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Old 11-04-2013, 06:55   #1
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Galvanic Isolator buzzing frequently but intermittently?

When connected to shore power (50 125/250) I get an intermittent loud buzzing from my galvanic isolator. Still buzzes as I turn off breakers, all of em. I think I'm picking up current on the ground line from the water or from the line, but I'm not sure how to understand for sure.

Some electrical person please make me smarter so I can solve this and not electrocute myself or plate the whole marina with my nice shiny new propeller bronze.
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Old 11-04-2013, 07:14   #2
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Re: Galvanic Isolator buzzing frequently but intermittently?

Hi Hal, I made my own gal iso from a coouple of bridge rectiviers (35a) from radio shack and some 2"x4'x1/8" aluminum bar... Somewhere I read where you needed so many sq inches of surface area(heat sink) to offset the bridges... simple to build with 2 screws to hold the rectifiers together and poprivits to put together the aluminum... I then separated my ground from the dock, and wired/soldered it to the rectifier... My buddy tested it with his fluke meter/probe in the water and it was less than 1 volt. reason for testing was my boat was glass and his was steel on the same elect wiring on the dock...
hope this helps...included is a note from the site listed below...
happy sailing
alan

just found the article using the bridge rectifiers:
http://www.yandina.com/acrobats/GIDIYAssy.pdf

also a good link on the subject:
http://forums.sbo.sailboatowners.com...d.php?t=114098

There are two ways for a galvanic isolator to fail Either the diodes are shorted, or they are blown open. You can test them with a digital volt meter that can read positive and negative voltages. At any time, with the voltmeter on the DC range, put it across the shore power side to the boat side of the isolator. There should always be some residual electrolytic voltage (unless you are hauled out) so the meter should read something less than one volt. If it always reads zero, the diodes are shorted out. If it reads greater than about 1.2 volts then the diodes are open circuit. Switch to AC volts and check again since if AC is flowing, the DC meter setting may not show any activity.

Galvanic Isolator Explained

I also have all my grounds inside the boat tied to the same point...ac/dc/whatever
I also have gfci's wired in and have never tripped except in a lightning storm a while back or guys rewiring the docks...never figured out which one did it...
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Old 11-04-2013, 07:28   #3
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Originally Posted by H Romberg View Post
When connected to shore power (50 125/250) I get an intermittent loud buzzing from my galvanic isolator. Still buzzes as I turn off breakers, all of em. I think I'm picking up current on the ground line from the water or from the line, but I'm not sure how to understand for sure.

Some electrical person please make me smarter so I can solve this and not electrocute myself or plate the whole marina with my nice shiny new propeller bronze.
Buzzing would worry me. Sometimes it's just due to loose hardware, but it also usually means that the diodes are conducting AC. Is the isolator getting warm?

[edit] LOUD buzzing would make me extremely worried. Get that looked at pronto. Might be a miswired shore-power cable [/edit]

Measure across the isolator with a good meter (volts). If the reading is more than half a volt AC, you need to determine whether there's actually AC current going into the water. At this point, there's a possibility that a shock hazard exists so you should get someone knowledgeable to assist with further testing.

Measurements need to be made of the net current flow through your shore power cable, by putting a good loop-current meter around the whole cable. Any reading higher than a few tens of milliamps means there's some current leaking from your boat into the water. Again, you should get some knowledgeable help.
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Old 11-04-2013, 08:45   #4
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Re: Galvanic Isolator buzzing frequently but intermittently?

Buzzing of a Galvanic isolator is virtually impossible. Are you sure that the device you are hearing is in fact a galvanic isolator and not an isolating transformer. The latter would make sense. There is nothing in the galvanic isolator that will cause a buzzing. All there is in it is a handfull of diodes wired to allow ac and block dc. Even if you have ac current running through your ground ( big problem) there still would be no noise generated unless your specific isolator has a ground current alarm (never seen one like this, but possible).
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Old 11-04-2013, 09:07   #5
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Buzzing of a Galvanic isolator is virtually impossible).
A hairline crack in a diode and enough current flowing will make a buzzing sound. If this is the case the diode is the least of your problems.
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Old 11-04-2013, 09:23   #6
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Buzzing of a Galvanic isolator is virtually impossible.
If there's any steel in the diode leads or the fastening hardware, and there's enough AC current , that can also cause buzz. Again, scary for a galvanic isolator to be doing that.

