View Full Version : 30a breaker for 40a spot on pdb
Can we buy 30a breakers that fit in the wide 40a breaker spot on the PDB?
Bruce
As long as they are identical to the 30A snap-action breakers provided in the KOP, yes. <R42-B>.
I am sure that you can buy one but you cannot use it. Only 40a breakers can go in the 40a breaker slots.
Can you tell me what rule denies this possibility?
Thanks
Bruce
I already did. <R42-B>. If you are using breakers that are not identical to the KOP snap-action ones, you are in violation of the rules.
I guess I was asking MPG what rule says they are illegal. I was wondering if the breaker supplier had 30a breakers taht fit in the 40a slots and if taht was legal. We have our cims on 40a breakers even though I warned the team that pulling 160a from 4 cims would result in the main tripping which is infinately worse than temprarilu tripping a snap action breaker. It poped in the last game of the championship match in Milwaukee so we want t change them to 30s. Problem is we will have to redo the entire PDB to make this change at Atlanta if we cannot find 30's that will fit int he 40a slots. Having only about 2 hours for pit setup and robot inspecctions and needed robot changes in Atlanta this year, we were looking for an easier way to switch to 30's.
Bruce
Tom Line
30-03-2010, 21:40
Bruce, we've got 4 cims, each on a 40, and you pop the 40's LONG before you should be popping the main breaker. In point of fact in 2008 we had 4 cims and 2 fisher price all drawing hard when we lifted a trackball and rounded the corner, and we STILL never popped our main breaker. That main breaker doesn't pop immediately at it's stated amperage - just like the snap-action breakers and have a small period of time where it can go over the rated amperage.
I'd be suspicious of your main breaker, or of some sort of short / wiring issue causing it to let go.
I've never heard of a team popping that main breaker simply through motor use (though I'm sure it's happened).
I can't find anything saying it's illegal to put a 30A in a 40A slot. Best practice? Maybe, maybe not--I'll defer to the EEs around here on that.
However, you have to use the supplied 30A breakers, or identical ones, in the PDB. That means that you're going to be redoing your PDB unless the KOP 30As will fit into the 40A slots (which I'm guessing you've already tried). If the 30As don't fit into the 40A slots, then <R42-B> effectively prohibits 30As in a 40A slot.
Unless you're coming in on Thursday, you've got Wednesday night and all morning Thursday to get ready to compete.
Chris is me
30-03-2010, 21:44
I guess I was asking MPG what rule says they are illegal. I was wondering if the breaker supplier had 30a breakers taht fit in the 40a slots and if taht was legal. We have our cims on 40a breakers even though I warned the team that pulling 160a from 4 cims would result in the main tripping which is infinately worse than temprarilu tripping a snap action breaker. It poped in the last game of the championship match in Milwaukee so we want t change them to 30s. Problem is we will have to redo the entire PDB to make this change at Atlanta if we cannot find 30's that will fit int he 40a slots. Having only about 2 hours for pit setup and robot inspecctions and needed robot changes in Atlanta this year, we were looking for an easier way to switch to 30's.
Bruce
I don't know for sure, so take my advice with a grain of salt, but I bet you were pulling more than 40 amps per motor at the time. I've been told the breakers don't instantly trip once 40 amps are drawn, so instantaneous current could get higher.
The best way to fix this issue would be to decrease your current draw, rather than forcing your circuit to break earlier. That would just change the issue from "my robot can't move anymore" to "my robot stops every few seconds", which both suck.
Jimmy Cao
30-03-2010, 22:55
Popping the 130A main breaker shouldn't be a big worry. Can it be done using standard KoP components in a safe and legal way? Of course. Is it easy? Nope.
I believe the 130A breaker is thermal based. Last year, we managed to trip it during practice, after running for ~1.5-2 hours stopping only to do battery changes. Our robot last year utilized just about every KoP motor, short of 1 globe and the window. At peak current, it was probably getting close to 250A. On average, I would guess it was approximately 100A (due to the nice slippery floor surface).
