Re: Leaking Batterys
 

the battery came off of the charger at around 13v we tested it. it went to 10.25 after driving for about an hour, but the robot was not on for all of that time

Re: Leaking Batterys
 

Unless it sat for a few hours first, or you put a small load on it for a few minutes before you tested it, you were measuring the battery's "surface charge". That tells you almost nothing about the actual state of health of the battery. A badly sulfated plate, or even a broken one that only has a small fraction of its bulk actually connected, can still be charged to full voltage. It just won't have anything like the capacity it should.

A stack of hearing aid batteries can also read 13v, but they won't run a robot.

Re: Leaking Batterys
 

On our driver station after running the robot for awhile it read at about 12.6 so the battery is in good condition. They have only been to one regional.

And for the hearing aid batteries... it might be able if you stack them and then wire them in parallel.

Re: Leaking Batterys
 

Thank you for this wealth of knowledge. As a former FIRST student and 3 year mentor i did know that running the batteries below 10.5 volts can ruin them.

All of the batteries are stored in upright positions and mounted in the robot in a horizontal position. None of them have been dropped or damaged in any way. We think that it's a combination of the battery voltage dropping and rookie luck of getting 2 bad batteries.

As a result of this, the team is looking into doing a load test this summer to further our knowledge of the batteries and understand for ourselves why the problems occurred. Thanks for the link to the load tester!

We are also looking into making is a rule to mount batteries in a vertical position in the following rules to help avoid any possibility of leaking because of the orientation of the battery.

- Ryan Epperson
Team 3256 Mentor

Re: Leaking Batterys
 

I know this is somewhat off topic, but I was under the impression that AGM batteries were more impact resistant than gel cells?

Re: Leaking Batterys
 

Sam,
There is relatively little difference in the two for impact resistance. The gel uses a cardboard separator and the AGM uses the glass mat. There are tradeoffs in using either technology but the AGM has proven useful for slightly better energy density in our application for the same size case. Although I have no data to prove my theory, I believe that certain impacts can lead to plates punching through the glass mat and shorting a cell. There just seems to be more shorted cell failures with the AGM over the gel cell in our use. MK did some forensic analysis of dead batteries over the past few years. They found nothing significant.
I agree that the CBA battery analyzers from West Mountain Radio give a good indication of battery health. They are repeatable and allow comparison (overlay graphs) over several tests. As pointed out, they can be set to current draws that are far less than our intermittent loads. However, a 7.5 amp draw from an 18 AH battery is sufficient to tell the health of the battery and calculate amp hour ratings that match the manufacturers spec sheets.
Please be careful when listening to anecdotal info on battery use and performance. Some teams use high current chargers especially when not in competition. Team batteries are stored in unheated areas in winter or uncooled areas in summer and may be left uncharged for months at a time between seasons. All of these lead to early battery failure. Above all realize that these batteries under normal conditions only have a 400 charge/discharge life. Under our use of high discharge rates, charging while warm and the other conditions described above, the battery life is significantly less.

Re: Leaking Batterys
 

There was one additional item I forgot to include. All teams will at one point or another read less than 7 volts on their battery under load. This is not an indication that your producing any damage to your battery. It is just an indication that you are drawing enough current from the battery to cause a voltage drop across the internal resistance of the battery and the resistance of the wiring between the Crio and the battery. The battery internal resistance is the normally the greater of these at 11 mohms. However, loose electrical connections and improper crimps can also account for high resistance. I have seen several teams who lost the hardware for their Power Distribution Panel and substituted 1/4-20 hardware. The PD uses metric hardware so substituting the 1/4-20 prevents you from making a tight connection to the PD. 100 amps across 10 mohm=1 volt.

Re: Leaking Batterys
 

Entirely apart from the electrical problems that substitution causes, if you manage to tighten a 1/4-20 nut on an M6 stud, you'll ruin it, probably by snapping the stud off. Don't do that; the studs can't be repaired—not even by replacing them entirely.