Popped Main Breaker

[Colin P]

At the Waterford District Event, my team managed to pop our main breaker. We believe there was an arc between two terminals resulting in a huge flow of current. My question is, has this happened to anyone else? Anyone have any interesting breaker stories?

[Grim Tuesday]

How did you do that!?

Was your frame grounded? Were there metal shavings nearby?

I haven't heard of this happening to any other teams, though.

[M.Wong]

I can only think of one time where we had a main breaker pop. From what I can remember, we never found out what caused it. Consequently we switched it out.

[Mark Sheridan]

It can be pretty easy to pop the main breaker if you chose the wrong gear ratio for your motors. Our robot runs 8 motors this year, if we managed to choose the gear wrong ratios for all of them, we could draw as much 210 amps of power without tripping any of the individual motor breakers. That would defiantly trip the main breaker.

The last time we tripped a breaker probably was in 2003 from repeated heavy loads from ramming other robots on the ramp.

[Alex Cormier]

Originally Posted by Colin P

At the Waterford District Event, my team managed to pop our main breaker. We believe there was an arc between two terminals resulting in a huge flow of current. My question is, has this happened to anyone else? Anyone have any interesting breaker stories?

Are you using any bane bots?

[IndySam]

These breakers are not on-off switches but that's how we use them.

They will go bad with repeated turning off and on just like your standard home breaker. If there is no obvious over current problem throw that breaker away, heck I would probably do it anyway.

[Colin P]

We think it arced between power out and ground in because the nut holding down the lead was welded to the bolt.
We had 4 CIM's, 2 RS 775's, and two window motors that didn't operate too much.
It seemed like a freak accident and never happened again, but the field crew was pretty surprised to see a smoking breaker. After I found out the rest of the electrical components were OK, I thought it was pretty cool too.

[theprgramerdude]

Originally Posted by Mark Sheridan

It can be pretty easy to pop the main breaker if you chose the wrong gear ratio for your motors. Our robot runs 8 motors this year, if we managed to choose the gear wrong ratios for all of them, we could draw as much 210 amps of power without tripping any of the individual motor breakers. That would defiantly trip the main breaker.

The last time we tripped a breaker probably was in 2003 from repeated heavy loads from ramming other robots on the ramp.

That is highly, highly, highly unlikely to pop your main breaker just by driving around. These breakers are short-circuit preventers for the battery, and not much else besides an on/off switch. Your system will brown-out before you could possibly throw the breaker by normal use. The breaker should be capable of doing at least 10-15 seconds at 210 amps, if not more.

[dez250]

The 120-amp marine style breaker is not designed for what we use them as. When we use them as an on/off switch and continually they wear out and can fail quite easily. The main spring that keeps them "engaged" is less than a 1/4" long and weighs only a few grams, will fatigue quickly. If you welded the nut on this to a bolt, I would suggest not only to swap it out for a new one, but also check for chassis grounding, especially with use of the Banebot 775 motors.

Many recent production 775 motors have been found to have a case short, which leads to chassis grounding if the motor is mounted directly to a metal frame. We found a team that showed no signs of damage to their robot this past weekend in DC that was chassis grounded through a 775 and had all ready competed at a prior regional with this issue existing. After going through their five 775 motors they had in stock, only two were not case shorted.

[Al Skierkiewicz]

Originally Posted by Colin P

We think it arced between power out and ground in because the nut holding down the lead was welded to the bolt.

Colin,
The robot was talking to you but you weren't listening. The only reason for a nut to weld itself to the bolt is because it was loose to begin with. Loose electrical connections cause excessive heat. Since the main breaker (and all of our breakers) is a thermal device, any heat internal or external will cause it to trip. Since your robot caused enough heat to weld the nut, this heat was transmitted to the breaker internals and that tripped the breaker.
Although this device is rated as a breaker, it is also in the switch category. The actuator is designed to act as a switch and the internal structures are designed to act a breaker. Using this switch with high currents flowing can cause damage to the internal contacts but most of the time, very little current is flowing when you turn your robot off.
A dead short somewhere else on the robot would not cause a nut to weld itself if it was tight to begin with. Remember that all robot current flows through this connection and that can be as high as the battery is capable of supplying. That is at least 500 amps for a fully charged battery.