GALVANIC ISOLATOR Vs ISOLATION TRANSFORMER

[Parfait's Provider]

Beyond cost is there any advantage or disadvantage to using a galvanic isolator rather than an isolation transformer? It seems to me that the galvanic isolator has more components to fail. Do they fail safe or just connect everything to promote corrosion?

[Oswego John]

Ken and mostly all,

Since no one else has jumped on this, I'll give it a feeble attempt.

But first, let me remind you that a few days ago I mentioned that I was amazed by the talent and ability of many members of this board. Here is a prime example of what I was referring to. The initiator of this thread is a gentleman sailor who has been eking out an existance as an engineer for the many past decades.

...and you expect me to answer his question. No way.

But I will toss out a few anemic, generic comments relative to his topic.

In my laic view, galvanic isolators and isolating xformers, if not brothers, could easily be called first cousins. They supply power to adjacent wiring systems while avoiding electrical contact between them..

In many cases, the xfrmer's windings are 1:1 ratio, neither step up nor step down.

Many of the breakdowns and problems are attributed to blown diodes. The ones that are equipped with condensers can short out, also.

There are many fine articles about isolation on the web. My go-to guy for a thorough explanation on all areas of marine electronics is Peter Kennedy Yacht Services, Annapolis, Md. Under this title are six or more addresses. What ever you do, don't overlook the section titled "FAQ". It is a treasure trove of marine electronics info.

O J

[moctrams]

In my estimation, Galvanic Isolators are way over priced. Several years ago, I bought one for my old boat at a cost of around $35.00. Once the word gets around about the benefit of having one on your boat, the price goes sky high. A Galvanic Isolator is basically four (4) diodes wired in such a manner to block stray emf and placed in parallel with the shore power ground.

[Parfait's Provider]

I was hoping that Oswego John would step up. He did recommend Peter Kennedy, so that is good. This is not my field of expertise; please step in if you have an opinion.

Here's what I think I know; please correct me if there are errors, especially glaring ones:

I believe galvanic isolation is provided in series with the safety ground connection between the boat and shore. This ground is necessary to allow full current of the hot AC lead to be dumped safely and force a circuit interruption. The diodes prevent low voltage differential from allowing current transfer, but break down if high voltages are applied, such as when the hot lead shorts to safety ground.

Galvanic corrosion usually occurs at these low voltages.

Simple galvanic isolators are not fail safe. If one or more diodes short, less protection is provided and there is no external indication. If all the diodes fail, there is no protection and no external indication. It is possible that there will be either no protection from galvanic corrosion or no protection from electrical shock and death.

This has been recognized and the ABYC requires additional electronics and controls to assess the status of the diodes. I call these complex galvanic isolators.

Peter Kennedy recommends DEI galvanic isolators priced at roughly $300 and $400 for 30 A service in two levels of "safety."

An isolation transformer is a low technology simple device that has been around since alternating current. Those large cylinders you see on power poles are transformers. They are reliable. They are also heavy.

A Charles Isolation Transformer for 30 A services can be purchased for less than $500 including shipping. Peter Kennedy has a very high price on this device. The transformer avoids any connection between the boat safety ground and the shore side safety ground, which is terminated at a shield in the isolation transformer. Google "Charles ISO-G2 Isolation Transformer" for leads to savings.

I feel that the isolation transformer is a much better solution for only a few hundred extra dollars of outlay.

Comments please.

[tmsc]

Ken,

David Rifkin, AMS is an electrical guru, and who I turn to when I'm over my head. He is recognized as an expert in the field and has an excellent website with articles that will answer your question and then some. His articles can explain things much more eloquently than I can, so here is a link. Just go to the documents page and open the, "Isolation or Polarization; Which is the Safest Transformer Installation?" article.

http://www.qualitymarineservices.net/

The transformer is much larger, heavier, and expensive. Though there size and price have been getting smaller. There are also advantages from a safety stand point that an isolator doesn't provide as the above suggested article will explain. There are a lot of the old style non fail safe model isolators out there that can be had for cheap. Mine is an older model Guest that I bought new in the box on Ebay for 35 dollars. Technically, to comply with ABYC recommendations the non fail safe types are supposed to have an indicator (lights) near the panel to be compliant. The newer fail safe models do not have to have this to comply with ABYC but are more expensive. The galvanic isolator is basically , as was previously stated, just diodes. They are simple devices compared to a transformer, but they are very effective, and I strongly recommended them. Granted if cost, size, and weight are not an issue, the transformer would be my pick. I just don't push them because of the reasons I listed. Plus, I have found that it is very hard to get people to buy and install an isolator even a cheap one. Suggesting a transformer would just be a steeper mountain to climb. Thats the problem with equipment that is not sexy or have all kinds of flashing lights. After all these things just sit there and don't look like they are doing anything. Oh well enough of my soap box. I'm just glad you are investigating and considering either of them.

[Parfait's Provider]

I'm the guy who raised his hand, the only hand, when at an annual meeting the speaker asked who left their boat "plugged in." Properly admonished and having seen what happened to the zincs, I stopped staying plugged, but I want to prevent freezing and still be able to sail on a good day in Winter, so I am on a quest. For the moment, I have a ceramic heater sitting on the stove grill and tethered to the portlight above. It is plugged to the shore cord through an adapter with GFI and it all floats relative to the boat. In some ways it is ideal, cost is one. The Marinco adapter and GFI with three outlets is $100. It can't possibly be to anyone's code.

However, I'd like to be able to charge the batteries too and isolating the charger and batteries from ground brings complications I'd rather not sort out, so I am going to isolate. Probably I'll buy one of those heavy bricks and mount it in the lazerette near the power inlet, with no blinking lights, but I'll read some more before proceeding.

Thanks for the link.

Ken

[Troy Scott]

This is an important subject. Thanks, guys!

[Parfait's Provider]

I have decided to install a Charles Isolation Transformer. The best price I could find was at iMarine with an advertised flat rate of $10 for shipping. That turned out to be too good to be true. If you live near someone who stocks these 60# bricks, you might do better to go pick it up. Defender has a pretty good price, maybe it is better during their Spring sale.

Here's some info:
CHARLES ISO-G2 TRANSFORMER 3.6KVA 30AMP, 120VAC, 60HZ - CHARLES MARINE 93-ISOG2/6-A

http://www.charlesindustries.com/main/iso_guard.html

[Andy Denmark]

Charles Industries equipment is the best out there. Expensive but worth every cent. An isolation transformer is the most trouble free, long term solution for anyone who is going to be hooked to shore power and wants max protection. There is almost nothing to fail. I keep my old NASA boss' statement that basic reliability is a direct function of the number of moving parts. If that's true this thing should last forever -- much like an anvil except the anvil is somewhat lighter!

Charles Industries battery chargers are the friendliest to batteries, too, and offset their higher initial cost against a much longer lifetime for the batteries.

Look forward to having you down the creek from me. Let me know when you want to move Parfait from Beaufort and I'll be glad to help.

[Parfait's Provider]

Let me know if you hear of a weather window worth considering. I don't usually look more than five days ahead and I really can't start until sometime in Jan. I'll try to get the boat moved from Town Creek back to MBYC before we head north to "your" creek.