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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 08-16-2006
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Tracking down shorts

Question regarding tracking down a short or current leak (DC):

How long should you wait after turning off charging sources and all sources of current drain before you try to measure stray currents/shorts? It's like the question of how long to wait to measure open circuit battery voltage at rest I suppose...

When I turn everything off, I still have a 0.2 amp DC current flow according to my Link 2000. I've checked everything I can think of and actually can't measure current loss away from the battery bank. Could this simply be flow between batteries (4 4D + starter that's isolated) and that eventually dies down or internal current flow i.e. self-discharge on a 900 ah bank. This seems a little high for self-discharge as 0.2amp x 24hrs = 12ah/day which means 50% discharge in 33 days...not likely. I'm sure I've got a current leak somewhere probably to my wife's 12volt hair dryer .
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Old 08-16-2006
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Start disconnecting thing until the problem goes away. Trouble shooting is all about isolating the problem.
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Old 08-17-2006
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200mA could be current through dirt and salts built up between an area where the positive and negative terminals are close. If you have both polarities on a single terminal block make sure its clean. (Windex does a good job) They don't have to be on the same block, just in close proximity with wet/dirty material between them.

GeneT is correct, isolate each branch until the current goes to zero. Most multimeters (voltmeters) will also read amps and are more accurate then your Link. Disconnect the batteries and run the voltage feed from the batteries through the meter to check and see if the Link is accurate and to be better enable you to identify the leakage when you disconnect it from the feed.
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Old 08-18-2006
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Thanks for the info. Already cleaned all the terminals and spaces between posts--that was my first thought. As far as tracking/isolating, even after removing everything outside connection from the bank but leaving the bank connected in parallel, I still see the 200ma current. And yes, my Radio Shack digital multimeter IS more accurate than the Link.

So, clean batteries, persistent small current flow--does this sound like a bad battery with an internal short? Haven't yet checked current flow with individual batteries but that's next
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Old 08-18-2006
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Sounds like the current flow is between the different batteries. I am assuming you have disconnected the batteries from everything else.

Next step is to disconnect the batteries, one at a time, from each other. FIRST REMOVE ALL JEWERLRY, EVEN THE WEDDING BAND. Measure your current draw while you disconnect them. You will find the problem child. It’s probably not a short, just a cell that’s weak or sulfated. Are your batteries wet or sealed? If wet, try and equalize them. If sealed, follow the batteries manufactures instructions.

Also if wet, you can measure the specific gravity of each cell. They should all be very close. You will probably find one that is low, that’s the problem one.

If they are sealed, you could also disconnect all from each other and measure the voltage of each battery after they have sat for 30 to 60 minutes. You will be measuring the open cell voltage. They should be reading all the same. The one that’s lower is the one with the bad cell. Hopefully you have a 4 Ĺ digit digital voltmeter (displays four digits) rather then an analog one. If not, see if you can borrow one. You will need that degree of accuracy.

Have patience and you will find the one that’s bad.
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