I have just completed the AC shore power system for FatDash. The new design incorporates a isolation transformer. The reason for the transformer is to isolate FatDash from the shore power. This results in extended life of the zincs and absolutely no chance of reverse polarity of the shore power.  As long as I keep the power cable out of the water there is also no way stray currents can enter the water from FatDash endangering swimmers in the water.

The down side of the isolation transformer is that it is heavy (the Charles 3.8 KVA IsoG2 Isolation Transformer weighs in at 60 pounds), and there can be a very noticeable “hum”. Fortunately the transformer is mounted on the forward bulkhead of the engine compartment and there is a lot of walls and air space between it and our living area.

I decided on the Charles 3.8 KVA IsoG2 isolation transformer. This transformer can be tapped for either 120 or 230 input voltage. This allows me to change the supply voltage for FatDash without having to change any wiring inside the boat.

The main components of the system are as follows:

  • Charles 3.8 KVA IsoG2 Isolation Transformer
  • Freedom Model 10 Inverter / Charger
  • [amazon:B004Q03PAC]
  • 2 – [amazon:B005T5GM26] with [amazon:B0052DL3MO]
  • Various crimp connectors
  • Crimper, wire cutter, screwdriver, and other tools as needed.

The diagram of the system is supplied below in AC Diagram.pdf .

I started by wiring up the transformer to 2 pigtails, one goes to the shore power breaker and the other goes to the Freedom Model 10 Inverter / Charger. This wire is marine grade 10/3 wire.DSCN3076-copy_1

I also made up 4 jumper straps, 2 using white #10 stranded wire and 2 using black #10 stranded wire. The transformer came with 2 cable clamps that I used to secure the pigtails to the transformer case.

The transformer is wired as follows:

  • Input 120 VAC 32A MAX
    • Ground (green) to transformer shield
    • Hot (black) to H1, H1 to H3
    • Neutral (white) to H4, H4 to H2
  • Output 120 VAC 32A MAX
    • Ground (green) to case
    • Hot (black) to X1, X1 to X3
    • Neutral (white) to X4, X4 to X2, X2 to case

The shore power is coming in on the right side and the boat power is on the left side. (note: I know there is a star washer laying there)

DSCN3066 (2)_1

As I stated earlier, I pre wired the transformer BEFORE I mounted it. The connections are on the bottom of the transformer and would be quite difficult to do after mounting (it will be difficult to switch to 230 VAC if I need to do it). To get the transformer in the proper position and mount it on the bulkhead I used a board I had laying around and placed it on the top of the battery cases and the top of my Whale auxiliary bilge pump mounting bracket. I then slid the transformer into place and marked holes for drilling. Then I removed the transformer and drilled the 2 upper holes for the lag bolts (These were also supplied with the transformer. They were holding the transformer down in it’s shipping crate). Again sliding the transformer along the board I bolted the transformer to the bulkhead. Then I removed the boards and drilled and installed the 2 additional lag bolts on the bottom of the transformer. This completed mounting the transformer, now time to rewire the AC.

I started by opening up the cable raceway and running the pigtail for the shore power side of the transformer to the new waterproof box. I had to go up and over the engine room access hatch so I used zip ties screwed down to the bulkhead. I didn’t tighten them up so I could use the same zip ties for the shore power wires from the plug on the outside of the boat. This completed what I could do with the power connected to the boat.

The first thing I did is turn off the shore power on the dock and unplug the shore power cable from the boat. Then using a VOM (volt ohm meter) I verified that there was no AC coming into the boat and that the inverter had not switched on and was supplying power. When I was sure all power was off I disconnected existing shore power from the original shore power breaker box and pulled them back to the new waterproof shore power box. I then connected them as follows:

  • Black to breaker than has the black wire connected to it
  • Red to the breaker that has the white wire connected to it
  • Green to the grounding bus bar.

Now I removed the old breaker box and all the wires connected to it. One problem I found was the green/ground wire in the box was connected to the ground buss bar in the power distribution box and it was connected to the main breaker in the breaker panel. The reason it is connected to the breaker panel is so you can detect that power is incorrectly wired and either the neutral or ground is hot instead of the hot/black wire. By connecting directly to the ground buss in the power distribution panel if there was power on the ground then you could introduce 120VAC into your DC electronics.

Now having removed the old shore power circuit breaker box I still had a couple of things to do. First I removed the wires going from the AC out of the inverter/charger and hard wired to the port and starboard outlets.DSCN2138_2 As you can see the connection is direct and bypasses the grounding buss not to mention there are no breakers on the line. I did have to extend the green / ground wire on each cable because it had been cut off and until I can replace the cable runs this will have to do.DSCN3078_2

There is still the main feed wire that needs to be connected to the main AC breaker. I routed the cable from the inverter / charger to the main breaker panel. I removed the existing wires going to the main breaker. I also removed the cable that had been installed to turn on/off the inverter/charger. I then routed the cable from the inverter / charger to the main breaker. From this point I ran a ground and neutral wire from their respective breakers to their buss bars in the power distribution panel. I also connected them together and to the engine ground.

Here is how the main power distribution panel looked before


and after.


Notice the AC cable missing in the top right corner.

Since switching to this configuration I have had no problems. I will be monitoring the zincs for deterioration.