T&T: Battery Charging in hot weather

[Jake2124 at aol.com]

Hey, a not new but different topic. We are on our second time doing the  
loop, but this time we are staying on mooring balls when we can instead of  
Marinas to offset some of the extra fuel cost. We just don't like anchoring, so  
please do not go there. We anchor only when we have to.  So, now we are  more 
dependent on our gen set and batteries. We have a house bank of 3 sets of 6  V 
batteries for a total house capacity of about 645 AH. We use the Prosin 2.0  
inverter/charger. The charging capacity is 105 amps. Because it's hot, we use  
about 16 amps, fairly continuously, when the gen set is not running.  
Refrigerator and a fan. I expected to get about 20 hours out of the bank  before it was 
discharged to 12.2 V, or 50%. Yeah, I know we probably do not get  it charged 
100%. And yes, the batteries are fairly new. But, we are only  getting about 8 
hours se before we are down to 12.2 V. So, I checked the SG on  the batteries 
at "full charge" That is, the inverter charger was in "float  mode". I found 
the SG to be only 1.225, indicating about 75% charge. I noticed  that the max 
charging voltage has been about 13.9 V. I actually read the charger  manual, 
and found that there is a temperature compensation of -15 M v per degree  F. 
So, that matches up perfectly, as the compensation is from 68 degrees F.  and 
the temp sensor says we are at 95 degrees F.  Because I had never  "equalized" 
my batteries before, I thought, OK, maybe they are sulfated. So, I  went 
through the equalize procedure, but the voltage only went to 14.1 V and 16  Amps.  
Even though the max available is 17 V. OK, more manual reading  and I found 
that the equalize current is limited to 2.5% of the bank capacity.  Again, the 
Prosin computer did it perfectly. SG didn't really go up at all,  and I expected 
1.265 for the SG after equalize. So, I told the charger that I  had 1600 AH 
capacity, that pushed 40 Amps through at about 16 V. Now I was  getting 
somewhere. Surprisingly, the batteries were not really spittin and  fuming all that 
much. I did that for 5 cycles, and lo and behold, now the SG is  1.265, 
temperature compensated from 80 degrees, lest one of you math guys think  I forgot 
about that. OK, so now here is my question. How on earth could  batteries ever 
get fully charged at 13.9 volts, given that the charger has some  time limits 
on absorption? In the case of my charger, it holds the voltage for  an 
additional hour beyond absorption, they call it over charge, then if floats  at right 
around 13.1 V (temp compensated, 13.5 V not temp compensated) OK,  so I pulled 
the plug in the temperature sensor, programmed the charger to "Warm"  which 
is 68 degrees F, and that gives uncompensated maximum voltage of 14.4, the  
number we all sort of have in our heads for charging voltage for flooded cell  
batteries. And I did put the bank capacity back to 645 AH. Just for more info.  
After the last equalize charge, I shut off the battery switch altogether,  
measured the V at about 13 ( surface charge)?  and came back in a day and  the V 
had not really dropped at all, still had a "surface charge" of almost 13  
volts, so I do not think I have a bad cell or shorted battery, and all the cells  
have the same SG. Just sulfated from continuously being under charged  maybe? 
Now I am getting closer to the number of hours I expected befor reaching  
12.2V. Not perfect, but much better. So here is the reason for this posting:  
What's going to happen to my batteries if I continue charging at 14.4 V despite  
the temp in the engine room and the batteries being at around 95 degrees? 
 
Thanks for your input.
 
Jake
 
 



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