Galvanic Isolators

DDW

Super Anarchist
6,239
972
A simple passive one is just two diodes. They have to be big enough with enough heat sink capacity to carry the entire current service. These used to exist, but current ABYC recommendations prohibit them, because they will fail into the open condition, ABYC requires they fail "safe", that is, shorted. That isn't easy to do, and the reason they cost so much now. 

 

axolotl

Super Anarchist
1,656
183
San Diego
[  .  .  .  ] Now Isolation Transformers - that's where you can start to spend real money, especially if (like me) you have two 30amp circuits coming in.
The ultimate solution for stray current corrosion protection from your poorly wired dock or marina neighbors.  Also will prevent your boat from ever causing electric-shock drowning

Heavy and costly though.  Hubble makes a 60a isolation transformer that would suit your situation, only $2,000 and weighs 250 pounds:  Hubble IT  With the optional ISO-Boost module which handles brownout shore power voltage drops of up to 12.5% it'll cost $7,000.

I've got a 20a ACME isolation transformer for my modest shorepower needs, about 40 pounds and a few hundred bucks when I installed it in the early 90s. Still working fine.

 

weightless

Super Anarchist
5,607
581
Why are they so expensive. 
To pay the salary of the ProM's guy on the ABYC committee? ;) I'm probably being way too cynical here.

IIRC, FWIW, and please don't: DIY instructions tended to be very simple. Basically you just want two diode drops. You can get diodes nicely packaged for bolting to a heat sink and in appropriate ratings as bridge rectifiers. You can wire them up in various ways and in various numbers to get more or less redundancy. Simplest, and least fail safe, is probably to just tie the  DC terminals together and run the shore connection to one AC terminal and the boat to the other. I've seen folks draw capacitors in (maybe class Y?) but I'm not sure if that's a good or useful idea. Well, none of it's a good and useful idea, IMO. Please, just don't. But the theory of operation is worth knowing, I suppose.

 
Last edited by a moderator:

Max Rockatansky

Max Rockatansky
3,537
816
The ULTIMATE solution is not plugging in at all, and that isn’t that big an ask these days with good solar, wind, and LFP batteries. I know bc I have done it

 

Bull City

Bull City
6,848
2,501
North Carolina
I am going to be plugging into 110v in a freshwater marina. Other boats report infinitesimal galvanic corrosion, although I din't know how many are plugged in 24/7 and have G.I.'s. What's your advice?

 
Last edited by a moderator:

Zonker

Super Anarchist
8,877
4,789
Canada
Heavy and costly though.  Hubble makes a 60a isolation transformer that would suit your situation, only $2,000 and weighs 250 pounds
Talk to your marina. Can you install it in a dockbox rather than sail with it? For the 99% of the time you will be plugged in...

 

weightless

Super Anarchist
5,607
581
I think that with no problems reported I'd just make sure I had whatever sacrificial anodes, "zincs", the manufacture suggests for fresh water installed and keep an eye on them. If the zincs waste away quickly then maybe a GI would make sense.

 

Baldur

Super Anarchist
I plug my SJ 24 directly into a 6amo marine battery charger connected directly to the battery. There is no other 120v. I do have 12v for the interior lights , nav lights, for Instruments. The outboard is lol fred from the water at the slip. A very experienced friend says I should still have a galvanic isolator or something to protect my keep bolts from stray voltage. But my keel bolts are not in the water. I have no metal in contact with the water. Note; I do have VC17 bottom, loaded with copper.

What day the peanut gallery?

 
Top