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Starter engaged light, was Starter and contactor wiring

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 05, 2010 11:20 am Post subject: Starter engaged light, was Starter and contactor wiring

At 10:04 AM 2/5/2010, you wrote:

 	  Quote: 	
		  

<aerobubba(at)earthlink.net>



Hi All-



It's been a while since I went down my decision tree on this topic, and I

might not recall all the details perfectly, but it seems to me that there

are a couple details of 'starter engaged' annunciation that might have been

overlooked.  First, it seems to me that the objective is to know whether

there is power on the starter or not, so tapping the fat wire between the

solenoid and  the motor would be in order.


	


    This is how it's done on TC aircraft when the

    feature is installed.



 	  Quote: 	
		  This would then annunciate that

there was power to the starter motor itself.  It also has the advantage of

monitoring the spin down of the motor.  Should the pinion hang and the

motor remain engaged after the solenoid opens, the back emf can keep the

engaged light illuminated.


	


    Not true. Every starter has an over-run clutch that

    prevents back-driving of the motor armature via a

    stuck pinion gear. This is especially important for

    modern, highly-geared starters where the armature

    is already running 4-6000 rpm while cranking the

    engine a couple hundred RPM.



    Without an over-run clutch, an engine idling at

    say 1000 rpm would either over-speed the armature

    perhaps to destruction from thrown windings or

    commutator bars or stripped gear teeth in the

    gearbox.



 	  Quote: 	
		  It might be especially zippy if one were to use

a bi-directional led for the indicator, such that one could perhaps have

amber indicate normal engagement and red to indicate run-on.


	


    If a starter WERE in a back-drive mode, the polarity

    of voltage would not reverse . . . hence the starter-stuck

    light would not change colors . . . only get much brighter.



 	  Quote: 	
		    Including a zener diode could clip the spin-down indication during

  normal operation while still allowing the run-on indication to

  function, should that become desirable.


	


    An interesting hypothesis but not consistent with

    either the physics of motor operations or with the

    configuration of starter drive-trains.



    Bob . . .

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Sat Feb 06, 2010 10:32 am Post subject: Starter engaged light, was Starter and contactor wiring

I am using a DPST momentary switch, with a lamp in  it that is switched independently, wired to the coil of a starter contactor for  my START button. I plan to wire the internal lamp to one side of the switch so  that it goes on when the START button is depressed and also have a parallel wire  going to the fat wire between the starter solenoid and the starter. So the lamp  will light when I depress the START button and will go out when it is  released...unless the starter solenoid is stuck closed and the fat wire between  the starter solenoid and the starter is energized.

  

 See any glitches?

   [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 06, 2010 11:16 am Post subject: Starter engaged light, was Starter and contactor wiring

 	  Quote: 	
		  There was an airframe lost a while back due to a stuck contactor and the

ensuing electrical fire, but that involved significantly different and more

robust hardware.


	


    Do you have a source for more information on this

    event?

 	  Quote: 	
		  As ever, thanks for your help with the rectal-cranial inversion!


	


    No problem my friend . . . it's what we do . . .

   Bob . . .

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