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Continuous duty contactor wiring question

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rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Sat Mar 04, 2006 4:38 am Post subject: Continuous duty contactor wiring question

Hi,



I've got a S701-1 contactor I purchased from B&C

http://www.bandc.biz/S701-1.html which I want to

use in a slightly different application.



I want to use it as suggested by Eric with his

OVP module. http://www.periheliondesign.com/LOVM.htm



The wiring for his OVP module requires that I

use the 12v line as the contactor control, not

the ground wire used in the battery contactor

application.



I've read the battery contactor information in

chapter 8 several times, but I still really

don't quite understand the role of the spike

suppression diode, nor whether or not I will

need one.



Should I use the spike suppression diode?

Should it be installed between the two

coil terminals?  If so, does it matter

which terminal is (+) and which is (-)?



Thanks for any tips!

Mickey



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

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paul.mcallister

Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA

Posted: Sat Mar 04, 2006 6:13 am Post subject: Continuous duty contactor wiring question

Mickey,



It is advisable to put spike suppression across the coil of any relay.  It

can be accomplished with a diode connected in the reverse polarity to the

voltage source being used to energize it, or a transorb device with a rating

greater than the voltage being used to energize the coil.



The spike suppression is required to dissipate the voltage generated as a

result of the magnetic field collapsing when the relay is de energized.



I am curious as to the application and wondering if a relay of this size

might be overkill.... it really depends on what your application.



Paul

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rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Sat Mar 04, 2006 7:45 am Post subject: Continuous duty contactor wiring question

 	  Quote: 	
		   It is advisable to put spike suppression across the coil of any relay.  It

 can be accomplished with a diode connected in the reverse polarity to the

 voltage source being used to energize it, or a transorb device with a rating

 greater than the voltage being used to energize the coil.


	


Paul,  Thanks for your help.



I've got the diode that was delivered with the contactor, so

I guess that would work.  I'm still not clear on which direction

to install the diode.  It seems like with the two coil terminals

it doesn't matter which side is positive or negative.  Should

the diode restrict flow from (+) to (-) or the other way around?



 	  Quote: 	
		   The spike suppression is required to dissipate the voltage generated as a

 result of the magnetic field collapsing when the relay is de energized.


	


I'll trust you on that one, but I don't understand.  No biggie.



 	  Quote: 	
		   I am curious as to the application and wondering if a relay of this size

 might be overkill.... it really depends on what your application.


	


It is overkill for just a b-lead switch, but to simplify

my wiring, the starter energy also flows through it.



Thanks again,

Mickey



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

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klehman(at)albedo.net
Guest

Posted: Sat Mar 04, 2006 8:13 am Post subject: Continuous duty contactor wiring question

Mickey

A  diode flows electrons (current) in one direction only exactly like a 

one way check valve. That is why the schematic diagram of a diode even 

looks like a one way arrow. The pointed end of the arrow is the end of 

the diode that is usually marked with a white bar and that end must go 

to the positive terminal of the coil. Otherwise the positive battery 

current will flow through it to ground which will destroy the diode 

and/or blow the fuse. Anytime you have a coil of wire just assume that 

the current wants to keep flowing after you turn off the power. So the 

diode lets the current keep flowing from the negative side of the coil 

back into the positive side of the coil instead of out through other 

circuitry where you might not want it to go. As mentioned the decaying 

magnetic field can initiate a significant voltage spike so the diode 

prevents that and lets the current goes round and round and lowly 

dissipate as heat.

(We could debate which way electrons really flow but most of us still 

think of electricity as flowing out of the positive battery terminal for 

the above explanation.)

Ken

Mickey Coggins wrote:

 	  Quote: 	

>It is advisable to put spike suppression across the coil of any relay.  It

>can be accomplished with a diode connected in the reverse polarity to the

>voltage source being used to energize it, or a transorb device with a rating

>greater than the voltage being used to energize the coil.

>    

>

Paul,  Thanks for your help.

I've got the diode that was delivered with the contactor, so

I guess that would work.  I'm still not clear on which direction

to install the diode.  It seems like with the two coil terminals

it doesn't matter which side is positive or negative.  Should

the diode restrict flow from (+) to (-) or the other way around?

>The spike suppression is required to dissipate the voltage generated as a

>result of the magnetic field collapsing when the relay is de energized.

>    

>

I'll trust you on that one, but I don't understand.  No biggie.

>I am curious as to the application and wondering if a relay of this size

>might be overkill.... it really depends on what your application.

>    

>

It is overkill for just a b-lead switch, but to simplify

my wiring, the starter energy also flows through it.

Thanks again,

Mickey

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rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Wed Mar 08, 2006 9:29 am Post subject: Continuous duty contactor wiring question

 	  Quote: 	
		       Remember folks, questions like this are ALWAYS

     best addressed to the designer/manufacturer

     of the product. ...


	


You are right.  I was thinking of the product as

the contactor, and Eric's product as a switch.

In any case, Eric has a nifty product to protect

the coils from doing whatever bad thing it is

that they do.  He calls them "snapjacks", and

they do the trick.



  http://www.periheliondesign.com/suppressors.htm



Just an aside - I *really* like doing business

with Eric.  He makes it easy to buy his stuff

(paypal, logical website) and gives me no hassle

about shipping international via USPS.  Stuff

usually arrives three to five days after ordering.

Not to mention that he has some cool products!



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

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