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ContinuousWave: Small Boat Electrical
Batteries Discharge With Switch in OFF
|Author||Topic: Batteries Discharge With Switch in OFF|
posted 09-25-2010 09:42 PM ET (US)
I have two marine batteries on my Montauk 17 and a battery switch where I can select OFF-1-ALL-2. When I turn [the battery switch to] OFF and store [the boat] for a few weeks, both batteries drain quite to the point where I can't start the motor. The batteries are almost brand new. I have had this problem with three sets of batteries. I have just learned to live with this over the years. Now honestly I am just tired of it. Give me some advice.
posted 09-25-2010 10:06 PM ET (US)
You need to check other current paths which may not be controlled by the battery switch. Often times this could be the bilge pump circuit which is protected by a circuit breaker. Ideally each battery would have just one heavy gauge wire connected from the + terminal to the On/Off switch and the other connected to a common bus.
If there is more than one wire coming from the positive terminal then determine what the extra wire is powering as this may be the source of your current drain. Next look at the battery switch. It is likely that the bilge pump circuit breaker is connected to the same terminal as the wire from the battery. Anything connected in this manner will bypass the switch. You may have a charger connected to your batteries which has a defective diode. The switch itself could be defective, that is unlikely and easily checked with a volt meter
Just some thoughts.
posted 09-25-2010 11:18 PM ET (US)
Check the wiring of the battery switch, the two batteries, and other loads in the boat. Check for a parasitic current drain when the battery switch is in the OFF position. Check for corrosion in the positive distribution of the battery that may be leaking current to the negative terminal.
Measure the battery terminal voltage with a digital voltmeter with readout of 0.001-volt and accuracy of 5-percent or better. Note the voltage after one hour of non-charging of the battery, then measure again in a few days. There should be very little change in the terminal voltage. If the terminal voltage is going down so fast you can measure a change in a matter of a day or two, there is something draining the battery.
With the battery switch in the OFF position, insert a digital multimeter configured as a milliammeter, and measure any current drain. There should be none.
posted 09-26-2010 05:16 PM ET (US)
Another test to perform is for voltage leaking through the water, saltwater, acid or other deposits on top of the battery case.
Use a digital voltmeter an put the red lead on the + terminal of the battery and touch the negative lead to various areas of the battery, especially near the - terminal. Do the same with the black lead on the - terminal. Watch for any voltage readings which show that the battery can self discharge without being hooked up to anything.
posted 09-26-2010 07:04 PM ET (US)
You have a short somewhere in your electrical system. As Jim mentioned - use a digital multimeter to find your problem. Use a self ranging meter as your current draw may be more than just a few milliamps - which could then blow a fuse in the meter.
Insert the multimeter in the circuit(s) - as, for example, removing a battery cable from the battery and putting one lead of the multimeter on the battery post and the other lead on the removed battery cable. With everything off, you should see no current flow. If there is current flow, remove, one at time, each component until the current flow is zero. That component (switch, cable, electrical component, et al.) is the culprit.
I suspect the problem might be the switch - as in the off position, both batteries are drained, yet are supposed to be isolated by the switch - and the short drains both batteries.
In the meantime - disconnect one terminal from each battery. --- Jerry/Idaho
posted 09-27-2010 02:54 PM ET (US)
The battery switch is certainly one suspect.
If it's not the switch, on many small boats the only circuit that is live with the battery switched off is the bilge pump. If you can find the postive end of the pump circuit (could be directly connected to one of the battery positives, or inside the switch, to one of the two battery input terminals), disconnect it and measure resistance between that and battery negative. It should be zero. If not, suspect the bilge pump switch or wiring to/from.
posted 09-27-2010 04:29 PM ET (US)
Swist makes a very valid point.
I, like the owner before me, had a constant problem of the #2 battery running down for no apparent reason.
I checked for a parasitic drain, loose connections, proper bilge pump operation, and anything else I could test for.
Turns out that the bilge pump would start with high water but would not shut off for extended periods of time due to the placement of the bilge pump float switch located at the lowest point of the bilge and the pump's inability to pump the water low enough to satisfy the float switch.
The cure was to elevate the float switch about 1" off the inner hull floor with some whalerboard.
posted 09-27-2010 10:05 PM ET (US)
Joe--You bring up a very good point. In an automatic system, the control mechanism must be able to shut itself off. I mentioned this specifically in my article about installation of bilge pumps.
