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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: 301

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

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: 1311
Location: Riley TWP Michigan

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

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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