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Re: Be aware of battery and charger inconsistencies!
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Re: Be aware of battery and charger inconsistencies!
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I can vouch for the don't argue with the LRI concept. Even if they find out they were mistaken, you will still have to make them happy in order to compete. Changing things to keep the inspector happy is no fun at competition. |
Re: Be aware of battery and charger inconsistencies!
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The rules in question do not state the max rating of a charger, but the max rate you charge at. |
Re: Be aware of battery and charger inconsistencies!
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Re: Be aware of battery and charger inconsistencies!
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I don't get how you guys as LRI have different instructions than what all the teams are aware of. You are telling me that a 100% legal(according to every written rule) and safe robot can have the entire season jeapordised over something no one is or can even be aware of beforehand that's purely up the the inspectors discretion? that's completely insane. "Putting a fuse inline will not help matters" why not when doing this will absolutely assure we fall within the only rule that mentions anything about it? " Using these chargers to "top off" the battery won't work.." ummm yes they will. it's precisely what we are doing now and is all we want to do. From the documentation all the charger does in trickle mode is set the output voltage to 13.8 and that's it. This is a very typical procedure for charging these batteries and why our other ones don't work as well i'm not sure. Perhaps it uses a different and not as effective charging method. maybe the voltage reference is off. maybe there is too much of a loss through the wire. I don't know the physics behind it and i'm not sure why but what I do know is these chargers work in the "top off" mode we want to use them in that you claim doesn't work. Buying these chargers was the investment into solving this issue. like other team's we arn't made of money so spending a few hundred dollars on new chargers simply isn't an option. |
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... Computers are stupid. They do EXACTLY what you (or whoever programmed them) tell them to do. Which means that as dumb as it may sound, it is entirely plausible that the charger doesn't quite detect that the battery is nearly fully charged and dishes out a full-power charge. As a reminder, this rule is NOT a made-up one. It logically follows from the rules regarding battery charging in the Safety Manual. |
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And while the enforcement may be based on a rule, it is not following the wording of the rule. |
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we have a 3lb weight on the arm to have enough inertia to have enough fallow through to get the ball at the trajectory we want. even 0.2lbs heavier or lighter will reduce our trajectory. We have also played with the transmission ratios, currently those are 16:1. we tried 12:1 and it didn't have enough force to get up to speed. anything higher ratio we won't have the speed we need to get the trajectory. We thought about adding a flywheel but we run into inertia issues as with the weight. We also require a full slam to the kicker to get the ball into the goal, just a tad less and it misses. So we require a fully charged battery but more importantly each battery we put on is the same. I can move forward before I shoot but that won't solve the issue if the next battery kicks even lower then the next one super high. As you can see from its motion a stored energy system isn't really an option. |
Re: Be aware of battery and charger inconsistencies!
It strikes me as problematic that we're essentially advocating for using the LRI's power as a roadblock to a team's participation. For many years, it's been FIRST's stated advice (e.g. at LRI training) and implied expectation that robot inspectors should do everything within the rules to permit every team to compete effectively. Although the implementation of that principle is at times complicated, I've long espoused the idea that in order to inspire confidence in the fairness of the competition, it's necessary to enforce the rules precisely, and to grant teams the benefit of the doubt when their creative interpretations of the rules lead to situations that were not envisioned by the rule-writers, even if that flies in the face of conventional wisdom.
In this particular situation, the robot rules prohibit unsafe robot systems and prescribe sanctions for violators. Concurrently, the event staff have a mandate to mitigate unsafe conditions off the field. But those are two separate kinds of authority; despite being vested in the same group of officials, those powers can't be used interchangeably, as is apparently being suggested here. So when the rules say a team should do something, rather than they must do something, it can't be enforced as if a contravention of a mandatory robot rule. That's the case with the battery chargers that do not meet FIRST's recommended specifications: when used safely but contrary to recommendations, there's no prohibition. If there's an actual hazard, the event staff have the responsibility to mitigate it and refer it to the regional director for final resolution (particularly if the mitigation is unsatisfactory to the team). If it's an enforcement action under the robot rules (e.g. because the charger rendered a robot battery unsafe and thus illegal), then the LRI has final jurisdiction over the illegal part, but not over the charger itself. |
Re: Be aware of battery and charger inconsistencies!
