I have a 08 - 40, I have found that the alarm is caused by voltage drop, not low batteries. The cable that runs from the battery switch to the electric panel at the chart table was 6 gauge. The run of that cable is close to 40 feet, the wire isn't large enough to carry volts to the panel. By the length it should be double zero, however that doesn't fit the connector in the panel. I shorten the run going under the engine to the another side up to the panel and used zero gauge wire fixing the alarms. I don't believe the batteries are the problem, its voltage drop because the wire is too small for the length of the run.
I noticed the same thing - wire gauge too small. I ended up doing two things:
1) Switch to LED lights. That reduced the current draw nicely.
2) When I installed a NMEA2000 battery monitor, I installed the sensors at the battery end. The new monitor properly monitors the battery voltage, not the voltage at the end of the line.
I would like to "double up" the wires to the panel, but that project will have to wait.
My dealer changed the 6 out for a 2 on our 2008 43. I still see about a 3% voltage drop which is pretty much acceptable. It had been closer to 7+V. At this point everything runs fine. BTW I turned off the alarm a long time ago and have no plans to turn it back on. I have a Victron BMV600 and use it to monitor the house bank so the VDO panel is for comparison only.
Mike
Going on our summer trip and living on the hook for a while.
At what voltage level indicated by the VDO for my 3 house batteries do I start the engine to recharge?
Chris
B40#197
Based on what I see on our 43 I would recharge when you get down to 12.1 to 12.3 on the VDO. This is based on lead acid batteries, Trojan T105s and total 450 amps. It will vary based on batter type (Wet Cell, AGMs, Gel) and total amps in the house bank.
Mike
Simply put, you cannot rely on the VDO to tell you the state of the batteries! Try this: Turn on lights, refrigerator, navigation, and everything else on the DC panel, and then check the voltage at the VDO. Now turn off everything and check again. The battery is at the same state of charge as before, and yet the voltage is different - in fact it went *way* up.
About the only time the voltage reading is accurate is when there is no load on the battery - and there hasn't been for at least an hour. At that point, you are reading something close to the actual "open circuit" voltage of the battery. If it's a flooded battery and it reads 12.2 volts, then you are at half charge. See: http://batteryuniversity.com/learn/article/how_to_measure_state_of_...
Of course in our boats it is never really possible to have zero load on the battery for several hours, and that's why everyone just installs a good battery monitor.
Have you had the cable replaced from the batteries to the panel? If so you should have near zero voltage drop. This chart is a good rule of thumb: state of charge 100% = 12.7 volts
90%=12.5
80%=12.4
70%=12.3
60%=12.2
50%=12.0
40%=11.9
30%=11.8
20%=11.6
trouble below that... If the cable has not been replaced yet, your VDO will read volts up to 30% less than the voltages shown on the chart. Charge at 12 to 12.2% Hope this help and enjoy your trip.....
I have a battery monitor but if I didn't have a battery monitor and I was on the hook for a weekend I would check the house bank each morning with a digital voltage meter to determine actual battery voltage and not allow that voltage to drop below 12.2 volts ( to extend battery life). Would not charge them up to 100% on hook cause it takes too long too"fill em up" (agm's) with the stock alternator ,. Batteries can take a lot of voltage (14.1 or more) below 80-85% but once they reach this percentage the voltage input should be more gradual. Other problem is the stock alternators are not going to generate 14.3 volts output on the hook with no load and low rpm's. This is why I use the Honda generator to run the battery charger to charge up our batteries on the hook. The battery charger increases voltage up to 14.3 volts immediately, chargers them up quickly to 85% (12.5 volts) then we shut down the Honda and enjoy the remainder of the weekend. Mike has a super duper alternator than can put out a bunch of amps quickly into the battery at low rpms, this is another great alternative though it does require running the engine to charge up batteries. Either way I would think you want to get those batteries back up to 80-85% quickly!
The VDO panel is basically worthless for considering up to the moment battery status at anchor! The battery alarms are a pain but I don't turn the alarm off since the water and fuel alarms are also on that circuit and I find them useful.
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