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Old 10-13-2015, 07:10 PM   #1
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Pesky Electrical Leakage

Hello all. I have 25' Formula BR (in addition to my 50' Seahorse Marine Diesel Duck sedan). The Formula has a standard A,B, Both and Off battery switch. When the switch is on Off position, after a week or two B battery, gets drawn down until it cannot start the engine or power any of the accessories. If the switch is left in the Both position it drains down both batteries. I have determined, using a clamp on meter and other means, that even though the switch is in the Off position, battery B still shows a small (about 2 Milli-amps) of draw even with all the circuit breakers shut off. This does not happen with the switch in the A position i.e battery A shows no current draw with all circuit breakers off.
I am mystified about what could be drawing this load. My only thought is that the bilge pump is directly wired to battery B and there is some sort of short in that circuit. Where could the current be going (the boat is out of the water)? There is little bit of water in the bilge. I replaced battery B a few months ago but it also got drawn down after two weeks.
Very irritating and puzzling. Any thoughts? and what more can I do try and find the cause of this? The bilge pump is under the engine and not easily accessible.

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Old 10-13-2015, 10:14 PM   #2
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How is the engine alternator output wired to charge the batteries? The voltage regulator in the alternator draws a small amount of current in single wire alternators.


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Old 10-14-2015, 12:33 AM   #3
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Modern electronics do not always turn off completely. If you have several pieces of equipment like that they can add up. Do not just assume because you pushed the off button that the piece of equipment is truly dead. If all you have to do is push that on/off button then some circuitrly is often still alive to read the button toggle.

ACRs, a help in charging batteries draw a small current so they can determine when to disconnect those batteries. Is it setup, for dropin and dropout voltages if adjustable and actually operating correctly.

Alternator diodes can short. One diode can drain a battery. Likely would draw more than just a few milliamps but still worth checking.

If there is only 2 mA then i wouldn't think that is going to cause your problem.

I would suggest stop depending upon a clamp on ampmeter. Unless you have one that will Accurately measure down to the milliamp level that they cannot be depended upon to measure less than 1 A.

Use a DMM with a 10A current measuring capacity and disconnect the batteries running the connection through the meter. That meter should be able to show much less than 1A reliably, even down to the few milliamp level. See what it reads. If you have more than just a few milliamps then start disconnecting equipment again, pulling fuses, turning C.B. off , even to disconnecting wires.

An isolation procedure should help by disconnecting groups of equipment by disconnecting feeders and figuring out which group is a problem. Then further narrow it down.

If you truly have a leak then it may take a concerted effort.

As for the B.P., if the wiring is in bilge water and the wiring is questionable then it can be amazing where current can find a way back to neg. You do not need access to the pump itself to test the wiring and pump for a leak. Use that DMM. Disconnect the fuse/c.b.

If no joy then do not discount that the battery itself may be at fault. But check all else first
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Old 10-14-2015, 06:44 AM   #4
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Put a piece of cardboard in the bilge and see if it has been wet when you get back.

A Hydrometer will test for a dead cell (which will run down a battery bank). But since you just replaced the battery, it is less likely. There are infant mortality batteries occasionally so new does not always mean good.

A simple draw test is to loosen one battery connector and see if it sparks when you close the gap between the post and the clamp. I wouldn't recommend this on a system with delicate electronics though.

I suspect you might have a slow leak and your bilge pump is powering up often enough to hide the leak and the dead battery bank is a symptom, not a cause.

If you can't easily see down under the engine, use a laptop and a cheap endoscope to stick a camera where you can't see / feel as a remote set of eyes. most are water rated so it won't get hurt if you submerge it.

I would run my hands under and around all the raw water lines and where they connect to the engine and heat exchanger plus the shaft log. You might have a slow drip under the engine and not know it.

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Old 10-14-2015, 07:08 AM   #5
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Agree that 2 milliamps is not the cause of the B battery going dead. Remove it, charge it fully, test with hydrometer, and have it load tested.
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Old 10-14-2015, 07:42 AM   #6
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The more electric toys , the more stuff that leaks electric .

The method we used for our 2 battery setup is simple and easy to understand .

The starter is connected with the usual rotary switch 1-both 2 to the batts.

A second 1 both 2 rotary switch selects the house loads.

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Old 10-14-2015, 06:42 PM   #7
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Agree with the suggestions so far and want to add some more. a CO detector that is sometimes hard wired can draw 40-60 ma. ACRs draw 10ma or so. A stereo typically has an "always on" wire to maintain programmed channels. Like has been said - it can add up.

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Old 10-16-2015, 01:33 PM   #8
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C Electric: I did exactly as you suggest about using a DMM rather than rely on the clamp on meter. I used alligator clips and put my DMM in line with the positive terminal of the battery. This is how i was able to determine the small (2MA) draw with every thing turned off.
The first thing I will do is to completely dry out my bilge and then snip the connection to the BP and see if that is the culprit.
If that does not do it, then on to the other suggestions posted here.
Thanks for all the suggestions. I will try them all and report back the findings.
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Old 10-16-2015, 08:58 PM   #9
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Sounds like a possible bad cell in the B battery. I've got a cell going south in my start battery.

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