Galvanic Isolator

[Catbird]

No offense taken. The readings were taken with the meters set for ohms. I tested both meters before reading the shorepower input by touching the probes to each other and both read approx .0003. At the first opportunity I plan to and will have an experienced tech do this check.

Re the Yandina: understood.

 

[Steve DAntonio]

Steve,

I had looked at this transformer and the literature says:

"The Mass GI features marine aluminium casing and professional connections with strain relief cable glands. All Mastervolt isolation transformers comply with the CE and ABYC (US norm) guidelines for vessels."

Not being an expert in ABYC, I am not sure what that means.

On the specification side, it says it is rated at 16A at 230V with make power of 3500W. With my limited knowledge of electricity that would seem to translate to 32A at 115V and be within the 3500W power handling capability of the transformer.

I am interested to see what you find on this as I was considering one for my boat. We are starting to see new harbor construction in SE Alaska with the newer ELCI breakers. Almost universally boat owners are finding that they only way to reliably plug in is with an isolation transformer between shore power and the boat.

Tom

Tom:

I read the entire installation manual and found this statement,
"4.2.1 Overload protection
The Mass GI is equipped with an integrated fuse
which limits the input current to 16A. This fuse will
switch the Mass GI to Stand by in overload
situations and trigger the MasterBus alarm."

Which would seem to indicated that a single unit could not be used at 120 volts/30 amps...

However, later on in the manual, under the specs, it lists a Mas GI 7.0 Multi Tap, which is rated for 32 amps and 120/230 VAC. None of it is self-evident, and it seems MV has a foot in each electrical camp, 50 and 60 Hz, without really making the US installation requirements crystal clear, or as clear as they should be.

In addition to inquiring about ABYC compliance, I've also requested clarification from them as to which one or ones are designed for use with N American 120/240 VAC 60 Hz power.

Given the choice, and all other things being equal, and unless weight is critically important, purely from a reliability, simplicity and potentially price perspective, the Charles models with Soft Start seem to make the most sense if your goal is to be able to plug into ground fault protected shore receptacles.

Stay tuned, I'll share what ever additional info I get from MV...

 

[tpbrady]

Thanks for the follow up Steve. Since I have dual 30A shore power connections, I would probably have to use two transformers. I haven't looked into the details of integrating an isolation transformer into dual 30A shore power.

I look forward to seeing what you learn on this.

Tom

 

[Steve DAntonio]

Thanks for the follow up Steve. Since I have dual 30A shore power connections, I would probably have to use two transformers. I haven't looked into the details of integrating an isolation transformer into dual 30A shore power.

I look forward to seeing what you learn on this.

Tom

With a conventional xfmr, a Charles for instance, you need two xfmrs for a twin 30 amp 120 volt system, the two shore supplies, xfmrs or not, must remain independent and isolated.

 

[kulas44]

Steve, I would like some clarification as to the need for 2 transformers. I used a standard GE (IIRC) 15 kw transformer on my trawler when at Sabine Pass Tx. marina due to being close to a few old al. boats that I suspected had problems. I wired it straight 240 volt on the input and 120/240 on the output.

 

[Steve DAntonio]

Steve, I would like some clarification as to the need for 2 transformers. I used a standard GE (IIRC) 15 kw transformer on my trawler when at Sabine Pass Tx. marina due to being close to a few old al. boats that I suspected had problems. I wired it straight 240 volt on the input and 120/240 on the output.

Indeed, 240 volts on the xfmr primary, that is a single 50 amp 240 volt dock supply, is typical and on 60 Hz (N American) wired vessels the secondary is wired for 120/240 output.

If you have twin 30 amp 120 volt inlets you need two transformers, period. If you have a single 50 amp 120/240 service, you need one transformer.

What you should not do is wire two 120 volt 30 amp dock supplies to a single transformer primary, that is a violation of ABYC E-11 Standards.

Hope that clarifies things.

 

[Steve DAntonio]

I've had ongoing exchanges with Mastervolt on their high frequency switching transformers, the GI series, nothing definitive yet on ABYC compliance. The last note I sent them showed that the transformer met one of the two required ABYC sub standards, mentioned earlier in this thread. They've promised to check on this and get back to me.

They did say...

"Yes the Mass GI...is available in a 16A (GI 3.5) and 32A (GI 7) model. Both models handle 120V or 230V (what you put in comes out) and up to 4 units can be paralleled to increase capacity. We currently do not have a 120/240V-50A model. You could technically series-parallel four of the GI 7’s but that’s not a very cost effective solution." And " The GI 7.0 is 30A at 120V. Only one unit is needed. The multi-tap 7.0 is indeed not available."

The GI 7, mentioned above, which is suitable for 120V 30A, is $2020.00, Dimensions: 13 3/8"H x 10 5/16"W x 9 13/16"D it weighs 22 lbs. A Charles 30A 120V unit is $574...Dimensions: 9.65" H x 10.5" W x 9" D 76 lbs.

 

[kulas44]

My boat did have 2 30 amp receptacles. I used a 50 amp cord from the xfrmr to the dock pedestal. I split the 120/240 volt output from the xfmr with one leg to each receptacle.

 

[FF]

" I used a 50 amp cord from the xfrmr to the dock pedestal. I split the 120/240 volt output from the xfmr with one leg to each receptacle."

This can supply 50A to each 30A leg onboard.

 

[mbevins]

This weeks Active Capt newsletter has isolation xformers for the Defender "pick of the week".
Both 30 and 50 amp sizes.

 

[Steve DAntonio]

The final word on this from Mastervolt...

"Hi Steve,
I think you found an error in our spec sheets and manuals….. 
I spoke to engineering today and we definitely comply with both IEC standards but our documentation is not reflecting it.
We will update our documentation shortly. Thank you for catching that.

