I haven’t seen this communicated on Chief Delphi yet, so I wanted to get this out there.
I know of three teams this weekend that had a cell/cells in their batteries die.
The battery appears to be fully charged, but when you put it on the bot it drops to 6-7 volts (or lower) very quickly. It killed a match for us, and two other teams we talked to have also had issues with the 2008 batteries dying on them.
Let’s get a record going - if these batteries are indeed an issue as I believe they are, we need to get word to First so they can rectify the issue. That is a lot of money to spend on batteries only to have them die in less than a year. We’ve still got 2006 batteries (from the old manufacturer) that are working!
We had this happen also, it says it is fully charged but as soon as you start the match it goes to 6-7 volts. Also we lost of our playoff matches that we could of won. BTW, the batteries are getting really hot, it melted the pneumatic tubing, there is no short on our whole board. We double checked.
At the beginning of the build season, the TechnoKats tested everyone of our batteries from previous years and from this year, and the ones from this year had mid to low range on them. I found this weird as we have batteries dating back to 2001 and we have never had problems with them. Also when we did the test, last years were the strongest! That was shocking to me that 1 year old batteries were stronger than new batteries from the same manufacturer.
They were charged. We’re not using the somewhat…lacking… charger from first either - we’re using a far better one. No - this is definitely something going on with the batteries. It’s nice to see other folks reporting the same thing.
We know the standard rules - you don’t put them on concrete, never overcharge them, don’t let them sit with no charge on them at all, fully discharge them before charging them again…
Unless the cases are unusually conductive, or there is a significant thermal gradient between the top and bottom of the batteries when they are placed on said concrete (or whatever they might be resting upon), I think you can stop worrying about putting them down on concrete. See the page at this URL http://www.thebatteryterminal.com/TechTalk_Batteries_on_Concrete.htm
For you who have had battery problems, the absolute cause comes down to a variety of issues. I have been in contact with the manufacturer who is testing batteries using the same charger supplied by First. To date they have not reported anything out of the ordinary. Teams should not compare MK batteries with previous years as they are different in construction. There is a difference, between gell cell batteries and the MK AGM batteries. It would appear that the MK batteries are a little more sensitive to shock and mishandling. The hotspots in a battery case are likely the result of two or more plates in a cell being forced together by this rough handling. The result is a short in that cell. Heat is an indication of high current flow. AGM batteries are also sensitive to overcurrent charging. Charge currents higher than 6 amps cause the plate structure to deform also resulting in cell shorts. This is also true of batteries that are stored at high temperature or repeatedly put on charge without rest. Allow batteries to cool before returning to charge following a match. I have also noted many teams who lift and carry the battery by the leads. The battery is not designed for that and internal damage is the result. If you have team members who practice this method, suspect that as one of your causes.
Finally, all batteries have a finite life cycle. First batteries since 2001 all have been about 400 charge/discharge cycles max. Repeated high current discharge (i.e. full discharge in a single match) shortens this life by half or more.
We were experiencing problems every other match at IRI and we kept checking our electronics but could not find anything wrong…
we told Cory from 254 and he told us they had similar problems in the past… he told us to check the charger… we took the charger out of the rotation, and didnt have any more problems the rest of the competition. The charger had no visible signs of failure, or malfunction. Cory really helped us out!
We had one bad battery this year, but that was due to the top of the battery coming loose and leaking somewhere. We disposed of it properly, but it took a few minutes to figure out why it wasn’t working. I noticed that the top was lose, peeled it back, found a rubber cap missing and an empty cell.
Speaking of battery problems. Anyone know why the battery on my laptop will last for 30 minutes at 70+% then instantly (and I really many instantly) go to 7%. It’s about a year old.
Please add another team to the list of documented issues. We also competed at Kettering this weekend and had batteries go from 12V to 5 or 6 during the match. They were extremely hot when we took them off. We only have 07 and 08 batteries as we are a newer team. We will segregate and monitor. Is there anyway to absolutely check for a “dead” cell?
Mentor HAZMATs - 2145
These batteries are made up of 6, 2 volt cells in series. A bad cell will be indicated by a two volt drop in terminal voltage. If the cell is truly dead, the battery will read 10 volts or slightly higher when removed from the charger but not higher than 12 volts. Each cell is made up of several plates, interleaved positive and negative, with a glass mat separating the plates. Should the electrical connection to any of the plates be broken then the cell will have reduced capacity. If any of the plates should be touching then the cell will self discharge causing high internal heat. There are two tests which will determine which defect is causing the problem.
Charge the battery and remove from the charger. Attach a voltmeter and monitor the terminal voltage. A good battery will show slightly higher than 12 volts for several minutes and then fall to 12 volts. If it begins to fall below 12 volts in the first 30-60 minutes and then remains at 10 volts (or a multiple of 2 volts), you have a battery with damaged plates touching in an individual cell. One area of the case should be warmer than the rest of the case. If the battery remains at 12 volts, then you must load test it. We use the Mountain Radio CBA-II. With this computer based tester, you can draw a steady 7 amps and chart the terminal voltage and it will calculate the amp-hour rating. A cell with a few broken plates will be indicated by an drop in terminal voltage of 2 volts before the battery becomes discharged. The following picture compares three bad batteries with a good battery using the CBA. You will see in this graph the normal discharge curve in black, two highly reduced capacity cells in blue, a single reduced capacity cell in green and a internittant cell in red. The “green” battery was reported to be suspect during practice at home where the robot was run for 15 minutes at a time. The “red” and “blue” batteries were also discoveered during practice but the intermittant nature of the red battery confused everyone until this test. Without the constant discharge, all of the batteries showed as 12 volts at the OI, when the robot was not moving except the “red” which showed a varying voltage.
It is likely, all of you have batteries that have one or more cells that are diminished capacity without knowing it. This is particularly true of batteries that are from 2006 or earlier due to the number of charge/discharge cycles they have been put through.
33 has had issues with a couple batteries, but we determined it was due to really hard impacts. This years game lended itself to some rather spectacular crashes. 1 battery had a visible deformation, and the other had a noticeable hot spot right after the match. As Al said we suspect internal damage on both of those batteries (the bulged one was rather obvious.
As pointed out by others, make sure you read up on your batteries, Lead acid, NiCD, NiMH, and Li-Ion all have unique peculiarities to them. Some like to be deep cycled, others will get destroyed doing this. Some have memory, some don’t. Some give off a superficial full-charge when really they aren’t full. Assuming whats good for one type is good for another can be very dangerous and at a minimum, costly.