in most cases the GIs have 4 diodes in them for 1.2V drop/isolation. (2 in series in each direction) Selecting components for a given amp rating is not hard. But, selecting components and enclosure that can withstand the environment is a bit of a challenge.
Leslie. Phoenix C&C32 1983 -------------------------------------------- On Wed, 10/28/15, Don Wagner via CnC-List <cnc-list@cnc-list.com> wrote: Subject: Re: Stus-List Galvanic isolator - Good idea? To: "C&C List" <cnc-list@cnc-list.com> Cc: "Don Wagner" <don.wag...@verizon.net> Date: Wednesday, October 28, 2015, 1:55 PM Josh To answer your question about “What are the shaft zincs protecting?” Assuming you are in saltwater such as the Chesapeake, Just a few things, including: the prop, the shaft, the rudder post, the keel bolts (especially if you have the C&C Smile), as well as any other of the usual underwater metals. You should protect these items as the can’t be easily inspected, but failure can be a real disaster. If you have a shaft isolator, you should install one or more copper jumpers between the engine coupling and the prop shaft coupling. Also Galvanic isolators are suggested for situations where you suspect the AC system at the marina or nearby boats may be compromised. Note: Galvanic isolators are a simple circuit made up 2 big diodes wired in parallel but pointed in opposite directions. Since the diodes are not perfect they create about .6 volt DC barriers to prevent the corrosion currents needed for electrolysis. A big capacitor is also connected in parallel with the diodes to allow AC current at low levels and in case of diode failure. All three components are mounted on a large heat sink to keep the parts cool and insure a longer life. Don’t try building this yourself, unless you can design the proper size diodes and capacitors and heat sink the box Just my $.02 Don Wagner C&C 41 CB Der Baron From: Josh Muckley via CnC-List Sent: Wednesday, October 28, 2015 12:48 PM To: C&C List Cc: Josh Muckley Subject: Re: Stus-List Galvanic isolator - Good idea? Since we're on topic. It seems that there is a bit of differing opinions on bonding the under water metals. What are the shaft and prop zincs protecting? If a shaft coupling isolator were installed and no bonding wire attached then the chance of stray galvanic currents is eliminated. Right? What is the risk of this situation? I don't have bonding plates, bronze through hulls, keel coolers or anything else except the keel that is metal and in contact with the water. I've considered possible corrosion effects on internal engine components and A/C components. Seems plausible but no one ever talks about it. Thoughts? I've also considered the anode in the water heater. Seems like the most likely to experience stray galvanic currents and the least likely to be replaced or checked on any regular periodicity despite its ease of access within the boat. I have 2 30 amp connections but use a y-adapter so only 1 shore power cord is required. I also built my own galvanic isolator for ~$30 with parts from mouser.com, I've just never had the urgent need to install it. Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Oct 28, 2015 12:32 PM, "Frederick G Street via CnC-List" <cnc-list@cnc-list.com> wrote: Also, the ProMariner FS Series is a “fail-safe” type isolator; no remote panel needed. Under $300 for a 30-amp unit. http://promariner.com/products/galvanic-isolation/prosafefs-series/ Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( On Oct 28, 2015, at 11:29 AM, Frederick G Street via CnC-List <cnc-list@cnc-list.com> wrote: Steve — the “fail-safe” versions of galvanic isolators are also ABYC-approved, and don’t require the remote panel. There’s a company up in our neck of the woods that started out making electrical equipment for dairy farms; they realized that their ground isolation products would also work well on boats, so they expanded into the marine market. All their units are the “fail-safe” types, and their prices are reasonable. http://www.dairyland.com/products/galvanic-isolator http://www.deimarine.com Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( On Oct 28, 2015, at 11:24 AM, S Thomas via CnC-List <cnc-list@cnc-list.com> wrote: Ed, What you say is true from the perspective of having effective galvanic isolation, but there are a couple of design issues that come to mind. In order for galvanic isolation to work, all wiring grounds to the boat must be interrupted by a galvanic isolator. This means that if there are two shore power receptacles then both of them would have to have their wiring grounds taken to the isolator and then out again to the distribution panel(s). From an engineering perspective, a wiring ground only needs to have enough capacity to reliably trip a circuit breaker without catching on fire, but most electrical codes require that they have the same capacity as the main conductors. In other words, if you care about regulations and some people on this list have indicated that they do, then the galvanic isolator would most likely have to have at least the current capacity of the sum of both shore power receptacles. According to the instructions that came with a galvanic isolator that a friend of mine bought last year, a galvanic isolator requires an (optional and at an additional cost for that particular product) indicator light to be ABYC compliant. I was shocked at the price tag on the commercial units. The prices are grossly out of line with what they actually contain. If you don't care about the light and just want something that works, then a big enough bridge rectifier, 30 amps for example, with the DC terminals connected together will work fine and cost a lot less than something that says "marine" on it. The voltage rating of the rectifier does not matter, just the current rating. It will provide about 1.2 volts of isolation from the mains ground. Steve Thomas Port Stanley, ON _______________________________________________ Email address: 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 _______________________________________________ Email address: 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 -----Inline Attachment Follows----- _______________________________________________ Email address: 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 _______________________________________________ Email address: 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
