MapisM
Well-Known Member
What's the most recommended brand/type nowadays, folks?
32A shorepower line, if that matters.
TIA!
32A shorepower line, if that matters.
TIA!
Which galvanic isolator
- Thread starter MapisM
- Start date
Solent sailer
Well-Known Member
Use an isolating transformer, its the only way to be sure.
BartW
Well-Known Member
Blue Angel has been running for 26 years, without any galvanic isolation.
It took two seasons before I realised that I didn't have a isolation transformer,
there was a big transformer (partially hidden) that was for another purpose (203Vac ->24Vac supply for halogen lights)
I'm aware that I do not have the best system, but as we didn't have ANY issue's with that, (corrosion nor safety)
I concluded that the installation must be good enough and save, and decided not to add that additional weight of a transformer.
back to OP, let me know if you want a price for a Victron transformer
It took two seasons before I realised that I didn't have a isolation transformer,
there was a big transformer (partially hidden) that was for another purpose (203Vac ->24Vac supply for halogen lights)
I'm aware that I do not have the best system, but as we didn't have ANY issue's with that, (corrosion nor safety)
I concluded that the installation must be good enough and save, and decided not to add that additional weight of a transformer.
back to OP, let me know if you want a price for a Victron transformer
rafiki_
Well-Known Member
I have one from Safeshore Marine on Rafiki http://www.safeshoremarine.com/
I’m not sure about the max current load, but I have found them very helpful.
I’m not sure about the max current load, but I have found them very helpful.
MapisM
Well-Known Member
Now, this is interesting. Three replies so far, and three conflicting suggestions:
1) fit an isolating transformer
2) do nothing
3) fit a galvanic isolator
I for one would be interested to better understand the pros/cons and the reasoning behind each choice!
1) fit an isolating transformer
2) do nothing
3) fit a galvanic isolator
I for one would be interested to better understand the pros/cons and the reasoning behind each choice!
kashurst
Well-Known Member
Isolation transformer will give you complete isolation from problematic earth issues - just make sure it has a link switch to join boat "earth "(the anodes) directly to shore power earth for when the boat is on the hard. Relatively expensive and heavy.
Doing nothing is perfectly OK, IF everything else on your boat, your neighbours boat and all the wiring/metal work in your marina is OK too. In the med if you antifoul your props and shafts that also slows down/reduces any galvanic effects because the paint insulates the metalwork.
Galvanic isolators, they provide a connection to shore power earth but only allow conduction of electricity if there is an electrical potential difference of greater than @ 0.9 Volts. So relatively low cost galvanic protection (i.e. your anodes only protect your boat) and a shore power earthing route is always established in the water and on the hard.
The downside is that they can fail (very unlikely) and unless you test them you won't know. But most (all?) boats these days have residual current detector(s) in the mains electrical supply panel so if there is an electrical problem they will isolate the problem automatically anyway.
My first boat in the med didn't have a galvanic isolator and the main anodes lasted @ 14 months. I fitted an onboard galvanic isolator and the anodes lasted @ 25 months. I found similar results on my last two boats that both had factory fitted galvanic isolators.
Doing nothing is perfectly OK, IF everything else on your boat, your neighbours boat and all the wiring/metal work in your marina is OK too. In the med if you antifoul your props and shafts that also slows down/reduces any galvanic effects because the paint insulates the metalwork.
Galvanic isolators, they provide a connection to shore power earth but only allow conduction of electricity if there is an electrical potential difference of greater than @ 0.9 Volts. So relatively low cost galvanic protection (i.e. your anodes only protect your boat) and a shore power earthing route is always established in the water and on the hard.
The downside is that they can fail (very unlikely) and unless you test them you won't know. But most (all?) boats these days have residual current detector(s) in the mains electrical supply panel so if there is an electrical problem they will isolate the problem automatically anyway.
My first boat in the med didn't have a galvanic isolator and the main anodes lasted @ 14 months. I fitted an onboard galvanic isolator and the anodes lasted @ 25 months. I found similar results on my last two boats that both had factory fitted galvanic isolators.
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superheat6k
Well-Known Member
The rating of the GI must match or exceed the power supply rating the boat uses. A GI can't sensibly be too big but can be too small. A 32 amp GI will safely cope with an earth fault current of 32 amps, whereas a 16amp won't.
