Keeping the main breaker from tripping
 

We have purchased the 3 CIM vex pro ball shifters. We used them last year but only with 2 CIMs because we tripped the main breaker multiple time. We want to go back to three but we need some tricks to stop the main breaker, we know about the canned air flipped upside down, do you guys have tricks or recommendations?

Re: Keeping the main breaker from tripping
 

Monitor current in code using the new PDB and adjust outputs accordingly. I'm sure multiple teams will post example codes of how to do this. (For all we know, multiple beta teams have code that does this, but they can't share them yet.)

Re: Keeping the main breaker from tripping
 

There isn't any one solution. We ran 6 CIMs, & 2 MiniCIMs through 7 events this past year counting off-season events and never tripped the main breaker.

We were running a butterfly type drive so we were mostly on 4 omni-wheels which means we have minimal wheel scrub.

Wire management is also important. Ensure that you have the shortest possible wire path from your battery to your drive train motors. This means your battery wires to PD board/panel should be short, your wires from speed controllers to PD panel should be short, and the wires from speed controllers to motors need to be short as well. This takes a lot of pre-planning to do well.

We also used a single reduction gearbox that made it very efficient compared to more complicated gear boxes and we also ensured that our wheels would slip before we ever stalled the drive train motors.

On our practice robot we ran fans over the motors to keep things cool during long sessions and we will likely look at adding fans over our motors and our main breaker on next year's robot.

Re: Keeping the main breaker from tripping
 

We ran the WCP 3CIM DS transmissions last year without any issues at all.

The biggest trick - Make sure you set up the gearing correctly for your load.
Most of the problems I have seen were based on trying to run too high of a FPS. Also USE the low gear range. I have also seen a lot of these dual speed transmissions running generally as a single speed.

We have been very pleased with these DS transmission. It just take some research to get it right.. Making sure that you are not stalling your motor for a long period of time is key.

Cooling by using canned air in a non approved method isn't safe. More than likely the trick will be illegal soon..
Perhaps adding a fan that helps cool the breaker could help, we run one for the compressor as it is..

Designing the robot with this in mind is a much better approach.

I understand using this process in a pinch but this should not be the standard solution to the issue.

Good luck this season,

Aloha!

Re: Keeping the main breaker from tripping
 

We ran ~2.1kW on our drivetrain. That's 4 big CIMS and 4 Mini CIMS on our drivetrain (1 CIM and 1 Mini CIM per wheel). We never tripped the breaker. We also had mecanum wheels which helped us reduce the load because they slipped a little.

Re: Keeping the main breaker from tripping
 

Excellent point. FIRST goes bananas about safety. There is a safety animation, a safety award, a safety manual, safety inspectors, and tons of safety rules on the robot. I understand the need for safety, but FIRST should be consistent with how they make calls like this. Why should canned air, used in an unrecommended situation be considered perfectly fine, while using an air compressor or a flap grinder in its recommended configuration be considered too dangerous for use in a pit?

It's not unreasonable to think that a safety inspector would call this out. FIRST seems to have given the okay on this for now since Einstein teams were visibly misusing the canned air to cool their breakers on the field, but I agree that the trick will be illegal very soon.

Re: Keeping the main breaker from tripping
 

Teams have been using air dusters to cool motors/breakers since I joined FIRST in 2001. It probably happened before then too. You'd have to be a complete idiot to endanger yourself or anyone else while using it. Clearly a properly used air grinder is exponentially more dangerous than spraying an air duster upside down.

Re: Keeping the main breaker from tripping
 

There is a version of air duster specific for cooling electronics. so they are ok to cool circuit breakers. also the air duster I buy actually says its ok to use upside down, it just warns about freezing liquid coming out and to not contact that liquid. This may be specific to the stuff I use, I don't know other air dusters.

Re: Keeping the main breaker from tripping
 

That would be me, and I disagree.

Using canned air to cool the main breaker is actually very effective and not unsafe or misuse. If they do make it illegal it will not be because of the unsafe nature of spraying canned air but instead because of the possible unprotected surges of current. I think it is much more likely that the use of a fan on the breaker will be made illegal.

That all being said the most effective way to prevent a breaker tripping is having a properly trained driver or having automatic shifting. I say this because often the breaker will trip when the drive train motors are both stalled in high gear. A driver who downshifts before a collision and does not rapidly change from moving forward to backward will not trip the main breaker. I would be wary of the current sensing limiting the driver train because it takes control away from a driver and has a high chance of failing.

