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Contactor Failure

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Speedy11(at)aol.com
Guest

Posted: Sun Nov 29, 2009 5:47 pm Post subject: Contactor Failure

Any folks had a contactor failure?

 My understanding was that contactors are not failure prone.  I  understood that was the reasoning behind inserting one between the battery and  the starter solenoid.

 I had one fail the other day (actually it stuck in the closed position)  after 40 hours of use.  It was an intermittent duty contactor installed  between the #4 welding cable from the positive battery post and the Skytec  starter.

 If my engine doesn't start on the third blade, I release the starter button  to check what I've missed and try it again.  When I released the starter  button, the prop kept turning.  I quickly hit the starter button again  thinking it might have stuck.  The blades kept turning.  I turned off  both batteries and all fuel source.  The blades had stopped by then (10  seconds) but the starter was still engaged.  Set the brake and ran to the  hangar for wrenches.  I had to disconnect the battery to stop the  starter.  There was no other way.

 Did I design in a fault?  Aren't most custom-built airplanes built  with a contactor between the hot battery and the starter?  Should I have  some other type of disconnect between the battery and the contactor?

 Stan Sutterfield

 RV-8A flying

  [quote][b]

rckol

Joined: 14 Nov 2008
Posts: 36

Posted: Sun Nov 29, 2009 6:28 pm Post subject: Re: Contactor Failure

If I understand your system, you have a circuit from the battery straight to the starter contactor.  



Running the  starter contactor in series with the master bus contactor allows you to kill the starter with the master switch in the event that your starter or starter contactor decides to run on.



Bob's Z designs typically have this feature.

_________________
rck

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Nov 29, 2009 7:39 pm Post subject: Contactor Failure

At 07:45 PM 11/29/2009, you wrote:

  	  Quote: 	
		   Any folks had a contactor failure?

 My understanding was that contactors are not failure prone. 	


    Don't know what you mean by "failure prone".

    All parts have service lives. The service

    lives of all parts are subject to the stresses

    of the installation combined with the effects

    of manufacturing variability.



  	  Quote: 	
		    I understood that was the reasoning behind inserting one between the battery and the starter solenoid.

 I had one fail the other day (actually it stuck in the closed position) after 40 hours of use.  It was an intermittent duty contactor installed between the #4 welding cable from the positive battery post and the Skytec starter. 	


    Does your starter feature a contactor/solenoid

    combination that controls both power to the motor

    while extending the pinion gear for engagement?



  	  Quote: 	
		   If my engine doesn't start on the third blade, I release the starter button to check what I've missed and try it again.  When I released the starter button, the prop kept turning.  I quickly hit the starter button again thinking it might have stuck.  The blades kept turning.  I turned off both batteries and all fuel source.  The blades had stopped by then (10 seconds) but the starter was still engaged.  Set the brake and ran to the hangar for wrenches.  I had to disconnect the battery to stop the starter.  There was no other way.

 Did I design in a fault? 	


    Does your starter current go through the battery

    master contactor as depicted on ALL z-figures and

    common to ALL type certificated aircraft?



  	  Quote: 	
		     Aren't most custom-built airplanes built with a contactor between the hot battery and the starter?  Should I have some other type of disconnect between the battery and the contactor? 	


    Yup, the TC aircraft do it too . . . it's called

    the battery master contactor.



    As to the original failure. Permanent magnet starters

    offer VERY high in-rush currents because the current

    limiting characteristics of the series field are not

    present. The device selected to actively control

    starter current is not up to the task.



    I was a participant in the deliberations that set

    design goals at B&C some years back when consideration

    was given to PM fields. For a several reasons, B&C

    stayed with the wound fields. One reason germane to

    your experience was the fact that battery internal

    impedances were going down while stall currents of

    "modern" PM starters was going up. This combination

    predicted a potential for increased stress in contact

    closing on the starter contactor.



    If memory serves me correctly, the Skytec's built in

    contactor is probably tailored to this extra stress

    but it DOES exhibit inrush current issues of its own.

    See . . .



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



    Suggest you rewire to eliminate the external, intermittant

    duty starter contactor. Run your starter current through

    the battery master as suggested in the drawings. Buffer

    the inrush current to your starter contactor as suggested

    in Z-22.   