Also be aware of false earth bypass to the GI along the neutral line. If you have any then the GI becomes useless.
I had this on my last boat where an LED had been used as a Earth to neutral indicator for reversed shore power polarity indication. The problem with an LED with its ballast resistor is that it provides a direct path to the neutral, which is earthed at the source point of the shorepower, for any stray galvanic currents. If you wish to have a polarity indicator then consider instead using a test plug that is plugged in when shore power is connected, then once the connection is confirmed correct the plug is removed and any earth GI bypass is removed with it.
It is also important that if you have a generator that the power connection switches both Live and Neutral lines, because the neutral should be grounded at the generator, so if left connected again this creates a false earth through the neutral line, again bypassing the GI.
Finally it is also worthwhile checking for +VE shorts to the bonding circuit, as these will also play havoc with anodes.
To do this turn all normal services off, which normally means the bilge pumps are still connected to power. Disconnect the +VE connection at the battery and measure for volts drop between the loose battery connection and the now bare battery post. Any reading other than 0 volts means there is a circuit to somewhere, and that a leakage current exists.
I now undertake this check once each year, and only when I had worked my way through several separate but equally culpable leakage / bypass defects did I finally get the anode wear under control on my last boat. This included failure of the above test which turned out to be a flapper type bilge pump switch that had let some saltwater in, providing a path for the 12 v +VE being switched by the flapper switch to leak into the salty water laying in the bilge and then into the bonding circuit. This made the bonding circuit very slightly +VE relative to the rest of the bonding circuit, in turn lighting up the anodes up stream of the leak connection point slightly more anodic than usual and causing them to fizz more vigorously. This was not a major battery leakage, but sufficient to cause accelerated anode wear, and nothing at all to do with the shore power and associated GI. Calder's Boatowner's Electrical & Mechanical Manual explains more of this.
Also be aware of false earth bypass to the GI along the neutral line. If you have any then the GI becomes useless.
I had this on my last boat where an LED had been used as a Earth to neutral indicator for reversed shore power polarity indication. The problem with an LED with its ballast resistor is that it provides a direct path to the neutral, which is earthed at the source point of the shorepower, for any stray galvanic currents. If you wish to have a polarity indicator then consider instead using a test plug that is plugged in when shore power is connected, then once the connection is confirmed correct the plug is removed and any earth GI bypass is removed with it.
It is also important that if you have a generator that the power connection switches both Live and Neutral lines, because the neutral should be grounded at the generator, so if left connected again this creates a false earth through the neutral line, again bypassing the GI.
Finally it is also worthwhile checking for +VE shorts to the bonding circuit, as these will also play havoc with anodes.
To do this turn all normal services off, which normally means the bilge pumps are still connected to power. Disconnect the +VE connection at the battery and measure for volts drop between the loose battery connection and the now bare battery post. Any reading other than 0 volts means there is a circuit to somewhere, and that a leakage current exists.
I now undertake this check once each year, and only when I had worked my way through several separate but equally culpable leakage / bypass defects did I finally get the anode wear under control on my last boat. This included failure of the above test which turned out to be a flapper type bilge pump switch that had let some saltwater in, providing a path for the 12 v +VE being switched by the flapper switch to leak into the salty water laying in the bilge and then into the bonding circuit. This made the bonding circuit very slightly +VE relative to the rest of the bonding circuit, in turn lighting up the anodes up stream of the leak connection point slightly more anodic than usual and causing them to fizz more vigorously. This was not a major battery leakage, but sufficient to cause accelerated anode wear, and nothing at all to do with the shore power and associated GI. Calder's Boatowner's Electrical & Mechanical Manual explains more of this.
JerryC
Well-Known Member
Good points there superheat6k, failing generators without bonding to their seacocks, and flapper type bilge pump switches are notorious for corrosion. Wish I could do the man maths to justify a proper isolation transformer, but I installed a Safeshore instead, which is basically a couple of imho overpriced fairly big diodes. Seems to have worked for the last two years though.
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MapisM
Well-Known Member
Thanks everybody, that's some useful food for thought.
There's one doubt and one conclusion which spring to my mind:
The conclusion is that a GI installation seems a no brainer on paper, because even if I see JerryC point about GIs being overpriced for what they actually are, their cost is neither here nor there in the big scheme.