That being said if you are going to sense current, you should make your own sensor instead of using the built in sensors in the power distribution panel. This is because from my understanding the power distribution panel only has current sensing on the outputs and not the input. You should put the current sensor on the main pole of the battery, it should also be inductive instead of resistive. I made one last year in twenty minutes with parts that cost 3-4 dollars.

Re: Keeping the main breaker from tripping
 

Please post details?

Re: Keeping the main breaker from tripping
 

Why not just sum the currents at the outputs to get the current at the input?

Re: Keeping the main breaker from tripping
 

One team will come up with a clever way to keep the breaker's temperature super cold for the duration of the match, then FIRST will likely ban these sorts of modifications. In my opinion, the freeze spray is totally illegal from two rules. FIRST knows that teams are doing this, and although they haven't said anything about it last season, I wouldn't be too surprised to see an addition disallowing methods to change the temperature of breakers.

The first is G3. Deliberately freezing a safety device so it does not operate as intended seems like it may qualify as an unsafe modification in the eyes of some inspectors. It also seems to violate R64, because it can easily be considered to be tampering, modifying, or adjusting. It's clear that they don't want you changing the "performance and specifications of the device".


Also, could you clarify about the input/output comment for the current sensor? You should be able to sum all the drive/big motors up, and everything else should only end up being a few amps in total.

Re: Keeping the main breaker from tripping
 

By cooling the breaker you merely restore it to its rated current level. You don't get "bonus" current. You just aren't de-rating it due to it being hot (since it is a thermal switch).

By extension, you are against fans on motors?

Re: Keeping the main breaker from tripping
 

What is tampering, modifying or adjusting about it? The breaker spec sheet lists it's operation characteristics to -50F, and that it's designed to operate down to -25F. It is still operating completely within its design, performance and specifications. Freezing the breaker does not physically change the way it works, it just changes the operating temperature at the start of the match. There's nothing inherently unsafe about operating the breaker within it's design range.

I personally would not want to rely on freezing my breaker as a primary method to keep my robot alive during a match, but under previous FIRST rules, I don't believe it was illegal.

Re: Keeping the main breaker from tripping
 

To all teams running six or more cims on their bot and say that they have zero breaker issues, what speeds were you running?
Because there are only miniscule gains from running six cims on anything under 15 fps according to my drivetrain calculator. Maybe a few extra inches out of ten feet if you go from four to six cims.
Why do you run such low speeds on six cims?

On freezing the breaker, I don't really like it if it's before a match. After a match, okay. But before a match I feel like it defeats some of the purpose of having a main breaker. If it is to limit power, then why are you allowed to give yourself more power like that?

To asnwer OP's question:
Current sensing. Autoshift to low gear when you hit a certain amount of current for an extended period of time.

Re: Keeping the main breaker from tripping
 

To clarify, I don't think anyone cools their breaker to keep alive...they (or at least we) just do so in order to not start with an elevated temperature due to short match turnaround. An elevated temperature means your breaker will trip under lower current draw than a room temperature breaker.

Re: Keeping the main breaker from tripping
 

I doubt FIRST would rule it's use illegal because it modifies performance of the item being sprayed.
That said, I definately believe they might ban it's use for health reasons.

Dust Off is difluoroethane, a refrigerant.

Here is the "Safety" text from Wikipedia on difluoroethane.

Re: Keeping the main breaker from tripping
 

It keeps the 40 amp breakers from tripping. By switching from 4 to 6 cims with a single speed the current gets divided through 6 40 amp breakers instead of 4 40 amp breakers. Thus you can push with a higher gear ratio and have decent enough speed to move around the field.

Re: Keeping the main breaker from tripping
 

Shouldint we be trying not to draw more current than the system is supposed to handle rather than stop a safety mechanism from activating? Like turning of a smoke alarm rather than putting out the fire?

Re: Keeping the main breaker from tripping
 

On this note, when I went in to buy some compressed air recently to use on our robot between matches, I needed to show my ID upon purchase. When I asked the clerk why out of curiosity, she replied that "people must be huffing it or something like that."

