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Unread 01-02-2008, 15:27
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
Posts: 10,798
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Re: Serious Problem of Unknown Origin

Jessie,
This more likely from a dirty contact on the battery than anything else. There is no explanation other than extreme low temperature for the battery voltage rising during play. It is also possible that there was some veryhigh friction in the drive train that worked itself out during the match. Loose hardware is a good example. If one of the motors is running near stall the terminal voltage on the battery will read low. The battery internal impedance is .011 ohms. Using Ohm's Law and fudging a current draw of 200 amps you would expect to see 2.2 volts dropped just across the battery. However, the RC stops functioning when that battery voltage falls below 8 volts, so I think the 7 volt display you saw was in error.
The battery on concrete was an issue long ago with car batteries and the case material and the fact that the battery was not sealed. Sneak paths through leaking electrolyte, minute caracks in the case and the concrete would serve to discharge a battery left in contact with the floor. A simple insulator like carboard usually prevented the discharge, which took several weeks. Our battery does not suffer from any of these issues. In fact most modern batteries have no problem sitting on concrete or steel for that matter.
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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.