Best way to charge batteries

[electroken]

Originally Posted by Ether

They may be accurate for what they do. But they do not measure the battery's capacity.

I have an old battery in my shed that passes with flying colors when tested with my "125 amps for 10 seconds" tester. But it fails miserably when subjected to a capacity test. So even if the high-load-short-duration test doesn't harm the battery, it doesn't really tell you what the true health of the battery is.

+1

We have a battery that tested as "good" with the Battery Beak and then minutes later dropped dead halfway though a semifinal match last weekend. Fortunately, it did not affect the outcome of the match.

Battery #6 is going to that farm for old batteries...

[ILAMtitan]

Thanks to everyone who pointed out the shortcomings of the Autozone test. My team uses a CBA, and I've just heard it recommended around the pits.

I personally like the CBA, but it really only measures ampacity via a low current draw, not real robot loads. It has the amplifiers, but those are out of the price range of most teams.

Does anyone have recommendations on a good way for a team to do their own controlled 150A discharge test? Even the Beak only does an 18A load test.

[Mr V]

Originally Posted by ILAMtitan

Thanks to everyone who pointed out the shortcomings of the Autozone test. My team uses a CBA, and I've just heard it recommended around the pits.

I personally like the CBA, but it really only measures ampacity via a low current draw, not real robot loads. It has the amplifiers, but those are out of the price range of most teams.

Does anyone have recommendations on a good way for a team to do their own controlled 150A discharge test? Even the Beak only does an 18A load test.

Spend the $20 bucks on a load tester at Harbor Freight. http://www.harborfreight.com/100-amp...l#.UzMU04WtJCA That is the closest you'll come to finding out how your battery performs with robot like loading. Yes that is a 100a unit but you can find 125a and 150a units too, but will likely pay much more since you'll have to go someplace other than Harbor Freight.

The CBA might be great for testing the battery against its designed usage but we don't use the battery anywhere near that discharge rate. The Beak is a great way to test the SOC and internal resistance but that only tells part of the picture.

[Bill_B]

How do you recommend hitching an FRC battery to that load tester, Mr V? Using clips to grab inside the battery's anderson connector is discouraged due to the scarring it can do on the faces of the terminals inside them.

[ILAMtitan]

Originally Posted by Mr V

Spend the $20 bucks on a load tester at Harbor Freight. http://www.harborfreight.com/100-amp...l#.UzMU04WtJCA That is the closest you'll come to finding out how your battery performs with robot like loading. Yes that is a 100a unit but you can find 125a and 150a units too, but will likely pay much more since you'll have to go someplace other than Harbor Freight.

The CBA might be great for testing the battery against its designed usage but we don't use the battery anywhere near that discharge rate. The Beak is a great way to test the SOC and internal resistance but that only tells part of the picture.

Thanks for the tool link, I'll have to pick one up for the team. I think your point about these all telling part of the picture is most important here. Being able to test all the aspects of your batteries is very important, especially with how much we rely on them.

A beginner team should be ok with using new batteries and a multimeter along with the driver station debug plots to evaluate battery health, but getting more advanced tools should be a priority for their second season. As you start to develop an arsenal of batteries, with some being several years old, proper care and testing to evaluate worthiness before regionals is critical. Combining good charging and storage with proper evaluation can really set your mind at ease about this when you're rushing to the next qual match.

Bill_B, I would just replace those jumper cables with an Anderson SBS (the big one on the batteries). It might not be a bad idea to put a breaker in line either. Then you just plug in the battery, and flip the switch to connect it. At the push of a button the test stops.

[Ether]

Originally Posted by Mr V

The CBA might be great for testing the battery against its designed usage but we don't use the battery anywhere near that discharge rate

The 125 amp for 10 seconds might be great for testing the battery against its ability to start a lawn tractor, but we don't use the battery anywhere near that short duration in competition.

I suppose it's not impossible in principle, but in practice I've never seen an FRC battery which will convincingly pass a CBA-style capacity test and yet fail a high-load-short duration test. I can't say the same for the converse.

[cgmv123]

Originally Posted by Bill_B

How do you recommend hitching an FRC battery to that load tester, Mr V? Using clips to grab inside the battery's anderson connector is discouraged due to the scarring it can do on the faces of the terminals inside them.

Cut the wires and solder them to a spare Anderson connector. If you need the clips back, you can connect them to another Anderson connector.

