Reverse Polarity Light

[coot]

Originally Posted by Alan Wheeler

Sorry I wasn't clear. I was refering to any current that was flowing in the ground as being Galvanic due to two boats tied together via a cable. Because this current is "normally" so low, the diodes effectively isolate that very small galvanic current.

I guess I should have mentioned this in my original post. Specifically, what Alan is talking about here is:

The voltage you get from galvanic corrosion in sea water depends on the specific metals involved, but is very low. The 1.4 volts was chosen as the lowest value that is sure to be higher than the voltage caused by the corrosion. A single diode blocking at 0.7 volts would prevent many types of corrosion, but if your neighbor happened to have a metal that is 1.0 volts away from yours, it wouldn't work. So we use two.

If your boat were sitting in sulphuric acid instead of sea water, you could get a higher voltage. But then you would have far worse problems...

b.t.w. The voltage depends on the type and condition of the metals involved, but not on the surface area. Larger surface area can provide more current (more amps, and faster corrosion), but not more volts. This is just like your batteries, where a Group 27 and an 8D both put out 12 volts from the same chemistry.

The purpose of the galvanic isolator is to prevent your zinc from protecting your neighbor's propeller. It works for that. It isn't expected to protect you from bad marina wiring or a short to ground inside your boat.

[Alan Wheeler]

Sorry for the offtopic everyone, but Hellosailor, the only way you will effectivly eliminate the buzz and hum and clicks and bells and whatever, is to create a simple balanced audio signal circuit. Very easy to do. A simple 1:1 audio transformer. The cost is in the transformer. The more expensive, the higher the quality(HF) of audio they will pass. Effectively it is just like using an isolation Tx on a AC system. It isolates the equipment from each other.

[hellosailor]

Mark-
So, if the purpose of the "galvanic isolator" in the AC line is to protect me from my neighbor's prop, then that protection is limited to "protection from bonded devices that are also grounded to the AC lines". Yes?

IOW, if the underwater fittings are bonded--but NOT grounded to the AC ground--then there would be no need or use for the "gi" in the AC line?

I'm remembering some of the arguments for "bond them but don't ground them" now, this seems to touch back on that.

[coot]

Originally Posted by hellosailor

IOW, if the underwater fittings are bonded--but NOT grounded to the AC ground--then there would be no need or use for the "gi" in the AC line?

I suppose, though I'm not sure how you would achieve that. I expect that your propeller connects to the shaft, the shaft connects to the engine, the engine connects to the DC ground, and the DC ground connects to the AC ground.

I've never understood bonding very well. As far as I know, it is sort of like lightning protection - it is vitally important that every boat have it, yet I've never seen it implemented on a real boat.

[hellosailor]

Coot-
Bonding per se just refers to running a good conductor between a set of objects, so they are at the same electrical potential. Those bonded objects may or may not be tied into the ship's power systems (AC & DC) and they may or may not include the engine block. The prop also may be isolated from the engine--remember, there are gizmos like the "shaftsaver" that will also electrically isolate the prop shaft.

Religion, sex, politics...and yes, the philosophy of grounding.<G>

A consolation for those who stay at moorings, to be sure.

[Rod Headlee]

Alan,

I had the same problem, turned out there was a loose connection at the bottom of the Blue Sea Panel. I'm no electrical pro but it was where the terminal strips connect at the panel. It actually fried the panel at this location, I bought a new one and kept the old one for parts. Now I check these 2 screws all of the time. I'm not at the boat or I could send you a pic. If you need one I'll be back to the boat in 2 weeks or so.

[alanperry]

Well thanks to everyone who replied, and thanks Gord for the links. I was planning on making my next step a call to Blue Sea which is right up the road from me. Anyway, I have opened and checked and re-checked all AC wiring from my shore receptacle to the last in-boat AC receptacle including the AC Panel and ALL connections are correct. While last I reported that the RP light went away when I connected the 12VDC to the Galvanic Isolator, the next day it was back! So it is intermittent. At the same time the AC Voltmeter on my Blue Sea panel shows about 80 volts. This situation could have existed all along in the power from the marina without me knowing as I was using an adapter to a power strip to run tools and light while I was working on the boat before I connected up the AC.

This is very aggravating.

[hellosailor]

Alan-
Have you tried plugging a simple 3-LED outlet tester (via $20 adapter I'm sure<G>) into the marina's power outlet, to see what the voltage looks like on THAT side of things? Just to find out what you're plugged into?

[alanperry]

Hellosailor, no I havn't tried that and what is a "3 LED tester? is it a polarity tester? I think I may need to try a new power cord. That would tell me if it is in my cord vs the Marina/ or is there a way to do a continuity test on the cord that would tell if I have a problem there?

[GordMay]

Receptacle Tester:
http://www.professionalequipment.com...qx/default.htm