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43 minutes ago, justsomeguy! said:

Build your own?

  

55 minutes ago, usedtobeoldestsailor said:

Why are they so expensive. 

 

 

Sorry, but that link no longer has "instructions".

I suppose it could be constructed by a reasonably competent DIYer, but there may be other factors to advise against that. Possibly legal ones?

 

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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. 

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I have one of these Promariner FS60. seems like small money for what it does.

https://www.defender.com/product.jsp?id=1353701

Now Isolation Transformers - that's where you can start to spend real money, especially if (like me) you have two 30amp circuits coming in. Promariner doesn't even make those anymore.

 

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On 4/15/2021 at 10:54 AM, ryley said:

[  .  .  .  ] 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.

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On 4/11/2021 at 4:11 AM, usedtobeoldestsailor said:

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.

 

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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?

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On 4/16/2021 at 12:32 PM, axolotl said:

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...

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1 hour ago, Bull City said:

Other boats report infinitesimal galvanic corrosion

You're probably fine then. G.I. are not that common IMO. Anybody want to guess what % of boats have them aboard? 10%??

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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.

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12 hours ago, weightless said:

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.

Magnesium anodes for fresh water.

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Thanks lots of good info.  We are at a very popular marina in the Salish sea and our particular dock obviously has some AC problems because everyone complains of having to change zincs often.  Have talked to the marina and so far they don't want to do anything about it.  Unplug is a good idea!

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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?

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