 

 

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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



     [quote][b]

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Nov 30, 2009 5:57 am Post subject: Re: Contactor Failure

After reviewing the endless promotion of the way it has always been done, please re-read the AeroElectric-Lists posts of October 12-13:

   

http://forums.matronics.com/viewtopic.php?p=267757



Then--Do it the way the manufacturer suggests. Hey, there's a radical 

idea!



Eric's five point plan for elimination contactor failure:



1) Don't use Type-70 contactors for critical tasks.

2) Don't use diodes for coil suppression duty. Use bi-directional Zeners.

3) Follow the manufacturers' suggestions. 

4) Ignore the man behind the curtain.

5) Examine carefully the ideas of anybody who claims he can't possibly be wrong.



"Every act of conscious learning requires the willingness to suffer an injury to one's self-esteem.That is why young children, before they are aware of their own self-importance, learn so easily; and why older persons, especially if vain or important, cannot learn at all." 

            -Thomas Szasz

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

klehman(at)albedo.net
Guest

Posted: Mon Nov 30, 2009 6:51 am Post subject: Contactor Failure

Yes I agree we should always use the latest greatest most expensive 

solution whether there is any demonstrated need or benefit. 

Manufacturers have never overstated or misled anyone. Sound engineering 

can't be trusted and we waste our time trying to understand physics anyway.

Ken



do not archive



Eric M. Jones wrote:

 	  Quote: 	
		   

 

 After reviewing the endless promotion of the way it has always been done, please re-read the AeroElectric-Lists posts of October 12-13:

    

 http://forums.matronics.com/viewtopic.php?p 67757

 

 Then--Do it the way the manufacturer suggests. Hey, there's a radical 

 idea!

 

 Eric's five point plan for elimination contactor failure:

 

 1) Don't use Type-70 contactors for critical tasks.

 2) Don't use diodes for coil suppression duty. Use bi-directional Zeners.

 3) Follow the manufacturers' suggestions. 

 4) Ignore the man behind the curtain.

 5) Examine carefully the ideas of anybody who claims he can't possibly be wrong.

 

 "Every act of conscious learning requires the willingness to suffer an injury to one's self-esteem.That is why young children, before they are aware of their own self-importance, learn so easily; and why older persons, especially if vain or important, cannot learn at all." 

             -Thomas Szasz

 

 --------

 Eric M. Jones

 www.PerihelionDesign.com

 113 Brentwood Drive

 Southbridge, MA 01550

 (508) 764-2072

 emjones(at)charter.net

bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Mon Nov 30, 2009 6:51 am Post subject: Contactor Failure

11/30/2009



Hello Stan, You wrote:



1)"Any folks had a contactor failure?"



Not on my airplane, but as an A&P I am aware of several contactor failures. 

Two failure modes that I have personally been involved in are: a) Fine 

contactor coil wire fractures because of vibration. b) Main current transfer 

bar inside the contactor gets eaten away and no longer makes contact.



Your contactor failure sounds like a third failure mode -- a welded main 

current transfer bar because of extremely high current transfer. If you 

still have the contactor why not cut it open to confirm?



2) "My understanding was that contactors are not failure prone."



"failure prone" is a very unquantifiable term, but they do definitely fail. 

That is why you need a plan B to permit recovery regardless of the mode of 

contactor failure.



3) "Did I design in a fault?"



Yes.



4) "Aren't most custom-built airplanes built  with a contactor between the 

hot battery and the starter?"



No, they are built with two contactors between the hot battery and the 

starter. A main battery contactor (continuous use type) and a starter 

contactor (intermittent use type).



Many starters now days have a contactor / solenoid as part of the starter 

itself for the purpose of moving the pinion gear into engagement. (This 

eliminates the old Bendix type mechanical starter engagement method.)



That is why when discussing this subject the term "starter contactor" can 

lead to some confusion unless the context makes it very clear which one of 

the two "starter contactors" one is referring to.



5) "Should I have  some other type of disconnect between the battery and the 

contactor?"



Yes.



6) "I  understood that was the reasoning behind inserting one between the 

battery and  the

starter solenoid."



