Galvanic transformers

[Gardner]

Has anyone got first hand knowledge of using a galvanic transformer(not isolator) to prevent galvanic corrosion on steel narrow boats? I've read several articles about them and how they supposedly work which to be honest is all a bit above my head. They are quite an expensive item, which is ok if they do in fact work. Any experiences of their use would be appreciated.

[GUMPY]

Yes they work, not all are expensive

http://www.airlinktransformers.com/boating_transformers/

 

Been using mine for 10 years no problems at all.

Edited May 3, 2015 by Loddon

[Tony Brooks]

Has anyone got first hand knowledge of using a galvanic transformer(not isolator) to prevent galvanic corrosion on steel narrow boats? I've read several articles about them and how they supposedly work which to be honest is all a bit above my head. They are quite an expensive item, which is ok if they do in fact work. Any experiences of their use would be appreciated.

 

Well I thought they were isolation transformers in that they isolate your boat's mains wiring from the shore side mains wiring. However The earthing for the transformer itself must be correctly configured.

 

Think 1:1 transformer in a plastic case or box so it is totally isolated from whatever it is mounted on. The current between the two coils is transferred by magnetic fields and induction so there is no actual electrical contact between your boat and the shore-side wiring. Any earth wiring or the transformer is connected to the shore side wiring.

 

The output is just a line and neutral so you have to "construct" the earth protection by earthing the neutral to your hull so although it seems you have a line, neutral and earth on the boat side they are in no way electronically connected to the mains. Now, that neutral-earth bond might upset or destroy certain on-board generators or inverters so if in doubt consult an expert (not me - try NMEA).

[jonathanA]

I suppose being pedantic I'm not sure thee is any such thing as a galvanic transformer. You have either an isolation transformer or galvanic isolator both prevent galvanic corrosion of your boat and it's fittings when connected to an shore line. People argue over which is best ....

 

You pays your money and takes your choice....

[by'eck]

Has anyone got first hand knowledge of using a galvanic transformer(not isolator) to prevent galvanic corrosion on steel narrow boats? I've read several articles about them and how they supposedly work which to be honest is all a bit above my head. They are quite an expensive item, which is ok if they do in fact work. Any experiences of their use would be appreciated.

 

Same thing although strictly speaking galvanic transformer is a misnoma - its an isolation transformer used in this case to prevent the ground based circulating currents that cause galvanic errosion.

 

They should be wired as below

 

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQH2hEgaHg0MNPURgJ391igAL-zSoJRA733-t5XuZqGi0ONzuM0Vw

[churchward]

I suppose being pedantic I'm not sure thee is any such thing as a galvanic transformer. You have either an isolation transformer or galvanic isolator both prevent galvanic corrosion of your boat and it's fittings when connected to an shore line. People argue over which is best ....

 

You pays your money and takes your choice....

I am not sure there is much of an argument over which is best. If you wish to have the earth completely isolated to stop stray galvanic currents an Isolator is best in all conditions when wired in correctly. However, the argument comes in when you consider cost particularly if you don't connect to the mains very often when a GI device will do much the same job for a fraction of the price but can fail over time so they need checking every so often.

[BruceinSanity]

I am not sure there is much of an argument over which is best. If you wish to have the earth completely isolated to stop stray galvanic currents an Isolator is best in all conditions when wired in correctly. However, the argument comes in when you consider cost particularly if you don't connect to the mains very often when a GI device will do much the same job for a fraction of the price but can fail over time so they need checking every so often.

I'd go with that. When we CC'ed we relied on a galvanic isolator, but since taking to spending the winter in a marina, I've got one of the standalone isolation transformers from Airlink. My anodes seem to lose less material between blackings since we have.

 

It also has the advantage that if the joint ELCB on the shared power bollard starts nuisance tripping, you only need to check the connections between the IT and the bollard to be able to say "it's not me". Obviously, by the same token, if you go down the IT route you need to ensure that you have adequate RCB protection in the boat, but you should anyway.

[boots]

We have the Airlink one also, and have used it for the last 4~5 years, on shoreline most of the time. No issues or problems to report.

 

So far, not aware of any galvanic corrosion, nor have we had to replace anodes in that time. However, no idea if it would have been any different with with a GI.

 

Would I have another one-Yes.

 

Not sure what else I could add to the above

[jonathanA]

I've a safe shore GI and have no sign of galvanic corrosion not any obvious problem with anode use. Of course no idea whether that would be any different with an ISO transformer.

I've a safe shore GI and have no sign of galvanic corrosion not any obvious problem with anode use. Of course no idea whether that would be any different with an ISO transformer.