My point is, during a 2 minute match, it would be near impossible to pop the main breaker without an electrical fault. If I were you, I would just run the motors through 40A breakers. I suspect that even stalling the motors for 2 minutes wouldn't trip the main breaker, although it would begin tripping the 40A ones pretty quick. Sustained 200-250A for 2 minutes through the main breaker might be enough, but I don't see how you can possibly sustain such a high current draw for a full match. I'd be more worried for the batteries at that point...
I guess I was asking MPG what rule says they are illegal. I was wondering if the breaker supplier had 30a breakers taht fit in the 40a slots and if taht was legal. We have our cims on 40a breakers even though I warned the team that pulling 160a from 4 cims would result in the main tripping which is infinately worse than temprarilu tripping a snap action breaker. It poped in the last game of the championship match in Milwaukee so we want t change them to 30s. Problem is we will have to redo the entire PDB to make this change at Atlanta if we cannot find 30's that will fit int he 40a slots. Having only about 2 hours for pit setup and robot inspecctions and needed robot changes in Atlanta this year, we were looking for an easier way to switch to 30's.
Bruce
Because there are no 30A breakers that come with the KOP that fit in the 40A slot, my interpritation of R42 was that they are not legal because the KOP does not provide a 30A breaker to fit in the 40A slot.
Al Skierkiewicz
30-03-2010, 23:46
OK,
The 120 amp main breaker and all the other breakers have basically the same construction. The only difference is the main breaker is not auto resettable. All the breakers are capable of over current up to 600% of rated current for a few seconds.
Changing to smaller breakers does not limit the current supplied to the motors. CIMs will still pull 129 amps in stall even if you feed them with 5 amp breakers. The main breaker occasionally trips but more often this is due to external forces rather than an over current condition.
Jon Stratis
31-03-2010, 00:23
Yes, the CIM's may be protected by a 40A breaker... but have you measured how much they're actually drawing? During normal (non-stall) operation, it's no where near as much. One year we were worried about current draw, and decided to measure... Turns out it was a fairly constant 40-50A during normal use - 7 total motors running almost constantly, 4 of those CIM's.
If you're really worried about it, i would suggest investing in a clamp meter. Simply put, it uses the magnetic field generated by the current traveling through a wire in order to measure that current. You can clamp it over one of the battery leads, or one of the wires going to your wheels, and see what sort of draw you're getting. It can be EXTREMELY helpful in diagnosing problems. specifically last year with our shooter... we used it after initial construction and saw numbers that we felt were too high (about 3 times what we expected). After some slight mechanical adjustments to reduce friction in the system, the numbers came in line with the expectations.
So get a clamp meter, and see if you have any issues in your system first - maybe one or more of your sprockets isn't properly aligned, generating a lot of friction and thus high current. Set the robot up to drive straight into a wall and see what happens - do the motors stall out because of high friction wheels? What sort of current does each motor draw in this scenario? (keep in mind, this is essentially the worst case for most robots)
James Tonthat
31-03-2010, 05:00
...The main breaker occasionally trips but more often this is due to external forces rather than an over current condition.
Echoing this, I worked field at Dallas and I saw a stop 20 seconds into an elimination match because their Lexan cover hit the breaker and physically turn it off, sad story but it happens. I've also see one that wasn't clicked all the way and turned off after the robot moved about 3 ft, it was out for basically all of teleop, again, sad story.
Thanks for all the great info. Our main tripped in the last match at Milwaukee with about a minute left. We were kind of angled into the tunnel trying to get past another robot that was blocking. The main tripped. There is no way anything mechanical tripped it, it is to well protected from that. What is confusing is that I don't think we were pulling any harder than we had at many other times that day. At the time we had a ball on our vacuum and it was running. Not sure what it draws with a ball on it but the 2 FP motors pull about 30a when running free. So, that in conjunction with stalled cims is what probably tripped the main??
Bruce
Literally thousands of teams have been using 4 CIM drivetrains with 40A breakers on each CIM for years. I doubt this is your issue.
Personally, my team has never tripped the 120A main breaker. We've had the 40A's in a 4CIM treaded tank drive stalled and popping, and never popping the main. I would look to something mechanical, or possibly a faulty main breaker.