Inserting only one contactor in this manner leaves you susceptible to the 

welded main bar transfer failure. A separate main battery contactor that in 

turn feeds the starter contactor would leave you a means of stopping current 

flow to the starter contactor in the case of this type of failure mode.



A separate battery fed essential or endurance bus would leave you a means of 

recovery if you suffer either a fine coil wire failure or an eaten away main 

transfer bar failure in your battery contactor while flying.



If your starter contactor suffers from either a fine wire failure or an 

eaten away main transfer bar failure then you should discover this problem 

on the ground because the engine won't crank and your recovery is to just 

replace the starter contactor.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



==================================================Time: 05:47:53 PM PST US

From: Speedy11(at)aol.com

Subject: Contactor Failure



Any folks had a contactor failure?

My understanding was that contactors are not failure prone.  I  understood

that was the reasoning behind inserting one between the battery and  the

starter solenoid.

I had one fail the other day (actually it stuck in the closed position)

after 40 hours of use.  It was an intermittent duty contactor installed

between the #4 welding cable from the positive battery post and the Skytec

starter.

If my engine doesn't start on the third blade, I release the starter button

 to check what I've missed and try it again.  When I released the starter

button, the prop kept turning.  I quickly hit the starter button again

thinking it might have stuck.  The blades kept turning.  I turned off  both

batteries and all fuel source.  The blades had stopped by then (10  seconds) 

but

the starter was still engaged.  Set the brake and ran to the  hangar for

wrenches.  I had to disconnect the battery to stop the  starter.  There was 

no

other way.



Did I design in a fault?  Aren't most custom-built airplanes built  with a

contactor between the hot battery and the starter?  Should I have  some

other type of disconnect between the battery and the contactor?

Stan Sutterfield

RV-8A flying

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 30, 2009 8:50 am Post subject: Contactor Failure

At 07:57 AM 11/30/2009, you wrote:

 	  Quote: 	
		  



After reviewing the endless promotion of the way it has always been 

done, please re-read the AeroElectric-Lists posts of October 12-13:



http://forums.matronics.com/viewtopic.php?p 67757



Then--Do it the way the manufacturer suggests. Hey, there's a radical

idea!



Eric's five point plan for elimination contactor failure:



1) Don't use Type-70 contactors for critical tasks.


	


     The failed contactor wasn't a type-70.



 	  Quote: 	
		  2) Don't use diodes for coil suppression duty. Use bi-directional Zeners.


	


     How is it that you deduce a plain diode suppression

     system as a contributing cause for the failure

     being discussed?  I hypothesized a cause for

     the failure based on 40+ years observation/

     experience with the PM motors in general and PM

     starters in particular. Do you have an alternative

   hypothesis? I'd be pleased to know it.



 	  Quote: 	
		  3) Follow the manufacturers' suggestions.


	


     Which suggestions, if any, were being ignored

     in the instance before us?

 	  Quote: 	
		  

4) Ignore the man behind the curtain.


	


     I'm not behind any curtain. Every word I've ever

     written has been archived and made available for

     critical review by anyone having an interest.



 	  Quote: 	
		  5) Examine carefully the ideas of anybody who claims he can't 

possibly be wrong.


	


     Eric, you've been invited numerous times to offer

     alternative recipes for success supported by analysis

     of simple-ideas and underlying physics. You have yet

     to offer anything beyond parroting bad articles

     with mis-applied data and/or facts taken out of context.



     I claim nothing about the infallibility of simple-

     ideas or recipes for success offered in my writing.

     Nobody would be more pleased than I to know of any

     errors of fact or logic. If you have a point of

     physics and/or proven practice for us to examine,

     please make it.

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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

joemotis(at)gmail.com
Guest

Posted: Mon Nov 30, 2009 8:57 am Post subject: Contactor Failure

Hey OC,

  

 What an accurate and reasoned answer to Stans question. Thank you for sharing it with the list.

  

 Joe Motis

 CH 750 WW Corvair

 do not archive

 On Mon, Nov 30, 2009 at 6:20 AM, <bakerocb(at)cox.net (bakerocb(at)cox.net)> wrote:

 [quote]--> AeroElectric-List message posted by: <bakerocb(at)cox.net (bakerocb(at)cox.net)>

 

11/30/2009



Hello Stan, You wrote:



1)"Any folks had a contactor failure?"