Re: Keeping the main breaker from tripping
 

I had to show ID to purchase a can of air (to be relabeled as "magic smoke" as a gift for a mentor) as well at a store that will not be named but whose logo is a bullseye. I wasn't yet 18 at the time so they wouldn't let me buy it after seeing my ID. I explained to my dad that canned air "used to be the way teenagers would get high" and then made him go to T**g** and buy it for me.

Re: Keeping the main breaker from tripping
 

But if you gear for like 12 fps anyway, why not just shift down? The 40 amp breakers autoreset, right?

Re: Keeping the main breaker from tripping
 

No teams that I know of used canned air to allow them to draw more current. They use it to cool down the main breaker during quick match turnarounds (such as during the finals) so that they can still draw as much current as they would be able to if the breaker was at room temperature. Running quick match turnarounds without cooling the main breaker off can result in tripping the breaker while not pulling more current then the breaker should be able to handle.

Re: Keeping the main breaker from tripping
 

I agree that this is likely the usual case for cooling breakers and I am generally doubtful that FIRST would call that illegal for the listed reasons.

Maybe a better question would be is the breaker thermally triggered because that is simply one of the many ways the creator decided to implement it, or is the "left over" heat from previous operation indicative of actual risk?

The question would be, what is the case where the breaker trips meant to prevent?

• Is it to protect the breaker itself from damage?
• Is it to protect the motors from excessive currents over time?
• Is it to protect the motors from excessive heat.

I can't find any documentation stating which is true, but I would guess that it is a combination of all of the above.

If so then in the last case (protecting motors and components from excessive heat), then cooling the breaker DOES circumvent the system and add risk. Risk of overheating a motor, controller, etc. because the breaker "thought" that the system was much cooler than it was.

Any thoughts?

Re: Keeping the main breaker from tripping
 

I also see small gains in acceleration and top speed in my model for conservatively geared robots. Some reasons I'd still consider 6 cims over 4 on a single speed bot geared at 12 ft/sec:

1. 6 cim is more efficient than 4 cim during high loads like pushing and turning (less motor heating, less speed drop under load, robot seems a little stronger)
2. Distribute load between motors to reduce heating for back to back matches
3. Redundancy, we lost a talon last year, robot was still very much driveable other than not driving straight

Re: Keeping the main breaker from tripping
 

Yes, they auto-reset. The datasheet is on AndyMark's site here.

Essentially the goal is to have a high speed which is great for getting across long distances fast and a low speed which is good for fine maneuvering/pushing.

If you are having your high speed at 12fps (I think that's what you're saying?) there really isn't much incentive to use shifters anyway.

When robots use shifters, its usually because they want to have a really fast gearing that would stall the motors if you tried to push at that gearing. Therefore, its best to be able to downshift so you can hold your own if you get into a confrontation. 12fps isn't much for a high gear, that's usually what people do in single speed setups.

Re: Keeping the main breaker from tripping
 

It is to protect from uncontrolled discharge of the battery. The breaker protects whatever the branch circuit is, so essentially the main breaker is protecting the wiring from battery-main breaker-PDB.

Re: Keeping the main breaker from tripping
 

So I'm guessing the reason it trips based on heat and not some sort of chip detecting high current is for lower price or some other manufacturing reason? In which case the residual heat is nothing more than a side effect. Well jeez, I'm surprised FIRST doesn't recommend cooling it down if what you say is true :D

Re: Keeping the main breaker from tripping
 

I can see it now - FIRST bans using canned air to cool parts. Teams then begin keeping multiple spare main breakers in a cooler on ice and swap them between elimination matches.

Re: Keeping the main breaker from tripping
 

Generally breakers have 2 methods of protection. If you have a slow increase of current until you get to a continuous amount that will trip the breaker, the trip occurs via a piece of metal bending as it heats up until it no longer makes contact with the circuit.

If you were to have a short you'd see a huge sudden surge of current, which would cause a solenoid to pull the contacts apart.

I assume the one we use features both methods, but I've never looked inside one before.

Re: Keeping the main breaker from tripping
 

The internal construction is actually a spring steel plate slightly warped to naturally press against a contact point. The off button springs this up (the plate bending is the resistance you feel), and lets the lever you flip to close the breaker swing between the plate and its contact.

So its performance is entirely thermal, warm that plate up and it will trip, do it fast or slow, doesn't matter, hit a certain temp and it pops (buckles) and when it buckles the "on" lever isolates the plate and its contact, leaving your robot off.

