pic: Battery connector.....

[Nirvash]

Originally Posted by BBray_T1296

The same amount of current leaves (red) the battery as enters (black). Either could have melted, the red just gave first

What I mean is, if your frame is 'grounded', it has the same potential of the negative terminal on the battery. No current should flow across it unless something with a positive potential is also shorted to the frame.

[Michael Hill]

Originally Posted by Nirvash

What I mean is, if your frame is 'grounded', it has the same potential of the negative terminal on the battery. No current should flow across it unless something with a positive potential is also shorted to the frame.

Agreed. Just because your chassis is grounded doesn't mean you're going to have battery melting problems. Heck, the chassis of most cars and airplanes are grounded and those batteries don't melt....well not usually (I'm looking at you lithium-ion...)

[apalrd]

I do not know if there were grounding issues with either robot, but neither robot acted erratically at any time (one of them was competing in an off-season).

We know that one of them was drawing significant drivetrain current because the frame re-bent. Our 2011 robot crate was dropped while loading on it's way to the championship and the frame bent, but we hammered it straight at CMP. It re-bent at the Kettering Kickoff off-season, and melted 2 battery connectors in the same day. The replacement connector was taken from a battery as we did not have spares (they had never failed before).

The other robot was a practice robot. We geared it a bit too high, and practiced with it very hard. Eventually we added large KOP fans (the metal kind that were in the kit for a few years) to the drive motors to help them cool down (the CIM motor wires were getting very hot). The front roller was also very lossy so we threw more motors at it to get it to a reasonable speed (we had a 'joe johnson style' cross feed roller using bevel gears). The robot in general was a power hog without any additional issues. The main breaker should have tripped if we were using too much current, it did not.

During the 2012 comp season, we tripped the main breaker 3 times, then started cooling the main breaker using a cold bag of washers (set in a cooler of dry ice between matches), and replaced the battery cable to prevent failures at MSC.


The point is there are robot use cases that can melt the battery connector BEFORE the main breaker trips. This is a SAFETY ISSUE. Even if we are drawing too much current, the whole point of the main breaker is to open before any major safety issues happen.