There is no need for the arguments. To summarize the issue:
The OP uses legal 6amp chargers that operate at or below their maximum of 6amps to bulk charge batteries. Afterwards, he switches to a charger that can operate at a maximum of 15amps that, according to OP, only operate at < 2-3 amps on the batteries and could prove/enforce this by putting a fuse on the charger. Appears safe, but I'm not a battery expert. The rule in question states that batteries may not be charged at higher than manufacturer recommended specifications - (5.4, enforced at 6amps for FRC). As written, this is a limit on the process of charging, not the charger. LRIs are also on the lookout for chargers that charge at greater than 6amps at events to be deemed illegal which would include the OPs charger. The OP is not breaking any rules in the manual BUT regional inspectors do get to make the final decision at the regional So, if I were the OP, I would post to Q&A as you were planning to and pending their response, go ahead and bring those chargers to competition. Explain to the onsite regional inspector your setup and why you feel its legal and allow them to make the decision. Be prepared for the worst. This guy posted this resource to help other teams, not to flaunt an unfair advantage. To negatively comment on his team's design insults everything he and all of the students on his team worked to accomplish this build season. Especially given the fact that they did consider the problem of inconsistencies in battery voltage and came up with a solution that they quite understandably think is within the rules. |
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There also are not enough resources to babysit the OP to make sure he only uses the car battery charger to "top off" - which is to say that the easiest way to enforce the rule is to disallow chargers that have higher ratings than 6A; especially chargers with ratings of 15A. There is also a risk of catastrophe - Sure, using a healthy motorcycle battery with a car charger might shorten the life, but it won't catch fire. A big assumption in that equation is the battery is healthy. These batteries go into robots that collide with one another. The batteries are routinely discharged at very high rates, they're abused. Using a 6A charger on a damaged battery might cause it to heat up or catch fire (I've had first hand experience with this). Using a 15A charger on a damaged battery is even more dangerous, and could cause it to explode. |
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Also you wouldn't need to baby sit the team, charger has inline fuse, show to inspector that it can not charge above a certain rate because of that, inspector sees this and can go about his day. If one wanted to be paranoid they could stop by the team's pit every once and awhile and looked to see if the fuse was still there. |
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Edits! Or was that in reference to efoote868 saying that it is easiest to just disallow them? |
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Honestly, my opinion (utterly worthless at inspection, mind you, unless I happen to be the one inspecting you, in which case, see "Lead Robot Inspector has more say than Robot Inspector in case of disagreement"), is that if a charger is used that CAN go above 6 Amps, it should also have the ability to be SET (not auto-set, manually set) to 6A or below, and on inspection, the inspector verifies the setting and applies a tape of choice to hold it there. Auto-setting chargers that can go above 6A and cannot be set at or below 6A should, by reason of being unenforceable in terms of setting for our battery manufacturers' specs, not be permitted--but that should be made clear somewhere in, let's just say, the Administrative Manual (which, BTW, is in fact enforceable as rules*--so if it says that something or other must be followed, then that something or other must be followed). *Enforceable does not necessarily mean enforced. Witness seat-saving, though that's getting better. |
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I don't think anyone is trying to insult the OP's robot design or team. He has mentioned limited resources a number of times; here are some new ones that are happy to try and help. And as someone pointed out, I suspect there will be many more at their regional who will absolutely be happy to help as well. |
Re: Be aware of battery and charger inconsistencies!
I have just gotten off of the phone with Big Al. He is at a double regional with over 100 teams. He said he will try and respond if not today, when he gets home tomorrow. For those that do not know Big Al, he is the Head Robot Inspector for FIRST. He works with FIRST personnel and the GDC.
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Re: Be aware of battery and charger inconsistencies!
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If your entire season relies on using a possibly illegal component to charge your batteries exactly the same way - I have a feeling that you're going to end up losing consistency even with said charger. |
Re: Be aware of battery and charger inconsistencies!
Minor point: I think the word you are looking for is "headroom", not "overhead". |
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Re: Be aware of battery and charger inconsistencies!
Wow guys! Let me explain a few things...
First to the decision to ask robot inspectors to check battery chargers in the pit... The Inspector is one of the first people on the pit floor to be present in your pit and looking for unsafe conditions of any type. These might be grinding, open flame, unsafe stored energy, power distribution and yes, high current chargers. While we are concerned about the standard 50 amp or greater automotive chargers, any high current charger is suspect. We have asked that LRIs ask teams to remove them from the competition areas citing the Safety Manual. Most high current chargers are brought in simply because of misinformation and misinterpretation of the specifications and instructions printed with the chargers. (More on that later) Robot Inspectors are only part of the crew of volunteers and staff that are charged with keeping all participants safe while in the venue during a FIRST Competition. Others are the UL Safety Advisers, CSAs, the Pit Staff, FTA, Referees and Judges. All of us communicate to insure a safe event for everyone, especially the public who walk in and observe. The Safety Manual is the definitive guide for all staff as to what should be followed by all teams at an event. The rule on battery chargers was moved from the Robot Rules so that these other volunteers would be aware of issues that previously were only known to the Inspection Staff through the robot rules. While the Inspection Staff may be the first to find your charger, any of the volunteers can make the same request based on the statement on page 8 of the Safety Manual. (Quoted several times above.) Please remember that the robot rules pertain to robot construction and specifications that are required