Monday, February 1, 2016

Getting Well Grounded

While the vinyl tubing was still on the workbench, decided now would be a good time to make measurements for the ground cables. Frequent readers of the blog may recall the grounding location on the DOG Aviation RV-12 is being moved from the powder coated battery box assembly to a ground stud/grounding block that was installed on the firewall. Because the grounding point will be on the firewall, both the #8 gauge ground cables P-149 (battery ground) & P-151 (starter ground) need to be made longer. Prior to making measurements, decided the time was right to install the Odyssey PC 680 battery so an exact measurement and safe routing for the battery ground cable could be established.  Because the battery cable passed in the vicinity of the overflow tank for the cooling system it too was installed to verify clearances. The overflow tank is affixed onto the firewall using a strap and two screws. Prior to installing the overflow tank, silicone is to be placed on the back of the tank onto a couple of ridges molded on the tank … the silicone will prevent the tank chafing on the firewall.

The battery sits directly on top of two of the F1257 rudder pedal support channels so prior to dropping the battery into the slot, 4 pieces of grommet material need to be placed on the edges of the support channels to prevent the battery from chafing on the metal edges. Sadly, I forgot to take a photo of the installed grommet pieces.  Once the protective grommet pieces were in place, the battery was slipped into position and is secured by a channel and two spacers bolted to the frame of the battery box.
Tightening one of the two bolts that secures the battery channel across the top of the battery preventing it from moving.

With the battery and overflow tank installed, a piece of vinyl tubing was used to determine a good routing path for the battery’s ground cable to the new ground stud on the firewall. Once happy with the routing, measurements were made for both the starter’s ground cable and battery ground.
A piece of vinyl tubing was used to determine the best path and length of cable needed to connect the battery ground terminal to the ground stud/block on the firewall. The hole where the ground wire would normally attach is under my finger … this hole is where a tie wrap will be used to pull down on the ground wire to insure it passes well under the wire on the positive post of the battery, as it does in this photo.

My understanding is Stein Air is the original manufacturer of the battery cables for the RV-12 … since I was already planning on purchasing fittings for the backup instruments from Stein Air, a call was made and in addition to ordering the instrument fittings, decided to let Stein fabricate the two ground cables as well and save the cost of a crimping tool I likely would never use again. For those interested, the new length of the P-149 battery ground cable will be 17" and the P-151 starter ground cable will be 11 1/4", as measured from center to center between the mounting holes in the lugs.