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Old 16-05-2011, 08:45   #1
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Galvanic Isolators

Recently, a couple of threads got me thinking about installing a galvanic isolator. The first was a discussion on zincs. I am burning through zincs every 2-3 months and I'm looking for ways to extend their life. The second was the discussion on galvanic isolators.

Before installing a galvanic isolator, I'm doing an experiment of disconnecting the shore power and seeing if that extends the life of the zincs. If so, either I keep the boat off of shore power as much as possible or I install a galvanic isolator.

My question is how does one compare these devices? Aside from ABYC A-28 and the use/not of a capacitor in the circuit, are there differences? Some sort of status light or health indicator might be nice and some models have a monitoring device. Any recommendations, brand, model, price....?

My other question is do these actually help block the ground current, contributing to the galvanic erosion eating the zincs (or other metals). I can't change the characteristics of the marina or surrounding boats. If I install one, will this extend the life of my zincs?

Thanks
Don
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Old 16-05-2011, 09:34   #2
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Re: Galvanic Isolators

  • Have an electrical corrosion test performed on the boat bonding system, electrical system, and dock shore power system. Try to find an ABYC Certified Corrosion Testing person to perform the inspection and testing. This will help determine where the electrical current is coming from - your boat or a neighbor's boat. If it's your boat, repair that situation (master of the obvious huh?) If it's a neighbor's boat, track down which one and try to talk with the owner to let them or the marina know about the issue (hope you're diplomatic).
  • Protect your boat with an isolation transformer. This is the best way to protect the boat. Isolation transformers are heavy and a bit expensive but well worth it. If you install a galvanic isolator make sure that it is the 'fail-safe' type but be aware that isolators normally only stop up to about 1.5 volts DC.
  • Make sure that the boat electrical and bonding system are up to current ABYC standards.
  • If you have any photos of the zincs that would help too. Pitted, cratered zincs are indications of electrical corrosion. If the zincs are smooth and being depleted rapidly it could be a few different things.

Above are just quick basics - PM me if you need more information.
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Old 16-05-2011, 09:44   #3
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Re: Galvanic Isolators

Do a visual check around your hull and see if your electrics and metalwork are bonded directly back to your shore power earth.

You cant do much about your marina or neighbours so be proactive and protect yourself and your boat, dont rely on them to help you out
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Old 16-05-2011, 17:51   #4
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I was having same problem with zinc since I only have room for one small zinc on the prop shaft. My concern is with damage to other underwater metals, including rudder hardware on our Seawind 30. I purchased a Guest 4531001 over the Winter and will install it before the boat is relaunched. Guest unit has fail-safe design. I will also disconnect my boat from shore power during extended periods when we are away from the marina.

I also installed a large mushroom zinc on bottom of rudder, which is working well based on the condition after one season.
Regards, Syzygy
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Old 16-05-2011, 18:09   #5
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Re: Galvanic Isolators

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Originally Posted by boatross View Post
..........but be aware that isolators normally only stop up to about 1.5 volts DC.
I'm curious, have you ever seen more than 1.5v of DC on a shorepower ground?
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Old 18-05-2011, 08:55   #6
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Re: Galvanic Isolators

Certainly make sure they meet or exceed ABYC specifications.
Apart from that, galvanic isolators are extremely reliable and it takes a direct lightning strike to kill them. So don't spend money on fancy monitoring equipment, an annual check when you haul out is adequate.

You can easily test if you need a capacitor, test after installing an isolator. Measure the AC voltage across the Galvanic Isolator while in use at the dock. It should be less than 0.25 volts. If you read more, before "covering up" the problem, turn each AC item off to see which one is causing the leakage and if you find one, check it in detail to find some salt or other problem that is creating the leakage. If none of them reduce the voltage, you have a problem in the wiring itself that can develop over years of accumulating small amounts of salt water spray. Then you will need a Capacitor to stop the AC leakage reducing the efficiency of the isolator. You can purchase Electrolytic Capacitors, do a Google search.
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Old 18-05-2011, 09:34   #7
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Re: Galvanic Isolators

The criteria for galvanic isolators is defined by ABYC Standard A-28.
Per the new A-28 standard, galvanic isolators meeting the fail-safe requirement will not require a monitoring system since the integrity of the grounding wire will not be compromised should the isolator fail.
All galvanic isolators not meeting the fail-safe criteria will still require a monitoring system to alert the boat owner that their grounding system may be compromised.

ABYC A-28 ➥ http://www.nmma.org/assets/cabinets/...s_Standard.pdf
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Old 18-05-2011, 13:46   #8
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Re: Galvanic Isolators

+1 on Gord's comments.

Also, isolators made by Dairyland Electrical Industries, Inc. Fail-Safe Galvanic Isolators | DEI Marine are robust and best in class, IMHO.

They are not cheap. They are the best.

Charlie
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Old 19-05-2011, 09:12   #9
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Re: Galvanic Isolators

Thanks everyone for the comments. Is it fair to say that with a galvanic isolator, when connected to shore power the zincs should last the same as if the boat were not connected to shore power? Effectively, both cases don't have the conducting ground wire completing the circuit causing the erosion.

I'm experimenting with the boat not on shore power and I'm awaiting the next report from the diver - hopefully the zincs last longer and by what factor.

If this is the case, there's potential for considerable cost savings. Say at $80 every 2-3 months for zinc replacement - even if the isolator extends the life of the zincs by double, that's saving $20/month. They pay for themselves in a year or two!
Don
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Old 31-01-2012, 11:28   #10
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Re: Galvanic Isolators

I am preparing to install galvanic isolator on my boat. Does anyone have any experience with the one I am looking at buying. It seems to be an older model but I like the price. Any comments welcome. I found this on e-bay.

Guest Galvanic Isolator 60 AMP Model 2460P, Fully Potted - Sealed, Boat / Marine (046904873173) | eBay


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Old 31-01-2012, 13:17   #11
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Re: Galvanic Isolators

Quote:
Originally Posted by CharlieJ View Post
+1 on Gord's comments.

Also, isolators made by Dairyland Electrical Industries, Inc. Fail-Safe Galvanic Isolators | DEI Marine are robust and best in class, IMHO.

They are not cheap. They are the best.

Charlie
I had the above unit installed. Zincs are lasting one year in Seattle.
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