main Breaker Problems

[Al Skierkiewicz]

This is a continuation of a discussion on the Peachtree forum. The main breaker has had some failure issues in the past. These are due to one of two problems. A misaligned part during manufacture causes intermittent operation or an over aggressive team member over tightens the mounting hardware and/or stresses the case before or during a match.
The first can be checked by insuring a firm click when turned on, indicating the internal latch has engaged with the actuating handle. Defective units may not latch properly. A second test is to lightly tap the red button and look for intermittent operation. A misalignment of the bimetal prior to spot welding can cause improper engagement of the electrical contacts.
Mounting produces another set of problems. Most often when mounting the breaker, teams will attempt to mount on an uneven surface. This cause stress related fractures in the case which lead to unreliable operation. Always insure you are mounting on a firm and flat surface and do not overtighten the mounting hardware. As always check all electrical connections and parts after every match using a bright light and another set of eyes. Small fractures in the bakelite case of the main breaker are not visible in normal lighting.

[Tom Bishop]

At Peachtree, there where several instances of robots not working that could possibly have been attributed to the main breaker.

It seems pretty clear that the WiredCats problem was with the main breaker, and Flash's too. But to have so many go out at once seems unlikely; not impossible, but unlikely. We have had main breakers go out before, but on older robots that have retired from competition. Never had one go out during a competition that I can remember. But I plan on bringing a spare to Championships

I can't remember an elims round where so many robots didn't work at some point in a round. Our alliance had problems, #1 had problems, seems like others did as well. I wonder if there's an issue with this batch of main breakers? Or maybe just an issue with teams getting excited and forgetting the basics

Any other main breaker issues at regionals out there?

[Mark Jones]

I'm not sure of the specs on this breaker; however, typical load center breakers (like those in your household breaker panel) are not "switching duty" rated.

This means that you cannot use the breaker as you would a light switch to frequently turn on and off the circuit, especially fluorescent lights. Most of the time, these load center breakers are intended to stay on and not switched on-and-off for many cycles.

Some load center breakers are "SWD" or "switching duty rated" to allow the breaker to be cycled many times.

Some of the issues may be due to the many cycles these breakers see and the wear of the catch nib onto the bimetallic strip.

[MrForbes]

Earlier this year a few teams reported problems with the "off" lever shaft breaking. I don't know if this is related...maybe there is a quality control issue at the factory? or we're being hard on them this year? Kind of strange since our power load is pretty low this year.

[Mike Betts]

Originally Posted by Mark Jones

I'm not sure of the specs on this breaker; however, typical load center breakers (like those in your household breaker panel) are not "switching duty" rated.

This means that you cannot use the breaker as you would a light switch to frequently turn on and off the circuit, especially fluorescent lights. Most of the time, these load center breakers are intended to stay on and not switched on-and-off for many cycles.

Some load center breakers are "SWD" or "switching duty rated" to allow the breaker to be cycled many times.

Some of the issues may be due to the many cycles these breakers see and the wear of the catch nib onto the bimetallic strip.

Mark,

We (the FIRST community) have used the 120A circuit breakers for quite a few years now with few issues that were not attributable to manufacturing defects or mounting issues (see Al's post).

SWD means that the CB can handle the high inrush current associated with a florescent or switching power supply load and not necessarily a high number of switch cycles.

Besides, a typical robot sees hundreds, not thousands, of cycles.

JMHO.

Mike

[Al Skierkiewicz]

Gentlemen (and ladies),
The circuit breaker was designed for switching DC loads under the hood of a vehicle or boat. It is intended for switching loads on and off. The internal design of the breaker is large electrical contact points attached to a bimetal plate that is pushed into position when the lever is actuated. Unlike load center breakers that have latches that wear with use, this breaker incorporates a design with little wear.

[Andy L]

Our breaker broke last week at Silicon Valley. It's stuck in the on position and the red button to turn it off won't do anything when pressed down.

[Al Skierkiewicz]

Originally Posted by Andy L

Our breaker broke last week at Silicon Valley. It's stuck in the on position and the red button to turn it off won't do anything when pressed down.

Andy,
I'll bet that the breaker has an errant plastic part that fell between that actuator and the bimetal or the contacts have fused themselves together. Pictures please.

[Al Skierkiewicz]

At least one more breaker died on Saturday at Boilermaker.

[dtengineering]

We had one die in the offseason a couple years back, but (crossing fingers) haven't had any problems with them in competition. The "dead" one followed the symptoms Al describes... the black lever would seem to fit into place, but kind of loosely, and would run for a bit, but vibration would swing it into a "half on/half off" position causing the robot to shut down.

One thing we do that may help reduce the mounting issues (other than the fact that we usually mount them to a flat, forgiving surface such as plywood or thin lexan) is that we use nylon bolts and nuts rather than steel. This makes it more difficult to over-tighten, but also significantly reduces weight. This year we dropped almost 1/4 lb from a fairly standard control board just by pulling out the steel nuts and bolts and replacing them with nylon.

Jason

[samir13k]

the plastic piece above the swinging on/off lever on ours came loose. if anyone was to pull the lever off and put it back on at an incorrect angle, it could have not been locking on the on position all the way and could have easily turned off easily. Luckily i was the first to catch it and a quick superglue fix took care of the potential problem.