T&T: Battery temperature sensor concern

[Chester Brummett]

Recent thread on battery temperature during charging relates to a problem that
I am experiencing.



Problem relates to charging from generator (or shore power).  Alternators when
running the engines use Balmar 612 regulators with attached battery and
alternator temperature sensors, and that system works good.



For generator or shore recharging, I have a Xantrex Prosine 3.0 and two each
40 amp TrueCharge chargers in parallel.  With full output, gives approx 200
amps charging.  I do see good load sharing with all three chargers on line.
Apparently the charge algorithm on all of these chargers is the same.



I don't want to get into another discussion on the "goodness" of the Xantrex
product line. If I was starting over, I would probably not use Xantrex, but it
is what I have, and I suspect that many list members also use Xantrex
products.



The chargers were installed with 3 separate temperature sensors on the battery
bank. The Prosine and TrueCharge threshold voltages with the temperature
sensors connected ("automatic mode") charges to 13.8 volts, and floats at 13.2
volts.  This 13.8 volt charge voltage does not adequately charge the
batteries, and results in an imbalance in measured specific gravity.  Any
attempt to equalize (overcharge) shuts down, voltage will not go over 13.8
volts.



Note same result with Prosine 3.0 only; the added parallel chargers do not
change the threshold.



Discussion with another boater, part time marine mechanic, who has installed a
number of Prosine 3.0.  His answer:  he has never been able to get the Prosine
to work properly with the battery temperature sensor attached.  His
recommendation:  unplug the sensor and "manually" set the temperature.  The
Prosine and TrueCharge have manual settings:  hot, warm, and cold for the
batteries.



When manually set to "warm" the chargers will charge to 14.2 - 14.3 volt
threshold, which I think is closer to desired.  After charging to this
threshold, the specific gravity does measure the same on all cells.



But, I am concerned about leaving the chargers without the battery temperature
sensors attached.  One possible partial solution:  a timer that starts each
time AC is applied to the chargers, and after two hours, trigger a relay to
"reconnect" the temperature sensor.  But this solution would still loose the
"protection" that the temperature sensor provides during high current charge,
when it is really needed.



Other information:  battery bank is 10 each Trojan T-145 batteries in
series-parallel, 1300 AH rated capacity.   I have not recorded engine room
temperature when the generator is running, I estimate 90 - 95 degrees.



Have others experienced similar issues when charging from the Prosine 3.0
and-or the TrueCharge 40?



Any advice on this concern will be appreciated.



Chet

Defever 44+5, Cygnet

Daytona Beach, FL