Battery life?

[bduddy]

Just a quick question that I couldn't find an answer to: How long would a typical FRC battery last under the "full load" of typical match conditions?

If anyone cares why, I'm turning around new game ideas in my head, and I'm in the camp that thinks 2:15 is a bit short....

[DonRotolo]

If we guess at 80A average continuous draw, and guess at 8 AH capacity at such a high discharge rate, we get 1/10 of an hour until voltage drops to about 9.4 volts. At 40A, 2/10 of an hour.

Don't think "first Q match of the day", think "Intense Einstein Activity" for your current draw estimates.

[Mike Betts]

Originally Posted by bduddy

Just a quick question that I couldn't find an answer to: How long would a typical FRC battery last under the "full load" of typical match conditions?

If anyone cares why, I'm turning around new game ideas in my head, and I'm in the camp that thinks 2:15 is a bit short....

You should be able to get a minimum of 3 full matches on a good battery under competitive conditions.

We usually limit to 2 matches on a battery and, if we have an ample supply, we change the battery after every match.

[MagiChau]

Originally Posted by Mike Betts

You should be able to get a minimum of 3 full matches on a good battery under competitive conditions.

We usually limit to 2 matches on a battery and, if we have an ample supply, we change the battery after every match.

We have 6 batteries including the one on the robot in cycle after every match.

[M.Wong]

Originally Posted by MagiChau

We have 6 batteries including the one on the robot in cycle after every match.

Same setup. We don't even take the chance to use a battery for two matches. This also depends on how old the battery is and what it has gone through. We've had batteries last for three years with no problems, others only last for a season.

[slijin]

It depends on just how inefficient/efficient your robot is, but as a general rule of thumb, swap the battery every one or two matches if you can.

[Karibou]

Originally Posted by Mike Betts

You should be able to get a minimum of 3 full matches on a good battery under competitive conditions.

We usually limit to 2 matches on a battery and, if we have an ample supply, we change the battery after every match.

That's impressive. If we put in a battery that isn't at full charge at the beginning of the match, it dies during the endgame or slightly before. I don't know how long they last beyond a match length, because we've never tried it. We know it doesn't work for us.

We have a cycle of 6 batteries. After experiencing several inconsistancy issues with older batteries last year, we purchased 6 new ones for this season. Even then, we discovered at our second competition that one of the batteries was a dud and we could not last half a match before we saw some failure in robot performance.

[Al Skierkiewicz]

Please keep in mind that perhaps as much as 25% of teams are running a battery into the ground by match end. These are due to a variety of factors but mostly due to inefficient drive trains or multiple turns with sticky wheels. With some experience it is easy to pick out robots that would die if matches were extended.

[AdamHeard]

Originally Posted by Al Skierkiewicz

Please keep in mind that perhaps as much as 25% of teams are running a battery into the ground by match end. These are due to a variety of factors but mostly due to inefficient drive trains or multiple turns with sticky wheels. With some experience it is easy to pick out robots that would die if matches were extended.

Also, many teams have not taken care of their batteries properly, so they are starting off with batteries that are incapable of even being close in capacity to a new battery.

[dez250]

Originally Posted by Karibou

We have a cycle of 6 batteries. After experiencing several inconsistancy issues with older batteries last year, we purchased 6 new ones for this season. Even then, we discovered at our second competition that one of the batteries was a dud and we could not last half a match before we saw some failure in robot performance.

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.

[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.