Excellent summary, Josh.
I recall the breakover voltage as .6 not .7, but the effect is the same. 1.2 or 1.4 volts of breakover from two diodes in series will stop the galvanic current. And for the frugal among us, and I think that covers most all sailors with boats under about 50 feet, the price of a 1000 volt, 50 amp diode at Radio Shack is about $2.99. Add a small project box, some wire, and a couple of stud terminals, and you've got a homemade galvanic isolator for about $20-25. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh Muckley via CnC-List Sent: Wednesday, April 01, 2015 8:23 PM To: C&C List; David Knecht Subject: Re: Stus-List New Wiring Diagram Draft If you are primarily on a mooring (or more specifically disconnected from shore power) then you are fine. The galvanic isolators prevent galvanic currents from being conducted along the common ground wire of mutiple boats at a marina. Since the zincs are usually electically on the ground wire of each boat then your zincs will be sacrificed to other boats at a lower galvanic potential (less/no zincs). Periodic plugging in will not significantly deplete your zincs. Always on shorepower charge or rather simply always keeping the shore power cable plugged in. Even turning the breaker off is not enough because the ground doesn't get disconnected. No your promariner charger does not provide any protection. The problem comes from the AC ground being tied to the boat's common ground/bonding sysyem (as required). Forward biased diodes normally have a breakover voltage of about 0.7v. Galvanic currents run about 1.0v...IIRC. so taking 2 diodes and placing them in a forward and reversed bias orientation will result in a circuit which cunducts freely in both directions at greater than 0.7v but will not conduct at all less than 0.7v. If you had a lightning strike or a fault which depended on the ground then the diodes would properly conduct and transmit the energy to the ground on the marina's electrical system. During all other times, the diodes are not reaching thier breakover potential so they are not conducting the galvanic potential to (or from) other people's boats. But wait didn't I say the galvanic potential could reach 1.0v and the breakover was only 0.7v? Wouldn't that be enough to forward bias the diode? Yes it would be so most GIs are made with 2 forward biased diodes in series and 2 reverse biased diodes in series. This brings the breakover voltage close to 1.4v which is above the 0.7v galvanic potential. The other thing to consider is that the diodes have to be rated at a minimum for the forward bias current and voltage which you could expect from a fault. So a 30a 120v shore power connection would be diodes of equal or greater size. Normal diodes will fail open when their ratings are exceeded. There are reports of lightning strikes taking out GIs and then the boat has no ground protection. Modern commercial GIs are desined to fail closed and are marketed as fail safe. So if you have an older model or don't know what type you have it is a good idea to test it regularly to ensure that it still has continuity. Again without a frequent connection via a shore power cable, there is no reason to even have a GI. http://www.pbase.com/mainecruising/galvanic_isolator Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Mar 29, 2015 4:22 PM, "David Knecht via CnC-List" <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > wrote: Hi Joe- Please educate me. If I have a galvanic isolator, I don't know it. I am on a mooring most of the time, so probably don't need one, but I periodically am plugged in at a dock, so is this important to have? Am I correct that my Promariner charger or inverter does not include this function as well? Thanks- Dave On Mar 29, 2015, at 1:22 PM, Joe Della Barba via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > wrote: You also left a galvanic isolator out of the diagram. See http://promariner.com/products/galvanic-isolation/prosafefs-series/ These keep you from sharing your zinc out to the entire marina ;) Joe Della Barba j...@dellabarba.com <mailto:j...@dellabarba.com> Coquina Dr. David Knecht Professor of Molecular and Cell Biology Core Microscopy Facility Director University of Connecticut 91 N. Eagleville Rd. Storrs, CT 06269 860-486-2200 <tel:860-486-2200> _______________________________________________ Email address: CnC-List@cnc-list.com <mailto:CnC-List@cnc-list.com> To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
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