Should I install a galvanic isolator ?

fjweaver

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I have shore power which enters the boat via a garage type consumer unit - and have a ring main for kettle, tv etc and is completely separate from the 12v boat electrics.

I have 2 AGM batteries - each with their own on/off switch that I switch off when I leave the boat.

I have started to take turns in charging each battery when I leave the boat, using a decent car type battery charger, plugged into the mains.

But apart from turning the switches off I don't disconnect anything on the batteries. And I'm now thinking that the negative is bonded to the boat and I might be causing myself future problems. ( I have a hull anode & shaft anode)

So I'm wondering whether I should I fit a galvanic isolator - and if so any recommendations?

thanks
Frank
 

Scotty_Tradewind

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Sorry I can't answer your questions but it may help to bump up your posting to the top again.
I'm no expert so I asked a recommended marine electrician to rewire all my shore power circuits with new breakers just for piece of mind.

His first request was that he should also wire in a galvanic isolator whilst he was doing it.
He made the point that there is a great likelyhood of stray currents around our boats when in the harbour or marine environment where shorepower is available and that for the outlay, a great long term saving may result. I think the unit was around £70.

He also fitted 2 gas alarms in the two bilge areas.

Since fitting, the mains breaker has dropped out due to what turned out to be a loose wire in a 240v socket and the gas alarms went wild last week as an upholsterer was doing some work with glue.
 

KellysEye

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Metal boats definitely must have them. We have a steel boat and have galvanic isolators on both the 12 and 240 volt systems. It fits on the earth cable so you need to cut the plastic cover to get to the wire, then cut the wire to length, then strip to fit the terminals.

On GRP it's optional, it would be useful if you had dirty anodes and either stray current in the marina or a mix of salt and fresh water, which would damage the prop and metal throughulls. Personally I would fit one/two on any boat just for peace of mind.
 

Playtime

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I have shore power which enters the boat via a garage type consumer unit.

I'm now thinking that the negative is bonded to the boat and I might be causing myself future problems. ( I have a hull anode & shaft anode)

So I'm wondering whether I should I fit a galvanic isolator - and if so any recommendations?

If the mains earth is bonded to battery negative and hence to the anodes, then a galvanic isolator is highly recommended.

If mains earth is NOT bonded (i.e. DC and mains circuits, including earths, are totally separated) then there is no benefit from fitting a galvanic isolator.

If you want to leave a battery charger connected then it may be simpler/cheaper to just run the mains cable direct into the cabin and plug the charger into that.

Before you do this, though, I would recommend double checking that there is no connection between DC negative and mains earth occurring in the battery charger. This is unlikely (most battery chargers these days are properly isolated) but if there was such a connection then the situation is as above for bonding and you would need a galvanic isolator.
 

VicS

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The shorepower earth should ideally bonded to the DC negative ( except in cases where the DC system is fully isolated) and the anodes etc. There is, however, provision within ISO13297 ( the standard for AC installations in small craft ) for it not to be so bonded provided the whole vessel is protected by an RCD. This is not so in other standards, it is not recommended and the concession will probabaly be removed when ISO 13297 is next revised.

If the shorepower is bonded to the anodes etc a galvanic isolator is next to essential if the shorepower is left connected , even if not in use, for prolonged periods.
If it is not bonded then there is no point in fitting a GI

Safeshore marine offer an "easy fit" GI amongst their range which might be of interest see http://www.safeshoremarine.com/

ISO 13297

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