galvanic isolators

[aah924]

I am in the process of completely rewiring my '72, 36' Hatteras and need info. on galvanic isolators. I have, what appears to be, the original isolator and need input on what type to replace it with. I am keeping the dual 30 amp power supplies. Does anyone have any suggestions?

Thanks,


Allen

 

[ELECTRA VI]

I would be interested in what you find out. I don't know if I have one or not. I seem to eat up zincs in 4 months when I leave the boat plugged in at the dock.

 

[67HAT34C]

GALVONIC ISOLATORS

Strange you mention this as I was researching this yesterday. Our 67 34c does not have one. we go through zincs every 90 days. We leave ours plugged in all the time at the marina. I believe the previous owners kept the boat at their homes and did not have the marina problems. records do not indicate a zinc problem and the underwater metal is all in good shape. It would appear we need the isolator. actualy it appears we need one for each hook up.

The question is , is it mounted at the hook up or at the power panel.

 

[PascalG]

galvanic isolator

i bought one which i havne't installed yet... my understanding is that it goes anywhere conveneient between the shore power inlet and the main ground bus.

on a boat with multiple shore feeds, i don't see why you can't put right before the ground bus and hook your multiple ground inputs to the isolator.

or if like me, you always use the same shore line, just put it on that one. you just won'd have protection on these occasional days where you use another line.

problem on my boat is to ID the right ground feed. havne't gotten to is yet, will probably use a continuity tester with extra wire between the shore power plug and the panel and disconnect the larger groundwire to find the right one :-(

pascal
miami, fl
1970 hatteras 53my

 

[mikep996]

isolator

I have always been under the impression that if you had shore power transformers - as the 53MY does, the transformers provide galvanic isolation and nothing else is necessary or useful.

Perhaps I'm wrong but I seem to recall that the 53MY owners manual says essentially the same thing. I don't have the manual here but I will check it this evening.

 

[PascalG]

isolator

true... but mine doesn't have a transformer... maybe later 53s had them?

pascal

 

[Genesis]

Add that instead

You're WAY ahead with the isolation transformer .vs. galvanic isolators.

I do not like the latter - at all. False senses of security are worse than none.

 

[mikep996]

Re: Add that instead

Pascal -

I mistakenly assumed that 53s all came with transformers. I guess they were added at some point in production (ours is a 1980) or perhaps they were always available as an ordering option.

In any case, the 2 shorepower transformers are definitely in the "big and heavy" category. In my experience, "heavy" always translates to "expensive."

 

[Gene]

Grounding, isolators and transformers

If you look you will probably find that the ground lead from the shore power inlet is connected to the dc ground (yellow), ac ground (green), ac neutral (white)and bonding system (green) in your boat. The isolation transformer is to correct polarity problems...that?Ls to say a hot & neutral reversal at the shore power inlet. That?Ls the way my 1990 65MY is wired (also as shown in the schematics).

The way to install a galvanic isolator (on boats Hatteras wired like mine) is to get into the main AC panel, remove the shore power inlet grounds from the non-insulated ground bus in the box, bolt them to a new insulated bus you will have to install. Place a jumper wire from the new common ground bus to the input of the galvanic isolator. Connect the output of the galvanic isolator to the old common ground bus in your AC panel.

You must be sure that the galvanic isolator and jumper wires can carry the max current (and according to ABYC a 35% overload current). I.E. you have 2 30 amp shore power inlets you should install a single 60 amp rated galvanic isolator. If you can?Lt find one you will need 2 separate 30 amp galvanic isolators - one on each shore power line.

If you almost always use the same line you?Lre right - you can simply cut the ground wire where it enters the boat or anywhere before it is tied to the boat grounding system and install the galvanic isolator there.

On a previous boat I was eating up zincs every 4-6 months and increased their life to more than 18 months by installing a galvanic isolator. I?Ld highly recommend it!

 

[jim rosenthal]

Isolation transformers..

...ARE better than galvanic isolators; the transformer completely eliminates the actual current connection between the boat and the shore current source. However they weigh a LOT and are very expensive.
Galvanic isolators, which are basically big diodes if I am not mistaken, work fine, subject to some caveats: they need to be rated as noted above, they should be watched to make sure they don't deteriorate, and they are not foolproof. What they do is block DC current coming through the AC ground leg, but they can be overloaded. I have two of them, one on each incoming AC 30amp circuit. They have worked fine so far (four years)- I use zincs up slowly, basically change them once a season, and none of the underwater hardware is excessively bright, which would really indicate a problem. Once you've seen a boat come up in the slings that does have a serious current problem, you won't forget it. All the underwater bronze parts practically glow.
I would use galvanic isolators, but keep track of them, make sure your shore cords are in good shape, and watch your zincs as you are doing. They only weigh a pound or two, by the way. Transformers are about 80-120 lbs each, and you would need two of them.

 

[ELECTRA VI]

As I said before, I do not know if I have a galvanic isolator, but I do know that one time shortly after I got the boat, I plugged in and I heard a loud buzz which let me know I had a polarity alarm in the system. Does that have anything to do with a galvanic isolator? In my 30' Chris Craft Sportfish, I did not eat up zincs like the Hatteras does and it also had a polarity alarm.

