Galvanic Isolators

[Neil2]

1 hour ago, WotEver said:

As for Gibbo's theoretical leakage currents, they remain just that; theoretical. 

Several folk on here have measured them in the past with all sorts of equipment connected and they have never exceeded the bias of a couple of diodes, namely 1.2V. Not even got close. 

Personally I believe that an IT is a superior solution if it is used correctly which includes its placement close to but remote from the boat and hence I usually recommend the Airlink IT which can be yours for £240. I would never recommend a bodge with butchered site transformers. 

A GI which meets the AYBC specification (and many do if you look for it) will be closer to the price of an IT anyway. 

I think this is the road I'm going down, on our marina there's no physical impediment to having an IT between the boat and the shore power plug.  IIRC Nigel Calder's book suggests an IT as and essential requirement on a metal hull boat though I suspect the sort of vessels he had in mind are somewhat larger than the average NB.

What sort of I/O connections do these Airlink transformers have? 

[WotEver]

22 minutes ago, Neil2 said:

What sort of I/O connections do these Airlink transformers have? 

They may have changed since I last saw one but it simply had two cable glands and then chock block inside. 

I guess you could ask them, or have an exciting time waiting for the surprise after you order one

http://www.airlinktransformers.com/boating_transformers/BT3231/

[Bazza954]

51 minutes ago, WotEver said:

They may have changed since I last saw one but it simply had two cable glands and then chock block inside. 

I guess you could ask them, or have an exciting time waiting for the surprise after you order one

http://www.airlinktransformers.com/boating_transformers/BT3231/

Hi, I fitted one last November, it had gland entries and 6mm studding with nuts/ washers for the connections, connections on end of cable were ring terminals.

ETA  It was pale blue not yellow as shown.

Bazza

Edited March 3, 2017 by Bazza954

[WotEver]

I think pale blue is a better colour. Firstly it's not as brash and secondly some scroat won't think it'd be good to nick for site use. (As opposed to someone thinking that two site transformers could replace an IT). 

[Neil2]

I thought the blue ones were for lower current applications?

[WotEver]

25 minutes ago, Neil2 said:

I thought the blue ones were for lower current applications?

Looks like you're right: http://www.airlinktransformers.com/boating_transformers/BT1631/

The 3.6kVA one definitely states that it comes in yellow. 

[Neil2]

Thanks for the info on connections guys, it wasn't clear to me from the technical information supplied.  

I might get away with the lower current model given that all I intend to use shore power for is the fridge, TV, a small battery charger and a frost stat heater (not all at once).  

It's interesting that these Airlink models are shipped as "on board" IT's.  In standard form the case is bonded to the output ground ie the boat hull.  If you intend to use the transformer on shore it has to be wired differently.     

[GUMPY]

20 minutes ago, Neil2 said:

Thanks for the info on connections guys, it wasn't clear to me from the technical information supplied.  

I might get away with the lower current model given that all I intend to use shore power for is the fridge, TV, a small battery charger and a frost stat heater (not all at once).  

It's interesting that these Airlink models are shipped as "on board" IT's.  In standard form the case is bonded to the output ground ie the boat hull.  If you intend to use the transformer on shore it has to be wired differently.     

How do you bond a plastic case?

In truth with a plastic case the wiring should be exactly the same whether its on board or not.

It is VERY bad practice verging on dangerous to ground the core of the transformer to the boat. In the case of an interwinding failure the boat can go live wheras if the core of the transformer is bonded to mains earth the shoreside trip will go.

I have the very first Airlink boat isolating transformer in my shed running Loddon its now about 11years old and is pre plastic case.

Edited March 3, 2017 by Loddon

[WotEver]

15 minutes ago, Neil2 said:

In standard form the case is bonded to the output ground ie the boat hull.  If you intend to use the transformer on shore it has to be wired differently.     

No it ain't cos it's plastic. 

Yes you can use them on board (because they're plastic) but if the shore power lead got crushed between the boat and the jetty and shorted the earth to the hull (okay I accept that's unlikely) then the IT would do nothing. 

[Neil2]

Doh,  yes the instructions do refer to their steel cased transformers they sell two types for boats steel and plastic and the blue/yellow types are clearly plastic.

[smileypete]

 

11 hours ago, nicknorman said:

Not specifically, but the ISO and the AYBC standards are in a similar vein. Give me a moment and I'll pull out what the ISO says...

OK it says "failure of the GI shall not result in an open circuit" which is one of the requirements of the AYBC standard. GIs that don't mention this issue probably don't comply. For example Sterling sell GIs which don't mention it, and GIs that meet the AYBC requirements. The latter are more expensive, of course. I have to say that whilst Safeshore seems a popular choice, as far as I can see they don't meet the ISO or the AYBC and have very limited information - nothing about the max short circuit surge current which, even for a 16A supply, can be a hell of a lot more than you might think. And let's hope their website doesn't reflect the professionalism of their products!

Go on then, how much is it?

You could probably derive a ballpark figure for earth fault loop impedance by measuring the amount the mains voltage drops at the boat when a 1kW or 2kW load is switched on.

Edited March 3, 2017 by smileypete