Not on my airplane, but as an A&P I am aware of several contactor failures. Two failure modes that I have personally been involved in are: a) Fine contactor coil wire fractures because of vibration. b) Main current transfer bar inside the contactor gets eaten away and no longer makes contact.

 

Your contactor failure sounds like a third failure mode -- a welded main current transfer bar because of extremely high current transfer. If you still have the contactor why not cut it open to confirm?



2) "My understanding was that contactors are not failure prone."

 

"failure prone" is a very unquantifiable term, but they do definitely fail. That is why you need a plan B to permit recovery regardless of the mode of contactor failure.



3) "Did I design in a fault?"

 

Yes.



4) "Aren't most custom-built airplanes built  with a contactor between the hot battery and the starter?"



No, they are built with two contactors between the hot battery and the starter. A main battery contactor (continuous use type) and a starter contactor (intermittent use type).

 

Many starters now days have a contactor / solenoid as part of the starter itself for the purpose of moving the pinion gear into engagement. (This eliminates the old Bendix type mechanical starter engagement method.)

 

That is why when discussing this subject the term "starter contactor" can lead to some confusion unless the context makes it very clear which one of the two "starter contactors" one is referring to.

 

5) "Should I have  some other type of disconnect between the battery and the contactor?"



Yes.



6) "I  understood that was the reasoning behind inserting one between the battery and  the

 starter solenoid."



Inserting only one contactor in this manner leaves you susceptible to the welded main bar transfer failure. A separate main battery contactor that in turn feeds the starter contactor would leave you a means of stopping current flow to the starter contactor in the case of this type of failure mode.

 

A separate battery fed essential or endurance bus would leave you a means of recovery if you suffer either a fine coil wire failure or an eaten away main transfer bar failure in your battery contactor while flying.

 

If your starter contactor suffers from either a fine wire failure or an eaten away main transfer bar failure then you should discover this problem on the ground because the engine won't crank and your recovery is to just replace the starter contactor.

 

'OC' Says: "The best investment we can make is the effort to gather and understand knowledge."



=========================Time: 05:47:53 PM PST US

From: Speedy11(at)aol.com (Speedy11(at)aol.com)

 Subject: Contactor Failure



Any folks had a contactor failure?

My understanding was that contactors are not failure prone.  I  understood

that was the reasoning behind inserting one between the battery and  the

 starter solenoid.

I had one fail the other day (actually it stuck in the closed position)

after 40 hours of use.  It was an intermittent duty contactor installed

between the #4 welding cable from the positive battery post and the Skytec

 starter.

If my engine doesn't start on the third blade, I release the starter button

to check what I've missed and try it again.  When I released the starter

button, the prop kept turning.  I quickly hit the starter button again

 thinking it might have stuck.  The blades kept turning.  I turned off  both

batteries and all fuel source.  The blades had stopped by then (10  seconds) but

the starter was still engaged.  Set the brake and ran to the  hangar for

 wrenches.  I had to disconnect the battery to stop the  starter.  There was no

other way.



Did I design in a fault?  Aren't most custom-built airplanes built  with a

contactor between the hot battery and the starter?  Should I have  some

 other type of disconnect between the battery and the contactor?

Stan Sut9;s Terrific Free Incentive Gifts provided

 he Builder's Bookstore www.buildersbooks.com

 s.com/contribution" target="_blank">http://www.matronics.com/contribution

                              -Matt Dralle, Li    - The AeroElectric-List Email Forum -

 :

 oElectric-List" target="_blank">http://www.matronics.com/Navigator?AeroEl====================

  http://forums.m===========



[b]

Speedy11(at)aol.com
Guest

Posted: Mon Nov 30, 2009 6:01 pm Post subject: Contactor Failure

I reviewed my wiring diagrams and I did not run my starter current through  the battery master prior to going to the starter contactor and then to the  starter solenoid.  I will make the correction.

 Stan Sutterfield

 Do not archive

  	  Quote: 	
		         Suggest you rewire to eliminate the external, intermittant

       duty starter contactor. Run your starter current through

       the battery master as suggested in the drawings. Buffer

       the inrush current to your starter contactor as suggested

       in Z-22. 	


