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Z19 first try and smoke/wire melted I did a mistake

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kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Sun Jun 17, 2018 11:35 am Post subject: Z19 first try and smoke/wire melted I did a mistake

If the OP had installed a "snapjack" rather than a diode on his battery contactor, would the contactor have closed, and delivered the reverse polarity current to the rest of the system? If so, then perhaps this is an argument in favor of diodes vs snapjacks.



Ken Ryan

On Sun, Jun 17, 2018 at 7:35 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 08:56 PM 6/16/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Achille" <mickael.t(at)live.fr (mickael.t(at)live.fr)>



 Thank you bob for you reply. I hope to find just the diode end the wire U/S. Many thanks.



 I have to check just the integrity of contactor ground wire (master switch to the ground bus) easily accessible or I could have other wire damaged ? 	


   If the burned wire is in a bundle, there is a

   probability for damage to adjacent wires that

   should be investigated.



  	  Quote: 	
		  Because all my wires are set in harness with sleeve. 	


    . . . oh . . . fooey. Not an enviable task.

    You might open just a portion of the sleeved

    bundle for inspection. Find the contactor control

    wire as assess damage to it's insulation and

    propagation of damage to other wires.



 

  	  Quote: 	
		  About the possible damage, with luck just this wire and diode. But without 

 Alternator diode couldn't be damage at least ? 	


    No, it's unlikely that the rest of the

    system suffered any damage. To connect the

    battery to the system, you have to close the

    battery contactor. When battery power is

    backwards, the diode across the contactor

    coil is essentially a dead short across the

    coil. If the diode is small (like a plastic

    1N4000 series) it may simply explode and

    remove itself from the equation. Not good.

    Then the contactor coil closes and reversed

    power is applied to the. This still isn't

    an automatic condition for total distaster.

    The alternator  diode array will now become

    reverse biased. The array is 6 to 9 diodes

    in series pairs that will (1) prevent the

    bus voltage from rising to more than a couple

    volts . . . for a short period of time. The

    b-lead protection device will operate and

    disconnect the alternator from the bus.



    After this time, all bets are off. But bus

    voltage does waayyyy negative to what ever

    the battery supplies.



    If your contactor diode is mechanically

    intact AND the control wire is burned, this

    tells us that the contactor never closed.

    You'll also find that your b-lead protection

    is closed.



  	  Quote: 	
		  and my ignitions and transpondeur ? (I checked on the user manuel they told that inversion of polarity damage it) But in the case of switch was in OFF on the transpondeur (for exemple) it can damage it ? (I ask the question because I was doing a quote of my error to be prepared in the event of I have to change part.. and total price become quickly crazy) 	


    I think your misery for having suffered this

    event will be limited to inspection and repair

    of the burned wire and replacement of the

    contactor coil suppression diode.



 

 

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sun Jun 17, 2018 12:52 pm Post subject: Re: Z19 first try and smoke/wire melted I did a mistake

It does not matter what kind of arc suppression device is in parallel with the contactor coil.  That coil is going to energize when the switch is turned on (unless the master switch wire burns open).  A diode in series with the contactor coil would prevent it from being energized by a reverse polarity battery.  If a builder were concerned about reverse polarity, two diodes could be used, one in parallel with the coil and one in series.  But what about protection against line boys with 24 volt jumper cables?

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