Rewired: Part 1

Vero Beach
No LL

I accomplished the biggest part of a major project today. I rewired all of Tarwathie's Power wiring according to a new design. Actually, I bought the materials for this project last February in Marathon. The actual project has been sitting on my to-do list ever since. Today, I finally tackled it.

The purpose of the project was twofold. First, I had been running four years with two identical house batteries. They were wired as bank 1 and bank 2, but I had to use them in parallel on the "BOTH" position of the battery switch.

The basic idea of having a 1-2-BOTH battery switch is to allow you to run house loads on one bank while the second bank stands in reserve to start the engine in case the first bank goes dead. That idea works very poorly if you have two identical batteries on banks 1 and 2. That means you have 50% of your capacity in reserve all the time. That shortens the lifetime of the house power battery and it wastes capacity.

My solution was to buy a third battery. The third one is a small car battery, not the deep discharge kind that we use for marine batteries. Therefore, I had to rewire to put the two house batteries on bank 1 and the third starting battery on bank 2.

Second, I also bought a Link 10 battery monitor on EBay last winter. It measures both battery voltage and current, and computes kw and amp-hours. To use, it, I had to wire in a shunt into the battery circuits. All battery current passes through the shunt, so the voltage drop across the shunt is proportional to battery current.

I started by drawing diagrams of the existing wiring. I used Microsoft Visio to do the drawing. Visio is a uniquely well suited program for making such drawings. It is object-oriented so you can create composite objects, copy them, move them around and the like. I carefully labeled every wire on the drawing. I was even able to draw the wires with thick or thin lines to show which were heavy gauge or lighter gauge.


The next step was to identify each wire in the engine compartment and to tape an identifier tag to it that matches the drawing. The tags make good documentation. They also give one time to become completely oriented with which wire goes where. After an hour or so, it doesn't look like a rat's nest of wires any more. It makes sense. I'll also tape a copy of the drawing, protected in a sandwich bag, to the engine compartment wall for future reference.

I also had to locate a place to mount the third battery. Space in the stern of a double ended boat is very tight. I finally gave up on mounting it in the engine compartment. I put it on the floor of my lazarette compartment instead.

Next, I made a second drawing for the new wiring scheme including the third battery and the shunt. I took time to think about which of the old wires I could re-use considering the wire length and the kinds of terminators on the ends. It worked out that I could re-use all the old wires. Only once did I have to cut off the old terminal and put on a new one of a different type. I also had to make up several new wires with new terminals.

This morning, I set out to actually do it. The re-wire job took only 4 hours. I expected it to take longer. Because of the planning and preparation, it went fairly smoothly. I committed no wiring errors that I know of. My only screw ups were that I dropped washers into the engine pan multiple times, and as I hooked up things again at the end, I twice let a hot wire end carelessly brush against the engine giving a zap sound and some sparks.

I think I did a fairly professional job. The only thing not kosher was that I did not have tinned ends on the new wires. In marine power wiring, it is customary to "tin" the ends. That means coating the strands in solder. The solder makes good connections, it is deformable and it protects the copper from corrosion.

I thought I could do it myself. I wrapped turns of solder around the ends after I stripped the ends. Then I heated it on the stove. It didn't work. The solder dripped off and refused to coat the wire strands for my. I'm not sure what to do now. I don't have a cup full of molten tin on board to dip wires in. Does anyone know how to properly tin the ends of a multi-strand wire cable?

Tomorrow, I do part 2 of the project. I'll write about it.