for play on the field. While you may not be aware of the communication that takes place, key volunteers meet daily to discuss issues and the LRI, Head Ref, FTA, Field Supervisor, UL Safety Advisers and the Judge Advisor meet informally throughout the competition to discuss teams, safety, and any item that can affect the participants or public. Next, for those who are guessing at the contents, I suggest you thoroughly read the Safety Manual including this quote from paragraph 2 (emphasis added)... PURPOSE This safety manual is an easy-to-use guide for important safety information and provides FRC participants with a basic set of requirements to maintain a safe environment during the build season and at competition events. I read that as teams and team members are required to follow the remainder of the manual. As to operation for batteries... Each battery type (VRLA, AGM, Gell Cell, wet cell lead acid, etc.) and chemistry carries different specifications, variables, and charging methods. In general for these lead/acid chemistry cells, the chargers used are constant voltage. In order to achieve the reversal of the chemical reaction, a voltage in excess of the nominal cell voltage is required. For our AGM type the nominal is 2.2 volts per cell at full charge while the automotive wet cell is between 2.3 and 2.38 volts per cell. In order for charge current to flow, the charger voltage must exceed the cell voltage. Smart chargers will regulate average charge current by switching the charge voltage on and off while testing the voltage delta of the previous voltage readings. The KOP chargers and other chargers listed as AGM/gell cell/VLRA chargers maintain the output voltage to levels consistent with the nominal cell voltage or about 15 volts. Automotive chargers (wet cell and no maintenance) typically use approx. 16 to 18 (or higher) volts to achieve the higher charge currents needed for these types. The listed Stanley device is targeted for these types and while the specifications are listed at 12 volts, we know that is not possible (no current will flow after the battery reaches 12 volts which is well below full charge). While a difference of only a few volts seems trivial, it is not. The plate design, separators and plate spacing on our AGM cells is much different than wet cell technologies. To use the wrong type of charger subjects the battery to conditions that will distort the plate material, cause internal arcing or chemical deposition that lead to cell failure, excessive heat and/or eventual rupture and leakage. Shortened life is of little concern when compared to these events. As to the KOP charger... Both the newer multi current and the previous single current chargers, the charge rate, timing and float specifications when selected at the 6 amp levels approximate the MK and Yuasa specifications for battery charge time, current and voltage and eventual float specifications. While the manufacturer product sheets differ in some respects, close examination will reveal different methods for stating and verifying the same criteria. To the referenced Stanley Charger... All the literature available on this device specifically states it's intended use is for automotive style, wet cell batteries. The manual has an extensive safety list for users and several references to automotive batteries. There is no reference made to AGM. In addition, there is a "quick start" feature that forces full current (with no smart charge control) to the battery under charge. This option is the button directly next to the "charge" button. If you ask a UL Safety Person about this charger (I have) the first question you will have to answer is "Does this carry a UL sticker?" I have found none and UL is not listed on the manual. As to the belief that the higher charge current/voltage is buying additional power and therefore accurate shooting... A battery that is removed from a charger will measure a higher, but temporary, terminal voltage due to the nature of the chemical reaction during charging. This is called "surface charge". This additional voltage will rapidly decrease with load and will also decrease to nominal terminal voltage with time. This means that on the off chance your first shot is accurate due only to this "surface charge", no other shots can/will be affected by this temporary increased voltage. I submit that there are several other variables that are involved in accuracy of shooting mechanisms. Those are losses in battery cables, terminations, and connectors, temperature of the battery during charging, temperature of the motor used for shooting, the shape of the ball, the inflation and the point of contact with the surface of the ball material. Every team that has an accurate shooter has learned to overcome these variables in some fashion that is repeatable or their design is such that the effect of these variables is minimized. If a team expresses that there is a significant difference between batteries, LRIs will gladly examine your electrical systems and point to components that can be affecting your performance. They will also help you overcome these issues when possible. Finally, as to the consequences... Many are stated in various parts of the manual chapters, in both the Game and Admin manuals. All of the listed staff and volunteers as well as the venue staff can have input. I know of at least one team that was forced to remove their robot from a venue by the venue staff, as a fire hazard. Please consider all manual sections in addition to your desire to be given an invitation to play on Saturday afternoon before making a final decision. |
Re: Be aware of battery and charger inconsistencies!
We have received an official answer from the Q&A:
Q435 Q. We are using Stanley 15 amp automatic battery chargers to float our charged batteries. Adhering to the safety guidelines, no battery is charged using more than 6amps. Is this acceptable at competition? A. Per the FRC Safety Manual, you should not be charging your batteries at higher than the manufacturer's recommended rate. The fact that your charger may be capable of charging at a high rate is not an issue, the question is how the charger is actually being used. Using a charger to float your charged batteries should not put you over the manufacturer's recommended rate. |
Re: Be aware of battery and charger inconsistencies!
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Re: Be aware of battery and charger inconsistencies!
I highly suspect that some inspectors will be spot checking you guys quite frequently. Just sayin', use at higher than rated charge is still illegal, and having the capability (not that you use it) is going to attract some attention. It's like why you really don't want to speed in a bright red sports car--the cops see "bright red sports car" and pay extra attention to it.
In other words, go ahead, but be prepared for extra attention from inspectors (and I recommend having the Q&A printed out--and taped to the charger if you can do that safely, otherwise just with you in the pit). |
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