And while in the worst case a GI could be useless (but never harmful), if and when it doubles the anodes life it can pay for itself in just one season.
The doubt is about all the points raised by kashurst and sh6k.
I mean, my understanding is that it should be sufficient to connect it directly along the earth line, right behind the socket where the cable coming from the dock is attached to the boat, without any need to fiddle with breakers, genset connector, whatever.
Is there anything I'm missing?
There's one doubt and one conclusion which spring to my mind:
The conclusion is that a GI installation seems a no brainer on paper, because even if I see JerryC point about GIs being overpriced for what they actually are, their cost is neither here nor there in the big scheme.
And while in the worst case a GI could be useless (but never harmful), if and when it doubles the anodes life it can pay for itself in just one season.
The doubt is about all the points raised by kashurst and sh6k.
I mean, my understanding is that it should be sufficient to connect it directly along the earth line, right behind the socket where the cable coming from the dock is attached to the boat, without any need to fiddle with breakers, genset connector, whatever.
Is there anything I'm missing?
JerryC
Well-Known Member
Mine is connected immediately behind the shore power connection, everything else is in series behind it. It works. BTW I think they are a tad pricey but I bought one anyway, lol.
superheat6k
Well-Known Member
Your proposed install position is spot on. My comments were to highlight other issues that can also cause excessive anode wasting or render a GI ineffective.
MapisM
Well-Known Member
Sooo.... I did a bit of homework, and I think to have better understood by now why having a GI is good, but an isolating transformer is better.
Trouble is, I'm at a loss is understanding whether the theoretical difference is worth the hassle in real world.
I mean, ballpark prices are 1 to 10 (100+ Eur for a GI, 1000+ for an IT).
And it ain't just a matter of cost - also size/weight/installation are 1 to 10, sort of.
Bottom line, whadduthink folks, is it worth going for the full monty while I am at that, or is a GI more than good enough?
Trouble is, I'm at a loss is understanding whether the theoretical difference is worth the hassle in real world.
I mean, ballpark prices are 1 to 10 (100+ Eur for a GI, 1000+ for an IT).
And it ain't just a matter of cost - also size/weight/installation are 1 to 10, sort of.
Bottom line, whadduthink folks, is it worth going for the full monty while I am at that, or is a GI more than good enough?
JerryC
Well-Known Member
I think the answer depends on what problem you're trying to solve. Is it really worth spending >1k on a transformer just to double the life of your anodes against galvanic corrosion? OTOH the effects of electrolytic corrosion can be drastic and expensive, so if that is a risk in your cruising area and outside your control (flaky electrical maintenance in marinas or neighbouring boats), maybe a transformer is the way to go.
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kashurst
Well-Known Member
a decent GI is more than enough (waits for JFM.............)
JerryC
Well-Known Member
A quick reply to kashurst's first post: why would I need to ensure my anodes are connected to the shore supply when my boat is blocked up on the hard? Sorry if this post appears twice, dunno where the first one went.
rafiki_
Well-Known Member
P, I will always fit a GI.
Montemar
Well-Known Member
maby
Well-Known Member
It's worth remembering that the current rating of a GI has nothing to do with the size or nature of the boat or the current drain of the boat. If there is no electrical fault on the boat, then the earth current will be zero and if there is any significant electrical fault, then the earth current will be many hundreds or even thousands of amps - transiently until a fuse blows somewhere or a circuit breaker trips out. None of the GIs on the market can carry that level of current for more than a short fraction of a second before they burn out - we buy more expensive (and notionally higher current rating) GIs on an act of faith that a 32A device will take a few milliseconds longer to fail than a 16A device and is more likely to survive until the breaker has tripped.
BartW
Well-Known Member
In this situation the anodes are not working / of no function;
but the reason to connect boat ground to shore supply earth, when a boat with a IT is on the dry,
is that you have onboard a "foating" ground, so there might be a different potential fe on the boat railing, compared to shore earth,
so in that situation, you must link boat 230V ground with shore supply earth.
JerryC
Well-Known Member
Yes BartW, totally agree with your first point, hence my question. As regards floating open-circuit induced voltages, in other non-boaty, faulty domestic mains electric supplies, the max I found was 27 volts. Was I lucky?