(Opened one up a few weeks ago to satisfy my curiosity...)

-Aren

Re: Keeping the main breaker from tripping
 

Guys,
FIRST hasn't ruled against the canned air because it really doesn't do that much. The thermal device is relatively isolated from the sealed case. You cool the case down but it doesn't reduce the temperature of the bimetal strip enough to change the characteristics. As Aren has pointed out, this is a simple and small piece of metal. It will heat or cool rapidly without intervention from the outside world. That is what it is designed to do. The current flowing through the contacts have the greatest effect. To a lesser extent, poor connections to the main breaker cause heat to be generated and conducted to the contacts through the metal carrying currents in the breaker. However, the thermal mass of the wiring and contact terminals on the breaker are sufficiently high that one would have to cool down the entire main electrical system to have the desired effect. No matter how you cut it, six CIMs are still drawing the maximum current from the battery in stall at full throttle. Teams that claim they are not tripping the main breaker have learned to ramp up to full throttle or prevent drivers from doing so in a match. In addition to the dangers of inhalation, the rapid cooling in a humid environment produces moisture on electrical parts and the chemicals tend to wash out lubricants. Your mileage will surely vary.

Re: Keeping the main breaker from tripping
 

The copper lugs going into the breaker are great conductors of heat. Chill them & it will affect the internal workings of the breaker. But when you stop & the breaker will quickly go back to working as designed. So it really is not an issue unless you have someone chasing the robot on the field with canned of air. :)

On a non FRC but related subject, the NEMA thermal motor overloads work on the same principle heating an element. The overload element is actually called a heater. In some styles the element actually melts in a controlled way. Anyway to properly size them for the general case you need to take into account the ambient temperature of the controller relative to the motor & they still need short circuit protection.

Re: Keeping the main breaker from tripping
 

For current readings, we are using the IC from this board:
http://www.panucatt.com/Current_Sens..._p/cs-100a.htm

I don't use this for FIRST, but on the Formula SAE team I am on, we are using this to read the alternator current and the total current output by the PDB.

I don't know exactly if it is legal to put this in between the board and breaker, in fact, I'm pretty sure it's not. Also, we use either a 150a or 200a version of this, I cannot remember. It is like $17 minimum order for these of digikey (I think, I didn't order them)

Re: Keeping the main breaker from tripping
 

Current monitoring like this seems to be what the second sentence of 2014 R53 has in mind.

Re: Keeping the main breaker from tripping
 

We don't, I'd bet 254 doesn't either.

Re: Keeping the main breaker from tripping
 

Sweet! I didn't have the rules handy, at the time. I will definitely think about putting these on the robot next year

Re: Keeping the main breaker from tripping
 

I think it's likely that you would exceed 200 amps for short periods of time. We measured total currents in excess of 300 amps with the 2015 PDP. http://www.chiefdelphi.com/forums/sh...&postcount=153

Re: Keeping the main breaker from tripping
 

Keep in mind that not all main breakers are created equal. The spec sheet has pretty large error bars on tripping current vs. time and tripping current vs. temperature (close to a 20% swing). This could easily be the difference between tripping a breaker and not tripping a breaker in a match. Many teams opt to replace a main breaker once it has been tripped. There are two reasons to do so:

1) Anecdotally, teams claim to have observed that a breaker may fatigue after repeated tripping (though this is not that likely until there have been dozens of cycles). Would love to see some actual data behind this.

2) A breaker that has tripped is statistically more likely to be from the less forgiving end of the main breaker distribution. By replacing a breaker every time it trips, you are likely to end up with a more robust breaker in your robot for most of your matches.

A few other quick thoughts on this topic:

* When driven fluidly (whether through practice or software help), your drive draws less current and preserves more momentum when maneuvering.

* Well known teams with 6 CIM drives still occasionally pop breakers. Maximizing performance is all about balancing on a knife edge, and occasionally things go the wrong way. Attention to every little detail (wiring, mechanical efficiency, software, pre- and post-match maintenance) is necessary to minimize the frequency of problems, and most teams would be better off being more conservative in their gearing and motor allocation.

* At some point, browning out your control system becomes the limiting factor in power draw. The RoboRIO doesn't like temporary low voltage spikes any more than the cRIO did, and in some ways it is less forgiving (ex. disabling PWM outputs at around 6.5V).