To lancerbye's point... buzzes are sometimes difficult to localize. Are you 100% certain it's the galvanic isolator? Have all other adjacent devices been disconnected to confirm the source?
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Old 11-04-2013, 10:00   #7
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Re: Galvanic Isolator buzzing frequently but intermittently?

With apologies I've removed the DIY instructions from the website. Although there was an obvious disclaimer that it would not meet ABYC specifications we were warned that we could be sued if somebody was electrocuted.

The problem with that DIY project is if the shore power connection was miswired the total current load could be going through the rectifiers which would rapidly destroy them. Since they would fail open circuit that could leave the ground disconnected and leave full line voltage connected to the boat metal which could be lethal.

For this reason galvanic isolators are required by ABYC to be able to carry 130% of rated current continuously.
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Old 11-04-2013, 10:21   #8
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Re: Galvanic Isolator buzzing frequently but intermittently?

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For this reason galvanic isolators are required by ABYC to be able to carry 130% of rated current continuously.
Yandina - Just a question... has anyone contemplated using the AC current sensed going through the galvanic isolator to trip something that disconnects the AC from the boat?

My thinking there is that if you're seeing anything over maybe half an amp AC going through the isolator, then something is seriously wrong and AC should be cut. Comments?
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Old 11-04-2013, 10:58   #9
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Originally Posted by Lake-Effect View Post
Yandina - Just a question... has anyone contemplated using the AC current sensed going through the galvanic isolator to trip something that disconnects the AC from the boat?

My thinking there is that if you're seeing anything over maybe half an amp AC going through the isolator, then something is seriously wrong and AC should be cut. Comments?
What you want is an ELCI. It trips at about 30mA ground current. Required on new boats in the EU. ABYC is considering the same requirement.
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Old 11-04-2013, 11:09   #10
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Required on new boats in the EU. ABYC is considering the same requirement.
I believe its now in the ABYC recommendations, its been in the European RCD since 1994.

Dave
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Old 11-04-2013, 19:44   #11
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Re: Galvanic Isolator buzzing frequently but intermittently?

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I believe its now in the ABYC recommendations, its been in the European RCD since 1994.

Dave
An RCD or ELCI won't stop stray current from finding a path to ground by your under water metals if it is being generated from the boat next to you or from bad marina wiring.

It will only stop stray current from your boat.

Lloyd
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Old 11-04-2013, 20:00   #12
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Re: Galvanic Isolator buzzing frequently but intermittently?

Well - an ELCI will trip if AC current loss is greater than 30ma. So stray AC current is still possible at levels less than 30ma.

In any case -- ELCI will have no effect on (the more threatening) DC stray current involving an adjoining boat. For that you need separate galvanic isolation.

Charles
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Old 11-04-2013, 20:29   #13
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Originally Posted by H Romberg View Post
When connected to shore power (50 125/250) I get an intermittent loud buzzing from my galvanic isolator. Still buzzes as I turn off breakers, all of em. I think I'm picking up current on the ground line from the water or from the line, but I'm not sure how to understand for sure.

Some electrical person please make me smarter so I can solve this and not electrocute myself or plate the whole marina with my nice shiny new propeller bronze.
Do you possibly mean an "Isolation Transformer" buzzing... For a GI to buzz would be an odd thing for sure as they are nothing more than some diodes... Transformers do have a tendency to buzz.
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Old 11-04-2013, 20:37   #14
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Re: Galvanic Isolator buzzing frequently but intermittently?

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Originally Posted by Chas Erwin View Post
Well - an ELCI will trip if AC current loss is greater than 30ma. So stray AC current is still possible at levels less than 30ma.
Huh?

An ELCI monitors the balance between L and N. When they are out by 30ma, it trips. An ELCI doesn't care about stray AC current at any level coming in via boat ground(s). Plus when an ELCI trips, it doesn't open the ground.
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Old 11-04-2013, 21:16   #15
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Re: Galvanic Isolator buzzing frequently but intermittently?

Completely correct. But - the topic here concerns an AC fault on your boat not a neighbor boat.

If Line - Neutral is < than 30ma on your boat then no ELCI trip. Thus 29ma can continue to "leak" - passing outside the neutral (thus as stray current) eventually back to ground. 29ma is in the fatal range as you know.

Also correct as to the DC risk. Since AC safety green conductor is never broken stray DC current can continue to pass from the faulted neighbor boat to and through your boat returning to the neighbor via the safety green wire. In order to stop this low level DC current one needs galvanic isolation. Obviously if the neighbor boat fault potential is greater than 1.3vdc the galvanic isolator does no good.

Charles
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