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bill good 25-06-2009 17:33

Electrolysis
 
Just want to get an idea from anyone out there that could advise me why the earth on the AC circuit should not be via something like a starting capacitor to ensure DC cannot get involved & hence not have electrolysis problems on boats. (not considering RF) It would seem a viable alternate to galvanic isolators.

Regards Bill

Christian Van H 25-06-2009 19:19

If I'm not mistaken, you've just reinvented the Galvanic Isolator. It's caps I believe, in them there boxes...

donradcliffe 26-06-2009 09:43

Not caps--its diodes, which only conduct when the voltage gets over 0.6 volts.

Rick 26-06-2009 11:12

Two diodes
 
Actually there are four diodes total; two in series paralleled with two others in series "facing" the opposite direction. If only one diode is used in each leg then the 0.8 to 0.9 Volt (approx.) developed by zinc-to-stainless (shaft, for example) potential would cause a galvanic isolator to conduct and waste the zincs.

Christian Van H 26-06-2009 11:30

Quote:

Originally Posted by donradcliffe (Post 297693)
Not caps--its diodes, which only conduct when the voltage gets over 0.6 volts.

My bad! What extra components do they add to make them "failsafe" for the ABYC?

CharlieJ 26-06-2009 14:23

The fail safe GIs utilize extremely rugged components and the unit is tested and certified by a third party. The testing protocol sorts out the contenders from the pretenders.

GordMay 29-06-2009 05:32

Quote:

Originally Posted by CharlieJ (Post 297794)
The fail safe GIs utilize extremely rugged components and the unit is tested and certified by a third party. The testing protocol sorts out the contenders from the pretenders.

A “Fail-Safe” galvanic isolator will “fail closed-circuit”; insuring that the shore power safety ground wire is maintained through the isolator, even in the event of isolation failure.

The criteria for galvanic isolators is defined by the American Boat and Yacht Council (ABYC) recommended standard A-28, which has recently been revised. This standard has a publication date of July 2008 and an effective date of July 2009.
Due to recommendations to the A-28 galvanic isolator standards committee concerning the need to retain safety grounding under all conditions, as required by the U.S. National Electric Code for all similar applications outside of A-28, this standard now makes provision for fail-safe galvanic isolators.
To be considered "fail-safe," an independent laboratory must confirm that the isolator will either remain fully functional or remain a permanent, effective grounding path if it fails when subject to the maximum current rating.
Per the new A-28 standard, galvanic isolators meeting the fail-safe requirement will not require a monitoring system since the integrity of the grounding wire will not be compromised should the isolator fail.
All galvanic isolators not meeting the fail-safe criteria will still require a monitoring system to alert the boat owner that their grounding system may be compromised.


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