Re: Keeping the main breaker from tripping
 

I agree with the people saying that canned-air cooling wouldn't last, but I wonder if anyone's ever considered mounting the breaker in a 'refrigerator' made with a 12volt peltier cooler? If you don't know what these are, here's one:

http://www.adafruit.com/products/133...FYKPMgodZhwAiQ


I'm nearly sure there will be some rule that negates this possibility and giving up 5 amps of battery isn't so good either, but you could shut it off under high driving current-draws.

Re: Keeping the main breaker from tripping
 

I think that would be actually something dangerous to do because it is altering the breakers operating parameters rather than just resetting it to normal operation after a match.

Re: Keeping the main breaker from tripping
 

I am not against fans on motors. I am also not against cooling the breaker. Our team cooled off our breaker with canned air too. I don't think it's any more dangerous than a lot of the other stuff we do. By my interpretation, the breaker spray is illegal, but FIRST doesn't think it is illegal. I have no problem with spraying the breaker, so I am more than happy to go with FIRST's interpretation.

The fans on motors comment isn't a good comparison. Motors don't operate based off of heat like the breakers do and fans are specifically called out as being allowed. Fans also don't involve spraying a dangerous liquid chemical on electronics, and don't involve dangerously cold temperatures.

Re: Keeping the main breaker from tripping
 

Personal preference. Both approaches are valid I just wanted to bring up that the input approach does exist and is what I would use.

Re: Keeping the main breaker from tripping
 

Considering the efficiency of a peltier (5-6%) it won't do much.

Re: Keeping the main breaker from tripping
 

Place a steel washer or ring(any ferrous metal works) around one of your main wires. Then cut a slot in a steel washer and place a linear hall sensor in the slot. We epoxied ours in to keep it intact. The hall sensor outputs voltage which is directly related to the total robot current, and it can be plugged directly into the analog breakout. This is the system we have implemented into our practice robot and the results so far look good.
http://www.jameco.com/webapp/wcs/sto...001_1915940_-1

Re: Keeping the main breaker from tripping
 

Have you compared the readings to a precision ammeter to determine the accuracy over the current range?

Re: Keeping the main breaker from tripping
 

No, we compared it to the voltage drop data

Re: Keeping the main breaker from tripping
 

Jared,
In some ways, replacing a tripped breaker is a good practice. When that breaker trips under high loads, the load is actually fairly inductive. As such when the contacts open under load, there is some pitting of the contact that takes place. This pitting can raise the series resistance, ultimately raising the heat generated for a fixed current.
These breakers are unlike the protection breakers used in your home. Those generally will have a design that both protects long term high currents and sudden overloads. The trip curve for these breakers has a wide range because they are simple (cheap) and provide the coverage needed for our designs.
No one has mentioned this yet so let me add this to the mix. (Yes, I am the one who said the king had no clothes.) If I observe a team tripping the main breaker for any reason other than a catastrophic electrical failure, I would not consider them a good alliance partner. If we need you to play an entire match to win, why would we take the chance at a good robot who trips the main breaker in the hopes it won't happen in a critical match. Personally, I would rather have an OK robot who doesn't break over a great robot that sometimes sits idle in the middle of the playing field. When I see a team spraying their breaker, I have to wonder...are they covering up a design flaw or are they just being cautious?

For those who think spray is illegal can you tell me why you think that?
For the peltier, I would consider the rule about being accessible and visible would not be accomplished by putting the breaker in an insulated box.

For general knowledge... when you see one or more of us run out on the field when a robot stops during a match, the first thing we are looking at is the main breaker status, followed by indicators on the DSC, cRio, PD and radio. This sweep will give us an indication of what might have occurred. It is the standard list of checks that was formed following the Einstein weekend a few years ago. We want to be sure every team is given every chance to compete.

Re: Keeping the main breaker from tripping
 

"Canned air" is generally not actually air. Some versions are flammable. If you are using one of those versions, I would avoid spraying it on energized components. :]

Re: Keeping the main breaker from tripping
 

I'm basing this off my experience with other types of circuit breakers and what we would permit with them. This is regardless of if it works or not.

