Re: Batteries
 

Do you typically run a fresh fully charged battery at the beginning of each match or is it possible the batteries had been used in one or more matches previously?

Our team rule is one match per battery per day. We put a freshly topped off battery in the bot at the start of every match and don't use it again that day if we can avoid it.

Re: Batteries
 

This was in 2009, during Lunacy.

We DID use a fresh battery every match, and still do.

One aspect that drained our battery, we had 2 large fans on the back of our robot. If we got into a pushing match (which, in lunacy, happened a LOT. And pushing matches draw a lot of current from the CIM motors), we would activate both of our rear fans, at 100% throttle, which caused a HUGE drain on the battery. However, it almost always would win the pushing match...

Re: Batteries
 

From the inspections I did, I didn't see many teams using many batteries other than MK and Enersys. Most teams don't do any testing or even keep track if a battery is good or not. It would be nice to know if any of the other brands are better than what we have been using.

Re: Batteries
 

We have a stock of batteries from the last few years and have only just retired our batteries from our first season this past year. We had the option to get a few batteries from our local Batteries Plus store with an excellent discount and gave them a shot.

They were the Werker brand battery and we had some good experience with the brand through electric car racing. We used them all season and never had an issue, but they did test low in the available current department and no load voltage. They tested comparable to Enersys batteries that were two seasons old when load tested. Of our ten batteries that we brought to competition, the Werkers were placed at number 9 and 10 in our rotation behind every other battery we used. I would have to get into our shop to see the numbers, but I do remember them being comparable to a three year old competition used Enersys battery that had also been used for practice for two years.

They also seemed to not last as long by the ever so scientific kids driving until the lights go out method.

Again, we still used them and never had any performance issues with either of them in competition.

Re: Batteries
 

I took a look at the most recent suite of CBA tests we ran on the 13 new Enersys batteries we got this build season (12 purchased new + 1 KoP). The test were run the week before our first event. We ran 4 separate 50A tests with cutoff voltages of 10.5V (same cutoff Allen uses). The 13 batteries ranged from ~3AHr to ~5.5Ahr. Each of the tests take about 5-7 minutes to complete.

We have an off season next weekend so maybe we should run them through again and see how they are holding up. I'll add it to the list of stuff to do this week!

Re: Batteries
 

We test down to 7 volts. This will show if any cells are bad more clearly. See previous thread with graph.

http://www.chiefdelphi.com/forums/sh...ad.php?t=82258

-Hugh

Re: Batteries
 

How would that not be seen on a test down to 10.5v, the amphr rating would be very small on that battery.

Re: Batteries
 

At some points during long practice we would get as few as 5V through during a high acceleration demand, and we never got brownouts either

Re: Batteries
 

Yes but was the resting battery voltage actually at 5v? The CBA testing at 7A over several hours isn't going to be able to simulate a 200A draw on a battery no matter what we do.

Re: Batteries
 

Allen,
I test down to the level shown on graphs just to prove that the battery matches published performance. However, not all cells are created equal. While the overall battery may perform well when fully charged, some cells may die off before others. Every cell that runs out of steam drops the output by 2 volts. See one of my early (search) posts with graphs done on a really bad battery. One cell runs out rather early and then another and then finally a third. That test is one of the reasons I like the CBA so much. A Battery Beak or other short testing method would not show this problem. It might show up as a change in battery impedance but I don't have any real data that I can quote for that condition.

Re: Batteries
 

Have you had a battery that only showed this behavior by taking it down past 10.5v? We've found bad cells before the voltage drops off rapidly and the batteries have much lower capacity.

Maybe I'm missing something but I don't think a battery with a bad cell would have a comparable AmpHr rating to other batteries for any sufficiently long test, am I wrong here? Is a 10.5v cut off not a sufficiently long test?

Re: Batteries
 

Our local Interstate Batteries store is a team sponsor. We've been using their batteries for 2 years now with no problems.

Each year we take all our batteries to the local auto parts store for testing and discard those that don't pass. And of course we always run matches with fresh batteries! But after reading this thread I wonder if we should do a more thorough test.

Re: Batteries
 

After using batteries for a parade on Saturday, the Werker batteries we have won't complete a charge cycle on our Battery Tender maintainer. They also are getting quite hot after charging at a 2 amp max charge. I think these ones are going off to be recycled. It's a shame they didn't even make it one full year.

Re: Batteries
 

Why so many every year? As long as you take care of them during the off-season, they should be fine for many seasons of use. My team still keeps around a couple of 2011 batteries because they actually perform just as well as the batteries we got this year.

To my knowledge, the lowest our DS has ever read in-match was 5V during a brutal pushing match. It is very important to know how your batteries perform at low levels.

We do our best to avoid using the same battery more than once a day. Our battery box holds 12 batteries and uses a raspberry pi to automatically cycle through the batteries and charge 3 at a time, so we never have a problem with having enough charged batteries. Of course, there are times that a battery must be used more than once per day, and as long as it has had plenty of time to sit, it should be okay.

Re: Batteries
 

We like to run new batteries. One of the reason we are testing them more now is to see if we can judge the differences better and maintain them better. We also give away some of the batteries that we no longer think we need to young teams. $250 in batteries isn't that much for what could be the most important part of the robot, with out the battery nothing else works.