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Old 21-08-2020, 11:52   #1
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Galvanic Isolator or Isolation Transformer

Hi,

Which one should I use? I have a 30 Amp 120 V shore power cord. I haven't done any testing at the marina I'm at but I wanted to be proactive.
I have gone back and looked at some of the old threads and it is confusing.
It looks like an isolation transformer can isolate the power conductors from shore power and provide galvanic isolation in the ground wire vs a galvanic isolator will just isolate the green ground wire from picking up stray current from other boats through the ground system.
Which one should I use? Is the Isolation Transformer the do all solution or do I just need a galvanic isolator.

Thanks for any help.
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Old 21-08-2020, 15:28   #2
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by markcleary View Post
Hi,

Which one should I use? I have a 30 Amp 120 V shore power cord. I haven't done any testing at the marina I'm at but I wanted to be proactive.
I have gone back and looked at some of the old threads and it is confusing.
It looks like an isolation transformer can isolate the power conductors from shore power and provide galvanic isolation in the ground wire vs a galvanic isolator will just isolate the green ground wire from picking up stray current from other boats through the ground system.
Which one should I use? Is the Isolation Transformer the do all solution or do I just need a galvanic isolator.

Thanks for any help.
The isolation transformer is, by far, the superior solution. It provides not only safety for the boat (eliminating galvanic corrosion) but also safety for the people aboard.

If you only stay at marinas that are 100% up to code with their shore power and it all looks new and clean in a 1st world country? the galvanic isolator will be fine. Many still choose the isolation transformer just to make sure
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Old 21-08-2020, 17:15   #3
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by s/v Jedi View Post
The isolation transformer is, by far, the superior solution. It provides not only safety for the boat (eliminating galvanic corrosion) but also safety for the people aboard.

If you only stay at marinas that are 100% up to code with their shore power and it all looks new and clean in a 1st world country? the galvanic isolator will be fine. Many still choose the isolation transformer just to make sure



If you have a Isolation Transformer, does that mean that you no longer need the Hull Anodes?
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Old 21-08-2020, 18:47   #4
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Re: Galvanic Isolator or Isolation Transformer

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If you have a Isolation Transformer, does that mean that you no longer need the Hull Anodes?
No you still need anode protection. The isolation transformer only protects against issues stemming from shore power.
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Old 21-08-2020, 19:20   #5
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Re: Galvanic Isolator or Isolation Transformer

The transformer is the better choice. But is way bigger, way heavier. And more money. Depends if you have a place to put it. A galvanic isolator is much easier to add.
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Old 22-08-2020, 07:07   #6
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Re: Galvanic Isolator or Isolation Transformer

The added bonus of the isolation transformer is that you can use multiple windings and voltage taps to adapt to any dock voltage when cruising internationally. The isolation transformer on our boat gave us a range of 80 to 430 volts by switching between series/parallel windings and the voltage taps.

We made a tap and winding switching box out of a reworked domestic breaker box. Since the switching between voltages was complex the advantage of using breakers for selector switches was that no damage was done if you made a mistake.
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Old 22-08-2020, 08:48   #7
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Re: Galvanic Isolator or Isolation Transformer

Transformer is better, but heavier. I made a research and video on why you need not only need a Galvanic Isolator, but what happens when you connect to shore power. What is the difference between sacrificial anodes and galvanic isolator? And stray currents? What is a Galvanic Isolator? What is Galvanic Currents? WHere does Galvanic Voltages come from?

https://youtu.be/Ai8fRiaurKU
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Old 22-08-2020, 09:17   #8
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Re: Galvanic Isolator or Isolation Transformer

My boat came with two huge, old-looking, heavy bricks that I later learned are Isolation Transformers.

I'm not an expert, but as a boat owner I try to do as much DIY as possible and learn from the experts. My electrical and electronics system refit was done by a master boat electrician and I learned a lot from him, including the incredible value of my isolation transformers.

