Marine Electronics Forum - Galvanic Isolator?

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View Full Version : Galvanic Isolator?


96TL
06-04-2007, 09:00 AM
I am adding a Dual Pro "Pro Series" 30 amp onboard battery charger to keep my batts fresh when not in use. I keep the boat in a wet slip from April to November. I don't plan on adding any shore power receptacles, just an onboard charger. Which Galvanic Isolator do you guys recommend? I saw a 30 amp Newmar for $189.99. Seemed kind of pricey. Any other recommendations? Thanks.

Dom :thumbsup:


yandina
06-04-2007, 02:04 PM
Defender have a 50 amp model for $95. http://www.defender.com/product.jsp?path=-1|328|303336&id=605562 It is the only one that comes with an unlimited warranty and is rated to operate under water.

96TL
06-04-2007, 02:06 PM
Are you a company rep? I notice you have the same user name as the name of the Galvanic Isolator. Do you feel that I need a galvanic isolator, even though I just have an onboard battery charger?


buzzk
06-04-2007, 08:46 PM
I don't know if the guy is a company rep but I bought a yandina galvanic isolator and it works fine on my boat. I called the company in Beaufort SC and talked to them about what I needed. They were very helpful. Buzz

yandina
06-05-2007, 12:45 PM
*** EDIT BY WILEY ***

Please contact advertising@thehulltruth.com

96TL
06-05-2007, 12:50 PM
Thanks for the info Ann-Marie. You may want to consider becoming a forum sponsor. There really isn't too much info on galvanic isolators on this forum, and we could use someone experienced. I'm sure it would boost your sales.

I have another question though. What causes a boat to NEED a GI? Does this happen when underwater metals are not bonded? My garboard drain and thru-hull pick-up are both not bonded, and they are both bronze. I am adding an on-board charger to keep my batts at 100% all the time. I'm a little confused as to the proper way to bond them, or if I even need to.

Thanks.

96TL
06-05-2007, 12:52 PM
yandina - 6/5/2007 12:45 PM

Just like STDs even the best looking boat can be infected with a DC leak that can cause gonorrhea on your underwater metal.



:rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

:thumbsup:

yandina
06-05-2007, 01:12 PM
Actually the opposite is the primary cause of electrolysis. Bonding underwater metal causes most electrolysis problems. So why does everybody bond and why is it required by authorities like the ABYC? I'm glad you asked. Bonding is primarily required as a safety measure. If a short circuit were to develop between the 120V Ac and the 12 V DC in your battery charger, that could put 120 volts on your underwater metal. So long as the underwater metal is "bonded" to the AC ground wire, a short like that will blow a fuse or circuit breaker and remove the dangerous voltage. Without that bonding, there is little danger to the boat passengers but it is lethal to swimmers in the vicinity. Read this :- http://www.mikeholt.com/newsletters.php?action=display&letterID=36

A piece of metal on its own in sea water is not a candidate for electrolysis. Electrolysis occurs when you create a "battery" by having two different types of metal in the water CONNECTED TOGETHER to complete the circuit. Examples of this are the bronze propeller on a stainless shaft. A Galvanic Isolator will do nothing to protect this. It is continuous and permanent and that is why you use a zinc to provide a "sacrificial" anode to be eroded instead of your machinery.

The primary source for DC current is the mandatory safety ground wire coming from the dock. This ground wire is connected to the underwater metal on all the boats at a marina so it is like one big battery and your underwater metal is another plate in the battery. A galvanic isolator BLOCKS any DC current flowing through the ground wire but still provides an AC path back to the breaker box to provide a safety AC ground.

baitkiller
06-05-2007, 01:15 PM
96TL, Here is the 5 cent version. A galvanic isolator, "isolates" the green wire in a shore cord. It effectively disconnects it unless a ground fault occurs exceeding a set parameter. This is important with a classic AC system because the green wire becomes one with all grounded things aboard and eventually makes contact with the bonded fittings. Without the isolator you are electrically connected to every thing else around via the green wire including the dock and neighboring craft etc. Because your electrically connected your metals are prone to metal transfer occurring from differing potentials, stray and galvanic currents.