Best regards,

Menno Ligterink"

 

[JDCAVE]

Zincs on my boat are degrading faster than I anticipated. I am relatively certain there are stray currents in my salt water marina.

I understand the whole subject can be complicated, so I am limiting this initial inquiry to one single element of the overall puzzle:

If my boat is the one leaking AC (or DC) current to the water, will installing a galvanic isolator on my own boat be of value?

Yes, I've got a similar problem and I've alerted my marina. Freshwater moored in the Fraser River. Older shore power setup. Replaced the zincs last year. Checked them after 10 weeks in saltwater while diving in August (Desolation Sound) and they were near new. Just pulled the boat almost exactly a year later and the prop, rudder and thruster zincs are completely gone. Fortunately no additional issues with the metals in the boat but clearly a problem. I have a Sterling Zinc Saver II Galvanic Isolator. Evidently this unit is no longer AYBC compliant as it is not Safe Fail.

I did the test outlined below, incidentally this is the unit a I have. If I did the test correctly, it is functioning: reads 0.927 in one direction and 0.907 in the other.

http://www.pbase.com/mainecruising/galvanic_isolator

So I'm going to go around the marina and test some of the power cords with a clamp meter to see if there is a reading. No reading a good thing? Something else a bad thing?

My marine electrician says it's a bit of a procedure to determine if there is something else going on. I'm not ruling out my boat but, I suspect now it's someone else who is the problem.

BTW. I've told the marina they need to look into this. They've been saying for the last two years they are upgrading the shore power but...it's still not done.

Any other actions I should take? The boat is out of the water right now, so in water tests will have to wait.


Jim
Sent from my iPad using Trawler Forum

 

[Steve DAntonio]

Jim:

Your electrician is correct, there is more to this than simply using a clamp meter on shore cords. Clamping a shore cord for AC current flow tells you very little about corrosion potential (although it does indicate a potentially dangerous fault that could lead to electrocution), as AC is almost never the corrosion culprit (and to the inevitable naysayers, if AC routinely caused corrosion on recreational vessels galvanic isolators, which only block DC, would be of little value). Measuring DC current flow on the shore power's safety ground wire would, on the other hand, alert you to a potential corrosion issue, to a point, hold that thought.

A galvanic isolator will block relatively low galvanic corrosion voltage, up to 1.4 volts DC. After that they begin to conduct and offer little protection. Fortunately this protects you from the most common type of corrosion, galvanic or dissimilar metal, that which you are also protected by with sacrificial zinc or aluminum anodes. The idea behind the GI is that it allows your anodes to protect only your boat's underwater metals, and not those of your neighbor's.

This type of corrosion is slow, it occurs over the course of months or years. It can be the result of dissimilar metal issues on your own vessel, or those nearby that are also plugged into shore power and have no galvanic isolators.

Stray current corrosion, on the other hand is much more rapid and much more destructive. It starts with a fault in the electrical system which ultimately "leaks" DC current into bilge water and/or through a hull fitting into the water in which the vessel floats. The GI does nothing to prevent this type of corrosion, and while it can originate on nearby vessels, causing damage to occur aboard your vessel, in most, but not all, cases the damage is limited to the boat on which it originates. Using well-established corrosion analysis procedures,finding the source is very straightforward, there should be very little mystery or speculation involved.

Before you berate your marina manager with accusations of stray current, get some solid facts (he likely won't know what to do about it anyway). The best, most effective and most definitive way to analyze this type of scenario is with a silver silver/chloride reference electrode and a multi-meter, in the hands of someone who knows how to use them, preferably an ABYC certified corrosion technician, although a handy do it yourselfers can learn how to use this tool.

If, by the way, you unplug your shore cord from the dock and have continuity between the shore cord ground blade, and the ground socket in a receptacle aboard, your galvanic isolator is not working, it's not present, it's not wired properly or it's been inadvertently bypassed.

One of the better books on this subject is written by Ev Collier, "The Boat Owners' Guide to Corrosion", it's used as the text book for the ABYC corrosion certification class. If you are really interested in learning about this process, and in how to clearly identify corrosion issues, then get a hold of a copy.

 

[JDCAVE]

Thanks for your reply, Steve. Much appreciated. I've just ordered that book you mentioned on Corrosion control from Amazon. Unfortunately it will take 2 weeks or more, not sure why. Also a hard copy of Calder's book. I find the kindle version difficult to navigate and flip back and forth between pages.

I did that test that Boatpoker recommended for neutral-to-ground connections, following the procedure he outlined. It seems I may have an issue, but am not certain what I am seeing as the readings flicker. My marine electrician is coming the weekend after next. We shall see what he finds out. I am concerned and want to ensure everything is safe.

Just when you think you've got things figured out...


Jim
Sent from my iPad using Trawler Forum

 

[JDCAVE]

BTW, I did the clamp meter test of the power cords of the neighbouring boats where I tie up. Most boats ranged 0-0.05 amps. One boat read 0.15 amps and another read 0.33 amps. The high reading was from an aluminum crab boat.

Jim
Sent from my iPad using Trawler Forum

 

[sdowney717]

I have no AC leakage, not enough to trip a standard 5 milliamp GFCI!
I can plug in my portable GFCI power cord between the boat and shore power, and power will not trip. Need to turn on all devices to verify no leak on any of them. So my AC system is tight.

I did of course over the years rewire and or verify existing wires going over the entire electrical system, DC and AC.

I do have an AC-DC clamp on current meter which shows no current losses.

Curious, if you had a DC leak running out the AC shore power line, would a GFCI trip, would the GFCI see a current imbalance?