Battery life?

[Karibou]

Originally Posted by dez250

Kara this sounds very interesting and I would go on a limb and say it is not the batteries themselves but how your team may be treating them. If you have gone through seven batteries in two years, I would look mainly at your chargers and how students are handling them. While it may not seem evident, handling the batteries by the cables or lugs directly can cause major damage, along with the obvious of dropping a battery will damage it. The plates that create the chemical reaction in them can shift or even pull out partially through mishandling.
Also what type of chargers are you using, and what connectors are on them? If you are not using a "smart" charger at the right current rating, you can be over or undercharging the batteries, thus again causing damage. Finally I would look at the connectors on the battery chargers, if they are alligator style clips, change the connector. The gator clips scratch the anderson connectors contacts and create an inefficient connection later on when in the robot. I would cut off the gator clips if present and swap them out for anderson half connectors, the same as used on the battery to make a solid connection.
As for failures with these batteries, if you see the battery dropping in 2 volt increments that is showing a failed single cell (per 2 volts) and means it is time to replace that battery.

I'm sure that a lot of the issues WERE caused by improper treatment of the batteries. As much as we stress how important it is to not carry a battery by the cables, it inevitably happens occasionally when someone is in a hurry between matches. Some of the batteries that we retired and replaced this year were as old as 2007, and had suffered through four full seasons of use and abuse. I know that a few of them had indeed been incorrectly charged.

We do use the Anderson half connectors instead of the gator clips. I don't know offhand what kind of chargers we use. We replaced our age-old ones this year because we had the money, and the old chargers were going bad in one way or another. We also acquired a load tester during the fall, and have used it.

Originally Posted by Mike Betts

We did the tests because the team thought that we had "bad" batteries. Several batteries had been marked as "bad" by the pit crew during a regional competition. That year, the game was "Aim High" and the requirements of the shooter mechanism, drive system, pneumatics pump, et cetera, was so great that the battery voltage would crash during a match.

I believe that, though I don't think that it was the case for us this year. We had one battery that consistently died during matches. As none of the other ones gave us problems when fully charged, I'm inclined to think that the failures were not coincidences related to gameplay.

Thank you both for your advice. Next time I have a chance to talk to my mentors with the batteries next to us, I'll pass on the information.

[Al Skierkiewicz]

Kari,
Batteries have a finite life. The batteries we use are speced at 400 charge/discharge cycles under normal use. Our use is pretty heavy with long periods of no use in between. I estimate a team can get realistically no more than 300 if their robots use a lot of current or 350 if they are more efficient. If you are still practicing with 2007 batteries you are getting some decent life.

[fsgond]

Our team uses 5-6 batteries changed out after EVERY match. We want our robot to have top performance during every match. We usually have a lot of motors and an air compressor that runs a lot of the match, so our battery is pretty low by the end of the match.

Also we buy all new batteries every year. Batteries from the one year previous are used for practice in the shop and programming and testing the bot in the pit.

Now to the question that you originally asked, I think that you could extend the matches a bit, but no more than 1 or 2 minutes.

Honestly from a field coach position, the matches are very fast, and done before you know it. Also I am not sure that I could take the stress for another minute or two.

[Warlord]

When I drive the practice bot we usually go for about 10-15 minutes before I see a noticeable drop in the performance of the robot (as in, it stops driving top speed). Sometimes a little bit longer.

Past robots haven't been quite as efficient, sometimes they have only lasted like 5 minutes or so.

No matter what though we always change the battery after every match, just to be safe.


I'd say that if you are just barely making it through a 2:15 second match with a full battery, there is a serious problem. Really anyone should be able to go at least double that without absolutely having to change the battery.

[Cory]

This thread has strayed from the OP's intent, but we buy 10 new batteries every year. We put so many hours on them throughout the season that they inevitably end up not being as good as new ones. We practice during the current year with the previous year's batteries. We never use a battery in a match more than once. We won't even use a battery that's been on the bot in the pit for system checks/testing.

You can never have too many batteries or be too careful with them. It is the most critical part on your robot.

On topic, matches will not get any longer unless more than 6 teams are on the field at once. Just won't happen from a scheduling standpoint.

[Don Wright]

We tell Gail at the beginning of the season "We need enough batteries for the season." and so she orders 110 so we never have to use a battery twice...

Just kidding...

Like Cory, we order a new set of 12 every season and use them only at competitions, never back to back (usually only once per day or twice at the most for each competition).

We use the previous year's batteries for practice and still swap after each practice match...

The 2 year old and older batteries are for the scrapbots that we use for defense practice...

As for how long...depends on a lot of things... Our 2006 robot used 10 motors I think including several that ran almost all the time (two big CIMs, two FP's), 4 little CIMs in the drive, and two bane bots plus the pump and we would almost kill the battery in 2 minutes...

[bduddy]

Originally Posted by Cory

On topic, matches will not get any longer unless more than 6 teams are on the field at once. Just won't happen from a scheduling standpoint.

I was actually thinking about 4v4 with one robot off the field in a "pit area", and something like :30 + 4:00 . From this topic, it sounds like the batteries could likely last for that long...