Galvanic Isolator confusion

I am at the point that I feel I really need a galvanic isolator. Problem is that I can't get a handle on what I really need in design type, and I'm trying to save boat bucks as much as possible and still get the job done. I am fully aware of the ABYC change for remote monitoring. For the sake of this discussion, let's eliminate this part of the topic.

For this discussion, I am trying to decide between a Newmar GI-30:

http://www.defender.com/product.jsp?path=-1|328|303336&id=52807

and the Yandina DI-50:

http://www.defender.com/product.jsp?path=-1|328|303336&id=605562

From the Newmar description on the first link above:

"the units feature a large capacitor, providing a secondary low impedance path for stray AC current and improved galvanic protection.
Note: galvanic isolators are available from other manufacturers without the secondary path because they eliminated the capacitor to reduce the cost. It is worth the few extra dollars to purchase a isolator that contains the very important capacitor"

Now, I go over to the Yandina site and find this general page:

http://www.yandina.com/galvanicIsolator.htm

"Since some electrolytic voltages are higher than 0.6 volts, a good galvanic isolator should have two diodes in series in each direction to give a 1.2 volt isolation. Some also add a capacitor to increase the ability to conduct AC current, however I personally think this is a mistake as it does allow low level AC currents to flow and cause electrolytic type activity, even if not true electrolysis. This activity can remove paint from the fitting and generate chlorine bubbles that damage surrounding antifouling paint."


and more detail on the capacitor side here:

http://www.yandina.com/GIsolCap.html

"NO. The galvanic isolator is designed to carry 130% of the maximum shore power AC current rating you are using. However very small AC leakage currents can reduce the level of DC protection available from a galvanic isolator.

There is no easy answer to the capacitor question. The use of a capacitor is sufficiently controversial that the ABYC continue to list it as optional in their specifications.

The theory is that if AC is leaking to ground through your galvanic isolator, then the isolating diodes are going into conduction for a percentage of each half cycle and while they are in conduction, they are no longer suppressing any superimposed DC current. The DC potential would be added to one half cycle and subtracted from the other. If the total voltage when they are added exceeds about 1.2 volts then there is a path for just a portion of the DC voltage you are trying to block.

So by adding a capacitor you are trying to provide a path for the AC current while still blocking the DC. The size of the capacitor boils down to what you consider acceptable leakage current from the AC equipment on your boat and you have to size the capacitor so the voltage across it at this current is typically small compared to the DC voltages you are trying to avoid. If you are protecting from DC voltages typically in the 0.9 volts range maximum, then you have to keep the AC voltage across the capacitor to less than 0.3 volts.

[snip]

Therein lies the dilemma and the original question. What is acceptable leakage? My philophosy is you shouldn't be trying to cover up a problem by conducting it to ground. I maintain you should check every item on your AC supply and if any show any leakage at all they need to be repaired. That is a safer alternative to just allowing the leakage to flow to ground."


So, with all of the above, which seems to reflect a lot of opinion, can any of our electrical gurus address this issue of whether a capacitor is or is not a good idea?

What else should I be looking at/am missing as I look at these units?

Thanks!

Emerald said:

My philophosy is you shouldn't be trying to cover up a problem by conducting it to ground.

Click to expand...

My initial reaction is to question the acceptability ground leaks from an AC system, into salt water, where people may swim (hull cleaning) in close proximity.

Gareth
Freyja E35 #241 1972

Little article on Galvanic Isolators, at the Boat US site.

http://www.boatus.com/seaworthy/galvanic/default.asp

Plus, perhaps this thread should refer to the similar related thread:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=2918&referrerid=28

FYI,
Loren

I'm feeling... Isolated

At the boat show last week a marine electrical company had some specials and new-old-stock items...
I picked up a Guest model 2433 for $50.
From my research on pricing, this appears to be from 2007, and the current ones all cost $200.+ but they do have a monitoring light. (Still, used ones at the local marine second hand store go for $100.)

Before buying this one I quizzed one of the best surveyors in the area and found that this is acceptable. It turns out that it is easy to test it with a standard diode checker and was told that that would be good to do annually.
It is a sturdy-appearing item, and the innards are potted. Specs say that it's waterproof.

Like all other boat projects, the installation took way too long and even a little more money for some #10 crimp rings... different size for each end of the link from the isolator to the ground strip on the panel.

These is one oddity that I found while working behind that panel: as far as I can tell, the AC ground buss bar is separate from the large DC buss nearby.
For some reason I thought that all grounds went to the engine block...


