Battery, Start and X-Tie Contactors

Since my electrical system will be redundant, with 2 batteries and a Main and Essential Bus, i will need 2 additional contactors than the plans call for. 

Here is the wiring of the contactors:

The blue lines represent the copper bars.

Since the doubler is already installed for the plans battery contactor and starter contactor, i will keep this in place and use it for the R Battery and Starter Contactors. I will need to make up 2 more doublers for the L Battery and the X-Tie Contactor. 

To work out where these doublers needed to go, i had to make up and bolt the contactors together with the copper bars, so i knew their relative locations for the doublers. The firewall forward kit came with a copper bar meant to go between the battery contactor and the starter contactor - my contactors must be slightly different, as this did not fit. 

Van's supplied copper bar.

The copper bars were made using 1/2" copper, 2mm thick bought from the eBay aviation section.

The bar needed slight bending to make it fit.

This is how far out the Van's bar was.

I found i had made the joining bars to the X-Tie contactor too short and i was unable to fit a spanner on the nut. This will not do! These were remade to be a bit longer. 

The new longer bar on the left.

Now the spanner fits.

These bases will hold the 100amp MIDI fuses for the Alternator B lead feed, as well as the main bus feed. 

Once the final relative location for the contactors was known, i could bolt them to the firewall and work our what doublers i would need for the additonal 2 contactors. I also decided to paint the existing installed doubler black, to match the rest of the parts FWF. 

I had to remove the starter contactor, as it interfered with the rotisserie. You can see the additional doublers in location under the contactors.

Contactor Wiring

Each of the contactors needs a diode, to handle the large voltage spike that occurs when the contactor opens. This will help to prolong the contact life and prevent contact arcing and damage. Any diode would do, but i chose 1N5408 diodes, as they have 1.2mm thick leads, which are hopefully sturdy enough to survive.

Each contactor needs 2 things:

1. A wire from the power source to the coil terminal, so that you can ground the other coil terminal to make the contactor work. 
2. A diode from the coil terminal which is grounded, back to the power source, to dump the voltage spike back to where the power came from. I do this by wiring the diode to the coil terminal supplied by the power wire. 

In addition, the X-Tie contactor needed a couple of diodes so that it would function with power available from either side. 

The coil supply wires - these go from the power terminal of the contactor, to one of the coil posts to give power to the coil. Grounding it at the other post will close the contactor. I used 20awg wire (22 awg is too small for FWF).

Due to the thick (1.2mm) leads, the diodes can be crimed straight to a #10 terminal. The whole thing is covered in heat shrink - i used clear so i could identidy the diode direction.

Power from the battery comes in on the big post to the left. Power is jumpered the the left hand coil terminal. The right hand one is grounded to close the contactor. The voltage spike when the contacts are open, is dumped back to the power source via the diode (not the diode direction above). 

The cross tie first gets a doide to source power from the right battery post side, to one of the coil posts.

Then a diode to take power from the left battery post side, to the same coil post.

Then a third diode from the coil grounding post, to dump the voltage spike back to whence it came.

The almost completed wiring. The starter contactor will also need a diode (see below). 

Since the starter contactor is provided with 12V to the S post, and gets its ground through the case, the diode needs to go from the ground to the power source at the S post (backwards to the other contactors). The diode didn't reach, so i crimed on a length of wire.

The Engine Bus contactors were given the same treatment (more later)

Finally everything was labelled:

Finally, the dolublers were installed using large AN4 nutplates and CCC-32 Pull-Rivets, and painted black. I also covered each of the copper bars in heatshrink, and each terminal was given a star washer

A nutplate was used as a drill jig. 

 

Then bolted to the firewall, and the holes match drilled.

Some creative deburring was in order.