Yes, ambient temperatures affect thermal circuit breakers. Using any sort of device to intentionally cool the breaker violates the intent of the safety mechanism. If a team is popping breakers after X time, they are then exceeding the ratings. The only reason for attempting to cool it down is to "cold soak" the breaker to attempt to uprate the breaker and increase the current required to trip it. I see little difference between intent in using compressed air and packing dry ice around a breaker during a match.

Now, if a team wishes to cherry pick which breaker they want to use, that is a different matter. But intentionally manipulating the environment around the breaker to prevent the breaker from tripping is a direct attempt to bypass the safety mechanism the breaker provides.

Re: Keeping the main breaker from tripping
 

Your fallacy is in assuming the intent of the breaker is to limit temperature of the bar inside and not to limit current through the breaker.

If the breaker under normal operating conditions (ie: starting at roomp temp) can reach current A before tripping, due to temperature A, then if a match is played shortly thereafter, and the temperature of the bar has not returned to room temp, it will actually trip at some current less than A.

How is restoring the breaker to the properties it has at room temperature a safety risk? If you accept that the breaker is meant to operate at room temperature in a safe manner, there is no justification for claiming that cooling it to room temperature rapidly is any different than operating it as if it were always at room temperature.

Re: Keeping the main breaker from tripping
 

As I read this thread, I'm more and more on the fence about this issue. I'm starting to thinks it's fine, mainly because of the point that Cory brought up: the breaker spray doesn't really keep the breaker any colder than ambient temperature, it just resets the temperature to what is was before.

My original opinion that the breaker spray was against the rules was from somebody who made the argument that it was similar to tampering with a thermostat by tricking it into thinking the room is colder than it is. I now realize that this isn't really an effective analogy.

Re: Keeping the main breaker from tripping
 

I would agree that a permanent solution to cooling (keeping the breaker below ambient) the internal temperature of the breaker would be a violation of safety protection for which the breaker is ultimately designed.
The breakers on the robot are intended to prevent fires due to high current in any circuit on the robot. The wiring from the battery to the main breaker is the only circuit not protected. All breakers are meant to protect the wiring for this reason, not the load. The current rating vs. wire size is a derivative of the NEC specifications for open frame wiring. We slightly derate the tables based on the short time in use. These are not continuous (24 hour) currents. Even with the protection, we sometimes do see fires or at least significant smoke events all the time.
While we are on the subject, if you remove a motor(s) but leave the wiring, you must remove the breaker feeding that branch. (Consider this a 'best practice" method.)

Re: Keeping the main breaker from tripping
 

Tim Allen would be proud of First this year. "more power" This year a large portion of First teams will be pushing the the robot power system to the limit. A large number of robots are going to push power draw beyond rating and eat up safety factor of many components of the power system. There are going to be problems. Saw many examples of this last year. Smart teams will develop power management strategies and be able to push the power system with out failures and reliability problems. Those who don't will learn the hard way of what happens when you push systems beyond their safe operating zone. Scouting needs to track teams that have "power problems". Bad alliance choice. Get smart or suffer. The new control system has the resource to help teams with power management. This is a comprehensive systems problem and is complex. Teams will need to put much effort into this. Positive is that this is an excellent opportunity for students to learn the process of data collection, analysis and the development of strategies based on this. The bad part what we are teaching future engineers. "More Power" is not an attitude future engineers should embrace. First could address this problem by limiting motor choice for drive trains. That would get the forum hopping. Or more like the real world, First could attach cost to the robot power. Like each cim above 4 costs a team xx points every match. With the new PDB they could asses a xx point penalty for every total robot power draw above xxxx watts. We should teach the cost of power.

Re: Keeping the main breaker from tripping
 

You are already penalized for using too much power. You trip the main breaker. :] As Al says, that should move you down the pick list for alliance selection. Kinda like mecanum wheels. :ahh: Maybe that should be a scouting question.

Re: Keeping the main breaker from tripping
 

No, I assume the intent of the breaker is to limit the temperature of the wiring. Your fallacy is in assuming cooling down the breaker resets the system. A breaker, including this one, is not intended to only protect against high current short duration short circuits but also longer duration overloads. This is why the breaker will trip after an overload which occurs for 30 seconds. Depending on the overload of some breakers, it can require one hour to trip. It depends on the amount of overload.

By cooling the breaker, you are trying to bypass the safety mechanism it represents which includes long duration overloads such as you are apparently inducing in your design. How long does it for the breaker to trip when you practice?