I never received any wiring schematic with the boat, so if anyone has one for the late 80's Ericson's or has happened to look behind their distribution panel at the buss bar systems, would you kindly let me know if the two grounds are separate on your boat?

Thanks,
Loren

There is one oddity that I found while working behind that panel: as far as I can tell, the AC ground buss bar is separate from the large DC buss nearby.
For some reason I thought that all grounds went to the engine block...

Click to expand...

Loren - The grounds are tied together at the engine, not at the panel. There is only one common ground point This shows on the wiring diagrams I've seen in the document section. 35-3 page 55, E-32 page 48.

This avoids most of the coupling between the AC & DC.

DC Ground and AC Ground Questions

Until I can get a look at a couple of other mid-80's Ericsons in our YC, I can verify that in our panel the ground buss for the AC is totally separate from the DC buss.

I was over at the local marine electronics store today on another errand and they got out their ABYC manual and looked up the recommendation. In theory the two grounds should be connected, but they said that actually it is not on many boats. Even in the industry opinions vary on whether it's really a good idea.

We got into this after studying the manual for a new Promariner ProTech 1220i battery charger I am installing (replacing the old '95 Statpower 20). This new charger has a prominent Chassis Ground stud on the side, separate from the DC ground connection on the bottom where the multiple pos. battery wires take off. The manual sez nothing about what sort of "ground" that stud is for, so they called up the company rep.

Turns out it is intended to go to the ship's DC ground and is normally part of the bonding wiring. Our boat has never had any bonding, and like all Ericsons of its generation came with Marlon thruhulls. Other than the strut/shaft and the refrigeration "keel cooler" I added, there is no metal under the water.

Opinion today is not to tie that "chassis ground" to the DC ground screw on the charger, since that would complete a circuit not in existence on our model now.

It occurs to me that it would be interesting and helpful if you other owners of similar-era Ericsons would pop open your breaker panel and see if those two different busses are connected in any way.

Tom, I should note that there is nothing on or near our engine that connects to the AC ground. You are correct about the 35-3 diagram showing such a wire, though. Confusing.

Thanks,
Loren

FWIW

I have found the easiest way to reduce galvanic corrosion problems that stem from shore power is to simply not plug the boat in. If I do plug in it is only for long enough to top off the batteries or maybe to run the air conditioning on a hot day at a marina. I thought about the isolator but quickly found other places to spend the time and money.

I ended up buying the Newmar GI-30 I originally posted about. For the first time in my ownership of Emerald, she didn't eat 4 zincs in one season (2 zincs at a time replacd by diver once per season, with zincs always down to the last remnants or gone at mid-season replacement and end of season haul-out). I do stay plugged in most of the time.

Just curious David, why do you stay plugged in all the time? Once your batteries are charged why not unplug? If you are running an electric heater for the winter why not do so by not running it through the boats AC system? Escape Plan was going through zincs pretty quickly when I was leaving her plugged in a lot which is why I stopped upon the reccomendation of my electrical guy. Now the engine zinc lasts all summer and the shaft collar zincs end the year at about 50%.

I'd say I stay plugged in from a range of convenience/laziness to superstition. I'm on the boat near daily, often at night, and I've noticed that even a short period of running several cabin lights etc. (10W and 20W each depending on the fixture) would result in my 3 stage charger dropping from float to the middle "trickle" rate. I just got about 7 years out of the last set of batteries, so this is where the superstition comes in. They were always left in the float state and I feel I got max life, so I'm just continuing here to make sure after these constant little power nibbles that they go back up to float. Then there's the lazy/convenience part. I run a mix of 12V and AC when puttering around, and if I leave her plugged in, whatever I need is a breaker switch away. I guess I'd also like to think that if for some reason I didn't get down for a long stretch and the auto bilge pump kicked on and ran near continuously, there might be a chance that I'd keep the batteries up. I do unplug her for high tides (our pier often goes under) and thunderstorms. The only items on when I leave her are the charger and auto bilge pump.

My E27 never had ac and i have heard that ericson mis-wired som of their ac anyways. A year ago I ripped out all wiring and started over. Dc and ac added plus bonding including keel and all thru-hulls and aft pulpit rail. All connects to engine. When i get to salt water this year i will add in a zinc plate that hangs over transom to sacrafice itself for my boat. Btw, as someone else said earlier, unplug your ac when you leave - a great idea. Consider adding a small solar panel to charge things. Then all you have to worry about is the stray current passing between those miswired stinkpots on either side of you.

