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martinsmit
martinsmit

Posted: Tue Apr 28, 2009 8:58am

Post Subject: galvonic isolaters

Hi Again Tony Could you tell me if i need to fit a galvonic isolater, the ones i've been looking at have a small gauge with needle on them. i was going to fit one before my consumer unit which then goes to my inverter, so that i can connect a earth from the engine mount through the galvonic isolater and into the earth bar on the RCD/consumer unit but i've read that if you dont have a shore 240v hook up then you dont need one, is this correct? Also just going away from this do you now of a good supplier of 12v freeview lcd tv's thanks again martin

Tony-B
Tony-B

Posted: Tue Apr 28, 2009 7:28pm

Post Subject: galvonic isolaters

Dear Martin, the idea of either an isolation transformer or a galvanic isolator is to separate your boat's earth connection to the hull from everything else connected to the electricity company's earth. If you are producing your own "mains" from an inverter or generator you should still have a hull earth bond but it will not be connected to anything else so no further "isolation" equipment is required. It is only needed with shorelines. As for the TVs, I Googled and hoped I would not get ripped off but most chandlers sell them (at suitable markups) and providing you take a simple precaution you could even use one from a supermarket that uses a 12 volt power supply plug in the mains socket. The only thing you need to consider is that these TVs may not be designed to operate on up to 15 volts AND deal with the voltage spikes you tend to find on boat systems. You overcome this by buying a voltage stabiliser designed to sit between the TV and a 12v outlet. However many people do not bother and find just connecting the TVs 12v dc input socket direct to a 12v outlet satisfactory. Personally I would not risk it and do have a stabiliser. You may well find special offers on proper 12v TVs at the Crick Show at the end of May. Tony Brooks

martinsmit
martinsmit

Posted: Wed Apr 29, 2009 8:09pm

Post Subject: galvonic isolaters/tv's

Hi Tony Thanks for the info again. Could i just ask with regards to the tv, 12 volt, can you fit and use a standard 240 volt socket and plug or does it need to be the round type that you find in cars, cigarette lighter. Also with regards to fuse ratings how would you work out what size's of fuses to use on lighting and other items where it dosent specify the rating in any manuals that come with equipment, 12 volt. Thanks again Martin

Tony-B
Tony-B

Posted: Thu Apr 30, 2009 8:28am

Post Subject: galvonic isolaters

If a piece of equipment requires protecting that protection should be built in or supplied. In the absence of any information the fuse is selected to protect the CABLES, so the fuse should be rated at less than the smallest cable in the circuit. You asked about a galvanic isolator so we must assume that you have mains on board. This means it would be both extremely dangerous and gross bad practise to use a mains type pug for the 12v outlets. Whatever you use must be polarised which means it is impossible to connect "backwards" and thus damage the 12v equipment. In the past when mains on boats was far rarer it was common to use the small 5 amp 3pin mains plugs and sockets for the 12v outlets. However it is vital with mains on board that you do not connect anything to the line (brown) pin so if a mistake is ever made 12v equipment can not be fed mains. Typically you would designate one of the other plugs to be positive and then you would have to stick to that. Often the earth pin was used as positive and the neutral as negative. I can not condone this on boats with mains available but any other form of polarised plug & socket is acceptable. The car "cigar lighter" ones are possible the most widely available. Tony Brooks

nbhenry
nbhenry

Posted: Sun May 03, 2009 9:09pm

Post Subject: galvonic isolaters

Hi Tony, I'd like a bit of advice about fitting a galvanic isolator - our 12 year-old boat has a normal land-line bulkhead connection in the cockpit, which feeds into the 240v switch/fuse/RCD board. In the interests of simplicity I use the same bulkhead connection for our Mastervolt Whispa 3.5 generator and also for our Moore Power 1800w inverter - all on separate leads & sockets, so only one at a time can be connected. I'd expect to wire the galvanic isolator into the earth cable immediately after the bulkhead connection, before the RCD etc., but I'm slightly concerned that it might affect the electronic safety systems of the generator or the inverter when they're connected up... can you advise if there's liable to be a problem? Thanks, Nick.

Tony-B
Tony-B

Posted: Mon May 04, 2009 6:22pm

Post Subject: galvonic isolaters

Dear Nick, it would be better to start this as another question because it is rather different from the original. I am not qualified to advise on 240V AC topics so you need to double check my answer with someone who is properly qualified in this area, but as far as I understand correctly fitting the GI where you propose in the circuit should have no effect on the inverter or generator. The diodes only conduct under fault conditions, so they do nothing for most of the time (subject to certain caveats) and as long as they are in working order will conduct any fault current whatever the electrical source. I trust you have noted my comments about the need to check how to earth any inverters that are not provided with an earth connection. Tony brooks

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