[George94]

As has been mentioned before, with an isolation transformer there is little to go wrong, but if there is a malfunction (basically a short or open circuit) then the lights will go out and you will know you have a problem. They are a true "fit and forget" item.

 

With a galvanic isolator, however, you will only know you have a problem when the boat sinks or (if you are one in a hundred owners) you check the GI everyday and find it's not working.

 

The other 99 owners probably don't know they have a GI, or if they do, they don't know where it is, or if they do, they never check it, or if they do, they don't know how to tell if it's faulty, but if they do, they are the one in a hundred mentioned earlier.

[Old Son]

With a galvanic isolator, however, you will only know you have a problem when the boat sinks or (if you are one in a hundred owners) you check the GI everyday and find it's not working.

 

The other 99 owners probably don't know they have a GI, or if they do, they don't know where it is, or if they do, they never check it, or if they do, they don't know how to tell if it's faulty, but if they do, they are the one in a hundred mentioned earlier.

 

So how do you check if its working?

[Tony Brooks]

 

So how do you check if its working?

 

 

I, as someone with some electrical knowledge, would open it and use the diode test function on a multi-meter to test both ways across each of the two diode sets. However that will not test the extra components many seem to have nowadays. If I did not have a multi-meter I would use a bulb and small battery type continuity tester. A multi-meter set to ohms may well not supply enough electrons to "open" the diodes, thus the diode tester or bulb and battery. However its not a good idea to encourage the less technical to open and mess about with mains devices.

[Old Son]

Thanks Tony, so the non electrical expert has no way of knowing if their GI is working?

 

Am I right in thinking that the GI can be removed and a transformer be installed using the same wires?

[Arnot]

Correct, the non electrical savvy can't really check a GI, it requires some good instrumentation and understanding of how they work. However, there are some that have a test facility built in.

 

My thoughts however are that an isolating transformer is a more reliable and safer option if you can afford the extra. If it was my boat, I'd have one but there's no real application in a 72' skip (working boat).

 

An isolation transformer is not a simple replacement for a GI and despite being a bit biased here, I really do suggest it is a professional installation job. A GI just interrupts the earth bond, an isolation transformer interrupts the entire mains inlet and has to be installed carefully to avoid problems.

 

Hope this helps...

 

Arnot

[by'eck]

Thanks Tony, so the non electrical expert has no way of knowing if their GI is working?

 

Am I right in thinking that the GI can be removed and a transformer be installed using the same wires?

 

As long as they allow the IT to be wired as below yes. Note total break in shore earth continuity to boats hull strapped earth system.

 

 

Neutral/earth(hull) strap on IT output ensures RCD's still provide full safety trip. Same requirement for installed inverter.

 

Image courtesy of Smartgauge site

[Tony Brooks]

Thanks Tony, so the non electrical expert has no way of knowing if their GI is working?

 

Am I right in thinking that the GI can be removed and a transformer be installed using the same wires?

 

1. That is why I say if fitting a GI always buy one with some form of indication it is working. Often LEDs or a little meter. Even then I do not know enough to say the indication is 100%. I think some may show "OK" if a diode has gone open circuit while no other fault exists.

 

2. Not as I understand it. The GI fits in the earth wire just before It attaches to the hull bond where as the IT fits in the mains feed to the boat with all three wires going in and just two coming out.

Edited May 6, 2015 by Tony Brooks

[GUMPY]

 

2. Not as I understand it. The GI fits in the earth wire just before It attaches to the hull bond where as the IT fits in the mains feed to the boat with all three wires going in and just two coming out.

A GI should be fitted in the input line from the shore power.

It should not be fitted between the consumer unit and the hull bond, which to me is what your post implies, even though it will work in that position there is a high chance it will be bypassed by an accidental earth to hull short such as a radio aerial or diesel heating exhaust.

 

There should be 3 wires coming from the transformer...

Edited May 6, 2015 by Loddon

[nicknorman]

A GI should be fitted in the input line from the shore power.

It should not be fitted between the consumer unit and the hull bond, which to me is what your post implies, even though it will work in that position there is a high chance it will be bypassed by an accidental earth to hull short such as a radio aerial or diesel heating exhaust.

 

Correct. On our boat the travel power earth is connected to the travel power alternator casing and thus to the hull, so any GI must be in the incoming shore earth line to have any effect. I do wonder if some reports of GI ineffectiveness are as a result of incorrect installation. When we got our boat the GI was installed as Tony describes and thus totally ineffective.

[BruceinSanity]

Correct, the non electrical savvy can't really check a GI, it requires some good instrumentation and understanding of how they work. However, there are some that have a test facility built in.

