Hi Folks - This weekend I installed a battery combiner, and also bought a better, 3 stage charger. My Catalina 27 never had a negative bus bar installed, so I added one of those too. So, I now have the ability to charge both banks simply by attaching the charger to one battery. Nice! Here is the bad part. I used to disconnect a battery when I charged it. I did this in an effort to keep electricity/excess voltage away from the engine. Now, the bus bar has a ground wire connected to the engine (necessary for the starter motor), so this option is no longer available. What I would like to do is put an on/off battery terminal switch between the bus bar and the engine, such that when I get back to the slip, I can charge the batteries while keeping the engine out of the loop. Good idea? Bad idea? Am I overly paranoid about galvanic corrosion? Thanks in advance - Rob
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Good Idea
Rob, What you have done is very good. In answer to your question, think about why you did it to begin with. You now have the ability to charge both your banks from (any) one source (i.e., solar, alternator, shorepower). Your engine IS the ground or the 12V side. It will not decay. Do NOT disconnect it, it is part of the overall 12 V circuit. If you once forget to switch it back on, you'll have MUCH bigger problems. This is because you may want to use the 12 V system onboard when you are charging. If you forget to make (use) the switch, either nothing will happen on the load side, or you'll damage something. Why complicate something you've just made easeer? Galvanic corrosion is caused by other improperly wired boats or bad shorepower connections. (Assuming your wiring is OK) With your new smart charger, you should be able to charge your batteries and then NOT need to leave the boat connected to shorepower during the week. You are now ahead of the game. Add a small solar panel to offset the natural dschrge of your batteries (assuming wet cells, gel cells are much better with little self-discharge), and you almost never need to connect to shorepower for any extended period of time that you are not present personally. Thus, no galvanic corrosion problem. Try Calder's Manual, if you haven't already.
Rob, What you have done is very good. In answer to your question, think about why you did it to begin with. You now have the ability to charge both your banks from (any) one source (i.e., solar, alternator, shorepower). Your engine IS the ground or the 12V side. It will not decay. Do NOT disconnect it, it is part of the overall 12 V circuit. If you once forget to switch it back on, you'll have MUCH bigger problems. This is because you may want to use the 12 V system onboard when you are charging. If you forget to make (use) the switch, either nothing will happen on the load side, or you'll damage something. Why complicate something you've just made easeer? Galvanic corrosion is caused by other improperly wired boats or bad shorepower connections. (Assuming your wiring is OK) With your new smart charger, you should be able to charge your batteries and then NOT need to leave the boat connected to shorepower during the week. You are now ahead of the game. Add a small solar panel to offset the natural dschrge of your batteries (assuming wet cells, gel cells are much better with little self-discharge), and you almost never need to connect to shorepower for any extended period of time that you are not present personally. Thus, no galvanic corrosion problem. Try Calder's Manual, if you haven't already.
A few other thoughts...
Stu's made several solid points, including treating yourself to the purchase of Nigel Calder's _Boatowner's Mechanical & Electrical Manual_, a gift that will keep on giving back for as long as you open it up. Galvanic corrosion CAN be a problem for you, tho'. Not all marinas have a routine electrical monitoring program and, even if yours does, this doesn't keep you from visiting another dock when weekending. If marina wiring is OK, a 'hot boat' can still move in next door - either permanently or as a guest - and his/her problem can become yours. In addition, wiring on your boat can fail over time. Altho' your boat's wiring is probably pretty simple, that doesn't mean it can't happen. E.g., a boat near me lost its prop and almost lost its rudder because its compass light + wire chafed thru and was grounding itself on the pedestal. The switch & fuse didn't protect it from doing serious damage. One option you might consider, especially if you think you'll be a boat owner for some time and perhaps move up or over to other boats, is to purchase a Galvanic Isolator, install it in your shore power wiring, and consider it a portable device that you plan to move from boat to boat. Newmar makes a good unit and, at approx. $100 over the span of time you are a boat owner, is a great investment in peace of mind. Wiring it in place is very simple and restoring the shore power wiring when you remove it should be, as well. Just remember that 120V can kill you and, as Calder mentions, you want to be certain of what you're doing. At this level of work, that should be easily accomplished. Jack
Stu's made several solid points, including treating yourself to the purchase of Nigel Calder's _Boatowner's Mechanical & Electrical Manual_, a gift that will keep on giving back for as long as you open it up. Galvanic corrosion CAN be a problem for you, tho'. Not all marinas have a routine electrical monitoring program and, even if yours does, this doesn't keep you from visiting another dock when weekending. If marina wiring is OK, a 'hot boat' can still move in next door - either permanently or as a guest - and his/her problem can become yours. In addition, wiring on your boat can fail over time. Altho' your boat's wiring is probably pretty simple, that doesn't mean it can't happen. E.g., a boat near me lost its prop and almost lost its rudder because its compass light + wire chafed thru and was grounding itself on the pedestal. The switch & fuse didn't protect it from doing serious damage. One option you might consider, especially if you think you'll be a boat owner for some time and perhaps move up or over to other boats, is to purchase a Galvanic Isolator, install it in your shore power wiring, and consider it a portable device that you plan to move from boat to boat. Newmar makes a good unit and, at approx. $100 over the span of time you are a boat owner, is a great investment in peace of mind. Wiring it in place is very simple and restoring the shore power wiring when you remove it should be, as well. Just remember that 120V can kill you and, as Calder mentions, you want to be certain of what you're doing. At this level of work, that should be easily accomplished. Jack
Disconnect?
I don't understand your reasoning for disconnecting the battery while charging with the AC battery charger. You don't disconnect the battery when it's being charged by the alternator, do you? The charger isn't going to hurt your engine. The slightly elevated voltages shouldn't be enough to damage any of the equipment on your boat, for that matter. The engine (and all of it's interconnected parts) are your main grounding/bonding point. Disconnecting it means your boat may not be grounded at all, depending on how the rest of your stuff is bonded (if at all). That is NOT a good thing. Jack's suggestion of adding a galvanic isolator to the shore power circuit is a very good one. That way the shore power ground (green) is isolated from your boat's ground. Your inside AC wiring can then be safely grounded to the rest of your grounds. (Yes, connected to that shiny new negative bus bar!) It's all in The Book (Nigel's, that is).
I don't understand your reasoning for disconnecting the battery while charging with the AC battery charger. You don't disconnect the battery when it's being charged by the alternator, do you? The charger isn't going to hurt your engine. The slightly elevated voltages shouldn't be enough to damage any of the equipment on your boat, for that matter. The engine (and all of it's interconnected parts) are your main grounding/bonding point. Disconnecting it means your boat may not be grounded at all, depending on how the rest of your stuff is bonded (if at all). That is NOT a good thing. Jack's suggestion of adding a galvanic isolator to the shore power circuit is a very good one. That way the shore power ground (green) is isolated from your boat's ground. Your inside AC wiring can then be safely grounded to the rest of your grounds. (Yes, connected to that shiny new negative bus bar!) It's all in The Book (Nigel's, that is).
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