I am confused about the charging of bateries on my sailbaot - mostly questions about charging with the engine. My specific problem is lack of knowledge of how the selector switch works. First let me state what I think is happening with the system, then a question or two. On my boat there is a battery selector switch. This has four settings. Off, #1, #2 and both. I understand that it isolates the batery bank #1 from #2 or connects them both. The batteries will also charge from shore power when the switch is set to off, but the boat can't draw any power. Good feature that. Now for the questions. Let's say you have one battery or set of batteries designated as the house and another battery as the start batery. So, far no problem. Now you are on a mooring and use the house bateries to the point they need charging - or worse they are dead. You set the batery selector to the start battery and start the engine - how do you now charge the house bateries? Will they charge off the engine even if they are wired to #1 and the selector is set to #2? Or, do you start on the engine batery then switch while running to the house batery set? If so will this harm the alternator? I was under the impression not to switch this selector while the alternator is suppling juice. Although I do think the switch is a connect prior to disconnect. I do know not to set the selector to "both" if one bank is very low as it will drain the good set. So, tell me how it should be done. Sorry to be so ill informed, but so far anyone I ask has a halfa** explanation as to what is going on and what to do. I was an engineer in a past life so am not totally ignorant of the working of systems if explained properly - can also tell when the explantion is BS which is all I have recived so far. This forum has many knowledgable people and you have provided good answers in the past. Thanks in advance Ed
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Dakota Jim Russell
You're doing great
I think you have most of it down. While on shore line, I like to keep my switch to both as it provides some drain on both - as I run the refrigerator all the time. At anchor, I like to start on starter battery, just to give it a work out. Whatever. But after the engine is started, I will switch to both as both will then change in contrast to shore power. If the house battery is really down, I would switch to it and charge it. Also, I always sail with only the house battery on, leaving the starter just for that. The older switches might give the alternator fits, but the new switches are okay switching between one, two,and both. But there is a no-no and that is switching to off while you are running the engine. As I recall it fries the diode in your alternator . . . (perhaps someone can correct me on this).
I think you have most of it down. While on shore line, I like to keep my switch to both as it provides some drain on both - as I run the refrigerator all the time. At anchor, I like to start on starter battery, just to give it a work out. Whatever. But after the engine is started, I will switch to both as both will then change in contrast to shore power. If the house battery is really down, I would switch to it and charge it. Also, I always sail with only the house battery on, leaving the starter just for that. The older switches might give the alternator fits, but the new switches are okay switching between one, two,and both. But there is a no-no and that is switching to off while you are running the engine. As I recall it fries the diode in your alternator . . . (perhaps someone can correct me on this).
They can be switched.
Ed: There are battery switches (and other devices) that can be switched while the engine is running. They have a "field disconnect" (or failsafe diode) built in. Other than that your assumptions seem to be correct. There are also devices to seperate your batteries (battery isolator). If you check in the marine cataloges they can help you understand some of the options.
Ed: There are battery switches (and other devices) that can be switched while the engine is running. They have a "field disconnect" (or failsafe diode) built in. Other than that your assumptions seem to be correct. There are also devices to seperate your batteries (battery isolator). If you check in the marine cataloges they can help you understand some of the options.
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Dan
Battery charging
You have it pretty well figured out. The reason the switch needs to be on to charge each battery (house, start, or both) is because the alternator charge wire (usually same wire as starter) is hooked to the switch common. The shore power charger is hooked either directly to the batteries, or in most newer Hunters to the #1 or #2 switch side of the battery switch. Therefore it will charge batteries even when the switch is off. The advice you have received so far is right on. Unless you are concerned about remembering to switch the battery switch to both after starting, and back to the house bank when you turn the engine off, no modifications to the system are necessary. If you want to make sure that charging off the alternator always gets to any battery that needs it (regardless of switch position) you can think about a combiner or isolator system as Steve has suggested. Our Hunter 290 is wired like you have described yours. Our 356 has been modified with two house banks, starter bank, combiner, high amp alternator with multistage regulator, etc. So, if you want to go a little nuts, there are things you can mess with. Dan Jonas (S/V Feije II)
You have it pretty well figured out. The reason the switch needs to be on to charge each battery (house, start, or both) is because the alternator charge wire (usually same wire as starter) is hooked to the switch common. The shore power charger is hooked either directly to the batteries, or in most newer Hunters to the #1 or #2 switch side of the battery switch. Therefore it will charge batteries even when the switch is off. The advice you have received so far is right on. Unless you are concerned about remembering to switch the battery switch to both after starting, and back to the house bank when you turn the engine off, no modifications to the system are necessary. If you want to make sure that charging off the alternator always gets to any battery that needs it (regardless of switch position) you can think about a combiner or isolator system as Steve has suggested. Our Hunter 290 is wired like you have described yours. Our 356 has been modified with two house banks, starter bank, combiner, high amp alternator with multistage regulator, etc. So, if you want to go a little nuts, there are things you can mess with. Dan Jonas (S/V Feije II)
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Steve
Agree with one slight exception...
It sounds like everyone has provided all the answers you asked for, but I did notice one small exception. I believe the switches are a "make-before-break", which allows switching from 1-both-2 without diconnecting the field from the batteries. Just don't go through OFF from 1 getting to 2. Steve
It sounds like everyone has provided all the answers you asked for, but I did notice one small exception. I believe the switches are a "make-before-break", which allows switching from 1-both-2 without diconnecting the field from the batteries. Just don't go through OFF from 1 getting to 2. Steve
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Paul Akers
Checking "Make-Before-Break"
You can check your battery switch for "Make-before-break" simply by switching from 1 to 2 to Both while the engine is NOT running. Turn on a light and rotate the switch. If the light flicks OFF between settings, you have an old "Break-before-Make" switch. Get rid of it and replace it with a new switch. Also, I installed a battery isolator. This prevents a higher bank from draining into a weaker bank when set to BOTH. So after starting from your starting battery, switch to BOTH and both banks will charge independently from one another. The isolator is smart enough not to overcharge the higher bank.
You can check your battery switch for "Make-before-break" simply by switching from 1 to 2 to Both while the engine is NOT running. Turn on a light and rotate the switch. If the light flicks OFF between settings, you have an old "Break-before-Make" switch. Get rid of it and replace it with a new switch. Also, I installed a battery isolator. This prevents a higher bank from draining into a weaker bank when set to BOTH. So after starting from your starting battery, switch to BOTH and both banks will charge independently from one another. The isolator is smart enough not to overcharge the higher bank.
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Ed
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