A stand alone charger is not effectively attached to the boat. (the green wire stops at the charger and never hits a ground bus, the transformer is shielded) So the isolator becomes a mute point. However the addition of a branch circuit necessitates the need for a system requiring single point grounds etc. etc. and will by default require an isolator.

Install the nice 15 amp Marinco extension cord receptacle, fuse the charge leads and insure your dockside outlet is GFCI and you'll be fine.

yandina
06-05-2007, 01:32 PM
Bloody discounters. You submit a 10 cent version and 3 minutes later there is a 5 cent version. :)

Although a GFCI can provide a level of protection for AC leakage shocks under normal circumstances, it is my understanding that the leakage they will permit before they trip is enough to kill you in water. A GFCI is not approved by ABYC as a substitute for a safety ground.

96TL
06-05-2007, 02:07 PM
Yandina, would you still recommend a GI if I'm only using an onboard charger? There will be no branch circuits.

And thanks for all the explanations. You guys are great.

Dom

baitkiller
06-05-2007, 02:15 PM
Sorry Yandina, I didnt mean to be the cheap guy.

E-11 only offers the one exception to dual pole breakers at 10', single phase design and single point grounds. And that exception adresses only stand alone battery chargers. I dont have time for chapter and verse now but I may later.

The risk of killing a swimmer is huge in fresh water and very little in salt.

Cheers, nice stuff you make BTW.
:thumbsup:

yandina
06-05-2007, 05:41 PM
I would only install a galvanic isolator if your zincs are being eaten up rapidly. While the zincs are adequate they will provide protection but if they are eroding away so that you need to replace them more than once a year then it would justify an isolator.

I give similar advise regarding bonding underwater metal items even though it contradicts the traditional requirements of surveyors and that is only bond if you see evidence of electrolysis. Don't fix it if it ain't broke. An isolated through hull is fairly immune to electrolysis but you may lose that immunity if you bond it to other items. Keep in mind, however, that "isolated" mean not connected electrically to the internal ground, typically the engine block on an inboard engine. A raw water through hull for engine cooling may appear to be isolated but it is in fact connected to the engine block through the salt water in the rubber hose.

fishy-a-knot-o
06-05-2007, 06:08 PM
Yandnia: I have a galvanic issue for you. I have a 36 ft twin inboard that is bonded. Has a factory-installed GI. The unit is installed behind by electrical pannel. When I got the boat, the external "monitor" pannel kept beeping "unprotected." I tried to test the bonding system with a galvanic activity tester. I couldn't really figure out what I was looking at. Someone told me to buy a new one and install it right next to the shore power inlet and that should solve the problem and protect me. Then remove the old one. What do you think?

Thanks in advance. BTW if the answer is "yes, do that" I'll buy it from you.

96TL
06-05-2007, 06:29 PM
Well, my boat is only one season old, and the zincs looked practically brand new at the end of the season. I'm in a new slip this year, and both guys to either side of me use shore power. I'm more concerned about electrolysis now, and I thought bonding the garboard drain and thru-hull would help. It sounds like I'm better off leaving them alone. I have one large zinc bolted to my engine bracket, and one large saddle zinc on my O/B tilt trim bracket. This bonding stuff really confuses me for some reason. I think there is too much contradicting info out there.

I just want to make sure I have this all right so far.

#1 - I do not NEED the GI, but it would not hurt to have one. It would protect my rig from the guy docked next to me, and from a faulty dock.

#2 - I should not bond the thru-hull and garboard drain as long as niether show any sign or electrolysis, and my zincs are not being eaten up rapidly.

I have another question. Since my thru-hulls and garboard drain are not bonded, would the GI still protect them from electrolysis, even though there is no physical connection?

yandina
06-06-2007, 03:36 PM
fishy-a-knot-o - 6/5/2007 6:08 PM

Yandina: I have a galvanic issue for you. I have a 36 ft twin inboard that is bonded. Has a factory-installed GI. The unit is installed behind by electrical pannel. When I got the boat, the external "monitor" pannel kept beeping "unprotected." I tried to test the bonding system with a galvanic activity tester. I couldn't really figure out what I was looking at. Someone told me to buy a new one and install it right next to the shore power inlet and that should solve the problem and protect me. Then remove the old one. What do you think?