David what size battery bank do you have and what type of batteries. I am going on 10 years on a set of Gels that were recently tested and showed 90% of original CCA. I can see your reasoning for convenience but it would seem to me to pretty easy to plug in and unplug when you come and go. As for the bilge pump how often does it run? I get rainwater in my bilge from the mast but even so the pump rarely cycles more than twice a month and when it does its taking maybe 2amp hours. Even if the pump pulled 8 amps and ran for 15 minutes you would only lose 2 amp hours. Dont get me wrong I like the idea of an isolator I just found they were expensive time consuming to install and from what I have heard they are not a pancea for corrosion. Most electrical guys I have spoken to advocate not plugging in as the best prevention.

My next boat I am plan to not have a shorepower connection at all. Solar and wind to charge batteries with a genset to run air conditioning and make juice when becalmed on a cloudy day. FWIW I am also not a fan of bonding as every boat that I have worked on that was bonded has had more corriosion issues than unbonded boats. I prefer to use a separate zinc for each underwater metal object. Conencting them all just ensures they all suffer. Bonding in theory is a good idea but it is not practical as too much resistance developes in the connections.

There is a publication called the Metal Boat Quarterly. Very good info on corrosion and bonding. Here is a link to a copy.

http://www.kastenmarine.com/mbqCref.pdf

Emerald said:

I'd say I stay plugged in from a range of convenience/laziness to superstition. I'm on the boat near daily, often at night, and I've noticed that even a short period of running several cabin lights etc. (10W and 20W each depending on the fixture) would result in my 3 stage charger dropping from float to the middle "trickle" rate. I just got about 7 years out of the last set of batteries, so this is where the superstition comes in. They were always left in the float state and I feel I got max life, so I'm just continuing here to make sure after these constant little power nibbles that they go back up to float. Then there's the lazy/convenience part. I run a mix of 12V and AC when puttering around, and if I leave her plugged in, whatever I need is a breaker switch away. I guess I'd also like to think that if for some reason I didn't get down for a long stretch and the auto bilge pump kicked on and ran near continuously, there might be a chance that I'd keep the batteries up. I do unplug her for high tides (our pier often goes under) and thunderstorms. The only items on when I leave her are the charger and auto bilge pump.

Click to expand...

While we moor at a dock, it is interesting to see that my reasons for staying plugged into shore power are very similar to yours. Matter of fact it is this "pass through" DC supply that keeps our fridge cold all summer so that we always have cold drinks at the boat. That and, of course having plenty of DC power for the "what if" worry of having a leak occur when no one is around for a day and the desirability of having both bilge pumps run.

Unless I am working on the electrical system our boat is always plugged in while at the dock.

Loren

Huh?

My next boat I am plan to not have a shorepower connection at all. Solar and wind to charge batteries with a genset to run air conditioning and make juice when becalmed on a cloudy day.

Click to expand...

I do have an argument with the idea that a galvanic isolator is too costly and time consuming, but solar, wind, and a genset are OK.

In my case, if the Admiral is happy I am happy, and the Admiral is not happy having to empty the fridge when we leave the boat only to return with the same stuff a few days later. We would also have to buy ice which is a problem on an E-34 because of the small box.

Not being racers, we could afford the added weight of having an extra zinc or two on the shaft.

Tom I see your point for sure. I would never bother with wind solar or a genset on an ericson. There is simply not enough room let alone the expense. My goals with my next boat are more self sufficient cruising and my plans involve spending signicant amounts of time in places where there is no shore power. On a boat with space wind and solar alone can easily keep up with the demands of a good fridge I have friends who live this way in the tropics with no engines as well. Granted the tropics afford better sun for solar and trades for the wind, which is why my plan involves a genset for providing AC power for tools and other things when I need it.

If you plan to leave your fridge running all the time on an Ericson then you certainly will need to stay plugged in. I cant imagine myself doing this unless I am living aboard though. It is a huge waste of energy in my opinion plus the factory ice box means you need to defrost pretty often. Then there is the wear and tear of the fridge unit cycling for days on end when no one is on the boat. Not to mention the risk of an electrical issue occuring when no one is on the boat. When I leave my boat all circuits are off, shorepower is unplugged, sea cocks closed. I prefer to just turn the fridge on the night before or often just dont worry about it and load up, turn the thing on and shove off. By noon the beers cold enough for me.