Joe Ross
31-03-2010, 10:19
There was a team at the Los Angeles regional who's circuit breaker would trip when they had a hard impact. After repositioning it and shock mounting it, it still occurred. They were able to reproduce the problem on the practice field by running it into the wall or over a bump hard. They replaced it with a new breaker and it didn't happen again.
What was the position of the black lever on the circuit breaker when you lost power?
it was in the tripped....lever sticking out position. Just like it is when you push the red button.
Also for EricH. You say we have Wednesday night to get ready for competition but the rules I have read say uncrating only on Wednesday night. Doesn't even look like they want you setting up the pit or working on the robot at all. What am I missing?
Bruce
Kris Verdeyen
31-03-2010, 12:16
The main breaker (http://www.cooperbussmann.com/pdf/d70101c3-1921-456a-8cdd-cdbe1fc8a85b.pdf) will run at 2x its rated current for at least ten and up to 40 seconds. That's 240 amps. If it tripped on the field, inspect your big wires and crimps (between the breaker and fuse panel) for shorts, and consider replacing the breaker itself. The big breaker is there to keep stuff from catching fire, it shouldn't trip in regular operation.
it was in the tripped....lever sticking out position. Just like it is when you push the red button.
Also for EricH. You say we have Wednesday night to get ready for competition but the rules I have read say uncrating only on Wednesday night. Doesn't even look like they want you setting up the pit or working on the robot at all. What am I missing?
Bruce
The FIRST email about the Championship is what you're missing.
They've been monkeying with the Championship schedule and similar things to allow the following on Wednesday night:
--Uncrating
--Pit setup
--Inspection
--work on robots (after all, you want to fix what you found out was illegal at inspection, right?)
They just haven't updated any Manual sections that cover this sort of thing--but all the info comes from Bill Miller and/or the FRC staff, so it's legit.
Are they allowing more then 5 people in to do all that stuff Wednesday night?
Bruce
Al Skierkiewicz
31-03-2010, 15:44
Bruce,
There was another team in Milwaukee that also tripped the main breaker. They thought is was protected as well but what we found was a small crack in the case. The slight misalignment was enough to cause the breaker to let go. There is another known issue with the breaker. A few over the years have shown up with manufacturing defect. A simple tap on the red button is sufficient to trip the breaker. The test is to tap with your finger and see if it fails. Over the last four years I think I have seen a total of less than ten.
Are they allowing more then 5 people in to do all that stuff Wednesday night?
Bruce
Nope. 5 is the max, unless you can steal some from another team that's already in there. (All the other teams are probably trying to do the same thing...)
robself705
31-03-2010, 17:09
Ok, I know what everyone is saying that the breakers should last well above their rated amperage but this is not true and it is not the issue or the question. I physically tested all of the breakers yesterday because we are adding a programmed throttling device that limits the cim motor power under high loads. We have an external ammeter that measures the amperage draw to 2 amps. Yesterday I WAS ACTUALLY STALLING A CIM and tripping the 40 amp breaker, the problem is each 40 amp breaker will let you pull 50 amps for about 2 seconds before it trips. They let you spike up to 80 amps for a fraction of a second. We can draw 180 + amps for over 30 seconds JUST FROM OUR CIMS. We also have a vacuum that draws up to 30 amps continuously. WE ACTUALLY TRIPPED OUR BREAKER IN A MATCH. So its not a question of whether or not it can happen, it did. Switching to 30 amp breakers would partially solve the issue. I tested them and they allow about 35 amps draw for a second before they trip. This would mean MAX from the cims we could draw 140 amps for just second. This would partially solve our issue, it would just be a lot easier to swap them they have to re wire. We are counting more on our current draw feedback to keep this issue from happening again. But it does happen, the main can be tripped.
However we might try swapping out our main breaker to see if that is the issue. I was looking at charts previously posted and it should last for 20 seconds with 200% draw. We didn't have low enough ohm resistors to test the main breaker.
I'm am not yelling so don't get the wrong impression :D I just want to make it clear what the issue is. Thanks for everyone's valuable input :)
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