[OCCRA]: A friendly reminder from team #2...

[Jimmy Cao]

a good way to test the batteries for capacity is to perform a load test on them.

I belive a battery that is still at 100% capacity should be able to run for about 1 hr with a 9amp load. (at least the batteries we have are like that, they have a 12AH rating, however that is the rating at a very slow (1 or 2 amp) load.

That is what our team (Team 469) did and we had no battery problems today, however we did discover that many of our batteries were in rather poor shape and therefore we decided not to use those batteries today during the competition.

Brief explination of batteries, sent out by one of Team 469's wonderful mentors, Tim Downey

The basic battery is formed by 2 dissimilar metals separate by a dielectric. In the standard lead acid battery consists of lead and lead oxide plates (lead/rusted lead) separated by sulphuric acid. The lead oxide scale can fall off of the plate and float around in the dielectric solution. If this comes in contact with between the lead plate and the lead oxide plate, the result is a shorted cell. This condition is easily measured with a volt meter. The battery output will be approx 10 vdc instead of 12. The batteries we have are of the gel-cell type. The dielectric is a gel instead of an aqueous solution. The result is less occurrence of the shorted cell. The gel cell creates a different problem, one less easily identified. When a battery is heated, as happens during an over charge cycle or during a rapid discharge cycle, H2 gas is released. In a conventional lead acid battery, the gas is easily dispelled from the acid. This creates a dangerous explosive condition but does not damage the battery. In a gel cell battery however, the gas is trapped inside of the battery. This is safer from an explosive stand point (that is why UPs systems and fire alarm systems use gel cells) but the gas bubbles form inside the gel and result in a diminished dielectric/plate surface area interface. The result is a diminished power output. This is not easily measured with a volt meter. In fact, the voltage readings will be normal. The damage will not be noticed until the power (current * voltage) is required.

Conclusion:
1) do not shake a battery - you may short out cells
2) do not over charge or over discharge a battery or you will lose available power
3) do not pick your nose in public (you will embarrass the rest of the team)

(thanx to Mr. Downey for that wonderful descrition)