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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance > Electrical Systems
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  #1  
Old 11-20-2012
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Battery monitor pays off!

Recently I installed a simple battery monitor (gives voltage on both batteries, has an alarm if battery voltage goes too high or low and shows actual charge rate and discharge load). Some say it isn't really a battery monitor, as it doesn't project usage and battery state. However, It reads Volts so it's more than a Ammeter, and reads Amps, so it's more than a Voltmeter. It monitors my batteries...so, I call it a simple Battery Monitor!
Anyway, I thought about installing it for years. Ironically, within weeks, it detected a problem that would have not been obvious otherwise, and probably saved a battery. The story evolved in another thread that isn't specifically about battery monitors Switching batteries to start the motor., so I thought I would mention it here, in case someone else is procrastinating about installing one (as I did!). I found the symptoms interesting and thought others might as well. Anyone else have a story of a monitor paying off, or a horror story where it would have avoided some grief?

Here is a summary from the other thread:
One of my batteries was showing a voltage in the low 12's and had always read around 13.3.
While sailing:
1.The battery monitor's alarm (over/under acceptable voltage) started sounding when I keyed the mic on the VHF radio. It would stay on until I turned the monitor off.
2. I had the boat's FM radio tuned to a talk show. The alarm would sound, ONLY when someone was speaking on the show. So, if someone on the radio said "What time did he leave?", the alarm (which usually is a continuous high pitched Beep) would sound; Beep Beep Bip Bip Beep, in cadence with the words being spoken.
When I started investigating, I found a major crack in the battery's positive terminal cable clamp (on the battery that had been showing low voltage in the OP). Fixed it, and Presto! - The battery is showing voltage in the 13's and all the other symptoms are gone!
Found out (in the other thread) that the load from broadcasting on the VHF and on the FM speakers was causing the voltage to drop on the battery (which was already low) and causing the the alarm.

Last edited by L124C; 11-20-2012 at 11:40 PM.
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Old 12-10-2012
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Re: Battery monitor pays off!

That was very interesting. I have seen a similar problem before in a backup battery system with a low voltage alarm. I once worked on a fire alarm system that only gave a battery system failure alarm when the fire alarm was sounding. Similar problem only with a bad connection to the ground terminal of the battery.
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Old 12-10-2012
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Re: Battery monitor pays off!

Most folks find that once they add a battery monitor, unless they keep their boats plugged in all the time, they are chronically undercharging their batteries. A solar panel is a very good idea.
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