First, due to their function, size, weight, and cost, it only makes sense for a full time cruiser to install as they will protect your boat from shore power faults. Your boat is not physically connected to the shore power ground, which is the path of problems if nearby boats or the shore power system isn't up to snuff.

If your boat stays in one marina you don't need this protection unless you don't trust that marina's shore power service.

Second, due to the way they function, it can be a problem connecting with newer shore power systems with sensitive GFCI breakers. The IT creates a short power spike as it connects the shore power to the boat that can trip sensitive shore power pedestal breakers. This has happened twice in the past 2 years when we started full time cruising.

But this problem is rare, and if you're interested I'll described both below.

The first time this happened was at an older, remote small harbor and I contacted my electrical guy and he informed me of the above and emailed me a diagram to bypass the IT if I really wanted to connect with that power source. I decided not to as we were only there for a couple of days to sit out a storm on our way to our destination.

The second time this happened was at a marina that I really wanted to return to in the future and followed the bypass procedure, which was easier than I thought it would be, involving switching some wires around (carefully!).

In the process I discovered a fault- the hot and neutral were reversed on the boat-side shore power connection! This hadn't been a problem visiting some 30 different marinas until the sensitive, new system of the one we were at. Amazing. Corrected the fault and now we can connect without tripping the breaker.

I've made friends with and have come to love my IT as it provides me a lot of peace of mind when connecting to different shore power systems when we visit unknown marinas (which is not often nowadays as we like to live on the hook).

Would I pony up the bucks if it wasn't already on my boat? As a full time cruiser, knowing what I know now, yes I would.
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Old 22-08-2020, 12:06   #9
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Re: Galvanic Isolator or Isolation Transformer

Good isolation transformers, like the Victron units, have a soft start that prevents any trouble with pedestal breakers.

The in-rush current is from building up the electromagnetic field around the primary windings. A soft start limits that current for the first couple of seconds.
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Old 22-08-2020, 13:48   #10
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Re: Galvanic Isolator or Isolation Transformer

A related question: I have 2 30-amp 120-volt power inlets on my boat. Do I need 2 isolation transformers, or can I use a single 240 volt isolation transformer and just split the 2 phases?
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Old 22-08-2020, 14:16   #11
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by SailingSisu View Post
Transformer is better, but heavier. I made a research and video on why you need not only need a Galvanic Isolator, but what happens when you connect to shore power. What is the difference between sacrificial anodes and galvanic isolator? And stray currents? What is a Galvanic Isolator? What is Galvanic Currents? WHere does Galvanic Voltages come from?

https://youtu.be/Ai8fRiaurKU
Quick answers if you don't have 24 minutes and/or are still thoroughly confused:-

Sacrificial anodes sacrifice themselves to DC currents flowing in the water so they corrode and get destroyed instead of metal boat parts underwater that you want to save from getting destroyed.

A galvanic isolator breaks the DC circuit so the current can't flow and minimizes the deterioration of the sacrificial anode.

Galvanic currents occur when there is a voltage difference between underwater metal items and an electrical connection is made between the metals. As the current leaves or enters the underwater metal, atoms of the metal get carried away too until you have nasty holes and disappearing parts.

When you connect a shore power cord you are completing an electrical circuit between any underwater parts on your boat which are connected to the ground wire, and the negative cable on the dock that is connected to hundreds of underwater metal such as other boats and dock structures.

A Galvanic isolator isolates your boat from that ground circuit so current can't flow.

A more effective way of breaking the ground connection would be to disconnect the ground lead in the shore power cable - no circuit = current can't flow. BUT this can land you in deep trouble if your boat develops a voltage leak in an appliance, especially a battery charger, because without the ground connection the AC is free to connect to your underwater metal and kill you when you go swimming. The odds of it happening are extremely low however the consequences are extremely high so a ground wire is mandatory for safety.

