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Unread 30-03-2014, 22:20
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: Best way to charge batteries

Boy, you go away for a few days to inspect in Minnesota and wow!
1. The 6 amp charger that comes in the KOP and virtually any of the smart 6 amp chargers will not force 6 amps into the battery. That is merely the maximum available current and it will not be supplied for any longer than is needed to start the charge process.
2. A warm battery will give a false reading to smart chargers. You should wait at least a half hour before putting the battery on charge to let it rest. Batteries should be in the open (not an enclosed space) while charging.
3. The CBA is capable of discharging the battery at a similar discharge current as is used in the test data printed with the battery. I use 7.5 amps (on the CBA III) to give me a very close approximation to test data while not taking forever to run the test. It will take about two hours to discharge to 8 volts. This level will show you not only the amp hour rating of the battery, it will also show you of any single cell failures or reduced capacity.
4. A short, high current test will not show up reduced capacity, damaged cells or predict performance during a match. Repetitive use of a high current tester or a lengthy high current test (greater than 20 amps for greater than 30-60 seconds) is asking for reduced life or permanent damage.
5. Likewise, high current charging may also produce permanent damage. Automotive chargers that are not smart, do not have settings for AGM, or can force currents in excess of 6 amps will cause permanent damage and a variety of other dangerous conditions.
6. As pointed out above, star washers do provide a positive locking of the two terminals so that hardware will not loosen with use. Likewise, the use of an Anderson SB50 mating plug on your charger is best. Scratching of the contacts with clip leads causes high resistance in the contact.
7. The 2 or 4 amp positions will not extend the battery life in our use. Battery life is reduced for our batteries simply because robots demand high current discharge over a short period of time. It is typical to expect about 400 charge/discharge cycles in our batteries before capacity is reduced. With six motor drives, expect this to be even less.
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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.