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Unread 24-09-2008, 07:38
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
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Re: First: 2008 Batteries are D-Y-I-N-G.

Quote:
Originally Posted by EricVanWyk View Post
I can't even begin to describe how bad an idea this is: This practice is a liability.
When charging any battery, some of the charge current is given up as heat within the battery. When you try to ram a lot of current, the internal heat does not have time to migrate to the outside of the battery case. So you may think by checking the case that the battery is doing fine at the higher current. However the internal (spot) heat may have exceeded the boiling point for the electrolyte causing excess gas pressure and spot heating of the plates. If the electrolyte actually boils enough, the plate becomes coated with residue which reduces the available plate area and therefore reduces the amount of current density in the battery. At some point, the pressure relief valve may also open releasing some moisture. The max current specification on the battery is dependent on the amount of electrolyte in contact with the plates. If you reduce the plate area, the amount of available electrolyte or raise the temperature of the battery, the output current is affected.
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.