My team was wondering about what chargers are legal this year. We have heard that in past years there has been a 6 amp limit but this year we cant find anything talking about chargers in either the game or administrative manual.
I consider 6 batteries to be an absolute minimum for a competition. Now that we are a district, with 12 matches (at least) per event, this became an even more solid conviction. We have a charger cart with four chargers that makes us comfortable with 8 batteries. This partly due to doing only one match per battery and monitoring the battery state after each match just before it joins the charging cycle. At matches we set the charge rate to 4a.
Giving each battery a name will also help you keep track of the good versus the marginal performers and allow a cogent cycle of use to be formed for them. We use a battery beak to monitor the battery state. They are pricey, but the beak helps you manage your several hundred dollar investment in electron storage and feel confident that your robot has as decent a chance at getting through a match as you can give it. You also get the chance to see which of your stable of energy may only be suitable for practice or control system testing.
With 6 CIMs, you’ll most likely want a new battery every match. This will come up most in eliminations. There are extra batteries available for teams in eliminations that need to play back to back matches, but plan on having at least 6 batteries fully charged and ready to go for eliminations.
I think the amount of batteries will depend on how you use them. Previous years with us not using pneumatics, 4-6 batteries with two chargers was very adequate.
If you have a lot of pneumatics and plan on pre charging a bunch of tanks in queue you could need quite a few batteries and chargers to keep up.
This year we are using a lot of pneumatics and are bringing 10 new batteries and some of our previous years batteries for pit demos (LED shows and such for the pit visitors). We will be bringing 5 (6amp) chargers as well. We also plan on using the previous matches battery for the pneumatic pre charging and swapping in a fully charged battery when the robot is ready to load on the field.
Yes in between SF 1 and SF 2 we switched out the main breaker. After that it never flipped again. We were also cooling it between matches. Realize we had 8 motors for our swerve drive. 4 CIMs and 4 BB RS775(I think). The wires between our battery and PDB were getting quite warm so we are planning on lowering the gauge for nationals to better handle the current.
I saw three robots with tripped main breakers at the Boilermaker regional. In each case, only one of the wires was warm. The apparent cause was not too much current, but simply too much heat from a poor connection caused by a loose nut where the wire connects to the breaker.
Loose main power connections – on battery terminals, SB-50 connectors, main circuit breakers, and/or Power Distribution Board inputs – were unfortunately very common. It’ll be interesting to see if the logging feature of next year’s PDB will help convince certain teams that their general animosity toward “the FMS” is misplaced, and that their loss of robot control on the field can usually be prevented with a bit more attention in the pits to checking and maintaining the robot’s electrical system.
I think the drivers just became a little less aggressive in the subsequent matches as I had suggested. If you go back to the old ways, this problem will revisit you. You know I have a vested interest in keeping you guys running, you gifted me and I am returning the favor.
Big thanks, Al! We did make some subtle adjustments to our drive style and the issue did not occur once after we made the breaker swap like Kyle mentioned. We were icing it down between matches, as well, and are looking at all of our options for making sure we keep that breaker cool and untripped in St. Louis whenever that defensive intensity cranks up. Thanks again for all your help!
I guess I’m hijacking the thread a bit but want to capture a potentially important “gotcha” issue related to battery connections that Alan’s post helped to job some cobwebs in my brain.
Loose main power connections – on battery terminals, SB-50 connectors, main circuit breakers, and/or Power Distribution Board inputs – were unfortunately very common. It’ll be interesting to see if the logging feature of next year’s PDB will help convince certain teams that their general animosity toward “the FMS” is misplaced, and that their loss of robot control on the field can usually be prevented with a bit more attention in the pits to checking and maintaining the robot’s electrical system
At the MI Howell district event we even had someone (FTA?, Inspector?) come by and inspect our PD distribution board connections (12V & ground) to the battery to help eliminate this potential problem issue (assume he was going around to all teams… we had not reported any issue). I can’t remember precisely but he quoted something like “teams commonly place a lock washer underneath the battery connection to the PD board when, if used, it should be placed on the top, next to the nut”.
Al S, is there any “best practice” on this battery connection to the PD board and main breaker that teams are missing?
I assume there should be a direct connection from the battery connector to the PD board post. Should the FRC
documentation trail capture this somewhere?
It is likely that someone visited you because the tracking logs showed you undervolt. The terminals on the main breaker and the PD are hard metal compared to the soft material used for the battery terminals and they don’t get handled as much. The lock washer between the battery terminal an the wire terminals keep the terminals from twisting and loosening the hardware. Both the PD and the main breaker have substantial hardware with lock washers. Most often these wires are also tied into the robot so that they cannot move and twist unlike the battery. Any loose connection in the primary wiring (All the #6 AWG) will cause significant voltage loss under the current demands of our typical robot. These losses are what shows as melted SB50 plugs and wiring and to a much lesser degree, tripped main breakers.
I hate to disagree with all of you but if you read the Enersys application manual for our batteries it does clearly state the maximum charging rates on page 6. The confusion seems to be the fact that the bolted terminal line says 6CA. All the other columns are specifically amps. If you go to page 17 you will see the definition of CA and the line above with c-rate.
The actual max charging rate on our battery is 6 times the Ah rating or 6*17.2 for a max of 103.2A. Would anyone ever charge at that high a rate? I would expect not. If you look at the other columns in the chart on page 6, why on earth would you be able to charge at 75A maximum through a normal spade terminal and only 6A through a physically bolted connection. That just doesn’t make any sense at all. The most important thing with these batteries is not the amperage that you charge at, it’s the voltage which should be 2.35-2.45 volts per cell or 14.1-14.7 volts.