We’ve been having some issues with the main breaker on our robot. For some reason, we have tripped the main breaker on our robot three times across two breakers. More unusually, we were not browning out before blowing the main breaker. Any idea what’s wrong?
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It would help to understand a more specific scenario … what were you doing with the robot and for how long?
Did you happen to notice is the breaker was warm after it tripped?
How about the wires connected to the breaker?
Did you check to see if the wires attached to the main breaker were tight - if you wiggle the wires, the compression lug shouldn’t move.
If the wires are not properly tightened at the main breaker, you will have higher than expected resistance; this resistance will result in heating; the heating may result in the main breaker tripping.
Make sense?
Check the main connections on your PDP and consider swapping it.
The suggestions above are very good. A robot like yours that had seen hard (and successful) driving through five events is very likely to have some wear and tear on it. The main electrical circuit (Batt, Main Breaker, PDP) connections should be checked to see that they are tight.
If that’s not it, other things to check for include mechanical jams, especially in the drive train, and worn insulation on the main circuit wire runs. Either of these can cause the main breaker to perform its intended function; i.e., interrupt high current. And either of them can appear momentarily; i.e., a jam or short-circuit may only be present for short duration under specific load conditions.
You may want to log the current on all of your PDP channels to gain some insight.
As others have hinted, the main breaker tripping without causing a brownout usually takes a good bit longer than a match - is this happening during practice, or other session where you run the robot pretty hard for an extended period of time? Again, as already suggested, check connections. An IR thermometer can also help you identify where heat is being generated - and heat is ultimately what trips the main breaker.
Finally, while one or two trips are not likely an issue, if you trip a breaker repeatedly, it becomes even more prone to tripping. If this goes on for very long, you will likely want to mark “not for competition” or toss the breaker(s) you have been tripping.
Our breaker started popping at the end of everymatch on the friday of our second event. We had no idea why, the driver station readings were totally wrong because a multimeter clearly showed us being well below the 120A limit. We replaced the breaker and never had another issue. I suggest that first, other than that, use a multimeter everywhere and see where all the extra current is coming from.
I’m really trying to figure out this post. The first and third sentence would make great sense on their own, but the second and fourth seem disjoint and largely irrelevant to the other two.
What did the driver station readings show? These are measured distinctly from the breaker’s tripping, so if both indicated a problem, it would take significant evidence to refute these. Also, few multimeters are capable of directly measuring 120A DC, or even the tens of amps individual breakers will draw. Most multimeters which measure tens of amps are clamp-on meters which are specifically designed to measure 50Hz or 60Hz alternating current (AC). What meter were you using?
Also, I notice that OP said “across two breakers”, so it seems unlikely that this is simply a bad breaker.
We opened the charts tab on our driver station, which showed us at 300A +, but at the same time we had someone with a mulimeter connected to the battery, and it was reading around 20-30 while running a few motors. Our multimeter was rated for over 150A DC, it is one of the clamp-on ones.
Yea I agree “across two breakers” probably means they tested another one, which is why I suggested trying to swap it Oneee more time just incase.
When you looked at the logs, did you happen to also look at which PDP channels were drawing most of the current? You would want to make sure you were running them under load when doing your test. Sitting in your pit driving the robot with the wheels off the ground, running an empty intake, and moving an arm or elevator is NOT going to give you real world numbers. Not even close. A drive train that’s off the ground may pull a couple of amps per motor. Put it on the ground, run it into a wall, and drive around d had like you’re in a match and you’ll see a lot more current draw. Toss a cube in the intake so the motors stall outhe and you have that added weight when moving your arm or elevator.
If the PDP is showing 300A during a match, the drive train if the first place I would look. I’d put it on a hard floor and check my drop center, I’d check the tension on my chains or belts to make sure it’s not to tight. I’d rotate it by hand to ensure there’s no binding.
As my post says, we saw 300A on the driver station chart and at the same time, we had a multimeter over the battery connectors. This was in the pit, the readings were completely incorrect on the driver station. We are aware of motor stall.
I don’t know about “longer than a match,” but if there’s a breaker popping without a brownout, it is an extended current draw, not momentary.
My guess would be either have a weak short before the PDP (low resistance = not much voltage drop) or some mechanical problem causing higher than usual current draw. I would not expect poor electrical connections to be the problem. In fact, popping the main breaker without browning out means your system resistance is probably good!
It’s probably not a short, but that’s easiest to check, so do that first.
Then take Jon’s advice to Brian and look at logs. Confirm you are drawing enough current that the breaker should be popping. If it’s not, you’ve got a bad breaker. Then check which PDP slots are drawing more current than you’d expect, and take a closer look at the corresponding mechanisms mechanically.
Gus and Peter asked what you were doing with the robot when the breaker is tripping. The answer to that question could definitely help us give you better advice.
I’ve heard of other teams experiencing this, even ours. It’s like once you trip the breaker one time, it’s more susceptible to tripping over and over again, with less current (like they break in). I know this occurrence happens with home breakers as well.
I see this is your second breaker, and it’s still doing it. You may or may not have a short. Your drive-train will likely be the most-current-hungry subsystem on your robot, but it should be intermittent.
Maybe it’s time to think about your current budget. What are the logs showing for total PDB current?
If your compressor is always running, it will pull roughly 10A. If you have an arm or lift system that relies on a CIM or mini-CIM, that could pull a lot of current as well, as well as burn up windings/brushes.
If you burn up the brushes, the current won’t increase, but the motor will simply stop working. If the windings start burning, they will short with each other, causing increased motor current and will provide less mechanical power with more thermal output.