Cheap and simple galvanic isolator?

[bluedragon]

We're only on shore power for a few days a month on average (but might be more if we have another crappy summer!). I haven't bothered fitting a GI for this reason, but feel it wouldn't be a bad idea. The cost (and complexity) of them seems very high...anyone found a cheap and simple solution?

 

[pvb]

You could make one yourself - see here for simple DIY instructions.

 

[dento29]

Anyone what Bridge rectifier to use?

 

[habeer]

there's little difference in cost once you're in the range of 25 Amps 200V or so. The reverse voltage is unimportant, it will be clamped to 1.5V or so.

I mounted the bridge rectifiers inside a diecast aluminium box (petrol engine in the cave), with three 1/4"-20 brass bolts mounted in nylon shoulder washers (electrical isolation). The box and one stud go to the ship's earth, and the other two studs are bussed together with a brass bar and go to the shore power earth. Why two? Occasionally, you'll have to test the forward voltage drop (~ 1.5V) by using a test lamp and your 12V battery. I test once a season. I think I spent around 20 US dollars.

Harold

 

[William_H]

Just to make sure you need a GI and understand the purpose.
A GI is not so much an add on to avoid corrosion but is needed where the earth of the ships mains system is connected to the earth wiring of the boat. ie negative power and anode grounding. This connection is broken by the GI and stops small currents flowing.

The connection to earth is made to enhance the safety of the mains system.
However the connection of the mains earth system therefor the marina earth system to your boat via your expensive bronze underwater gear can provide a path for stray current. This current can damage your underwater gear. The GI isoaltes the small current/voltage while still providing the current path for a fault situation which could cause a shock.

If you don't have or need that connection mains earth to ships earth you don't need a GI. Indeed there is no where to fit it. If you only occasionally connect to the mains for a limited period then even if you have that earth connection you won't need GI.


You don't need that connection if you only use an extension cord for a few portable appliances. This especially so if they are so called double insulated. ie plastic body of electric jug heater. Your battery charger may be of slight concern. With possibly a metal box and possibly the box connected to both mains earth as it should be but also to the negative output which you connect to ships negative. If this is the case you still can break the earth line for a GI. If it only has a metal box just be wary of touching the charger when connected to the mains if you are touching any thing earthed. good luck olewill

 

[bluedragon]

Yes, that's a good explanation William. I did not connect the AC earth to boat DC -ve, so considered I didn't need a GI. It's the battery charger that bothers me a little. It's only connected when I'm on board, but I guess those days do add up. I'm going to check today if the shore power earth and yacht -ve are connected when this is on.