Switching battery banks with engine running - Page 2 - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 09-27-2008
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OK..Just in case, from now on I will make sure all is off when switching.

Thank you for the good thread.

Alex
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Old 09-27-2008
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I might agree if I hadn't done it myself over a hundred times. If I had ever once had a problem I would agree with you. The keel could fall off at any moment as well, but I still go sailing. If you want to avoid all possible stay in bed in the morning. As I said before you can avoid the problem by running on all batteries as much as possible, which is better for your batteries anyway, but if you find yourself in the situation where you have to switch while running, I promise, the keel wont fall off.
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OK Steve, I'll let people make their own decision.
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There is absolutely no question that my switch is a make before break....I have tested it and examined it phyisically and it does not have this field protect device....whatever that is. So I'm still back to what harm to the alternator if I all of a sudden connect in a parallel battery?
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There is no question that the switch is a make before break...I have tested it and examined it physically....and there is no field protect device....whatever that is. So what is that would damage an alternator by all of a sudden connecting in a parallel battery?
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There is no harm in connecting in a parallel battery. It's no different than suddenly having a larger battery.

Using a battery switch that has a field disconnect only works if you have an externally regulated alternator, as far as I know.

Battery switches are very simple devices. The chances that it will fail in a way that disables the make-before-break connection and does not completely disable the switch all together is extremely remote. If you worry about this possibility I would say you take much much bigger personal risks setting foot on a boat in the first place than you do putting your alternator at risk by switching batteries while the motor is running.
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Old 09-27-2008
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This directly from Guest:

You must hook up the AFD (alternator field disconnect terminals) to both the alternator and the external regulator for it to operate properly. Since you have an internal regulator, you cannot use the AFD feature and you will harm the alternator by going to or through the Off position of the switch with the engine running.
**********
Note that nothing is said about going through batery1, both, or battery2 with an INTERNALLY regulated alternator.
Perhaps those that have said, they've gone through the off position have the AFD terminals and external regulators?
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I think the best advice is to install a battery combiner and never worry about it again. We've had one since we aquired our boat 9 years ago and it works flawlessly. I feel like it's pretty cheap insurance and assures all battery banks are charged, makes sense too.
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battery combiner

ketch --- i have one also. i installed it for the previous owner a year before i bought the boat from him. a combiner does not have voltage drop like diode isolators which causes the the regulator cut the charging before the batteries are fully charged.
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Quote:
Originally Posted by SteveInMD View Post
I disagree that it's bad practice. I don't think your going to come up with one right answer on this one.
You may disagree, but that doesn't change the fact that if you remove the battery while the alternator is running, the sudden surge can, and quite frequently will, damage or destroy the alternator. This is why they make switches with field disconnect circuits.

Jim
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