Galvanic Isolators

[addicted]

Does anybody have a take on the merits or not of installing a galvanic isolator.  We're a  bit concerned at the speed with which our sacrificial anode disappeared.

 

 

Carole

[BrundallNavy]

When I first moved Nipper to the wet shed within 6 months half my rudder had disappeared. I have since fitted a galvanic isolator together with a stainless rudder but have not had her lifted for 18 months so don't know if it has worked.

i guess it depends on where you moor and how many boats with shore power are close by, at the rear of my mooring is steel pillings so not sure if this had a bigger effect.

Not cheap to buy but cheaper than a new rudder etc.

Doug.

Edited June 5, 2017 by brundallNavy
Predict text !!!

[JawsOrca]

If you are in a marina beside boats which are connected to shore power then these are a must.  Safeshore are the only ones really. The chaps website is here http://www.safeshoremarine.com/ he's very very helpful and will answer any and all questions. He doesn't need to sell these as they sell like hotcakes, but call him and talk to him.

He will also advise what other bits to check. It's very complicated stuff hence best just to talk to the right chap.

[LondonRascal]

I should also mention 'Isolation Transformers' - have a Google to learn about these clever bits of kit

[dnks34]

Im sure i have commented or read about this before but in my case as all metal parts on my GRP boat are not earth bonded I dont see how a galavanic isolator is going to be of any help to me.  

I could easily install one on the shore earth but I dont quite understand how this helps my rudder, skeg shaft or prop.  

[LondonRascal]

Here’s how it works: As soon as you plug your shore power cable into the socket on the quay —before you’ve switched on anything—you’ve connected your boat and all of its earthed underwater metals, zinc anodes, sea cocks, shaft, strut, and so on to the quay's AC earthed power and, theoretically, to every other boat in the marina and all of their underwater metals.

Such an arrangement can cause havoc with the consumption rates of  anodes and the corrosion of underwater metals.

Lets say that the owner of the boat in the mooring next to you hasn’t replaced their anodes in a year, but you dutifully have been then your anodes will protect both boats or even several boats, until they’re depleted, which is likely to happen very rapidly which is likely what happened with Nipper.

You may wonder if doing away with the earth wire and its connection to adjacent boats is the solution. The short answer no way!  That connection must exist in order to carry fault current back to its source, such as the RCD on your boat on in the shore power socket connection on the shore. Not only must the earth remain in place but also must be sound and free of corrosion (which can happen on the earth pin of the shore power lead) and as a result could cause excess resistance.

A galvanic isolator  device is inserted in line with the earth as it enters your boat typically between the shore power inlet and the boats AC distribution panel/RCD 

Its simple mission is to allow AC fault current to pass unimpeded while blocking, to a degree, DC current. This way AC faults are safely conveyed back to their source while destructive galvanic DC current is stopped or at least slowed right down.. With a galvanic isolator in place, your anodes protect your underwater metals and not those of other vessels, thus eliminating any fears of 'rudder rot'

 

 

[ExSurveyor]

I have one fitted even though the boat has never had anodes fitted.

Can't be too careful.

[dnks34]

But none of my underwater metal is bonded to the shore earth so unless I bond everything I could put a galvanic isolator in but it wouldnt really be doing a lot would it?! 

Am I right in thinking then that unless I bond everything I dont have a problem?  

I thought a galvanic isolator was more for metal hulled boats.

[Springsong]

We have one .

[Poppy]

15 hours ago, brundallNavy said:

When I first moved Nipper to the wet shed within 6 months half my rudder had disappeared. I have since fitted a galvanic isolator together with a stainless rudder but have not had her lifted for 18 months so don't know if it has worked.

i guess it depends on where you moor and how many boats with shore power are close by, at the rear of my mooring is steel pillings so not sure if this had a bigger effect.

Not cheap to buy but cheaper than a new rudder etc.

Doug.

My mooring has steel piling alongside. There is no mains supply.

QED!  

Mains electric supply shoud certainly be a MANDATORY part of the BSS !!

