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.

[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.

[Mike Betts]

Originally Posted by Karibou

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.

Kara,

Even a new battery with a fresh charge will give you low voltage if the load is high enough.

I have uploaded a battery test I performed for team 177 back in 2006. You will find it here.

This was the last time I did an "exhaustive" test. I usually only test suspect batteries...

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.

The drive team needed to learn that, if they were pushing against another robot and shooting at the same time, their shooting distance would be compromised.

You will also note that the batteries did not significantly degrade over time. In fact, ignoring batteries dropped on a concrete floor or having the terminals ripped off because they were handled by the wires, I don't think we have had a single battery failure in less than 7 or 8 years of use and abuse...

We have always used the KOP chargers. We always store the batteries in a charged condition for the summer. Storage temperature is always between 55F and 95F (we have unheated/unconditioned storage). We always charge a battery as soon as possible after use. We try not to leave batteries on a charger more than 48 or 72 hours.

I would suggest that your team invest in a clamp-on DC amp-meter and a good battery analyzer and do some engineering in the off season to understand what is going on.

And before I hear from the peanut gallery: Yes, the current KOP batteries are a different part number but, IMHO, their performance should be very similar...

Regards,

Mike

Edit: At our next competition, I tested two batteries as they came off the field after a match to measure the charge left. This was my criteria for recommending "A battery will definitely last two matches and you can get three matches from a battery if you really need to.".

[lpickett]

My husband and I procured a battery load tester for the team. We load test the batteries at the first of the season to see if there is a need to buy new ones. Anything that is 50 to 70 percent is relegated to use for shop use, not competition. They can also be used in the stands for the laptops, if necessary. There was a battery cart built this year to hold six chargers and six batteries. The team cycles through them to make sure we have not power issues. My husband has also been teaching the students to solder the connections and shrink-sleeve to insure no loose connections.

[Al Skierkiewicz]

Originally Posted by lpickett

My husband has also been teaching the students to solder the connections and shrink-sleeve to insure no loose connections.

Linda,
I hope that means soldering the wire terminal after wire insertion instead of soldering to the battery terminal. I have frequently suggested teams use an external tooth lock washer between the wire terminal and the battery terminal to prevent slippage. Using locking washers on the hardware is simply not enough to prevent loosening on this critical termination. All of the above with heatshrink added is an ideal solution.

[wireties]

Originally Posted by lpickett

My husband and I procured a battery load tester for the team. We load test the batteries at the first of the season to see if there is a need to buy new ones. Anything that is 50 to 70 percent is relegated to use for shop use, not competition.

We take all the batteries to a local auto parts store for load-testing at the beginning of each season. They will test them for free.

The batteries need to last for a single match w/o impairing performance. Normal engineering practice is to design for a 2X margin so our robot generally will run 2 matches on a single charge but we NEVER do that (always replace the battery for a new match).

HTH

[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.

[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.