 

[Gene]

Polarity alarm & ground

Your polarity alarm indicates that the hot (black) wire and the neutral (white) wire are swapped. The neutral and the ground are normally tied together at the main electrical panel in your house or the marina. If the alarm went off, it warns that your ground could become energized at 120V if you turn on your boat?Ls main circuit breaker. This is something you might not notice right away but if someone were to swim around your boat, or hold onto a metal part of your boat and a grounded dock ladder etc. it could be a dangerous situation.

The isolation transformer can be as effective as a galvanic isolator, but it depends on how the boat is wired. If there is ANY connection between your bonding system and the ground wire in your shore power inlet, the transformer does nothing to prevent corrosion.

A galvanic isolator works by adding 2 diodes in series in each direction on parallel circuits in the ground connection. A diode will conduct electricity but only if the voltage is over .7 volts. With 2 in series any voltage of less than 1.4 volts cannot pass to your boat. Galvanic corrosion is caused when your bonding system is at a different voltage than the water your boat sits in. By blocking these low voltages from your boat, you can drastically reduce corrosion.

 

[Trojan]

isolators

Jim has the right idea.West Marine had a great write-up on this topic in there 2003 catalog.2 In depth articles can be found at 2 web sights.A great read if you would like learn about this stuff.(www.yachtsurvey.com/corrosion_in_marinas.htm)(www.yachtsurvey.com/corrosion.htm).It makes you wonder if your ever safe from this crap.Bill

 

[Doug.T]

Gene hit the nail on the head. I have two 240V 50A isolation transformers on my '86 53MY. If I read the wiring diagrams correctly, the case ground on the transformers is connected to both the incoming power and to the boat ground bus. That is where the galvanic isolator will go.

The galvanic isolator introduces about 1.4V of voltage drop in the ground system, which effectively decouples your zinks from all the other boats in your marina that don't have zinks and are using yours instead. What makes it work is that, should there be a fault, you won't notice the 1.4V drop in the ground line, but it's enough of a voltage hurdle that the galvanic corrosion voltages can't overcome it.

Beach Girl is going through zinks in 5 or 6 months, and that's a lot of zinks. I plan to check if the grounds are indeed connected, and if they are to add isolators. My old Beneteau Idylle 11.5 used to go through zinks in 3 months. I added a home made isolator and then they were less than half gone at the end of a 9 month season.

Doug T
"Beach Girl"
1986 53 MY

 

[MikeP]

I have never looked at the wiring of the transformers but per what you are saying, it sounds to me like the Hatt transformers are not actually isolation transformers…or at least they are not installed/wired that way. I had ASSumed all these years that we had "isolation" transformers, which make a galvanic isolator redundant and unnecessary.

 

[GJH]

You assumed right to begin with all these years, Mike.

 

[bobk]

You guys are beginning to confuse this old organic chemist. I have what looks to be a factory installed isolation transformer and have seen varying zinc life depending on which marina I'm in and what the condition of my neighbor's boats are. If the isolation transformer does the job of a galvanic isolator, what explains the different zinc life?

Bobk
1981 48MY

 

[Maynard Rupp]

We beat this topic to death 2 years ago. Check that out. Short story is Hatteras installed isolation transformers but chose to carry the ground inputs through these units and to the underwater ground system. Many said the grounds should terminate at the transformer. Hatteras does not like galvanic isolators as they could fail open and you would lose your ground connection.

We installed a $70.00 isolator that works with both of our 30m amp inputs. The company that makes ours said they sell lots of them and have never had a failure. This solved our zinc eating problem.

 

[fissioneng]

We beat this topic to death 2 years ago. Check that out.

For sure. Time for a little more I guess.

Hatteras does not like galvanic isolators as they could fail open and you would lose your ground connection.

We installed a $70.00 isolator that works with both of our 30m amp inputs. The company that makes ours said they sell lots of them and have never had a failure. This solved our zinc eating problem.

Things have changed since Hatteras had that opinion about isolators. There is now a revised ABYC requirement that includes a failsafe feature that the inexpensive isolators ($100) don't have. It subjects the isolator to high currents to see if it fails. If it passes the test in the standard, it is rated as failsafe.

"A-28 GALVANIC ISOLATORS
Based on ABYC's assessment of the existing technology, and the problems associated with achieving the goals of this standard, ABYC recommends compliance with this standard for all boats, associated equipment, and systems manufactured and/or installed after July 31, 2009."

Here's a link to the standard:
http://www.nmma.net/Lib/docs/nmma/cert/techupdates/A-28_Galvanic_Isolators_Standard.pdf

My transformer as designed by Hatteras did not isolate the shorepower ground, that's why I installed a failsafe isolator. Zincs used to go in 6 months, now they're in good shape after 14.

 

[Vincentc]

We installed a $70.00 isolator that works with both of our 30m amp inputs. The company that makes ours said they sell lots of them and have never had a failure. This solved our zinc eating problem.

Like Maynard said. The engineer at Yandina gave me the same advice. My zincs now last 4x as long. There is a simple manual test you can use to test the GI.