemble/emulate a 'failure'.



   Once your switch is sufficiently 'failed', then

   deduce how the same condition can be repeated in

   your airplane.



   Most 'failures' are soft and progressive. Something

   becomes intermittent or quits and is usually a function

   of age and environmental conditions . . . not service

   stresses.



   I have only once in my lifetime had to diagnose and

   deal with 'failure' of a Honeywell toggle switch in

   an airplane. It was a spring loaded toggle used as

   press to test on BeechJet ground fault system.



   The OPERATING current carried by this switch was

   a few tens of milliamps. Upon opening the panel

   and testing the switch with a meter, it was indeed

   found to be open circuit on the normally open

   side.



   The tech I was working with was ready to start

   filling out the paperwork to bet a new switch.

   I asked him to hold off for a few minutes. I

   got a small bench supply out of the lab and

   drug an extension cord into the airplane. I

   unhooked one wire from the switch so as not

   to 'power the airplane' and put 28v at 10A

   current limit on the switch. I then

   wiggled the switch until it suddenly began

   to show continuity across the 'failed' contacts.



   In this case, the relatively high-current,

   silver-cadmium contacts of the power rated

   switch had never been blessed with enough

   current flow to keep its contacts clean!



   After a few dozen 10A whacks to the switch,

   I put the wire back on and we signed off

   the squawk. Didn't get to charge the customer

   $200 for a new switch.



   We have seen some switch failures on the

   List.



  http://tinyurl.com/yapmtot4

  http://tinyurl.com/yd4tz8qd



   We also had a rash of loose terminals

   at the riveted joints on the Carling

   toggle switches.



   But none of those failures manifested as

   a sudden hazard to flight.



   the point is, be cautious about stirring

   the worry-pot with "what ifs?"  The the vast

   majority of what ifs thrashed around on the

   various forums are not well understood nor

   backed up with historical data.



   I wouldn't hazard a guess as to how many

   GA aircraft have been flown over the last 100

   years . . . certainly hundreds of thousands

   if not millions. Yet system architectures and

   materials used have not materially changed.



   From the time they put the first battery in

   a C120 to make it a C140 . . . up through the

   pressurized 1986 P210, the battery contactors

   have been made on the same, commercial grade

   production lines.  



 [img]cid:.0[/img]



 

   The rocker switches have the same back-side

   guts as the toggle switches sold by B&C and

   made by Carling.

 [img]cid:.1[/img]



   I'm certain that this same constellation

   of components persisted for a decade or

   two after 1986.



   The point is, there is a field history in both

   hardware and architectures that makes our

   job here on the List easier . . . it suggests

   that we need not waste a lot of time hypothesizing

   and mitigating every conceivable component failure

   while concentrating on failure tolerant architectures.



   Z-12 as published represents a well considered

   and field proven solution to the single battery,

   two-alternator option for a light airplane.



 

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Mon Aug 14, 2017 6:08 pm Post subject: Re: Alternator Question - Redux

After the engine is started and running, the battery is no longer supplying electrical power to the aircraft.  The alternator is.  And the alternator is supplying power to its own field.  If the battery is then disconnected, nothing changes.  The alternator continues to power the electrical system including the alternator field.  Without the battery, the voltage might be unstable and vary plus and minus one volt or so from the voltage regulator set point.  But electrical loads will still work.

  If both halves of the Master/Alternator switch fail simultaneously, then yes, the electrical system will go down.  But that switch would have to completely fall apart inside in order for that to happen, which is unlikely.  If it did fall apart, it would most likely happen when the switch is turned on or turned off, not during cruise.  I would not worry about it.  There are other things more likely to fail, like the engine or prop or a pilot.

  You could use Bob's favorite electrical architecture , Z-13/8.  The aux alternator output connects to the battery, not directly to the bus.

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