Chief Delphi - 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.