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Mounting BATT/START Relays

RVG8tor

RVG8tor

Well Known Member
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.
 
Why are you mounting the battery on the back side? Mounting it as per plans works great and everything is accessible. Relays do go bad. My master relay went bad at 120 hrs and ruined the battery. Don
 
Hmm

I will use the 1n5400 on the battery an starter relay that is recommended in most of the 'Z' diagrams. I am not sure what type that is.
 
RVG8tor said:
I will use the 1n5400 on the battery an starter relay that is recommended in most of the 'Z' diagrams. I am not sure what type that is.
Click to expand...


No on the zener. Just use a standard 3 Amp 50 (1N5400) or 100 (1N5401) Volt (whichever you can find cheaper). You can pay Vans $8 for a fancy sleeved one or you can just buy a plain one for $0.12.
 
RVG8tor said:
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.
Click to expand...

Your idea should work fine, just use all-metal lock nuts. Like the MS21042-L4

http://www.aircraftspruce.com/catalog/hapages/MS21042.php
 
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