T&T: Battery Monitor

[John Wix]

I installed a Xantrex Battery Monitor as part of a significant upgrade to 
the electrical system on my Monk 36.  With this simple device, I now know 
the exact load created by every current-sucking DC device on the boat.  No 
more guessing!  But, there is much more value to be had.

While on a recent three-week cruise, I noticed that the house batteries 
weren't being fully charged (another battery monitor use) even at the end of 
8-hour cruising days.  The house batteries are four golf carts (450 AH 
total) and the alternator is 110 amps.  Typically, I would be trying to 
restore 125 to 175 amp hours.  While under way one day, I happened to glance 
at the battery monitor and notice that it was displaying net negative amps 
at the house batteries.  Before I had a chance to sort through the various 
possibilities of the cause, the net amps switched to + 54.  This positive 
and negative cycle repeated all day with the net effect being positive about 
50% of the time.  If I had high enough DC load, it was theoretically 
possible to end the day worse off than I started!!

I decided to see what the regulator had to say about what it saw was going 
on.  The regulator is a Balmar ARS-5.  It has an LED display that includes 
the temperature being reported by the battery temperature sensor.  It showed 
60 degrees C (about 140 degrees F if my math is right).  Another battery 
temperature sensor attached to the inverter/charger showed 40 degrees C - a 
huge difference.  Using a simple thermometer, I verified that the 
inverter/charger was correct.  So, the regulator was doing what it should do 
in the presence of high battery temperature.  But the temperature being 
reported was waaaay wrong on the high side.  The bad temperature sensor has 
been replaced (under warranty) and all is well.

Installing the battery monitor was fairly straight forward.  However, the 
monitor shunt must have the ONLY connection to the negative side of the 
battery bank being monitored.  I highly recommend this device (or one 
similar).  It removes a lot of guesswork.

John Wix
Monk 36
"Safe Return"
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/