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Old 21-07-2010, 01:56   #1
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Shore Power and Galvanic Corrosion

Hi,

I was hoping someone well versed in this topic could give me a bit of advice on the best solution to prevent galvanic corrosion via shore power connection.

I understand that isolation transformers pass the current from the shore side to the boat through induction of the coils and as such there is no actual physical connection to the shore side and therefor corrosion will not be induced. This makes sense to me. An example of such a product is:

VICTRON Phoenix Isolation Transformer 230V 30A 7000W | Transformers | Product Range | Bainbridge Technologies

I expressed this to someone who informed me that there boats use an 'Electrolysis Blocker / Galvanic Isolator" to achieve this. An example of such a product is

MPS Electrolysis Blocker | Marine Protection | Product Range | Bainbridge Technologies

Anyway any guidance on this would be greatly appreciated.

Thanks in advance.

Simon
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Old 21-07-2010, 04:54   #2
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I had a galvanic isolator installed. I don't have a corrosion problem......but I don't have a base line either.... ie no idea if without it I would have a problem. Seems like a cheap and easy way to control it...thats why I put it on!
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Old 21-07-2010, 05:02   #3
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Galvanic isolators are popular and work well. Isolation can work too, but is more expensive for big wattage.

We're cruisers: my boat is never plugged in. No shore power wiring in the boat. Saves about a hundred pounds in chargers, panels, cords, adaptors for 120 and 240 in every country, etc. etc. and countless dollars. Sitting at the dock she gets all she needs from solar just like in the middle of the ocean. One small cord for when a heater (stray into high latitudes), charger (endless gloomy weather) or power tool is needed. Those are completely isolated and rarely connected at all.
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Old 21-07-2010, 05:35   #4
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Quote:
Originally Posted by scalleia View Post
Hi,

I was hoping someone well versed in this topic could give me a bit of advice on the best solution to prevent galvanic corrosion via shore power connection.

I understand that isolation transformers pass the current from the shore side to the boat through induction of the coils and as such there is no actual physical connection to the shore side and therefor corrosion will not be induced. This makes sense to me. An example of such a product is:

VICTRON Phoenix Isolation Transformer 230V 30A 7000W | Transformers | Product Range | Bainbridge Technologies

I expressed this to someone who informed me that there boats use an 'Electrolysis Blocker / Galvanic Isolator" to achieve this. An example of such a product is

MPS Electrolysis Blocker | Marine Protection | Product Range | Bainbridge Technologies

Anyway any guidance on this would be greatly appreciated.

Thanks in advance.

Simon
Read the archives. The Search function is your friend. There is a lot of discussion here about all of this.

The Clif's Notes version is that galvanic isolators might be somewhat dangerous and might be somewhat ineffective, sometimes. The isolation transformer is the really good solution. I was persuaded by people here, when I faced the same problem earlier this year, to spring for a Victron isolation transformer instead of installing a galvanic isolator.

The isolation transformer has significant disadvantages, as I found out, namely:

1. Expensive.

2. Bulky.

3. Makes an irritating hum.

4. Extremely sensitive to being overloaded, even briefly.

We installed the 3.6kW version on the theory that our shore power connection is nominally 15 amps (at 240 volts), so should have been enough. The 7kW version would be even much more expensive, bulky, and noisy, to the point that I'm not sure it would really work even on our 54 foot boat.

Well, the nominally 15 amp shore power was able to handle any combination of loads on our boat without tripping. Not so the Victron! If you even briefly touch 15 amps of load, it trips. We are running back and forth to the laz sometimes even several times a day, when on shore power, to reset the circuit breaker on the Victron.

We had a very bad case of galvanic corrosion so we felt we needed to take effective action. But if I thought that a galvanic isolator would do the job, I might think hard about that, in order to avoid all of the above.
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Old 21-07-2010, 06:21   #5
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If you are going to do extensive cruising and jump back and forth between the 110v and 220v shore power areas, it makes more sense to put in a transformer which will not only isolate, but will step up/down as needed (not all step up/down transformers are also isolation transformers, but some are).
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Old 21-07-2010, 07:21   #6
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See Victron’s data sheet & manual

http://www.victronenergy.com/upload/...2%20-%20EN.pdf

http://www.victronenergy.com/upload/...2%20-%20EN.pdf

Their 3.6kVA isolation transformer should handle 16A @ 230V instantaneous, and at least 12.5A continuous.
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Old 21-07-2010, 18:18   #7
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3.6kVA transformers on a sailboat? Humor me for a second and consider this:

Run an extension cord into a hatch. As you cruise around the world buy the various dock-end connectors you need. Swap them out as needed. Plug in a little 10, 15 or 20A (120v or 240v) switching charger, available anywhere, into the cord. You are done. The entire system weighs a few pounds. Requires no maintenance, can be replaced anywhere in the world. Everything but the chargers is 12V.

Essentially ZERO galvanic leakage thru the chargers.

But then I'm on solar, so the extension cord has not been uncoiled for months.

Consider that if your are not wedded to shore power it's that much easier to go sailing, to cruise. All the electrical gizmos that worked at the dock work offshore. Simple.
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Old 21-07-2010, 20:05   #8
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The simplicity of skipping shore power entirely is very appealing right now, as I'm just starting a Charles 3.8 KVA (IsoG2) installation. No real choice here in the Pacific Northwest in a boat with lots of systems and development tools, though once the 420-watt solar array is installed (along with the existing 7.5 KW genset) I will skip the cord more and more.

Having said that, I'll offer a couple of other comments. I have a steel boat that came with a Newmar galvanic isolator. I'm not aware of any problems, but zinc loss has been variable depending on the marinas... so I've opted for the fancy solution that seems to be well recognized as the most robust. The hassle at the moment is that the existing wiring is complex and not well-documented: breakers and distribution in different panels 6 feet apart, obscure wiring to source-select and automatic changeover relay (which should now be irrelevant with new Outback inverter/charger), and very difficult access to the shore power inlet where I need to place a new main breaker.

But yes... once I finish making the ship even *more* complicated, I look forward to minimizing shore power use. I've just moved to a famously hot marina, so there's a bit of urgency around this at the moment.

BTW, I haven't fired it up yet, but have been very impressed with direct telephone tech support from Charles. They never answered a pre-sales email, but when I called to ask a couple of engineering questions I got an immediate and friendly response.

Cheers,
Steve
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