How can minibot battery short circuit when it isn't on or being charged?

[Techhexium]

I'm not in FRC, but when my FTC team meet today to build a robot (not a minibot), and one of our batteries short circuited without being on or charged so one side of the battery was burned. The 20A fuse did not blow, the battery was plugged into the motor controller through the connector wire but not the power switch so we can't turn it on, and the robot was not in motion. The battery is a year and a half old, and we have been charging it in 1.8 Amps. (I know we should be charging it at 0.9 Amps) Also the battery was being secured by a couple standoffs on the right and a channel on the left. Sorry I don't have pictures.

My coach told me that the battery would have burned like that if it was charging, but in fact it was not being charged or used. My question is how was it possible for a minibot battery to short-circuit if it is only connected to the controller through the connector but not to the power switch so it can't be turned on?

[Mike Betts]

Originally Posted by Techhexium

I'm not in FRC, but when my FTC team meet today to build a robot (not a minibot), and one of our batteries short circuited without being on or charged so one side of the battery was burned. The 20A fuse did not blow, the battery was plugged into the motor controller through the connector wire but not the power switch so we can't turn it on, and the robot was not in motion. The battery is a year and a half old, and we have been charging it in 1.8 Amps. (I know we should be charging it at 0.9 Amps) Also the battery was being secured by a couple standoffs on the right and a channel on the left. Sorry I don't have pictures.

My coach told me that the battery would have burned like that if it was charging, but in fact it was not being charged or used. My question is how was it possible for a minibot battery to short-circuit if it is only connected to the controller through the connector but not to the power switch so it can't be turned on?

The insulation must have worn away between two adjacent cells which were wired in series. In this case the short would be internal and irregardless of the fuse or if it was being used at all.

This kind of failure is usually caused by vibration over time and is not common. However, it can be accelerated by a small, sharp protrusion under the insulation.

[Al Skierkiewicz]

I am going to go on the assumption that the battery was dropped at some point and damage to the insulation as Mike has pointed out above eventually led to a short between cells. In a dead short, even one cell is capable of full current discharge for several seconds. You can consider that the battery is capable of at least 20 amps sustained since that is the value of the fuse.

[DavidGitz]

We had this problem, due to how our battery was installed on our minibot. The battery fit inside a piece of the Tetrix C-Channel which was a little too small for the battery. We had put some electrical tape on the battery and the C-Channel to remove the sharp edges but it wore away. We were prototyping with the minibot one day and I noticed the battery started smoking with nothing plugged in. The C-Channel had cut into the battery and was shorting the batteries together. The battery got quite hot and took about 20 minutes to cool down to safe levels, but after wrapping it in electrical tape the battery has been fine in operation. Since this event we spread the C-Channel wider and use zip-ties to hold the battery in place instead.

[jspatz1]

We had the identicle thing happen to our battery when it was nearly new and had been handled very little. At that time their were reports of it happening from several teams. We considered it a defect. If you have the time, and another battery to use, you can return the damaged battery to the supplier and they will replace it. I believe they are seeing many of these.