Galvanic isolator

[drs3317]

What size galvanic isolator is required or suggested? I can find little information on sizing and now I'm working on the electrics of my twin engine cruiser. Thanks for any help.

[gonzo]

One that can handle the load on your boat. It is basically a transformer.

[LADYLOVE]

This quote (by Ed Sherman) helped me out regarding this particular matter :"Your boat can be in great electrical shape, but once plugged into shore power it becomes electrically connected to its neigbors via the green grounding wire in the AC system. This connection completes an electrical circuit betwee multiple boats, each with potentially dissimilar underwater metals exposed to the surrounding seawater." "Load "was not mentioned in text reviewed, but make be important. Suggest you invest in a good referenced book on boat electrical sytems.

I watch a Direct TV boat show with John Griviscus? in it . They had a galvanic Isolator company REP. explain with volt and ammeter leads in the water beside the boat, how to adjust YOUR boats potentials to be ZERO!

[MikeJohns]

The galvanic/electrolysis Isolators used today are not isolating transformers but devices that block DC currents in the mA range, commomly they are a couple of back to back diodes with a capacitor across them installed in the earth return, the diodes block the small DC component required for a galvanic couple to work, while the cap still conducts sufficient fault current at low levels to trip the ELCB.

[kkimble]

The last reply by MikeJohns is correct. You purchase a galvanic isolator by the rating of your shorepower connection, so it will be a 30 amp or a 50 amp unit.

[LADYLOVE]

NUMBER 1. Which is best and easiest (if equal in desired performance) to install?

My current battery system is similar to the diagram shown on page 549 of Boatus catalog except I have twin engines without the zap stop and of course, the battery combiner. Not certain about that diagram's wire that appear to run between the DC panel and engine starter. I have a battery 1,2, and 3 selector switch which to my knowledge only let me monitor the batteries? But I do have circuit breakers for Batteries 1 and 2 on the panel.

Twin engines
2 agm (G31) batteries (one per engine) with a parallel switch at the helm)
Note: both batteries also share separate house duties.
2 A/C's, and usual other electrical items found on a 1990 40 feet boat)
Also a 5000 SP 40 amp 12volts 3-stage Charger
NO Inverter
Kohler 7.5 GEN with it own battery (see note below)
Crusader Gas Engines (plan to install the 8.1's this year)

Note: the GEN raw water pump went out 2 years ago and had a problem with the yard's attempt to fix it (a bolt broke off). I had to take the applicable part to a machine shop to remove the bolt, etc., and never put it back together). Anyway, have not had any use for it the last 4 or 5 years. May get a new one or try to fix this one myself (lol). IN THE MEANTIME, THINKING ABOUT RUNNING MY NEWLY ADDED FISH FINDER AND GPS TO THAT PARTICULAR BATTERY. NUMBER 2. WHAT DO YOU GUYS THINK??????

Again, will appreciate any comments provided.

Wm.

[LADYLOVE]

Sorry, everyone, that my last reply/question is in the wrong subject area. I saw the wor isolator and .... well you know the rest.

[kkimble]

Ladylove, you sound confused at times. E-mail me at
kkimble@northeastmarineelectric.com and I'll help you get straightened out. I have a business card that says "reasonable amount of free information" on the back of it. Sounds like you need some. There is also a Northeast Marine Electric website at northeastmarineelectric.com, but it's what known as a business card website.

[Ragtime]

The current rating for these can be far less than your shore power rating if your vessel is equipped with RDC protection which can typically trip at less than 30 milliamps leakage current.

[drs3317]

Thanks for the info. But what is RDC?

[Ragtime]

Sorry!! Should of course read RCD - or Residual Current Device. Commonly available from electrical dealers. An RCD basically replaces the now obsolescent ELCB or Earth Leakage Circuit Breaker. An RCD is a partly electronic device and is far more sensitive than the old ELCB tripping in the most sensitive types at less than 30mA.

[cyclops]

The RCD sounds very close to a GFCI breaker. Is it one of the same with a Marine name and price?

[Ragtime]

Sorry but I am not familiar with American product to which I assume you refer. European RCDs are not specific to marine use and are common in commercial and domestic applications.

[readingr]

I am looking into Galvanic Isolators and want to know if these things really do stop your anode corroding?

I have a Feeling 32 with just a 25mm Anode which sits on the end of the prop nut. This corrodes over about 3 months to nothing and I am getting fed up with changing it so often.


Will a Galvanic Isolator really slow down the corrosion I see. Most of the time the boat is not connected to the mains and the batteries are off. We only connect to the mains when in Marina's and quays which provide electrics.

Any help will be greatly recieved.

Sincerely
Roger R.