More on battery management [RE-wrenches]

[Ray Walters]

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Hi All;

I just thought I'd add a little tid bit I found while overlaying various 
battery temperature info onto the same chart. It seems that while energy 
storage capacity diminishes with temperature, Battery cycle life 
increases at lower temperatures. From my rough research, it looks like 
the sweet spot (maximum cycle life x capacity) is actually much colder 
than I thought: around 55 to 60 degrees F. Capacity is reduced about 5% 
from rated, but cycle life looks to be about 20% higher. Anyone care to 
check me on that? I'm just taking data from Trojan, and other battery 
books and combining it, but it makes sense from a chemical reaction 
standpoint. Heat kills, extreme cold freezes, but cool is good.

Ray

>Hi Windy,
>
>I'm working on Sunday too, but I have a few minutes here at the Honolulu airport waiting for the flight to Kona to attend the IEEE PV conference to get my mental and physical batteries recharged. Working in PV sure beats other kinds of work.
>
>I like between 2.4 and 2.46 volts/cell for flooded lead antimony batteries with a nice equalization charge every 2 to 4 months depending on system configuration and use. Batteries and people thrive or die depending on how their electro-chemical processes function. Batteries, like living things, need special care and feeding in different situations. While anthropomorphizing batteries may seem simplistic, the human/battery comparison is an easy-to-understand way for users to think about the critters being fed by their solar panels.
>
>Aloha,
>Joel Davidson
>
>  
>
>>Joel, Kelly,
>>
>>The manual you refer to is written from the conventional assumption  
>>of 27/7 utility-supplied power to charge batteries. It is typical of  
>>the advice also given by battery manufacturers who are not  
>>specifically oriented to RE. Stand-alone RE charging requires  
>>different timing and voltage strategies.  Anyone who deals with  
>>batteries should have this manual (and similar information), but  
>>should understand that it does not fully address our situations.
>>
>>We push the charging faster, in order to "get it while we can". Many  
>>flooded battery installations suffer from max. voltage set-points of  
>>about 14.2V because that's what the battery manufacturer recommended.  
>>That's fine when you have full charge power from a wall socket and  
>>can take a few extra hours to gently charge the batteries. In an RE  
>>system it must be 14.7 or 14.8V, or else the charge current is  
>>tapering off, and the battery is not fully absorbing the last hours  
>>of available sunlight. Or, it is  not charging as much as possible  
>>before the generator is turned off for the sake of peace and quiet or  
>>economy.
>>
>>We push battery charging beyond the conventional comfort level that  
>>is optimum in a utility-charging scheme. This is a compromise, but it  
>>is MUCH more desirable than attaining a 75% charge by wasting  
>>precious solar power, on a day that it could have been pushed to 95%  
>>by delaying the voltage regulation.
>>
>>Windy
>>
>>    
>>
>
>
>
>  
>


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