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Another start contactor/switch question

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RVdan

Joined: 20 Sep 2012
Posts: 3

Posted: Thu Sep 20, 2012 9:02 am Post subject: Another start contactor/switch question

I searched the archives and didn't find an answer to this.



This is in regards to start contactor control.   



I notice that many of the start contactor coil circuits show the coil locally or internally grounded.  Power comes from the bus, through a start CB, to the start switch, to the coil.  Similar to this (although the CB is missing)



http://www.skytecair.com/images/P1/Certified%20LS%20Wiring_1100.jpg



Another approach which seems simpler, it to supply power to the coil from the main contactor terminal (battery side) and provide the ground through the start switch.  This is the same approach typically used for the master contactor (also shown) and eliminates a CB. 



Is the first approach really preferred (yes/no), and if so why?  



Thanks,

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Dan Morris

KISS
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nuckolls.bob(at)aeroelect
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Posted: Thu Sep 20, 2012 11:13 am Post subject: Another start contactor/switch question

At 12:02 PM 9/20/2012, you wrote:




I searched the archives and didn't find an answer to this.



This is in regards to start contactor control.



I notice that many of the start contactor coil circuits show the coil 

locally or internally grounded.  Power comes from the bus, through a 

start CB, to the start switch, to the coil.  Similar to this 

(although the CB is missing)



http://www.skytecair.com/images/P1/Certified%20LS%20Wiring_1100.jpg

Another approach which seems simpler, it to supply power to the coil 

from the main contactor terminal (battery side) and provide the 

ground through the start switch.  This is the same approach typically 

used for the master contactor (also shown) and eliminates a CB.



Is the first approach really preferred (yes/no), and if so why?



    It needs to match your style of contactor. The popular automotive

    contactors are internally grounded and legacy off-l-r-both-start

    key-switches are set up to support this philosophy along with

    the possibility for adding a shower-of-sparks system to a magneto.



    Pull up to energize is also consistent with design philosophy of

    the starters having built in contactors.



    Doing a pull-down control philosophy increases risk of an uncontrolled,

    starter engagement due to wire rubbing to ground.

   Bob . . .

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RVdan

Joined: 20 Sep 2012
Posts: 3

Posted: Thu Sep 20, 2012 11:41 am Post subject: Re: Another start contactor/switch question

Thanks Bob, good succinct answers.  Pretty much what I was thinking.  I am using an external contactor and push button sw, so the design lends itself to go either way.  



Do you think the ground fault risk is high enough to warrant adding a CB assuming good wiring practices?

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