[Fej]

Originally Posted by ILAMtitan

A beginner team should be ok with using new batteries and a multimeter along with the driver station debug plots to evaluate battery health, but getting more advanced tools should be a priority for their second season. As you start to develop an arsenal of batteries, with some being several years old, proper care and testing to evaluate worthiness before regionals is critical. Combining good charging and storage with proper evaluation can really set your mind at ease about this when you're rushing to the next qual match.

My team is 10 years old. While none of the batteries left are that old, I feel that we really don't have much of a clue about how to check whether batteries are good or bad for competition use.

One of our mentors used to work in auto repair. He still has a carbon-pile tester. Apparently, that harms the batteries, correct? Should we go about using it?

I like to think that we'll be okay, but the next competition is on Saturday and we have 3 known good batteries (two MKs - brand new - and one Genesis, came in this year's KoP).

With that in mind, should we bother bringing down the charge rate to 4A or 2A or should we leave it at 6A during the competition?

On one hand, we have to have a full battery. On the other, if it dies halfway through the match, well it didn't do much good now did it xD

[electroken]

Originally Posted by Fej

With that in mind, should we bother bringing down the charge rate to 4A or 2A or should we leave it at 6A during the competition?

I try to keep the battery chargers set to less than 6A unless we're at a competition, then they're set to 6A. In my opinion, 6A is a bit "hot" for an 18 ampere-hour battery, but even with 6 batteries and chargers we come close to running out of charged batteries during eliminations.

I'm starting to think the "right" number of batteries and chargers is 8.

[Mark Sheridan]

Originally Posted by Fej

I like to think that we'll be okay, but the next competition is on Saturday and we have 3 known good batteries (two MKs - brand new - and one Genesis, came in this year's KoP).

With that in mind, should we bother bringing down the charge rate to 4A or 2A or should we leave it at 6A during the competition?

According the data sheet for the MK batteries, the max charge rate is 5.4 amps.
http://www.mkbattery.com/images/ES17-12.pdf

These batteries can get abused in a match, especially playing defense and discharging a lot of power. Charging at 6A will just abuse the batteries more and damage it more. I had a few batteries that swelled up from charging at 6A, I standardized to 4a a long time ago. Also in the long run, charging at a lower rate will keep costs down because your batteries will last longer. I have a battery from 2009 that still works, its not the best but we use it at competition to charge our pneumatics in the pit.

If you keep charging at 4 amps, you can keep buying 4 new batteries each year so at competition you will be using 4 new and 4 from the previous year. I liked this option because I felt it was very economical with my old team (we did not do the practice bot). Plus there will be a few extra old batteries for emergencies, demos or testing.

Originally Posted by electroken

I try to keep the battery chargers set to less than 6A unless we're at a competition, then they're set to 6A. In my opinion, 6A is a bit "hot" for an 18 ampere-hour battery, but even with 6 batteries and chargers we come close to running out of charged batteries during eliminations.

I'm starting to think the "right" number of batteries and chargers is 8.

I had to throw out a bunch of 2012 batteries because they were accidentally being charged at 6A. We increased our total chargers to 9 (so 8 plus an extra) and we have been doing fine, the batteries from 2013 are still going strong.

We have 9 competition batteries and 9 older batteries, a few of the 9 old batteries can act as backup for the competition batteries. Our system is to charge the pneumatics with an older battery and then swap to a new battery one the field. We found this helps in preventing the batteries from discharging too much.

Code Orange and us noticed that when we practice, if we adhere to a match timer and swap the batteries at the end of the timer, the batteries charge quicker, stay in better condition and we get to practice more.

In the long term (i.e. when we fund raise more money), I think we will be upgrading to 12 new chargers. I am considering an automatic charger that only goes to 4amps to eliminate accidentally charging at 6 amps. Plus practice time uses up way more batteries than a competition. I used 9 last night. I hope 21 chargers should be enough, right?

[Mr V]

Originally Posted by Fej

One of our mentors used to work in auto repair. He still has a carbon-pile tester. Apparently, that harms the batteries, correct? Should we go about using it?

If used properly it will not harm the batteries. Hopefully if he was an auto technician he should know how to properly use the tool and select a discharge rate that will not harm the battery and will give the best indication possible as to how a battery would perform in a match.

[MrForbes]

Originally Posted by electroken

I'm starting to think the "right" number of batteries and chargers is 8.

That sounds right. We have 10 batteries, and 5 chargers...it works out OK. We were able to loan a few batteries to the rookie team we mentor at our last regional.

We have got satisfactory battery life charging at 6 amps. The main reason we charge at that rate, is having a bunch of older 6A chargers that used to come in the KOP. Most of our batteries are from 2011. We made it thru Finals at the AZ regional with no issues. Although our robot this year is not particularly power hungry, with only 4 drive motors, one RS550, and the compressor.