This gives the Galvanic isolator a dual purpose, they must BLOCK voltage without blocking the safety ground connection. Fortunately the electrolytic voltage levels are typically below 1 volt so the Galvanic isolator only blocks the first 1.2 volts letting all the rest go through. 1.2 volts in the water won't kill anyone.
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Old 22-08-2020, 19:13   #12
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Re: Galvanic Isolator or Isolation Transformer

following. Our boat was built for EU/Asia power (230v 3-wire AC). When we arrived in the Caribbean, we tried several "inexpensive" (ebay, etc) transformers, none of which lasted more than a few weeks. We ended up buying and installing a Victron Auto-Sensing Isolation transformer, and removed the galvanic isolator I had installed some 15 years previous. And suddenly we developed a significant stray current corrosion-looking display around most (not all?) of our bronze thruhulls. And the paint being "blown off" our thruhulls seemed to only happen when we were in a marina, and plugged into shore power. After several discussions with "experts", multiple phone calls to Victron, and 2 or 3 forum discussions, we bought a half cell and I started checking our boat. Long story short....we found nothing out of order. And while I know it should not make a difference, I bought a new galvanic isolator, and installed it along with complete new wiring from the shore power inlet to the power distribution center. We have since cruised 2 seasons here in the Caribb-and seemingly our "problem" has been solved??? I don't understand it, we should not need a galvanic isolator with that isolation transformer installed......but adding it back in has stopped blowing the paint off our thruhulls!!! I can't explain it...but it works. It's magic!
PS...I should add...the Victron Xfmr works perfectly. We can plug into 110v or 230v shore power, the Victron recognizes the incoming power and transforms it to the 230v AC the boat wants to see. Works automatically and perfectly! 'Course it does not change the 60cps to 50cps, but we've bought equipment that is tolerant of either.
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Old 23-08-2020, 08:16   #13
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by oldjags View Post
A related question: I have 2 30-amp 120-volt power inlets on my boat. Do I need 2 isolation transformers, or can I use a single 240 volt isolation transformer and just split the 2 phases?
I nstalled a 60 amp galvanic isolator (as opposed to a 30 amp unit) for my two 30 amp circuits. Works like a champ. Easy install.
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Old 23-08-2020, 11:24   #14
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by oldjags View Post
A related question: I have 2 30-amp 120-volt power inlets on my boat. Do I need 2 isolation transformers, or can I use a single 240 volt isolation transformer and just split the 2 phases?
You would need 2. Some docks you may have in phase 30a plugs. And many docks are moving to gfi dock plugs. Which can not be split / joined.
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Old 23-08-2020, 12:05   #15
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Re: Galvanic Isolator or Isolation Transformer

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Originally Posted by sailcrazy View Post
We ended up buying and installing a Victron Auto-Sensing Isolation transformer, and removed the galvanic isolator I had installed some 15 years previous. And suddenly we developed a significant stray current corrosion-looking display around most (not all?) of our bronze thruhulls. And the paint being "blown off" our thruhulls seemed to only happen when we were in a marina, and plugged into shore power. After several discussions with "experts", multiple phone calls to Victron, and 2 or 3 forum discussions, we bought a half cell and I started checking our boat. Long story short....we found nothing out of order. And while I know it should not make a difference, I bought a new galvanic isolator, and installed it along with complete new wiring from the shore power inlet to the power distribution center.
I think you will find that the problem was that you connected the ground from shore power to your Victron isolation transformer as though it were a USA-standard unit with a shield. Victron transformers have toroidal windings which do not allow a shield to be placed between the primary and secondary windings. USA/ABYC wiring practices require a shield, and the shore power ground is brought to the shield (only!) which has its own special clearly-marked ground terminal in the transformer enclosure.

European wiring practices don't require the shield. Use of the shield significantly increases the size, weight, and cost of the transformer. In European practice it is believed that a residual current breaker provides sufficient protection so the shield isn't necessary.


Had the isolation transformer been wired correctly, the shore power ground would not have been connected to anything, and so there would have been no place to connect the galvanic isolator.
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