Re: Lithion-Ion Batteries
 

Andrew,
While I have seen some teams trip the main breaker, the majority of those were due to significant vibration imparted to the breaker assembly or in a very few cases, a manufacturing defect within the breaker. This year, with the additional motors allowed, main breaker trips occurred more often than anytime in the past but those were still few and far between. While I have inspected many melting failures of the Anderson Power connector on the battery, all were due to damaged connector parts or improper crimp of the terminals used. By far and away, scratching of the surface of the terminals is the most destructive. This is caused by teams who use the alligator clips supplied with the battery charger to clamp on the Anderson terminals to charge the battery. The clips cause significant scratching and gouging of the terminal face which results in high resistance and skyrocketing temperatures. In some cases, teams deformed the springs that support the terminals to allow easier mating/unmating of the connector. This again results in high resistance and localized heating of the terminal. For instance, imagine a damaged or poorly mated terminal that has a series resistance of only 0.1 ohms. At a 200 amp load current, the terminal resistance is trying to dissipate 200^2 amps * 0.1 ohms=4000 watts. Yes, that is the same as 40 100 watt light bulbs in the space of 0.0625 sq. in. And as you can imagine, that is capable of melting plastic.

Re: Lithion-Ion Batteries
 

When I was young (and immortal and reckless) I tried to change the starter motor on my 68 Camaro without disconnecting the battery.

My metal watch band shorted out, and the surge of current melted the metal and popped the watch right off my wrist.

Re: Lithion-Ion Batteries
 

Al,
I can personally vouch for Apalard on this one that it appeasred to be an over-current issue.
Our robot this year had a very high top gear which tended to draw a lot of current. The first trip occurred at Troy, when our bot was beat to the bridge and had 10 seconds of stalled acceleration in high gear. Shortly after the start of the match, the breaker tripped when another stall condition occurred.
This condition was repeated again in anotehr series of matches at Troy. After that weekend, we pulled up the spec, tracked voltages, and figured out currents. The current, and time at current matched the likelihood of tripping the breaker.

We then bought a handful of breakers and tested them with a power-supply versus the loads we were seeing on that powertrain, and the tripping of the breaker matched.

We had also been warned by our friends across the state that ran a similar drivetrain in 2010, that the layout is "power hungry" and a "battery hog".

I wish we would have documented the testing process on the breaker better to do a little white-paper on "what not to do" when doing a wide bot.

The combination of a longer wheelbase (even though it was wide), higher traction profile, taller gearing along with Apalard's aggressive drive style tended to cause high drivetrain loads. The inefficiency of our collector also tended to have the collector motor (a 550 or 775 depending on event) running at/near peak power.
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The pit crew re-geared the drivetrain at MSC and then again at Champs, and the tripping of the main breaker issues went away. With the re-geared drivetrain, it pulled significantly lower current in the drivetrain. There were a lot of hard crashes, and hard bumps may have tripped the breaker, but I believe the high current draws played a big part in it due to the specific times I saw the breaker trip.

Re: Lithion-Ion Batteries
 

Ether,
You were very lucky. I may ask you to describe in detail this story when we discuss battery safety during the build season.
Ike, if you have the battery connector that melted, I would really like to see it. Also might you have a picture of the robot side of the battery cable and main breaker? On occasion, the temperature rise from damage at the connector has been transmitted through the #6 wire to the main breaker causing early trip.