 

  

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 30, 2009 6:16 pm Post subject: Contactor Failure

At 07:59 PM 11/30/2009, you wrote:

  	  Quote: 	
		   I reviewed my wiring diagrams and I did not run my starter current through the battery master prior to going to the starter contactor and then to the starter solenoid.  I will make the correction. 	


   That change would prevent a repeat of your most

   recent experience. But if the failed intermittent

   duty contactor has been replaced with the same

   part, then you may be setting yourself up for

   an identical albeit less traumatic repeat.



   It may be that your starter contactor is not necessary

   at all. Have you considered using only that contactor

   which is fitted to the starter? How did you wire the

   starter contactor's engagement power terminal?



 

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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



     [quote][b]

Speedy11(at)aol.com
Guest

Posted: Tue Dec 01, 2009 11:06 am Post subject: Contactor Failure

The contactor in question is a B&C S702-1.  I talked to Bill  Bainbridge at B&C and he suggested trying the contactor again.  I will  bench test it (actually already have but will do it again) and rewire according  to B&C diagram with battery switch between battery and starter  contactor.  That way I can remove power to the contactor if needed.   Right now I have installed a continuous duty contactor that I had lying on the  shelf, but it doesn't fit into my space as well as the B&C contactor.

 I did consider using only the starter-fitted contactor, but was trying to  follow Aeroelectric advice so inserted the additional contactor.  It would  take additional wiring effort now to change.

 The B&C S702-1 contactor has an internal diode so the starter switch  was connected to the S terminal with no external diode.  I did not install  a starter engaged light, but plan to add one as I rewire things.

 Rewiring will consist of adding #2 welding cable from the battery to the  battery switch and then to the contactor.  Also I'll wire up a  starter engaged light.

 Stan Sutterfield

  

  	  Quote: 	
		  >I    reviewed my wiring diagrams and I did not run my starter current    

 	  Quote: 	
		  through the battery master prior to going to the starter contactor    

and then to the starter solenoid.  I will make the    correction.


	


   That change would prevent a repeat of your    most

   recent experience. But if the failed    intermittent

   duty contactor has been replaced with the    same

   part, then you may be setting yourself up    for

   an identical albeit less traumatic    repeat.



   It may be that your starter contactor is not    necessary

   at all. Have you considered using only that    contactor

   which is fitted to the starter? How did you wire    the

   starter contactor's engagement power  terminal? 	


 

  

  [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Dec 01, 2009 2:26 pm Post subject: Contactor Failure

At 01:01 PM 12/1/2009, you wrote:

  	  Quote: 	
		   The contactor in question is a B&C S702-1.  I talked to Bill Bainbridge at B&C and he suggested trying the contactor again.  I will bench test it (actually already have but will do it again) and rewire according to B&C diagram with battery switch between battery and starter contactor.  That way I can remove power to the contactor if needed. 	


   That particular design has been applied in the

   gazillions in automotive applications and is well

   proven. There are so many clones of the concept

   I'd be hard pressed to identify the original any

   more.  I don't know where B&C buys their inventory

   now. At one time, they were offering two versions

   of that form factor in intermittent duty contactors.



   One version was qualified onto his first STC'd starter

   installations. The second came with the inventory I sold

   him and included a built in coil collapse suppression

   diode. Yes, it's a lowly diode.  



  	  Quote: 	
		     Right now I have installed a continuous duty contactor that I had lying on the shelf, but it doesn't fit into my space as well as the B&C contactor. 	


   A continuous duty contactor is never a suitable

   substitute for controlling starter motors.



  	  Quote: 	
		   I did consider using only the starter-fitted contactor, but was trying to follow Aeroelectric advice so inserted the additional contactor.  It would take additional wiring effort now to change. 	


   The "AeroElectric advice" has foundations in a lot of

   discussion threads involving starters, styles of motors,

   and system characteristics. If you're running a Skytec

   PM starter and have jumpered the built in contactor's

   control line to the main terminal, then it's almost

   a certainty that your starter suffers from what we've

   calls "starter run on" . . . a delayed disengagement

   of the pinion gear due to counter-EMF generated by

   a motor's armature spinning down in a permanent

   magnet field. Ideas discovered and recipes developed

   from those discussions spawned Figure Z-22.