My thoughts however are that an isolating transformer is a more reliable and safer option if you can afford the extra. If it was my boat, I'd have one but there's no real application in a 72' skip (working boat).

An isolation transformer is not a simple replacement for a GI and despite being a bit biased here, I really do suggest it is a professional installation job. A GI just interrupts the earth bond, an isolation transformer interrupts the entire mains inlet and has to be installed carefully to avoid problems.

Hope this helps...

Arnot

Our Airlink IT is a standalone waterproof unit, just like a 230 - 110 site transformer. It has a couple of leads with blue ceeform connectors on and goes between the shore supply and the boat inlet. We put it away under the bed when cruising.

[ralphclaydon]

If i was to purchase a galvanic transformer how would i work out what VA i required?

[by'eck]

Well start by deciding the total max wattage of all AC equipment you are likely to use simultaneously then add say 20% to get the VA. Fit RCBO in AC distribution system that trips before overloading chosen IT.

 

ETA: If you want to make full use of the typical 16 amp shore supply, around 4kVA IT would be needed.

Edited May 6, 2015 by by'eck

[ralphclaydon]

Thank You

[Tony Brooks]

A GI should be fitted in the input line from the shore power.

It should not be fitted between the consumer unit and the hull bond, which to me is what your post implies, even though it will work in that position there is a high chance it will be bypassed by an accidental earth to hull short such as a radio aerial or diesel heating exhaust.

 

There should be 3 wires coming from the transformer...

 

First point - sorry about that, but I have said many times I am not qualified in mains work.

 

Second point. Surely three wires exiting the isolation transformer rather depends upon where the neutral earth bond is connected. I agree it should be as close to the IT as possible so that means ideally inside it, but are they always configured like this?

[Arnot]

If i was to purchase a galvanic transformer how would i work out what VA i required?

There are a few things to consider...

 

1) The power rating of the transformer should not be less than the power rating for the incoming connector. So; as in the majority of cases the inlet is 16A, 16 x 230 = 3680W or as near as you can get. Any smaller and it could get unintentionally overloaded and in addition will tend to be less efficient.

 

2) You need to consider how much power you will use for extended periods when attached to a shore line. For those who use incoming power for heating the water, ironing, kettle boiling and other such loads then an air cooled unit would probably be best.

So why? Well, the transformers in sealed cases (IP 67) whilst being good at surviving being located in a damp and cold environment such as on a swim, because of the encapsulation tend to lack cooling ability and overheat. Remember this sort of casing was intended for site work tools and these don't stress the transformer for long, are located where they can be easily seen (that's why they are yellow) and the loads they serve tend to be intermittent.

Conversely, the air cooled units (IP23 metal case) whilst handling higher extended loads better because of their cooling ability are prone to damage from damp. These really need to be located inside the cabin in a cupboard or some such warm and dry location.

 

3) It is important to have some sort of thermal overload cut off switch located inside the windings of the transformer and it is very sensible to be able to replace this if it fails (as they sometimes do). If the transformer starts to overheat, the heat is generated deep inside the windings (or at least the temperature rise is greatest) and if there is no thermal protection then the overheating fast becomes very dangerous.

 

4) Transformers usually generate some mains hum at 50Hz and this can become annoying if it has been located under a bed or near where you are likely to be enjoying peace and quiet. Also, since they operate on the basis of a cyclical magnetic field, any magnetic conductive item in the vicinity may well vibrate as well. So; it's best to locate them somewhere where they are not likely to be surrounded by clutter.

 

5) For the purposes of fault finding and diagnosis it is a good idea for them to be installed with male/female BS4343 ( blue three pin) connectors on the inlet and outlet arranged to that they can be temporarily bypassed.

 

6) As previously mentioned, they can and usually do generate a bit of heat if under load so it is essential that they are located in a space that has some ventilation and not tucked up in spare bedding, wet weather gear, towels, upholstery etc. etc.

 

So it's not as simple as it seems but then electrickery never was...

 

Hope this helps

 

Arnot

[GUMPY]

First point - sorry about that, but I have said many times I am not qualified in mains work.

 

Second point. Surely three wires exiting the isolation transformer rather depends upon where the neutral earth bond is connected. I agree it should be as close to the IT as possible so that means ideally inside it, but are they always configured like this?

Most have N/E bonded in the transformer box, saves user confusion

 

eta

Technically and being really picky the transformer should be located at source and not on the boat. This prevents a shore earth from entering the boat and making possible contact with the hull.

Edited May 6, 2015 by Loddon