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Relay vs Continuous Duty Contactor

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tx_jayhawk

Joined: 10 Jun 2006
Posts: 9

Posted: Thu Apr 09, 2009 9:19 pm Post subject: Relay vs Continuous Duty Contactor

All,



In comparing the continuous contactor (S701-1) to the relay (S704-1), I assume that the reason people choose the relay is due to the lower coil current draw?  Drawback is obviously that it is limited to 20 amp.  Should the 20 amp limitation be based on the max continuous or max intermittent current draw of items connected to the relay?  Also, in looking at some other 12V coil units, they listed the max continuous voltage at 13.2 volts.  I assume that is not a concern with the S704-1?



Any local sources for equivalent relays / contactors? 



THanks,

Scott

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Apr 10, 2009 6:35 am Post subject: Relay vs Continuous Duty Contactor

At 12:19 AM 4/10/2009, you wrote:

 	  Quote: 	
		  



All,



In comparing the continuous contactor (S701-1) to the relay 

(S704-1), I assume that the reason people choose the relay is due to 

the lower coil current draw?  Drawback is obviously that it is 

limited to 20 amp.  Should the 20 amp limitation be based on the max 

continuous or max intermittent current draw of items connected to 

the relay?  Also, in looking at some other 12V coil units, they 

listed the max continuous voltage at 13.2 volts.  I assume that is 

not a concern with the S704-1?


	


   You don't say how you intend to use the relay

   or contactor you're searching for.



   Your 'comparison' of the two devices cited reveals

   that they are entirely different breeds of cat. One

   can buy relays/contactors rated at milliamps to tens of

   thousands of amps. Further, they'll be offered in

   a constellation of coil or control voltages and

   currents. Finally, they may be tailored to specific

   tasks that present unusual problems for meeting

   design goals.



   Ratings for contactors, switches and relays are

   driven mostly by SWITCHING loads. This is a dynamic

   thing that can be all over the map depending on

   voltage level, AC vs. DC, and how the load's

   characteristics affect what's going on during

   contact closure and opening events.



   But comparing published ratings of the various

   devices is fraught with intellectual potholes.

   One manufacturer's ratings may cite some level

   of pass-fail, post-test performance after

   10,000 cycles while others shoot for the moon

    . . . say 500,000 cycles.



   In your OBAM aircraft, you are unlikely to put

   1,000 pilot-operated cycles on any power relay or

   contactor over the time you own the airplane.

   If you're designing with failure tolerance in

   mind, then $time$ expended pouring over spec

   sheets with some notion of improving on the

   service life of the device is probably not

   going yield a positive return on your expenditure.



   So now that we've expanded the universe of

   parts from which you might select a suitable

   device, what is the application for which you're

   seeking a relay or contactor?

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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tx_jayhawk

Joined: 10 Jun 2006
Posts: 9

Posted: Fri Apr 10, 2009 7:04 am Post subject: Re: Relay vs Continuous Duty Contactor

It is for various reasons...possibly an essential bus alternate feed (14 amp continuous, 23 max intermittent) or for a separate dedicated avionics bus that powers redundant avionics equipment with similar bus loads (no worries..."essential" avionics are not switched).  I know my essential load and architecture may differ from other people's objective, but I'm good with it.



Question is this...for that type of rating (14 amp continuous, 24 max intermittent) for something that is going to be switched on and left on the the flight, what is the preferred contactor/relay?

1) S701 (don't like the hefty current draw).

2) S704

3) A similar automotive relay.  Any reason why something like the below wouldn't work just fine?



http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=171460&



Oreilly's has these for $5.



Thanks,

Scott

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Apr 10, 2009 7:14 am Post subject: Relay vs Continuous Duty Contactor

At 10:04 AM 4/10/2009, you wrote:

 	  Quote: 	
		  



It is for various reasons...possibly an essential bus alternate feed 

(14 amp continuous, 23 max intermittent) or for a separate dedicated 

avionics bus that powers redundant avionics equipment with similar 

bus loads (no worries..."essential" avionics are not switched).  I 

know my essential load and architecture may differ from other 

people's objective, but I'm good with it.


	


   The S704-1 would work fine

 	  Quote: 	
		  Question is this...for that type of rating (14 amp continuous, 24 

max intermittent) for something that is going to be switched on and 

left on the the flight, what is the preferred contactor/relay?

1) S701 (don't like the hefty current draw).

2) S704

3) A similar automotive relay.  Any reason why something like the 

below wouldn't work just fine?



http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=171460&


	


    The S701-1 contactor is not suite to the tasks

    you've cited. Relays of the class that includes

    the S704-1 are sold by a host of sources including

    those you've noted. Given the once-per-flight-cycle

    operating duty, you're not going to loose one of

    these relays to contact damage induced by 'overload'.

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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