 

  	  Quote: 	
		   The B&C S702-1 contactor has an internal diode so the starter switch was connected to the S terminal with no external diode.  I did not install a starter engaged light, but plan to add one as I rewire things.

 Rewiring will consist of adding #2 welding cable from the battery to the battery switch and then to the contactor.  Also I'll wire up a starter engaged light. 	




   Please rewire per Z-22. This is important for several

   reasons:



   (1) You have a PM starter motor and the

   change will improve the life of your starter motor,

   pinion gear and ring gear.



   (2) You'll eliminate the potential for sticking

   the contactor again.



   (3) This also reduces the number of metallic joints

   and contact sets in series with the starter. All of

   these are good things.



 

 

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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



     [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Dec 02, 2009 8:44 am Post subject: Contactor Failure

At 08:46 AM 12/2/2009, you wrote:

The continuous duty contactor I have installed is temporary.  I will 

replace it with an intermittent duty one.



I installed the Skytec starter as it arrived from the manufacturer - 

that is, with the jumper from the contactor's control line to the 

main terminal installed.  I left the jumper installed because Skytec 

recommend it - see 

http://www.skytecair.com/images/Certified%20LS%20Wiring_1100.jpg.  My 

error, of course, was that I left out what they call the master solenoid.



   I'm just guessing . . . but this configuration was probably

   crafted to MINIMIZE changes to an existing system in a TC

   aircraft. Adding the jumper to the starter contactor (a

   technique adopted by B&C many years earlier) offers three

   advantages. (1) you get a drop-in replacement of a previously

   installed starter and (2) buffers existing ship's wiring from

   experiencing the extra-ordinary inrush offered by the two-stage

   solenoids as described in my article and (3) the PM motor inrush

   current doesn't hit the system until BOTH the standard starter

   and built-in contactors close. Since the standard contactor

   closes first, there's a potential for improving life of this

   contactor IF it's contacts are closed and stable when the

   second set of contacts on the starter get closed a few milliseconds

   later. The DOWNSIDE is the potential for suffering delayed

   pinion dis-engagement.

This is Van's recommended wiring 

http://www.skytecair.com/images/Van's%20Starter%20Wiring%20Lg.jpg, 

but Skytec recommends against wiring this way.



   This is pretty slick. The diagram suggests using the auxiliary

   "I" (ignition boost) terminal available on most starter

   contactors to close the starter-mounted contactor  . . . again

   with the idea of shifting motor inrush currents to the

   starter's internal contactor. It has the advantage of breaking

   the internal contactor's coil current when the external starter

   contactor opens.  This accomplishes the same goals as Z-22

   but with an external STARTER CONTACTOR as opposed to an external

   BUFFER RELAY.

Bob, are you implying that I should have removed the jumper wire from 

the starter?



   Not implying, recommending . . . based on what we learned

   about (1) delayed disengagement and (2) higher stresses

   on starter control contactor with substitution of PM

   motor technology. If you already have an external contactor

   installed (a la Van's suggestion) then making a simple change

   to remove the jumper and wire the internal contactor control

   terminal to the external contactor "I" terminal would be

   a good move.



   Van's drawing or Z-22 is the elegant solution for new design

   in an OBAM aircraft. Skytec's drawing is the less than elegant

   solution for minimizing changes to a TC aircraft when replacing

   original starter called out on the ship's certification documents.

   The way you had it wired ORIGINALLY wasn't all that hard on

   the external contactor . . . assuming that it's contacts were

   closed and stable before the internal contactor gets closed.

   I've not had an opportunity to measure it but I suspect this

   is the case. THEREFORE, I'm comfortable with suggesting that

   your original sticking failure was probably an isolated case

   and not indicative of a system design error. ADDING the battery

   master contactor in series with cranking currents is the

   firewall against a future repeat causing you to burn a battery

   or starter.



   Adding the wire to conform to Van's suggested configuration

   would be a good move to take care of the potential for delayed

   disengagement.



        Bob . . .

                    ////

                   (o o)

    ===========o00o=(_)=o00o=========

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

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