[Bound2Please]

16 minutes ago, Poppy said:

 

Mains electric supply shoud certainly be a MANDATORY part of the BSS !!

I'll second that Poppy

Charlie

[Viking23]

10 hours ago, dnks34 said:

Im sure i have commented or read about this before but in my case as all metal parts on my GRP boat are not earth bonded I dont see how a galavanic isolator is going to be of any help to me.  

I could easily install one on the shore earth but I dont quite understand how this helps my rudder, skeg shaft or prop.  

I fitted a galvanic isolator to our GRP cruiser, the only thing in the water is the Honda outboard.

We have shore power that connects to the battery charger, and fridge, so the fridge is earthed, so is the gas copper piping, so is the Propex warm central heating, via the copper gas pipe. The fridge also connects to 12 volts dc and the electric starter motor of the outboard connects the negative of the battery to the chassis of the outboard. Plenty of unforseen routes that can connect the engine to shore earth.

I was not convinced of this earth connection, so I placed a multimeter set on dc across the shore power earth and boat earth, and I measured 150 mV dc This is one way of testing the galvanic isolators, now 150 mV is high enough to cause galvanic corrosion, the higher the dc component, the worse it is. Some of the 150 mV dc is caused by dissimilar metals, aluminium, steel, stainless, alloys etc. 

For the leakage current to cause a problem it would have to exceed over two volts dc to cause the back to back diodes in the galvanic isolator to conduct. 

If you measure an ac component of current across the shore earth and boat earth, this might be a couple of volts if you have leaky or faulty mains equipment, then this can put the diodes into conduct mode, and dc will start to flow, making the galvanic isolator obsolete, and allowing galvanic corrosion to take place when you thought you were safe. So proceed with caution, they are not fool proof.

You also have to test the galvanic isolator regularly, and after every rcd or mcb trip, or over current. An over current fault could blow the diodes in the galvanic isolator gaving the effect of disconnecting your safety earth.

 

I can see my outboard anode, and so far holding up well since November last year, when I first connected to shore power.

I test my galvanic isolator with a small 9 volt battery with a current limit, and measure the dc voltage across the terminals, both forward and reverse biased, depending on the design, you might see between 2-3 volts dc during the test. There are testing procedures on the internet, and on Galvanic suppliers websites, so make youself familiar.

A great device, but treat them with respect, test them regularly, but they are not fool proof. 

Richard

 

[Poppy]

Just now, Bound2Please said:

I'll second that Poppy

Charlie

Doubtless there will be those who disagree.....

[Viking23]

2 hours ago, Poppy said:

... Mains electric supply shoud certainly be a MANDATORY part of the BSS !!

I totally agree with you 100% BUT...

For the BSS inspector to test the installation they would require specialist calibrated test equipment that can measure the rcd leakage current over various currents and log the time and check vs standard tables. 

He would also need MCB and fuse testing equipment to measure a range of fault currents vs time. The boat in question being tested would require a shore supply capable of supplying the high fault currents too. 

He would also require earth continuity test equipment, and he would need a lot if experience to sort out the bird nests of wiring that evolves over the years on most boats.

To test a galvanic isolator would require specialist equipment too.

The BSS inspector would require specialist training, and technical updates, as other products are brought to market.

At best only a few inspectors would go that extra mile, at best you would see BSS inspection fees triple or worse. 

 

At the moment, the BSS look to see if connector pins could be live under fault or normal conditions, they don't even check to see if 32Amp to 16 Amp adaptors are fitted with either 15 or 16 amp fuses to be legally safe... YES another dig from me to get those unfused lethal adaptors outlawed, actually, they are outlawed, as they are not legal. So use at your peril, and if someone is injured or property is damaged, you might find yourself in court, and the insurance company wiping their hands of the situation.

I have successfully stopped the sale on ebay of some of these adaptors when I explain their personal liability.

 

Electricity and water, with amateurs who might be inebriated with alcohol,  allowed to connect up 240 volts with potentially wet hands in the pouring rain... hmmm...  with an electrical system that has never been tested to test the effectiveness of breakers etc... So how many electrocutions are reported?

