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S704-1 on Hot Side of Firewall?

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Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Tue Apr 20, 2010 2:36 pm Post subject: S704-1 on Hot Side of Firewall?

I requested the spec sheet for the S704-1 relay from B&C, and it is a Tyco T9A with an operating temp limit of 85C (185F).  This seems a bit low for mounting in the engine compartment on the firewall. where I had been planning to mount it.  I called B&C to ask them if they recommended mounting these in the engine compartment and the gentleman I spoke with was not sure - he recommended a post here.



Anybody know what the firewall temps can climb to??  Anybody mounted one of these firewall forward in an RV and had problems?  Or had it last 2000 hours without issue??

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_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 20, 2010 7:30 pm Post subject: S704-1 on Hot Side of Firewall?

At 05:36 PM 4/20/2010, you wrote:

 	  Quote: 	
		  



I requested the spec sheet for the S704-1 relay from B&C, and it is 

a Tyco T9A with an operating temp limit of 85C (185F).  This seems a 

bit low for mounting in the engine compartment on the firewall. 

where I had been planning to mount it.  I called B&C to ask them if 

they recommended mounting these in the engine compartment and the 

gentleman I spoke with was not sure - he recommended a post here.



Anybody know what the firewall temps can climb to??  Anybody mounted 

one of these firewall forward in an RV and had problems?  Or had it 

last 2000 hours without issue??


	


   It will be fine. These devices and their close

   cousins are used under the hood of motor vehicles

   and they're fine.



   The various companies I've worked for have done

   numerous studies of temperature under the cowl

   and found that nothing gets really all that hot

   as long as it's not exposed to direct infra-red

   radiation from stacks (particularly turbochargers).

   I've seen some RG battery cases melted because they

   were too close to exhaust pipes.



   Bob . . .

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Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Wed Apr 21, 2010 7:03 pm Post subject: Re: S704-1 on Hot Side of Firewall?

Thanks Bob.  Prior to your response, I moved the battery bus and E-bus relay south of the firewall on my schematic.  I think I like that better anyway.  Roughly the same number of wires transiting the firewall feed-thru.  Does require a fusible link on the battery bus feed however.

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_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 22, 2010 6:22 am Post subject: S704-1 on Hot Side of Firewall?

At 10:03 PM 4/21/2010, you wrote:

 	  Quote: 	
		  



Thanks Bob.  Prior to your response, I moved the battery bus and 

E-bus relay south of the firewall on my schematic.  I think I like 

that better anyway.  Roughly the same number of wires transiting the 

firewall feed-thru.  Does require a fusible link on the battery bus 

feed however.


	


   . . . on the battery bus feed? Fusible links are

   ROBUST protection on the order of ANL type current

   limiters and should not be used in an always-hot feed

   from a battery. Everything coming off the battery

   should be a 7A or less fuse except where you need

   a robust alternate path for the e-bus. In that case,

   the battery bus fuse size goes up accordingly but the

   e-bus relay becomes a "mini battery contactor" for

   the e-bus . . . and should be as close as practical

   to the battery bus.



   Bob . . .

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