isolator

tcm

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A GI protects the boaty from the effects of all boats being cnected to the same earth by a shortepower cable being pluggedin. So, if not cneccted to shorepower, blimin irrelevant.

i think it depends where you are - on your own on a pontoon, not too important, but cheek by jowl with a stack of other boats on a busy pontoon - praps quite important, as the combined effect of all the boats mighyt be turned on your sterngear. How quickly do your anodes get eaten? Is there evidence of elctrolytic attack on the underwater metal things? You should be able to get a couple of years from decent size anodes.

Theres is another things that they have on big aluminium boats to adjust and elminate stray currents, lot more spensive, and the anodes last for years and years. But dunno wot it is...
 

Gunfleet

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<<Theres is another things that they have on big aluminium boats to adjust and elminate stray currents, lot more spensive, and the anodes last for years and years. But dunno wot it is...>>
Isolation transformer.
 

roger

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Re: isolation Transformer is uncomplicated

An isolation transformer is not at all complicated by nature. It is just a large 1:1 transformer. Ithas an appallingly low shiny knob count.
I dunno how an aluminium biat is kept intact. From a galvanic point of view its a disaster in waiting!
 

Phoenix of Hamble

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Re: isolation Transformer is uncomplicated

Micky,

IMHO the single factor that determines whether you need a GI is whether or not you are bonding your AC and DC earths together.

You only need bond these together if you are using the AC service for DC purposes... eg to charge your batteries......in which case you need to bond AC and DC to ensure effective operation of your RCDs

So in other words.... if you are using your shore power to charge your batteries then connect your shore supply earth to a GI, and connect together the AC earth and the negative side of the batteries (or the engine/anodes/etc) on the boat side of the GI

Otherwise, you risk seeing your nice seacocks etc vanish over the course of a season!

At least this is what I understand to be correct after hours of reading and research....
 

William_H

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Re: isolation Transformer is uncomplicated

Perhaps you appreciate already but a galvanic isollator is a device containing 2 silicon diodes back to back. That is one conducts in one direction and the other conducts in the opposite direction. so that any AC violtage that needs to be connected to the earth via the GI runs straight through like a piece of wire. However the trick is that the diodes have an inherent vollt drop across them of .7 volt in the conducting direction. This is not a resistance but a volt drop regardless (almost) of current. Now .7 volt drop when conducting 240 volts is nothing but for the voltages of electrolytic action it is enough to stop the current flow. So as stated if you need to or must connect the earth line of the incoming power to the ships negative and hence to the water via engine and fittings then a GI can stop the harmful currents in the electrolytic corrosion circuit.
Regards olewill
 

rusland

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Re: isolation Transformer is uncomplicated

William, is there a test that a simple person can carry out to check and know that the GI that was installed recently is really working? (I mean apart from waiting to see if the anodes are disappearing less quickly than previously)
 

William_H

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Re: isolation Transformer is uncomplicated

The test for a GI is fairly simple. It has 2 terminals. best disconnect it for test preferably after disconnecting shore power. bear in mind the connection to ships earth of the mains earth is for your protection. if you can arrange some wire and a battery so that current flows through the GI to a lamp then the lamp should light. (if you use a single cell torch battery you will get quite a dim light as the voltage dropped .7 v becomes significant to the 1.5 volt cell. Then reverse the connections on the GI. So current for a lamp should flow reasonably easily. If you had a multimeter while the current is flowing through the GI you should measure about .7 volt drop. test again in the other direction. (swap the terminals on the GI.) Note the voltage drop measured may be as low as .5 volt it depends on temperature and diode type.
Another test is using a digital multimeter. Mine has a diode test position and if you have that then you should measure .7v(swap the leads and you should get the same thing. If you don't have a diode position then use the ohms (resistance) scale. The result here may be variable but shouuld not measure very low resistance and possibly up to 100K ohms. The problem being that the volt drop of the diode effects the multimeter in different ways on different meters. The possible failure modes of the GI are a shorted diode which will give zero resistance and no volt drop. (that would be bad for your electrolysis) or one open circuit diode or both. ( this could be dangerous if you had a failty electrical appliance particularly your charger.
As for testing the whole electrical system for efficacy regarding protecting your bronze work with sacrificial anodes that is a very difficult question best answered by close monitoring of the anodes and bronze work.
hope that all makes sense PM me if you have problems olewill
 

Micky

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Re: isolation Transformer is uncomplicated

Ah, so am i correct to say, that a GI is only required IF the boats earthing cables are connected and the negative side of a battery charger is connected.

Soooo IF i disconnect my batteries before charging with a mains charger, all would be OK and no GI needed.
 

fireball

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Re: isolation Transformer is uncomplicated

The battery charger might be double insulated too .... so no connection back to the AC earth ... and no need for the GI ...

What the GI does is break the connection between a cathode and anode in the water ... this is more likely to occur when you get several boats close together all sharing some sort of electrical connection (shore power) ...
So, if your ships earth is not connected then your unlikely to suffer .... but your RCD won't work either.
A lot of electrical goods with transformers are double insulated so shouldn't be the cause... the problem comes when you start getting an electrical connection between the ships negative and the shorepower earth..
Well - thats my understanding ... so - even with shorepower we don't have a GI or even any hull anodes - cos we're on a mooring 99% of the time and the other 1% the shorepower only really does the hot water and perhaps a light and laptop ...
 
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