pic: Battery connector.....
 

Re: pic: Battery connector.....
 

Yowza. I haven't been in FRC too long, but I've never seen a battery cable melt like that.

I actually see this on the larger versions of these connectors on the fork trucks we drive at work. Not too often, but try getting a battery off a charger when the two connectors melt together.

Re: pic: Battery connector.....
 

Someone once told me that the 6AWG connectors were only rated for 80Amps...

Re: pic: Battery connector.....
 

I once met a rep from Anderson who was amazed and seemed concerned at how many amps we pull through them. So take that for what you will.

Re: pic: Battery connector.....
 

This connector is the Anderson SB-50. The 50 is for 50 amps.

Anderson makes larger connectors, the SB-120, SB-175, and SB-300. Those are larger connectors, commonly used on electric forklifts and other really big things.

Using #4 wire certainly helped with this, but the SB-50 does not go up to #4 wire so we had to play with it a lot to make it work. It would be nice to use the SB-120 which comes with #4 size crimps.

Re: pic: Battery connector.....
 

Around 10 years ago, they did an analysis that showed that for the short time that FIRST robots are run, there was enough margin. However, since that time, average current draws have increased significantly, and many more teams are running practice robots for much longer then 2 minutes. Because of that, I hope that in the near future, FIRST will allow a better connector.

Re: pic: Battery connector.....
 

Would you mind if I used the image at the top of this thread in a blog post for Mooshim? We're posting a video on how to measure contact resistance to identify this type of situation before it manifests as shown.

Re: pic: Battery connector.....
 

Was that pre-assembled or did your team fasten the wires?

I've seen students (and mentors) get the connector in the shell upside down/backwards.

Re: pic: Battery connector.....
 

Eric: Sure, go ahead, I have 2 pics of this one if you want them.

This particular connector came from the KOP, where it was pre-terminated on the Anderson end and we crimped/dip soldered the other end with a large ring terminal.

We now buy fully terminated cables from AM or CTRE for the batteries, and make our own from #4 wire for the robot. We crimp both ends on a large press crimp, and dip solder the ring ends (not the connector ends) before assembly.

This cable came from the 2012 practice robot which melted 3 connectors. we also melted two on our 2011 comp bot during the off-season. This is the least bad failure of all of those, in two cases the black wire came through the red connector so the copper was showing all the way down the connector.


FIRST should really switch to the next size up connector.

Re: pic: Battery connector.....
 

Especially since the curent rating on the next size up connector matches the size of the robot main breaker.

Re: pic: Battery connector.....
 

Andrew,
I would like to examine this connector up close. I may need to disassemble the connector. Any way you can ship this to me? Jim or Ike has my contact info.
What hit me first off in the picture is why the red wire is not melted as the black wire is. They both pass the same amount of current.

Re: pic: Battery connector.....
 

Both wires were hot when the connector failure happened.

When this happens, the terminal begins to sink into the plastic connector. As soon as this happens, it rapidly increases in resistance and melts away (at this point, the current drops, so the other wire would not fail).

I have seen both wires fail, it seems random.


While getting battery cable today (several feet of #4 red and black), I saw some #1 high flex battery cable and smiled. Maybe when we go to the SB-120 I'll use it.

Re: pic: Battery connector.....
 

I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely.

It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for.

This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

Re: pic: Battery connector.....
 

It's a safety issue. In ANY electrical system, you have safety measures designed to prevent this from happening. In our system, that is supposed to be the 120amp main breaker. FIRST has determined that drawing excess of 120amps continuous causes an unsafe condition and requires the robot shut down. What Andrew has shown, and has been repeated on several other robots, is that under certain circumstances the main battery connector fails before the main breaker, thus circumventing the entire safety system as it is designed.