Did my VDI-16 go wrong?

DIY
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1

Hi,

I have a VDI-16 galvanic isolator on my aluminum boat, and I’m having some weird issues.

I disconnected the boat from shore power, got into the helm, and tried to start the engine—nothing happened. The voltage was low everywhere on the boat. I checked the batteries, and they were fine. I went through all the cables and connections but couldn’t find anything wrong.

Then I measured the voltage between the battery negative and the hull and found about 1.5 volts. I connected (shorted) the battery negative to the hull, and suddenly, everything came back to life—except the engine. It still didn’t have enough current to turn the starter motor.

I decided to pull the boat out of the water (I need to service the engine anyway) and continue troubleshooting onshore.

The next day, I went back to the boat, removed the temporary connection between the battery negative and the hull, and started checking things again. Strangely, the issue was gone. The engine started up just fine without any hesitation.

Now, I’m scratching my head a bit.

My questions:

  1. Could a faulty galvanic isolator cause a 1.5V difference between the hull and the battery negative?
  2. How do I check the isolator to see if it’s working properly?

Thanks for your support in advance