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post #1 of 16 Old 07-25-2012 Thread Starter
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Battery alarm while moored.

2008 Beneteau 37'
Two batteries - Cranking and deep cycle
Battery age - <1 year

While on a ball recently our low voltage alarm went off in the middle of the night at 10.8V

All systems were off - main breaker was off - fridge was off - nothing was on. Started engine to charge for 30 minutes - All good

Three hours later.....same thing.

Ground problem ?
Suggestions on a troubleshooting starting point ?

Last edited by jklingenstein; 07-25-2012 at 08:57 AM.
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post #2 of 16 Old 07-25-2012
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Battery alarm while moored.

Time to pull out the multimeter and check it. First, the obvious, what's the actual voltage of the batteries. Then measure the voltage at the meter and see what it's seeing. There are only a few possibilities, either the voltage was actually low, the wiring is flaky, the meter is on a point where there is a voltage drop (inadequate wiring/large load), or the meter is bad or programmed wrong. Another thought is electrical noise, are your sense leads too long and going past something "noisy" the fridge motor, a transmitter etc?

Ground is one of two wires, it's no more likely to be the black/yellow one than the red one..
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Re: Battery alarm while moored.

We've never had this occur in the last three years.

Wouldn't there need to be a voltage drain somewhere for the battery to discharge without anything drawing current?
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post #4 of 16 Old 07-25-2012
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Re: Battery alarm while moored.

How easy did the motor start at 10.8 volts? Perhaps your meter and or the sensor has a short/resistence etc?


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Re: Battery alarm while moored.

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Originally Posted by aeventyr60 View Post
How easy did the motor start at 10.8 volts? Perhaps your meter and or the sensor has a short/resistence etc?
I believe the alarm monitors the house battery (deep cycle)

The motor started without a problem (cranking battery)
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Quote:
Originally Posted by jklingenstein View Post
We've never had this occur in the last three years.

Wouldn't there need to be a voltage drain somewhere for the battery to discharge without anything drawing current?
I took from your first post that you thought it was an issue with the meter (perhaps incorrectly). If your batteries are actually discharged then you either have a dying house bank, or yes, you have a load on your batteries that your not accounting for. I'd guess you have a bad bank, or you're just not accounting for something that's on (fridge door open?). It would be very unusual to find a device malfunction or wiring issue that didn't just result in a short and blow a fuse.

Last edited by asdf38; 07-25-2012 at 02:22 PM.
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Re: Battery alarm while moored.

All panel breakers were OFF.... including the fridge breaker.

Nothing on the boat had electricity yet the battery voltage dropped enough to cause the voltage alarm to sound.
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Sounds like your house battery has expired. Drag it out and give it a good charge than stop by autozone and have it tested
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Re: Battery alarm while moored.

Quote:
Originally Posted by jklingenstein View Post
All panel breakers were OFF.... including the fridge breaker.

Nothing on the boat had electricity yet the battery voltage dropped enough to cause the voltage alarm to sound.
Often essential equipment, like bilge pumps, will be wired directly to the house battery bank - not via the breaker panel.

It could be that the house battery is on it's last legs and the bilge pump is telling you.

Like others have already suggested, you'll need to get out a multimeter and find out. Good luck!

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Re: Battery alarm while moored.

Quote:
Originally Posted by jklingenstein View Post
We've never had this occur in the last three years.

Wouldn't there need to be a voltage drain somewhere for the battery to discharge without anything drawing current?
No, not a voltage drain, a current drain. Current is flowing charge, so it means the current drain is discharging the battery. This old EE says the following:

1) I agree with the others - you need to dig out your VOM, set it to measure voltage, and see what (a) the voltage is at your battery when the alarm goes off, and (b) what the voltage is at alarm when it goes off. There are a number of likely possibilities (and a grunch of less likely possibilities). I'll talk about how to find the likely ones. You are likely to find one of these possibilities:

a. Your battery is actually well charged, voltage at the battery is OK, and you get the same voltage at your alarm. The alarm is not going off a the right voltage -- adjust or replace the alarm.

b. Voltage at the battery is OK but voltage at the alarm is different and lower. Look for poor connections from the battery to the alarm, or bad or inadequate wiring.

c. Voltage at the battery is actually low, and you read the same voltage at your alarm. It could be bad wiring, or it could be a bad battery. You need to perform one more test to tell which it is. So ...

Set your VOM to measure current instead of voltage, range up to 5 amps. Turn everything off as you had it before when the alarm went off. Remove the hot lead (+) from the battery and connect it to the black lead of your VOM. Attach the red lead of your VOM to the hot lead of your battery. Read the current flow. If it reads zero, keep switching the range down until you read microamps (which probably isn't accurate, so if it is zero or a few microamps, consider it to be zero).

c.1 -- if the current reads zero or nearly so, then you have a bad battery. Replace it. Have a battery place test it first, if you like.

c.2 -- if you read non zero current, then you have a high resistance ground. That could be a bad semiconductor in some electronic gear, it could be a corroded wire where the insulation has also failed and it touches a ground. It could be a poor connection to something, It could be a bad circuit breaker or switch, It could be anything wired directly to the battery, such as your bilge pump. It could be something you left on or plugged in inadvertently.

If c.2 is your answer, you will have to do some fault isolation. Start unplugging stuff one thing at a time until the current drops to zero or nearly so. If that doesn't work for you, start disconnecting circuits one at a time from your battery or the power distribution panel until the current drops.

Personally, I'd start with the bilge pump, especially if it has an electronic water level sensor. Both the pump and the wiring sit in grungy water, an environment that is fairly hostile to electronics.

Regards,

Tom

T. P. Donnelly
S/V Tranquility Base
1984 Islander 30 Bahama
Pasadena, MD

Last edited by dacap06; 07-28-2012 at 12:54 PM.
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