Both Batteries Drain Even When Only Bank Is Selected - SailNet Community
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post #1 of 22 Old 09-29-2009 Thread Starter
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Both Batteries Drain Even When Only Bank Is Selected

Hi All,

I have recently purchased a 1982 Pearson 37. I have spent the last month discovering the things that let's just say the previous owner failed to mention and the surveyor failed to find. It's a great boat, but in need of some love, cash and a lot of elbow grease. I have three batteries that I know are not properly wired. One deep cycle type 24 paralleled with a wet 4d for my #1 and a single type 24 deep cycle for my # 2. I think they are all of different ages and plan on scrapping them before next season. I have a "new" 85a alternator with internal regulator.

My problem is that with the selector switch off all three batteries will hold a
decent charge for several weeks. With only #1 or #2 battery on overnight with just a very small hotel load, both #1 and #2 are dead by morning.

I have checked draw on the main distribution panel and after thinking I had an aha moment found the vhf wired to the hot bus.This accounted for the draw when the panel was 1st energized.

The only thing common besides the switch is the alternator.

Any thoughts?

Thanks,

pkilty
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post #2 of 22 Old 09-30-2009
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Something is definitely wired wrong. Trace the wiring from batteries to main switch - I assume it's 1-2-both-off type. Find out if any wires go anywhere besides the switch and where they go. Make sure the main switch is wired properly. The hot from bank 1 should go to #1 position, hot from bank 2 should go to #2 position and common (output) should go to your distribution panel and the engine starter. Somehow I think your battery banks are common to each other regardless of the switch position and there is a draw on them with the switch on #1 or #2. I guess you should get in there with a multimeter and with the switch on 1 or 2 see which items are getting voltage. That's my best guess right now. Good luck and let us know what happens.
Brian
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Write it down and make a map. If you cant actually see and feel the wire the whole long way it is no guarantee it goes where you think. Label the wires as you figure out what goes to what. You also may have a bad battery that drains the system. I would take them all out to a battery store and have them charger and tested. Also batteries should be the same type and size and age as different types (gel and wet) charge at different rates.

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post #4 of 22 Old 09-30-2009
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Do you have a multimeter? If so, perhaps your alternator is either wired incorrectly or broken. Can you disconnect the cables from the alternator and measure resistance (simple "infinite" or "full'" continuity is enough)?


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Quote:
Originally Posted by pkilty View Post
Hi All,

....

The only thing common besides the switch is the alternator.

Any thoughts?

Thanks,

pkilty
There you have it! If the alternator is indeed "common" to both banks, then they are effectively paralleled, unless there is a battery isolator installed.

Bill
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post #6 of 22 Old 09-30-2009
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yes, but that doesn't explain the dead batteries with only a small load overnight. There has to be another issue.
Brian
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post #7 of 22 Old 09-30-2009
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Here I assumed that your alternator had 2 outputs and that an internal diode might have been broken. With a multimeter, measure the voltage across the + and - poles of one battery after the switch has been set to "off" for a while. With all devices switched off and breakers off, switch "on" and see if the voltage changes - even a small short dip will tell you that you've got a consumer switched on or have a current drain in your power lines. Short of an ammeter you'll have to start disconnecting devices one by one to find your problem source.


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post #8 of 22 Old 09-30-2009
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I think you need to use a load test device on the batteries to see if they are actually good or not. If not, trouble shooting is going to be difficult.
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post #9 of 22 Old 09-30-2009
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Quote:
Originally Posted by SteveInMD View Post
I think you need to use a load test device on the batteries to see if they are actually good or not. If not, trouble shooting is going to be difficult.

I second this option. First thing to find out is the condition of the batteries.

Some bad cells can cause all kinds of odd behavior. They seem to hold a charge unders some conditions then loose the charge way too fast.

First rule of troubleshooting. Don't go first to the exotic problems, rule out the mundane first.

I have taken my batteries to the nearest NAPPA store and let them charge and load test them.
They can tell you their exact condition.

Last edited by davidpm; 09-30-2009 at 03:29 PM.
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post #10 of 22 Old 09-30-2009
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I thinking the batteries also.

It seems like with three batteries you should be able to pull 10 amps all night and not kill the batteries and it should be easy to find a load that big.

Rick
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