Thanks in advance. BTW if the answer is "yes, do that" I'll buy it from you.
LOL, "Galvanic Activity Testers" and similar instruments will give you pages of nearly useless data that then needs to be analyzed to give you which ever answer you wanted in the first place.

We don't sell monitors for our GIs. The ABYC specifications for the monitor are a fairly recent addition since we started production and they are very badly specified. To meet the intention of the ABYC would add over $100 to the cost. Many manufacturers just include just a polarity tester. The specifications call for a remote indicator "visible to the operator " - DUH you don't use a shore power cable when operating the boat. Galvanic isolators are incredibly reliable. If you are going to spend over $100 on monitoring something there are much higher priorities than a a GI, such as exhaust manifold temperature, high level bilge alarm etc.!!!!

We always recommend installing it at the shore power entry - see Owner's Manual at http://www.yandina.com/acrobats/GalvOwnManual.pdf. The reason for this is that someone subsequently adding equipment to the boat may pick up the ground between the isolator and the cable entry for the addition and end up using a common ground to short out the isolator. It is more a physical protection to make sure all the ground goes through the isolator, it is not an "electrical" requirement. However if it is installed in an electrical panel it can be quite a detective job to trace the incoming ground back to the entry to make sure there are no other connections to it.

OK it is unlikely there is anything wrong with your isolator. Not knowing what or how they are monitoring, I can't comment on the condition of the monitor.

Here is how to test a galvanic isolator once it is installed.

With the boat on shore power and normal electrical items running, preferably including any on-board chargers or inverters, take a fairly good quality DC volt meter and measure the DC voltage across the isolator. If it reads zero that would indicate a shorted isolator or a wiring error that is shorting it out. It should read something above about 0.1 volts and less than 1.2 volts which will show how much it is blocking. This does not check for an open circuit isolator.

Occasionally an older boat will need a galvanic capacitor. AC leakage due to old salty wiring will cause AC to flow back through the isolator. This can reduce the effectiveness of the isolator up to 50% because the DC will ride through piggyback on top of the AC. A galvanic capacitor bypasses this AC current and maintains the isolation at 100%. However again, ABYC have no specifications on capacitor size so manufacturers include a "token" capacitor that is woefully inadequate just to say they have one. Not one that I've found will supply specifications on their capacitor. We don't play tricks. We do not include a capacitor and it is rarely needed. If you do need one we supply one that can be installed that is rated for 5 amps. Try to find THAT specification on our competition!!

Do I need a Galvanic Capacitor? Probably not but here is how to measure AC leakage after installing the isolator. http://www.yandina.com/GIsolCap.html

yandina
06-06-2007, 03:48 PM
96TL - 6/5/2007 6:29 PM

Well, my boat is only one season old, and the zincs looked practically brand new at the end of the season. - - CUT - -
I just want to make sure I have this all right so far.

#1 - I do not NEED the GI, but it would not hurt to have one. It would protect my rig from the guy docked next to me, and from a faulty dock.

#2 - I should not bond the thru-hull and garboard drain as long as niether show any sign or electrolysis, and my zincs are not being eaten up rapidly.

I have another question. Since my thru-hulls and garboard drain are not bonded, would the GI still protect them from electrolysis, even though there is no physical connection?