By all means if you plan to leave your boat plugged in and even more so if you are going to be cycling electrical devices all week long then a galvanic isolator is a must. There is no way zincs could keep up with that sort of action.

Ted - I don't think the use of a boat affects the zincs, just the fact that it is tied to an earth ground.

The common failure mode for sailboat fridges is the seals going bad. I suspect that this is more of an age problem than use. My previous Adler Barbour leaked in the winter. Maybe if I kept it running year around it would still be running.

In my case I am on the boat generally five or six daze a week, some of them in the marina. Living two hours away doesn't afford the luxury of stopping by the night before to turn on the fridge for the week enders. The marina is not downtown.

Hi Ted,

I've opted for trying to keep my electrical use as low and simple as possible. Yes, I know my 10W and 20W bulbs don't mesh with that, but what I omitted is that once I'm away from the pier, if I need light for any duration, I use oil lamps and the electric lights come on as needed only as long as needed. So, with this as the background, I am using a pair of standard deep cycle group 27 flooded batteries. I'm fully aware of the differences on starting batteries versus deep cycles versus hybrids, so we don't need to go there as, yes, I start my 3GM30F off the deep cycles.

I played around with plugging/unplugging while only on the boat, but what I noticed was that my charger really seemed to spend most of its time in the trickle stage when I did this, and I didn't seem to be on float like I had been. I attributed this to going on the boat, plugging in, using electric, and then unplugging and the batteries really never getting a chance to be charged back to the float level, so back to my superstition approach of duplicating what had gotten me good life out of the prior set. Also, knowing that flooded lead acid batteries don't like staying discharged for any period of time, this would seem to keep them toped off and happy. Of course, this approach had the downside of galvanic action that was unacceptable, and hence the isolator.

Regarding bilge pumps and leaks. It's the thing you don't expect that's the gotcha. Last year I was having all sorts of fun with my packing failing in my stuffing box. I could write a mini novel on what I wrestled with, but bottom line was that I would go through periods with no leaking, and then we could be spraying water the next day (while running). Not good. There was a period where I came down for my boat checks to find the stuffing box had leaked enough to activate the automatic bilge pump. This was a scenario where the slow trickle was enough to flood the boat without the pump, but not so much as to be beyond the pump or to cause the pump to run continuously. This seemed to reinforce the idea of having the batteries running the pump on a charger to make sure the pump would always have a chance of running.

My experiences on bonding everything mesh with others. Connecting it all just means you eat it all up. I've had better luck keeping thru-hulls etc. separate. Also, if I remember this correctly, true marine grade hose, unlike automotive hose, does not have carbon black in it, which can promote electrolysis. Make sure you don't connect items electrically via the rubber hose, which you would never think of as conductive.

I think maybe the only conclusion we can draw from all this is that depending on your needs, motivations etc., there are a couple different approaches on staying plugged in or not all with their respective pros and cons. I have a little solar trickle charger back from many years ago. I often look at it and think I should give it another whirl. Perhaps when the sun comes out after this weekends blizzard - 18"-26" is the current forecast I'm seeing. Good thing I like snow, but in all seriousness, I have once again had to cancel a weekend sail. Had crew lined up for Sunday, and I don't think it's happening

Electricity is an interesting topic. Consider the fact that in an AC dock power disribution, the Neutral (white ) wire is connected to the Equipment Grounding Conductor, (the green or bare wire) at the main disconnect (where the Marina is metered from the Utility source) and that along the electrical path to the dock outlets there are numerous loads (the boats that are plugged in, and the dock lights, fire supression/alarm system, and who knows what all) there is always the likely hood of a ground loop. This occurs where another inadvertant connection is made between the white and the green wires. Some on-board referidgerators cause this, (in our marina this was determined to be the cause) or a miswired boat electrical panel...That ground loop fault current is often the cause of zinc degredation in the marina. We had numerous complaints at our marina of rapid dezincafacation until the dock power was checked out and it was discovered that a connection box was half full of water (rain) and this likely caused a leakage current....
Any hoo, the main topic was AC to DC grounding...If the DC ground is connected to the AC ground in your boat, you may be allowing sinusoidal noise into sensitive DC equipment, i.e., the pc, gps, sounder, vhf or SSB radio, etc.... which probably is at best an annoyance at the dock. So, when underway, you only have to deal with your altenator AC noise. BUT If a stray current is allowed onto my electrical system, I dont want it to flow through my shaft, or through hull expensive :nerd:bits, so I would rather seperate AC from DC....OK, I have rambled long enough.:nerd: