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Old 30-07-2008, 20:08   #1
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Isolation transformer

What I am looking at is the decision between galvanic isolators or an isolation transformer. The later (isolation transformer) seems to be the most positive answer to the problem. Of course it comes with a price tag. But from all that I can read it isnít to hard to bypass all your hard work and open your self to that stray ground current to eating at my boat using galvanic isolators. Has any one installed an isolation transformer ? Thoughts?
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Old 31-07-2008, 03:18   #2
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A 3.6 KVA Marine Isolation Transformer (30A @ 120V 1∅ 3W) would weigh about 60 - 75 Lbs, and take up about a cubic foot of space, and might cost about $1,000.

A 30A, ABYC A-28 Compliant (brand new standard July 21/08), Galvanic Isolator would weigh under 5 Lbs, take up about 6" square x 3" deep, and might cost about $250.
The ďold basicĒ isolators sold for about $150.

See also "Transformers" at:
Professional BoatBuilder - August/September 2007

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Old 31-07-2008, 03:53   #3
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I had the same question when I moved my boat to the Subic Bay Marina which has a pretty rough electrical service with little maintenance.

I am not an electrician, but this article* I researched convinced me to bite the bullet and go with the Isolation transformer.

* Which is the best choice?
A Galvanic Isolator or an Isolation Transformer?
"Until relatively recently this was quite a simple question. With a simple set of answers ...
... The goalposts have now been moved and the decision is no longer this straightforward...
... In order to understand why, it is necessary to look at how each device breaks the connection between the shorepower earth and the hull of the boat...

... The only alternative is to fit an isolation transformer..."


See the complete
(Copyright) article, c/w graphics, at:
http://www.smartgauge.co.uk/galv_tran.html

More Technical Information from SmartGauge Electronics:
http://www.smartgauge.co.uk/technical1.html

* Web site and all contents Copyright SmartGauge Electronics
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Old 31-07-2008, 04:13   #4
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Thanks for that excellent tutorial, Pelagic.

Have you had a chance to review the brand new Galvanic Isolator Stand (ABYC A-28), that just came into effect? If so, what are the significant changes?

For the record, what (if anything) do you sell, service, or install?
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Old 31-07-2008, 04:22   #5
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Sorry Gord, I went back and put quotation marks around the piece. This was an article amongst many that I found useful in making my decision.
Can neither defend nor challenge it!
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Old 31-07-2008, 14:15   #6
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It is technically correct. But the question really is, who much SMPS equipment in reality is on our average boats. Battery Charger with SMPS would be one. Computer PS, TV Ps and "maybe" a home type stereo. But there would be little else. A large vessel with many of those devices could have a problem. But a transformer's size and weight is not an issue. The other problem with an Iso tranny is it's own earth connection on it's own output side. Many don't have the earth and IMV it is just as important on a boat where the possibility of many outputs and many appliances are connected around the boat, so a "true Marine" tranny is important and most likely more expensive. Then the possible load. My 230V system is rated to 16A. So at 110V you are looking at 30+Amps. That is a whopping big transformer. I am not saying either is right or wrong, just each still have even today an important difference that needs consideration and a diode isolator can still have it's place. Easy and cheap to make too. Mine cost NZ$50.
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Old 31-07-2008, 14:23   #7
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Originally Posted by Pa La O La View Post
What I am looking at is the decision between galvanic isolators or an isolation transformer. The later (isolation transformer) seems to be the most positive answer to the problem. Of course it comes with a price tag. But from all that I can read it isn’t to hard to bypass all your hard work and open your self to that stray ground current to eating at my boat using galvanic isolators. Has any one installed an isolation transformer ? Thoughts?
What type of hull do you have? Composite, aluminum or steel?

What is most important is to isolate stray DC currents. I have an aluminum boat with an isolator on the ground side and have never had a need for an isolation transformer. I did this so my aluminum hull does not become the sacrificial anode for the entire marina.

Unless you are already have electrolysis problems, an isolation transformer is probably completely unnecessary.

So what on your boat is being "eaten" by electrolysis?
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Old 03-08-2008, 08:20   #8
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Trouble it seems so

Good day to all,
I have a fiberglass hull. (Prout37 Snow Goose Elite) In my prep to move to the yard for a bottom job I found a loose thru hull. Long story short the valve broke OFF and I sat for a week with a bung wedged and wired in the thru hull. I moved the engine cooling line to the galley sink line we have never used. I get to the yard and I had to cut the three old thru hulls out. I have bright red color on the inside of the bronze fittings. So I replace the thru hulls, the yard work is done and Iím back in my slip but now I have to decided what I am going to do about the galvanic corrosion I seem to be suffering. I have been on the boat for four years. This is our first real encounter with this problem. Our first marina up in south Florida had a problem with stray voltage but we dodged the bullet there.I replaced thru hulls in the other hull while there for size reasons. I guess not so lucky here. I guess I have to pull my head out of the sand (be kind) and deal with this. It is my understanding I need to isolate the safety ground in shore connection to break the corrosion path. But with the inverter charger (Pro Sine 3000) and anything else I might miss has to be dealt with or any work done is for naught. From what I have read so far the transformer takes all that out of the picture. Money is a factor to be sure but knowing the problem is being dealt with is right there too. When that valve broke off I must say I was happy for the bung I had tied to the thru hull years before. I donít want to be looking at this same story some stormy night with the only land anywhere near -straight down. I am trying to make an informed decision as to what to do for this problem and to resolve this correctly.
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Old 03-08-2008, 10:00   #9
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I am interested in this thread and ahve the same questions. I can tellyou that in Caulders Book on maintenace he has a good section on Galvanic isolators and isolation transformers.
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Old 03-08-2008, 10:31   #10
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Have you consulted with the boatyard, surveyor or another professional on the subject to get his opinion? I would try that next because that person is actually there to see first hand what is going on and hopefully they are knowledgeable enough on the subject as well.

Although this is an indicator and obviously not a solution, I would check to see if you have a DC voltage difference across your shore power ground. If there is, that's not a good thing.
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Old 12-08-2008, 13:57   #11
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Unhappy Autohelm 3000 repair

Anyone happen to know of anyone in the Seattle area who will still work on an autohelm 3000? I have called around, but to no avail.
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Old 12-08-2008, 14:14   #12
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Anyone happen to know of anyone in the Seattle area who will still work on an autohelm 3000? I have called around, but to no avail.
I don't think it is relevant to this thread and you would probably get a better response by posting it as a new thread in the proper discussion area.
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