DIY galvanic isolator?

Sorry I could give you a link to a circuit for a basic one but not one with fairy lights. Reckon you have to spend some of that surplus dosh and buy a commercially made one.
 
A very basic GI can be made with a couple of appropriately rated bridge rectifiers. Bridge rectifiers because the are something readily available. You could do the same sort of thing with separate diodes but you specifically said you did not want a bunch of diodes.

The one described on the Yandina website is HERE

Remember since this thing goes in the safety earth connection. In attempting to save a few £ you are playing with the safety of yourself and your crew.
 
There are only two possible faults with galvanic isolators. Open circuit and short circuit of the diodes. Open circuit is very possible if the diodes overload and blow. Short circuit is very unlikely IMHO.

A simple neon indicator across live and earth will show it the diodes have gon open circuit and in fact will show any open circuit earth fault.

A loss of earth due to open circuit diodes is dangerous as the RCD will NOT work.

Short circuit diodes will only cause your anodes to erode quicker and will not cause and potential danger due to earth leakage electric shocks as the earth is still connected so the RCD will work
 
I have 2 neon indicator lamps (not LEDs) connected at the input side of the main AC fuse box (i.e. after the Galvanic Isolator but before the RCD).

A green neon is connected between live and earth. This should glow if the shore power is connected, but will not glow if there is a break in the earth circuit.

A red neon is connected between neutral and earth. This should not glow - if it does it means that the supply polarity is reversed.

John
 
That is my total setup but the green (live to earth) is the only one testing the galvanic isolator the other is testing the neutral line for asy you say reverse supply polarity.
 
[ QUOTE ]
A green neon is connected between live and earth. This should glow if the shore power is connected, but will not glow if there is a break in the earth circuit.


[/ QUOTE ] Ah but

If the boat is wired as per current (UK) recommendations ( BMEA and CE regulations to be more precise) with the earth of the onboard mains voltage system connected to engine block, sterngear, anodes etc, steel hull even, there will be a path to earth via that lot and the water. So even if there is a break the shorepower earth connection be that due to an open circuited GI or another reason the green neon will still glow!

Or have I missed something.

Also if there is a current flow from the neon through the GI doesnt that mean that the diodes are conducting and therefore not giving the protection they should be by blocking current from low voltage "galvanic" sources.
Sorry I cant get my head around that one!
 
Vic:

I think you are right - I had my doubts which is why I posted it.

My green neon is probably giving me a false sense of security (it was there before I fitted the GI), and so I will re-wire it L-N just to confirm that shore power is present.

The red neon (N-E) stays as this will tell me if the polarity of the shore power is reversed - or have I missed something else ?

Thanks

John
 
[ QUOTE ]
Open circuit is very possible if the diodes overload and blow. Short circuit is very unlikely IMHO.

[/ QUOTE ]

I beg to differ on this - I've seen many rectifier diodes fail to short circuit. In fact, I would go as far as saying that this is their normal failure mode when overloaded.

One web site promotes 'fail safe' technology (or something similar) where the fault current rating of the diodes in the isolator exceeds that necessary to melt the earth cable. That's the way I'd go. (N.B. this is a current squared x time rating, rather than the normal steady current rating).

Andy
 
[ QUOTE ]
or have I missed something else

[/ QUOTE ] I dont think so, if you have so have I!
 
[ QUOTE ]

there will be a path to earth via that lot and the water.


[/ QUOTE ]

Yes that is possable depending on the resistance of the earth peth through the water.

I have always had a question as to the validity of connecting the mains earth to the engine block, sterngear, anodes of a plastic hull /decked boat.

A steel hull and deck is a different matter

[ QUOTE ]


Also if there is a current flow from the neon through the GI doesnt that mean that the diodes are conducting and therefore not giving the protection they should be by blocking current from low voltage "galvanic" sources

[/ QUOTE ]

The neon is connected to an AC supply and the diode only allows the one side of the current to flow but blocking the other which is in the same direction as the potential galvanic current.

thus will still stop the galvanic current but allow the some to light the neon.
 
[ QUOTE ]
I have always had a question as to the validity of connecting the mains earth to the engine block, sterngear, anodes of a plastic hull /decked boat.


[/ QUOTE ] Yes I know you do and you are by no means alone, however, that is the requirement of the BMEA and CE regulations where they are applicable!
[ QUOTE ]
The neon is connected to an AC supply and the diode only allows the one side of the current to flow but blocking the other which is in the same direction as the potential galvanic current. thus will still stop the galvanic current but allow the some to light the neon.

[/ QUOTE ] The galvanic isolator is in effect two diodes (or banks of diodes) connected in parallel in with opposite polarities so it will conduct in both directions. However i suppose if you wanted to get clever you could include another diode in series with the neon so that only conducted on alternate half cycles. That would mean that the GI was only conducting in one direction. If you figured out which way would still give your underwater fittings the protection that the GI is intended to then maybe that would solve the problem.
Maybe you have also got to look at the need for a capacitor along with the GI. Maybe a capacitor would over comes my objection to the neon anyway.
 
[ QUOTE ]

The galvanic isolator is in effect two diodes (or banks of diodes) connected in parallel in with opposite polarities so it will conduct in both directions.


[/ QUOTE ]

You are correct of cause it does I must have had brain fade this morning.

The current introduced by the neon connection will still not effect the blocking of the galvanic current as this is driven by a voltage below the volt drip induced by the 2 diodes in series which are in parallel with a second pair for bi direction current flow, but you know that already

Just added for other people's info.
 
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