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undervoltage lamps

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rvdave

Joined: 24 Jan 2009
Posts: 191

Posted: Mon Nov 15, 2010 7:48 pm Post subject: undervoltage lamps

I had a recent failure that is prompting me to at least get a couple of idiot lights for indicators, tell me what you think.  I have a FADEC system with dual alternators/batteries isolated.  My main battery is an Odyssey PC680, charged by B&C standard alternator.  Backup ess buss and primary FADEC battery is a 7 amp/h smaller battery charged by the B&C SD-8 alternator.  Architecture is Z-14 with crowbar protection only on the 7 amp battery.  For whatever reasoning I had 7 years ago this is what I was comfortable with...until now.  



On a recent pre-flight I had to charge the primary fadec battery(non starting) to get the engine to fire because it was low in voltage after using it to check awos, tune frequencies, etc.  This had never happened before as I usually replace this battery annually.   After starting & running while taxiing & before takeoff it is standard to remove alternately primary & secondary busses from engine as a verification of buss operation.   Everything was ok so after the flight I replaced the battery.  I have voltage readout on the Dynon but didn't notice any abnormality (but there could have been). 



Next flight, flew 90 miles to Grand Rapids for the day, no problem on the way down.  After departure and telling departure control I was going to 6500 feet and arriving there I noticed my Dynon showing a red bar & message indicating the unit was powering down.  Also happening was a red fadec warning light followed by a sputtering engine, I was losing power!!  I immediately noticed (because the dynon red bar had happened before) that I had inadvertently put the primary alternator switch to the "battery only" position, the main alternator was not on.  This engine sputtering was also telling me the primary fadec battery was in a discharging state.  Both batteries were being operated with no method of charging either battery.  Even though I have voltage readout on the dynon for both busses, I was lax in looking at it.  Kicking in the main bat/alt switch brought everything back to seeming normal, but I knew I still had a primary battery/charging problem.  After landing & the next!

 

  day I saw that my SD-8 was not coupled and was spinning inside--the coupler had broken.  I now have parts on order & that should fix that problem. 



Questions:



1)  What would I need to get a warning light to indicate I do not have a charging mode on the batteries?  Is an LR-3 system the only choice?

2)  The bat/alt 2 position switch per Z-14 has bitten me more than once, I'm not sure why I don't just use a bat/alt single position switch?  What is the purpose of the bat only postition?  When would I really need this?

3)  The caveat of the fadec is a 9 volt operating threshold--it is what it is---should I have a way of joining busses in a real emergency to couple all available current to fadec?

Dave Ford

Cadillac, MI  

RV6 flying

RV10 building

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_________________
Dave Ford
Cadillac, MI

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 15, 2010 11:32 pm Post subject: undervoltage lamps

 	  Quote: 	
		     Even though I have voltage readout on the dynon for both busses, 

 I was lax in looking at it.  Kicking in the main bat/alt switch 

 brought everything back to seeming normal, but I knew I still had a 

 primary battery/charging problem.  After landing & the next!


	


    Have you availed yourself of a copy of the AeroElectric Connection.

    In the chapters on electrical system instrumentation and system

    reliability we emphasize the need for ACTIVE NOTIFICATION OF

    LOW VOLTAGE. EVERY one of the Z-figures illustrates this feature.

 	  Quote: 	
		  

   day I saw that my SD-8 was not coupled and was spinning 

 inside--the coupler had broken.  I now have parts on order & that 

 should fix that problem.



Questions:



1)  What would I need to get a warning light to indicate I do not 

have a charging mode on the batteries?  Is an LR-3 system the only choice?


	


    A low voltage warning light. Preferably bright and flashes

    at 2-3 times per second and located to be easily seen

    by the pilot. It is automatically preflight tested because

    the light(s) come on as soon as battery switches are on

    and before the engine is started. Once alternator(s) pick

    up the loads, the lights go out.



 	  Quote: 	
		  2)  The bat/alt 2 position switch per Z-14 has bitten me more than 

once, I'm not sure why I don't just use a bat/alt single position switch?


	


    This is explained in the 'Connection. The switch is

    a way to emulate the functionality of the split-rocker

    used on most light singles for over 40 years. It

    allows you to run battery only for ground ops without

    burdening the battery with field current drain of a

    non-rotating alternator. This configuration is no

    different than what has flown on tens of thousands

    of TC aircraft.



    Since you're flying an electrically dependent engine,

    the need for active notification of low voltage is

    still more critical and the 'reliability' of dual

    electrical systems can be compromised without it as

    you've discovered.



    I don't have any inventory on LV warning right now

    but you should have one on EACH system before you

    fly again. Check with Eric at



http://www.periheliondesign.com/moreproductsfiles/LV_Annunciator%20Manual.pdf



    and see if he can fix you up.



 	  Quote: 	
		     What is the purpose of the bat only postition?  When would I 

 really need this?

3)  The caveat of the fadec is a 9 volt operating threshold--it is 

what it is---should I have a way of joining busses in a real 

emergency to couple all available current to fadec?


	


    The point of having 4 pouwer sources in

    Z-14 is to NOT have an emergency. What's

    your game plan for detecting and dealing with

    any single failure? What's you plan for maintaining

    both batteries at some capacity that you've

    established as a design goal?



    12v lead acid batteries are 100% used up at 10v.

    If you find yourself down to this voltage level

    and wondering what to do next . . . you've really

    missed the opportunity offered by a Z-14 system

    combined with a preventative maintenance program

    that insures this will never happen.



    Bob . . .

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