Contactor Locations?

szicree · #1 09-30-2007, 12:24 AM

I've mounted my battery in the standard location between the feet and am now wondering what the heck the standard approach to placing the relays would be? I figure I could put em both on either side of the firewall and am seeing pros and cons with every arrangement. I'm hoping that there is some tried and true spot for them that a past -4 builder can share with me. Thanks.

Gsuit · #2 09-30-2007, 10:19 AM

I put mine here. I used Bob Knuckolls Z-13 diagram which calls for 3 contactors.

This pic doesn't show them all wired up, but wiring to here from the starter, battery, and alternator was easy and easy to get to. Plus it keeps them out of the way of touching anything else around and causing more problems than you'd probably like. Plus, when I was wrestling with this same question I looked a several RV6/7's and most had this configuration, if the battery was on the firewall. For 6's with the battery in the back, it varies somewhat.

Kevin Horton · #3 09-30-2007, 05:22 PM

You want the master contactor as close to the battery as possible, as the cable between the battery and contactor is always hot. You want that piece of cable as short as possible, to reduce the risk of a major short.

The ideal location for the starter contactor will depend on your electrical system architecture.

szicree · #4 09-30-2007, 06:36 PM

Kevin,

Thanks for the input. I think I came to the same conclusion earlier today after reading old posts, so now I'm gonna mount the main contactor right next to the battery. Of course now I've gotta figure out where to put the starter contactor. If I put it FWF, then I'll have a big always-hot wire running through the firewall, which I'm not to thrilled with. If I put it right next to the main contactor, I'll only have the sometimes-hot starter wire running through the firewall. The second option seems safer; however, I think this option would also require the B-lead from the alternator to pass through the firewall. Too many choices with these darn airplanes

. Right about now I expect to hear from the battery on the firewall crowd, which is a fine way to go, but I'm not going that route. Any advice is definitely welcomed.

Kevin Horton · #5 09-30-2007, 07:02 PM

Quote:

Originally Posted by szicree

Of course now I've gotta figure out where to put the starter contactor. If I put it FWF, then I'll have a big always-hot wire running through the firewall, which I'm not to thrilled with. If I put it right next to the main contactor, I'll only have the sometimes-hot starter wire running through the firewall. The second option seems safer; however, I think this option would also require the B-lead from the alternator to pass through the firewall.

You are correct that no matter which starter contactor location you plan, you'll have a hot line going through the firewall. But, if that cable every shorts out and creates smoke, you can open the battery contactor to stop feeding that end of it. The other end will be fed by the alternator, but your Smoke in the Cockpit Emergency Procedure should call for the alternator to be shut down, as well as opening the master contactor. I've got both those wired from one three position switch - down is both OFF, the middle position is battery master ON, alternator OFF, and the up position is battery master ON and alternator ON.

I like the plan where the starter contactor is ahead of the firewall, and the cable from the starter contactor to the battery contactor also carries the alternator current. This is a bit lighter and simpler than putting the starter contactor aft of the firewall next to the battery.

szicree · #6 09-30-2007, 07:18 PM

Quote:

Originally Posted by Kevin Horton

I've got both those wired from one three position switch - down is both OFF, the middle position is battery master ON, alternator OFF, and the up position is battery master ON and alternator ON.

I like the plan where the starter contactor is ahead of the firewall, and the cable from the starter contactor to the battery contactor also carries the alternator current. This is a bit lighter and simpler than putting the starter contactor aft of the firewall next to the battery.

Man, it's been so long since I drew up my wiring diagram I can barely remember it at all. Turns out my switch arrangement is exactly as you describe. I think I agree that putting the start relay up front is simple and will fit. Now I just have to decide exactly where to mount them, my LSE, my ground block, my fuel/oil pressure transducer manifold, etc. This thing really needs an extra firewall