[RE-wrenches] discharging Rolls batteries

[James Surrette]

Hi Hugh, 

Based on your earlier number - regardless of temp effects - you were only removing ~25% of capacity.  You will need to lower your low voltage cut off to improve performance.   

Remember, as batteries cool actual capacity is reduced, so if 200AH is 50% @ 25C it is significantly more than 50% @ 5C.   Thus, you are discharging more deeply.  However, batteries produce heat during recharge and discharge. 

Hope this is of some use. 

Jamie 

>>> Hugh <hugh at scoraigwind.co.uk> 1/14/2010 6:35 PM >>>

Hi Jamie and Dan, 



Thanks for keeping up this thread!  And sorry for being impatient. 



Now, if the capacity 'loss' is simply due to reduced performance, is it logical to say that one can push the battery to lower voltages under low temperature conditions without actually cycling it harder or reducign its life that way? 



On the question of inverter temperature compensation for discharge set points, these would surely be adjusted downward in low temperatures whereas the charging setpoints are adjusted upwards.  I had never heard of such adjustment to discharge setpoints (low battery disconnect, genstart, etc).  I would be interested to know if this type of temperature compensation exists and indeed whether it is legitimate in terms of sustainable battery management. 



Hugh 






 


Hugh,
 



 


Sorry if you found my response limited but have been traveling since early this am and don't have all information at hand, at the moment.
 



 


Regarding temperature effects on capacity, earlier responses are spot on as the lower capacity is totally as a result of slower reaction times as a result of lower temperatures.  
 



 


Approximate Temp effects;
 



 


40C = 104%
 


25C = 100%
 


5 to 10C = 90%
 


-5C = 80%
 


-22C = 60%  




-- 

Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk 


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