Date: Tue, 17 Mar 1998 09:38:06 -0800 (PST) From: Todd C. Klaus Subject: lv-ab: Summary for battery combiner and AC groundThanks to all who answered my questions on battery combiners and AC grounding.The battery combiner answer was straight forward. My concern was that when the combiner combined a fully-charged starter battery with a discharged house bank, there would be a high current flow from the starter battery to the house bank. Several people pointed out that this should not happen, as the combiner will only be triggered by a high charging voltage (from the alternator or battery charger), in which case the potential difference between the charging current and the house bank will be higher than the potential difference between the starter battery and the house bank, and hence, most of the current flow will come from the charging source.
The second question generated more debate. The question was whether the AC ground should be connected to the DC grounding system, in order to provide a redundant path to ground in the case that the marina's ground is faultly or not connected. There seems to be disagreement on this issue, even amoung professional marine electricians! I have two books, "Boatowners Mechanical and Electrical Manual" by Nigel Calder, and "Marine Electrical Guide" (not sure on that title), by John Payne. They each each recommend the opposite (Calder says to connect them, Payne says not to), and they both claim that not following their advice can lead to electrocution. I have heard the same thing from members of this list. I guess the bottom line is that electrocutions can happen either way. The best solution is an isolation transformer, but this seems impractical (it's big and heavy, and if I had room for it, I would put in another battery instead:) for a 30' sailboat that will use the AC only for powering a 10 amp charger and maybe one outlet occasionally. One useful piece of information: If you choose to connect the AC ground to the DC ground, you should put a galvanic isolator on the AC ground to prevent galvanic corrosion.
Thanks again to all who responded! This list is a great source of wisdom!
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