[Alan Anderson]

Originally Posted by electroken

I'm starting to think the "right" number of batteries and chargers is 8.

I figure a healthy robot battery will not take longer than three hours to charge at the fastest recommended rate. I think you should have enough batteries and chargers to handle the number of matches you expect to run in that time, plus an extra "pit" battery or two.

[Al Skierkiewicz]

Boy, you go away for a few days to inspect in Minnesota and wow!
1. The 6 amp charger that comes in the KOP and virtually any of the smart 6 amp chargers will not force 6 amps into the battery. That is merely the maximum available current and it will not be supplied for any longer than is needed to start the charge process.
2. A warm battery will give a false reading to smart chargers. You should wait at least a half hour before putting the battery on charge to let it rest. Batteries should be in the open (not an enclosed space) while charging.
3. The CBA is capable of discharging the battery at a similar discharge current as is used in the test data printed with the battery. I use 7.5 amps (on the CBA III) to give me a very close approximation to test data while not taking forever to run the test. It will take about two hours to discharge to 8 volts. This level will show you not only the amp hour rating of the battery, it will also show you of any single cell failures or reduced capacity.
4. A short, high current test will not show up reduced capacity, damaged cells or predict performance during a match. Repetitive use of a high current tester or a lengthy high current test (greater than 20 amps for greater than 30-60 seconds) is asking for reduced life or permanent damage.
5. Likewise, high current charging may also produce permanent damage. Automotive chargers that are not smart, do not have settings for AGM, or can force currents in excess of 6 amps will cause permanent damage and a variety of other dangerous conditions.
6. As pointed out above, star washers do provide a positive locking of the two terminals so that hardware will not loosen with use. Likewise, the use of an Anderson SB50 mating plug on your charger is best. Scratching of the contacts with clip leads causes high resistance in the contact.
7. The 2 or 4 amp positions will not extend the battery life in our use. Battery life is reduced for our batteries simply because robots demand high current discharge over a short period of time. It is typical to expect about 400 charge/discharge cycles in our batteries before capacity is reduced. With six motor drives, expect this to be even less.

[Doc Wu]

+1 to what Al said.

I have found that the biggest cause of damage or reduced life of the batteries is ourselves.

The typical competition match is not bad for a good battery. You put a fully charged battery in the robot, go run the match, then come back to the pits and take the battery and put it on charge again.

This should not come even close to fully depleting the battery and it should only need a relatively short period of time to fully charge the battery again.

If you are killing your battery in a single match, maybe you should re-think that 6-CIM drivetrain...

What are the things we do that damage our batteries? Practice. Demonstrations. Testing. Any time you drive that robot until the drivers notice that the voltage is getting too low to turn, or your cRio is rebooting, you are risking damaging the battery due to over-discharge. We all do it. We all forget how long it's been in the robot.

What do we do to avoid it? Well, the obvious is change batteries more frequently. Let them cool, charge, then cool again before reusing. Less obvious is to try to equalize the use of your batteries. Rotate through them so that one battery doesn't get overused while another sees little use. Try to spread the usage around so that all the batteries are in equal condition and you don't end up with one that unexpectedly leaves you short in the middle of a match.

I have been keeping a set of batteries for my team that is for competition only. All the testing, demos, prototyping, etc. is done with older, but still good batteries. They tend to suffer the abuse, while the competition batteries live a sheltered life.

I test the batteries each year on a CBA III. I then use those results to decide what batteries will be kept and which will get recycled. Even new batteries get a test (time permitting). It's surprising how much variation there is with brand new batteries. They do seem to settle out after some break-in too.

My only problem with the CBA is it is time-consuming at 2-4 hours per battery.

We use a Battery Beak to confirm charge status. Or did until ours died.

We keep a record sheet for battery use during competitions. We use each battery only for one match, then use the next one, in order, until all have been used once, then start over at the beginning. Match number, time and battery beak data are recorded for each battery on the sheet. If a battery develops a problem, it can often be spotted on the sheet and removed from use. We bring some practice batteries for the practice field, testing, and charging up air tanks.

This practice maximizes the time for each battery between each use/charge cycle, allows time to cool, and equalizes the use of all the batteries.

This year, we took six brand-new batteries to competition, plus six of the best ones that were 1-2 years old. We also took six for practice use. We have six chargers. This is more than enough to keep up even in the final rounds. In fact, it's probably overkill. I say, if you stick to this type of plan you could get through a regional with six good batteries.