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Mounting BATT/START Relays

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Fri Sep 25, 2009 6:11 am Post subject: Mounting BATT/START Relays

My battery will be just aft of the firewall so the battery relay will be mounted on the aft side of the firewall, the start relay will be just opposite on the forward side of the firewall.  I see some who install plate nuts to mount these relays individually, 4 nuts + 4 bolts+4 holes in the firewall.  The holes on the two relays work out so that one could just use 2 bolts and two normal nuts (not anchor nuts) and mount the two relays through common holes in the firewall. The only drawback I can see is that if one or the other needs to be replaced then both you can't remove one without disturbing the other, this does not seem like a big deal to me as they are fairly long lasting devices.  Can anyone see why my idea is a bad one?  I though of heat transfer from the hot side of the firewall, but bolts into nut plates would do that to some degree, and all of the relays could be mounted forward of the firewall like many factory airplanes have them.

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Sep 25, 2009 9:55 am Post subject: Mounting BATT/START Relays

 	  Quote: 	
		  The holes on the two relays work out so that one could just use 2 

bolts and two normal nuts (not anchor nuts) and mount the two relays 

through common holes in the firewall.

  The only drawback I can see is that if one or the other needs to 

 be replaced then both you can't remove one without disturbing the 

 other, this does not seem like a big deal to me as they are fairly 

 long lasting devices.  Can anyone see why my idea is a bad one?


	


   The TC aircraft guys do things like this all the time . . .

 	  Quote: 	
		     I though of heat transfer from the hot side of the firewall, but 

 bolts into nut plates would do that to some degree, and all of the 

 relays could be mounted forward of the firewall like many factory 

 airplanes have them.


	


   ??? not sure of the rationale here. The

   battery relay should be as close to the battery

   as practical and certainly positioned so that

   the battery(+) lead doesn't penetrate the firewall

   before reaching the relay's fat terminal.

        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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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sat Sep 26, 2009 11:16 am Post subject: Mounting BATT/START Relays

9/26/2009



Hello Mike, You wrote: "........ this does not seem like a big deal to me as 

they are fairly long lasting devices."**



I began my real plane aviation career as a US Navy airplane mechanic some 59 

years ago. Since then I have spent thousands of hours working on airplanes, 

acquired an A&P rating, a Master's Degree in Aeronautical Engineering, built 

my own airplane, and flown several thousand hours.



I had plenty of opportunity during that time to confront many 

maintainability issues. These issues come in many different forms, but one 

of the most important ones is accessibility -- if you can't access a part 

you can't fix it, adjust it, or replace it.



It is very easy in the early stages of building a homebuilt to significantly 

underestimate the effort that will be required to access a part when the 

airplane is completed.



I want you to envision your airplane completed and someone someday 

attempting to remove and replace one of the contactors which is held in 

place by through bolts also holding the other contactor in place on the 

other side of the firewall. It will require a wrench simultaneously on both 

the bolt head and the bolt nut. This means that two people will be required. 

One of those persons must dive down under the instrument panel -- not always 

an easy task (take it from an old man). What frequently happens when 

building the airplane is that one is able to use both hands on the part 

being worked on. When diving down under the instrument panel sometimes only 

one hand can reach the part. Realize also that some fairly heavy guage wires 

must be disconnected.



Then on reinstall both contactors must be in alignment for the holding bolts 

to go through and wires must be reconnected.



Mounting the contactors with anchor nuts can turn this into a one man job 

and reduce the time and effort significantly.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



**PS: I am aware locally of three that have failed just in the last few 

years.



==============================================

Time: 07:13:11 AM PST US

Subject: Mounting BATT/START Relays

From: "rvg8tor" <rvg8tor(at)comcast.net>

My battery will be just aft of the firewall so the battery relay will be 

mounted

on the aft side of the firewall, the start relay will be just opposite on 

the

forward side of the firewall.  I see some who install plate nuts to mount 

these

relays individually, 4 nuts + 4 bolts+4 holes in the firewall.  The holes

on the two relays work out so that one could just use 2 bolts and two normal 

nuts

(not anchor nuts) and mount the two relays through common holes in the 

firewall.

The only drawback I can see is that if one or the other needs to be replaced

then both you can't remove one without disturbing the other, this does not

seem like a big deal to me as they are fairly long lasting devices.  Can 

anyone

see why my idea is a bad one?  I though of heat transfer from the hot side

of the firewall, but bolts into nut plates would do that to some degree, and

all of the relays could be mounted forward of the firewall like many factory

airplanes have them.



--------

Mike &quot;Nemo&quot; Elliott

RV-8A QB (Fuselage)

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Sat Sep 26, 2009 2:19 pm Post subject: Re: Mounting BATT/START Relays

BAKEROCB,



All very good points.  I do try to look at future maintenance when I am building my airplane.  One of the reasons I am putting my battery just aft of the firewall is I will have easy access to it via the front baggage area for charging or jumping if it goes dead, it is also a more hospitable environment for the battery.  



I can get to both sides of the bolts holding the relays because the front baggage door gives access.  The only limiting factor I have now made for myself is if the battery relay is the only thing I needed to replace then I would not have to remove the cowl if I had used nut plates.  My thought at this point is I can always go that route in the future, for now I like the fact that I have two less holes in the firewall.  See my log for pictures of the completed installation, done yesterday.



http://www.mykitlog.com/users/display_log.php?user=rvg8tor&project=403&category=0&log=88927&row=1

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

blackoaks(at)gmail.com
Guest

Posted: Tue Sep 29, 2009 8:24 am Post subject: Mounting BATT/START Relays

Mike,  How about using a piece of 'all thread rod' through the firewall with a nut on each side of the firewall to secure it, then mount the contactors  with another nut.  Now either contactor can be removed from one side without disturbing the other. 



My .02



On Sat, Sep 26, 2009 at 12:02 PM,  <bakerocb(at)cox.net (bakerocb(at)cox.net)> wrote:

 	  Quote: 	
		   --> AeroElectric-List message posted by: <bakerocb(at)cox.net (bakerocb(at)cox.net)>

 

 9/26/2009

 

 Hello Mike, You wrote: "........ this does not seem like a big deal to me as they are fairly long lasting devices."**

 

	


John McMahon

Lancair Super ES, S/N 170, N9637M (Reserved)

 

  [quote][b]

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