One is too much...

Richard

 

[Poppy]

Exactly - and well put Richard.  But what is wrong with the principle of paying more IF you chose to have and use mains ?  After all, we are told that the safety of your boat is also of importance to thase moored around you, are we not ?

[ExSurveyor]

I choose to have the 240v system checked each year by a qualified electrician,  I do the same on my rental properties,  it isn't a legal requirement,  but it doesn't stop you opting to do it.

I like to sleep  soundly at night knowing I have done what I can for those I have a responsibility to,  myself and onboard guests included.

Surely it isn't necessary to bring in laws for everything.

[Poppy]

1 hour ago, psychicsurveyor said:

I choose to have the 240v system checked each year by a qualified electrician,  I do the same on my rental properties,  it isn't a legal requirement,  but it doesn't stop you opting to do it.

I like to sleep  soundly at night knowing I have done what I can for those I have a responsibility to,  myself and onboard guests included.

Surely it isn't necessary to bring in laws for everything.

When people are inclined to take short cuts and not take a similar responsible attitude, I'm afraid it often is.

[TheQ]

I will be fitting a galvanic isolator, I already have the bits to build it. Unfortunately the better solution is a isolating transformer but they are very very expensive.

Galvanic isolators like most things for boats are a rip off in prices, but unless you are lucky enough to have many years of experience in electronics I would not recommend building your own.

[ranworthbreeze]

7 minutes ago, TheQ said:

I will be fitting a galvanic isolator, I already have the bits to build it. Unfortunately the better solution is a isolating transformer but they are very very expensive.

Galvanic isolators like most things for boats are a rip off in prices, but unless you are lucky enough to have many years of experience in electronics I would not recommend building your own.

Hi Q,

What are your specifications on your required transformer? voltage trappings and VA rating, I may have something suitable.

Regards

Alan

[Viking23]

Just now, TheQ said:

I will be fitting a galvanic isolator, I already have the bits to build it. Unfortunately the better solution is a isolating transformer but they are very very expensive.

Galvanic isolators like most things for boats are a rip off in prices, but unless you are lucky enough to have many years of experience in electronics I would not recommend building your own.

I did a lot or research, and I designed and built my own, there are a few iffy designs on the internet, and in a well known boating magazine, which has been slated.

The reason being is under fault conditions when the unit might draw the full supply load, as this goes through the diodes, then these can heat up, burn out, become open circuit as well as a fire risk, and you can loose your safety earth. 

I have used 4 sets of bridge rectifiers that can individually carry a minimum of 50 amps when fitted to the correct size heat sink, the fault surge current may exceed several thousand amps, and the voltage in excess of 600 ac, so choose your components with care. 

Some time ago I saw a set of 4 single diodes on ebay,  that claim to make a galvanic isolator for boats, it was a kit, the buyer soldered it up, wired it in,  and the seller claimed it was effective.

 

No... it is not, under fault conditions, which ironically is when you really need it to work, the diodes can overheat, and burn out. They are not capable of taking the surge current as they are not mounted on a large suitable heat sink. There is no fail safe or redundancy.

I used the double bridge design, which allows led indicators to illuminate if the DC voltage exceeds the turn on voltage of red led indicators. This can be a good indication if the leakage currents are getting out of hand.

Luckily I had a spare heatsink, it was about 5" long, 4" wide 2" deep made of aluminium, extruded in the form of a large surface area heatsink, similar in size to the well known suppliers of Zinc Savers, this is no coincidence, more a case of getting your calculations right first time lol.

 

Hope it helps.

It is also not just about the quality and specification of the components, but also about size of wiring, quality of soldering, insulation and general labelling of the unit. 

I am sure many qualified and experienced electronic engineers can design and build one too, but if starting from scratch, when you see what you are buying when you buy a good quality unit, you are actually getting a good piece of well engineered electronics, with good back up and support, with hopefully a long service life.

Not for the amateur engineer.

 

Hope it helps.

Richard.