Re: Keeping the main breaker from tripping
 

That's right up there with always making sure you have female pwms on both ends of the wires connected to the digital sidecar, roborio, etc. It prevents someone from unplugging a wire from a motor or sensor and accidentally shorting the power pin to ground. I've always assumed that's the same reason the prongs always go into your wall at home, but never verified it.

Re: Keeping the main breaker from tripping
 

This one is really more about safety than short circuts. Touching live prong would be quite dangerous and undesireable, so the outlet design offers a level of safety. European plugs are actually better, because your finger can never touch energized metal, but the US design is better than having prongs stick out of the wall.

Re: Keeping the main breaker from tripping
 

A circuit breaker is a circuit protection device so its purpose it to protect the circuit, ie the wiring. So yes it is to prevent the wiring from getting hot enough to cause the insulation to start to flow, melt, or catch on fire.

So I feel that cooling the breaker is a bad idea because you are "resetting it" to ambient temps but not doing the same for the wiring which it is supposed to protect.

Re: Keeping the main breaker from tripping
 

For anyone trying to implement this --the voltage produced by the ring (which merely needs to be conductive, not ferrous) is directly related to the RATE OF CHANGE of the current. You will need to keep a running total of the voltage to get a good value for current draw. I don't see how you're going to keep from having significant drift in a practice session unless you pause and recalibrate regularly, though perhaps over the duration of an FRC match it wouldn't be too bad. This trick works well for A/C meters because the current is constantly changing (and adds up to zero), so that the average voltage induced over a 1/60 sec cycle is proportional to the RMS current flow. For DC, no such luck - if you draw a steady curent, whether 1A or 110A, the voltage will be zero after it stabilizes.

Re: Keeping the main breaker from tripping
 

That might be true if using an inductive sensor, but a Hall effect transducer responds to magnetic flux directly. The ring is not acting as a transformer element, but as a flux concentrator, and does need to be ferrous.

Re: Keeping the main breaker from tripping
 

We use a lot of commercially made Hall Effect current sensors at work. They all have ferrous flux concentrators. For certain applications, we get custom sensors made with special ferrous materials that work to higher frequencies than the silicon-steel they normally use.


Change to a ferrous ring then use an oscilloscope to check the output of your homemade sensor again. You may want to compare the output of your homemade sensor against the output of a commercially available current sensor that is capable of reading DC; i.e. a current clamp probe. Depending on what you are trying to do and your accuracy requirements, you may have to calibrate your sensor against a known standard.

You may be much happier using a commercially made sensor such as the one in the link below.

http://www.digikey.com/product-detai...168-ND/4990649

LEM has put a lot of hard work into reducing the inherent drift in the offset voltage (over temperature and time) and to linearize the output. For comparison, the SS49E/SS59ET Series from Honeywell has an effective offset of +-10% at 25 C. It is likely to be worse at other temperatures. There is no spec for linearity.

Get in touch if you want help choosing a commercially made Hall Effect current sensor.

Re: Keeping the main breaker from tripping
 

Tom,
That is generally the case for powered connectors but in my work, the signal direction determines the male plug. That is why all microphones have male XLR connectors and mixers have female XLR sockets. For fixed installations we provide connectors of both flavors so that the direction convention can be maintained. (yes, we cheat with turn arounds when needed) Camera hardware is the same whether it was the old TV 81 cable, Triax or fiber. TV81 had some reversed pins because voltage(s) was generally sent to the camera for operation. In some cases this was pretty high. In the case of Triax, original cameras could have 220 VAC running to the camera on the inner conductors but the female connector was designed so you can't contact both of those easily. Newer designs have far less voltage feeding the camera.

Re: Keeping the main breaker from tripping
 

You're right. Extension cords with two male ends are sometimes called suicide cords because they're so dangerous, and they really should never be used. I've only seen two, one to plug a generator into a dryer outlet, and one that was used for stage lighting.

Re: Keeping the main breaker from tripping
 

Jared,
That adapter used for stage lighting is prohibited in my jurisdiction (Cook County, Il). Someone caught doing that could potentially lose their job and/or incur a large fine. In your area, I suspect older venues may get a pass if they have not upgraded their equipment. I believe the manufacturer of the plug set I am thinking of was Mole Richardson.

http://i347.photobucket.com/albums/p...g?t=1272819042