1. Correct, installing a GI is good insurance and won't do any harm if you didn't need it.
2. Correct, if it ain't breaking, don't fix it, you may be inviting problems. (Not all experts will agree with me here and it conflicts with standard specifications so surveyors may list it as a defect. So connect it up to get the survey and then take it off again!!!.
3. The isolator will only protect underwater metal from electrolysis currents arriving through the ground conductor, which unfortunately, is necessary for safety reasons. Unbonded and isolated metal that is not connected directly or indirectly to the ground lead is not at risk from ground cable electrolysis UNTIL you bond it to the ground. So an isolator will not provide protection to that isolated plug but it doesn't need protection. Once you bond it, the isolator can provide the protection it didn't need until you bonded it. :)

Keep in mind too, that there is another source of electrolysis that has nothing to do with the shore power cable or isolators. It is the galvanic effect of two different metals in water that are electrically connected together. If you bond an item unnecessarily it now becomes a candidate for "on board" electrolysis and will now be dependent on the zinc for protection. I repeat, if it ain't broke, don't fix it. "Broke" being evidence of electrolysis - paint pitting off with shiny spots or cavities.

MrPat
06-07-2007, 10:38 AM
Buy one! I installed a charger on my old boat. It did not have an isolator. I used to leave the charger connected 24/7 in a wet slip. In less than 3 months I had to replace the outboard engine brackets on both Yamahas. If you only connect the charger for a few hours to top off the batteries you should be OK. I did that and also added one of those zinc groupers and stopped the problem.

mortond
06-07-2007, 01:02 PM
Isolation transformers are slowly coming down in price (shipping is a bear at 65 pounds each)
If you have a metal boat, as I do, or a fairly large boat, with extensive AC systems and really want to isolate the boat from shore power this is the way to go.
3.6Kw units, ProSafe and Charles, are ABYC approved and go for about $455 each.
Ensuring the unit's neutral and grounding secondaries are bonded to the boats ground system is important; whereas, making sure the units primaries are NOT is even more important. Once installed correctly everything electrical on the boat is isolated from the marina

David Morton

BajaFeeling
06-07-2007, 01:18 PM
MrPat - 6/6/2007 6:38 PMBuy one! I installed a charger on my old boat. It did not have an isolator. I used to leave the charger connected 24/7 in a wet slip. In less than 3 months I had to replace the outboard engine brackets on both Yamahas. If you only connect the charger for a few hours to top off the batteries you should be OK. I did that and also added one of those zinc groupers and stopped the problem.

MrPat,
Can you give us the make and name of the Charger. Also did you check for correct polarity on the shore connection?

Jim_Arndt
06-07-2007, 01:41 PM
I was fine for months, then some bozo moved in with a "Hot" boat. My outdrive was flaking paint and pitted before I caught the problem. The damage occurred in less than a week, I checked my zinc's one week previous and they were at 80%. When I noted the problem the zinc's were 95% gone and the outdrive was damaged.

Get a GI, it's cheap insurance.

tonybanco
06-08-2007, 02:37 AM
yandina - 6/6/2007 2:45 AM

Galvanic isolators are like condoms. You don't really need one 99% of the time until you tie up to an infected dock OR THE BOAT THAT JUST TIED UP NEXT TO YOU IS INFECTED. With most docking you don't need a condom but that one time you do it will pay for itself. Just like STDs even the best looking boat can be infected with a DC leak that can cause gonorrhea on your underwater metal.

.


Anne-Marie,

Please help me here as I am becoming very confused, you state here that a GI will stop leakage from an infected dock or infected neighbouring boats.

I thought that you stated GI are only effective when YOU are connected to shore power and it is your faulty connection that causes galvanic corrosion to your fittings and neighbouring boats.

If my understanding is correct here HOW can we protect ourselves from electrically leakey vessels around us.

Could you please clear this up for us?

Tony

MrPat
06-08-2007, 07:59 AM
BajaFeeling - 6/7/2007 1:18 PM



MrPat - 6/6/2007 6:38 PMBuy one! I installed a charger on my old boat. It did not have an isolator. I used to leave the charger connected 24/7 in a wet slip. In less than 3 months I had to replace the outboard engine brackets on both Yamahas. If you only connect the charger for a few hours to top off the batteries you should be OK. I did that and also added one of those zinc groupers and stopped the problem.

MrPat,
Can you give us the make and name of the Charger. Also did you check for correct polarity on the shore connection?