[dnks34]

From what Im reading it sounds to me that even though there are benefits to having a galvanic isolator you may be putting your life at risk by fitting one off the shelf if it goes wrong and disconnects your mains earth.  

I dont think Im convinced I need one just yet! 

[addicted]

Your replies to this have been very helpful and as a result I think I'm going to recommend to my husband that it may be better to err on the side of caution and not fit one of these in view of the danger of losing the earth under certain circumstances While he is wealth of knowledge in a lot of boating related things, his knowledge of electrical matters is zero so best not to dabble  as he wouldn't  be able to test for problems if needed. Thanks one and all ,NBN to the rescue again!!

 

Carole

[Viking23]

1 hour ago, addicted said:

Your replies to this have been very helpful and as a result I think I'm going to recommend to my husband that it may be better to err on the side of caution and not fit one of these in view of the danger of losing the earth under certain circumstances While he is wealth of knowledge in a lot of boating related things, his knowledge of electrical matters is zero so best not to dabble  as he wouldn't  be able to test for problems if needed. Thanks one and all ,NBN to the rescue again!!

 

Carole

 

15 hours ago, dnks34 said:

From what Im reading it sounds to me that even though there are benefits to having a galvanic isolator you may be putting your life at risk by fitting one off the shelf if it goes wrong and disconnects your mains earth.  

I dont think Im convinced I need one just yet! 

There are many reputable companies that design and fully test galvanic isolators, they are designed to withstand all what can be thrown at them, this is one of the reasons that they are bulky, heavy and of course, at first glance, expensive. 

These will withstand many many cycles of faults without failure, they are well over designed. I think you'll find that the manufacturers will recommend testing them after such a fault. Please contact them, check their website. 

It is the other so called galvanic isolators, built in a shed that may not have test results to go with the unit. These could be more vulnerable to early failure. 

In fact, in America, they don't readily accept the "European type" as there is no automatic way of testing them, for particularly open circuit on the earth. Things like this, sit in the bilge, corrode away, never tested.

The Americans have opted for the next generation version, this has a fault indicator, and if the indicator illuminates, you simply dig a hole and bury the unit, and buy a new one.

You will now start to see these appear on the UK market, maybe it's the next generation units that we should also look at.

I hope it helps, I have done a lot of research on these, some information excellent, and some, diabolical, misleading and dangerous.  

 

Standard Isolation Transformers designed for the application are great, the only down side apart from cost, is size and weight. There is also the issue if you chose one that is too small, with too low a VA (Wattage) rating. Then you need to upsize, and the old unit becomes obsolete, or can be sold on.

 

I will mention about "other"  isolation transformers, some uneducated and misinformed have a go diy'ers, I will not insult engineers by calling these people Engineers, have decided that they could take two of the yellow industrial  110 volt ac isolation transformers, and wire them in series to create an isolated supply to give 220/240 Volts.  DO NOT TRY THIS AT HOME !!

Will it produce an isolated 220/240v ac supply.. well... yes it will. But don't get too close, and don't plug anything in.

Is it legal, and once more, is it safe?   The answer is NO, not in 1000 years.

 

So what am I talking about...? 110 volt transformers are designed to take 220/240 volts, drop it to 55-0-55 volts. Only 55 volts above earth, survivable if you shared a puddle of water with an electric tool.

However, the insulation of the transformer only has to withstand 55 volts, now placing two of these transformers in series to give 55 - 55   55- 55 to give 220 volts clearly shows the earth or 0 volt has to be disconnected, and now the upper 55 volt terminal, is now sitting at 220 volts, where the withstand voltage, ie breakdown voltage is only designed and tested for 55 volts ac

This is clearly a breach of the original design, and as such will be illegal and of course unsafe and a risk to persons and property. 

It can never be awarded the CE mark of conformity in this application.

So please avoid anything to do with these. If you have a boat with what looks like this type of installation, best to disconnect and take professional advice.

I hope this helps some to avoid the pitfalls and stay safe. A properly installed electrical system on a boat can be perfectly safe, but like most things, they do require regular maintenance, inspection, or testing. 

Best regards, 

Richard