It would not surprise me much at all that you might find a float switch that was not in a proper position to reliably shut off the pump it controls. A list on the boat could also affect how the float switch works, too.
posted 09-28-2010 12:10 AM ET (US)
An automatic bilge pump is certainly a load that would discharge a battery. But, I would suspect (as I don't use one) that it is normally hooked to one battery. What is common to both batteries - as both batteries are discharged? ---- Jerry/Idaho
posted 09-28-2010 07:11 AM ET (US)
A two bank mounted charger? I've had problems with one of them as well.
posted 09-28-2010 01:53 PM ET (US)
Thanks for all of the advice. I will say this and again I appreciate all of the feedback;
1) I removed the automatic bilge pump some time ago as I could not leave my batteries on while away so unless the leak can occur with the bilge not connected with just the wiring - then I can't imagine it is that.
2) I also removed the trolling motor completely off the boat as i never use it. However, the wiring is still in tact and capped off. So again I can't imagine it is that.
3) i don't have a radio but do have a gps that is only connected when I used the boat. I would imagine again that the wiring without the actual unit would draw from the batteries?
I am going to buy a new switch and see if that does the trick.
Otherwise, again I am not electrical guru, but I plan on disconnecting the batteries everytime I leave. Now if these batteries discharge without even being connected... then that is the sign that my boat is possessed.
Thanks all. Greg
posted 09-29-2010 10:07 AM ET (US)
Before you purchase a new switch, are there any other wires attached to your battery + terminals other than the one going to the switch for each battery ? If so, remove them.
Are there any other leads attached to the switch at the battery input terminals ? (There is probably at least the wire for the bilge pump that you left in place) Remove them.
If your batteries still run down when the switch is off then your switch is defective but you still have something else going on downstream of the switch.
You should not leave wires in place that are still powered at the source. Either remove them or disconnect them from the power source. Salt water does conduct current so a possibility is that even without the bilge pump and trolling motor in place the leads could be draining you batteries.
posted 09-29-2010 11:37 AM ET (US)
Thanks for the info. The bilge and trolling wires are not connected directly to the battery terminals but to a strip further downstream. The only connections to the battery terminals are the switch wires - again there are no wires connected to the actual batteries for any of the external devices such as trolling motor, GPS, bilge.
That said, does it still make sense to remove the wires from the bilge and trolling motor even though it is not connected to the battery itself? And does this lead to the fact that the switch has to be the problem.
posted 09-29-2010 04:22 PM ET (US)
Yes, I would still disconnect any unused wires at the power source.
You said earlier that you removed the bilge pump because it was coming on and draining the battery with the switch off. Therefore, there must have been an electrical path from the battery to the bilge pump float switch (or the pump if it has an internal float switch) that bypassed the switch. This is common. Now if there is a busbar that has the bilge pump and other devices attached to it this is uncommon. I would next inspect the switch to make certain it is wired correctly. One wire only to battery 1 in and one wire only to battery 2 in. I will bet that one of the battery input switch terminals has more than one lead attached.
If the wiring looks ok then you should get a volt meter and check the voltage at the common terminal of the switch. In the off position it should be "0".
posted 10-06-2010 01:30 PM ET (US)
I found that the GPS continued to somehow drain my battery even with the unit off. and, if you have a trolling motor with co-pilot and/or autopilot these too will draw current even when off. I put a toggle switch inline and stopped it.
posted 10-06-2010 02:53 PM ET (US)
brainstormer - your finding the problem and fixing it is good - but your problem also suggests that both batteries are connected - as both batteries were being discharged.
Consider reconnecting all loads, except the trolling motor, "downstream" of the master switch- perhaps to a buss bar or terminal strip - to which all "utility" loads are connected. --- Jerry/Idaho
posted 10-06-2010 05:21 PM ET (US)
Hold it! He has a battery switch between the two batteries and any other wires, if the switch is wired correctly and working it should not matter what is going on downstream. Whatever is wrong or not connected, like pumps and GPS are not the problem with draining the batteries. I would disconnect the batteries and check the switch out. There can be debris there causing connection across the open switch or the switch is bad. A ohm meter can be used to also test for leakage across the switch....Jack
posted 10-06-2010 05:25 PM ET (US)
After fixing the switch, then start searching downstream for possible shorts. Montauks have a wiring box for the nav. lights that is in a terrible place for getting wet...Jack
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