Guest Sportsman Power Center, 2633-OS

BajaFeeling
06-08-2007, 03:53 PM
Interesting, I am running the Guest Cruising Series #2614, I installed it over a year ago it runs 24/7 without an GI.
Replaced the Zink 11 month later and still had 63% of the Zink left by weight. My boat is in a Bottom-Liner and that also isolates it from other boats on the dock.

MrPat
06-09-2007, 06:55 AM
BajaFeeling - 6/8/2007 3:53 PM

Interesting, I am running the Guest Cruising Series #2614, I installed it over a year ago it runs 24/7 without an GI.
Replaced the Zink 11 month later and still had 63% of the Zink left by weight. My boat is in a Bottom-Liner and that also isolates it from other boats on the dock.

Your AC Power at the dock may not be introducing stray current through the AC ground wire. No Stray current, no problem.

yandina
06-09-2007, 12:08 PM
tonybanco - 6/8/2007 2:37 AM
Anne-Marie,

Please help me here as I am becoming very confused, you state here that a GI will stop leakage from an infected dock or infected neighboring boats.

I thought that you stated GI are only effective when YOU are connected to shore power and it is your faulty connection that causes galvanic corrosion to your fittings and neighboring boats.

If my understanding is correct here HOW can we protect ourselves from electrically leaky vessels around us.

Could you please clear this up for us?

Tony

Some you can stop, some you can't.

The ones you can:-

When an infected boat snuggles up beside you and is spewing electrons out into the water, those electrons will take the nearest path back to the source to complete the circuit. If you have shore power connected, then even though your boat and your dock supply are clean, the electrolysis currents will flow through your boat to the shore power cable and back to the infected boat via the ground line in the dock. A galvanic isolator in your shore power cord will block this current and make it find another path that doesn't eat your boat up in the process.

The ones you can't.

However having installed a galvanic isolator so your boat is no longer a "direct" target, it may never the less be a link in the shortest path to another boat that doesn't have a galvanic isolator. So the current may enter your boat at one point, take a short cut of 20 feet and exit your boat at another point on its way to the destination. In this case, zincs are your only protection however the threat is usually secondary compared to a direct run to shore without an isolator.

Jim_Arndt
06-22-2007, 05:56 PM
baitkiller - 6/5/2007 10:15 AM

A stand alone charger is not effectively attached to the boat. (the green wire stops at the charger and never hits a ground bus, the transformer is shielded) So the isolator becomes a mute point. However the addition of a branch circuit necessitates the need for a system requiring single point grounds etc. etc. and will by default require an isolator.

Install the nice 15 amp Marinco extension cord receptacle, fuse the charge leads and insure your dockside outlet is GFCI and you'll be fine.


Here's a question regarding the above. The AC Neutral (White Wire) is effectively the same as the AC Ground (Green or bare copper.) The difference is the AC Ground is typically grounded by a ground rod driven into the earth (or a cold water supply line.) The Neutral is run to the power pole, then a copper wire is run down the side of the power poles and grounded with a ground rod. At my house, I have underground wiring. The AC Neutral AND the AC ground both terminate at the same bus bar.

So if that's true, wouldn't the AC Neutral also be a risk for electrolysis? Does an Isolator only block the AC ground, and not the Neutral? Just thinking out loud....

mikeporterinmd
06-22-2007, 10:57 PM
AC neutral and ground are never connected together on a boat's panel in the same way they are in a house. Doing so is very dangerous. However AC ground should be connected to DC neutral, so this is the path between boats. DC
neutral is connected to the underwater bonding circuit, which is connected to AC ground. Breaking this path in
a safe manner using the isolator is the goal. You could also disconnect AC ground from DC neutral, but if an AC/DC
device ever shorts AC to DC neutral, you will kill any swimmers or anyone that happens to touch anything connected
to DC neutral. In other words, if your charger malfunctions and shorts to the DC neutral, you are going to get zapped.

There is a good section on this in Nigel Caulder's book. Anyone installing this sort of setup really should read this
book first and then seek clarification here if needed.

Mike



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