Best way to charge batteries
 

Hey guys.

My team has been having a big problem with dying batteries. I'll cut right to the chase - is there any benefit to charging the batteries more slowly?

We charge all of our batteries on the 6 amp setting. Even the one we got this year dies pretty quick. (They're all Genesis batteries)

We've ordered some more batteries, but we need to know if the charger is going to cause the same problem.

Re: Best way to charge batteries
 

Generally, you will want to charge at the lower rate.
Charging a battery at it's max charge rate will lower it's life.

Re: Best way to charge batteries
 

I know my team has been eating up batteries like never before this year, but then again we did design a drive train that drew much more power. I guessing based on your question this isn't the case for you guys, because this, naturally, makes a difference. Just trying to clear up the question for more discussion :)

Re: Best way to charge batteries
 

Yes, definitely. Charging the batteries slower prolong their life. Here are a few tips that I've been told over the years:

(1) Do not deep-cycle the batteries if possible. By "Deep Cycle", I mean don't drain the battery until it's near-dead. Batteries don't ever really fully-recover from being run until they're basically dead, a couple of times of doing this and your battery will never get back to full charge. Fun Fact: Lithium Ion batteries like to explode if you completely drain them and then try to recharge them, so many batteries have a "suicide switch" in them that will prevent the battery from recharging if they get below a set level.

(2) Do not charge batteries while hot. It's best to pull the battery off the robot and just set them aside INSTEAD of immediately putting them on the charger. Give the batteries about 30 minutes to cool, and then put them on charge. You'll get a much better charge on the battery that way. Interesting fact: The difference between a fast charge (charging in 2-4 hours @ 6A or 10A) versus a slow charge (charging in 8-10 hours @ 2A) is heat and gas buildup. Charging a battery quicker causes the battery to heat up quicker while charging, which damages the battery. It can cause hydrogen gas to build up inside the battery and if the gas isn't vented properly can cause a dangerous situation.

(3) If you think your batteries aren't charging properly, check the voltage on the charger itself. It must be charging at a voltage higher than the battery itself in order for the battery to get a good charge. You can detect a dying battery charger by checking its charging voltage.

(4) Never trust the voltage off a recently-charged battery. If you merely test the voltage with a voltmeter, you will be seeing what's known as a "surface charge", you won't actually know how "good" a battery really is. My team really likes a product known as a Battery Beak from Cross the Road Electronics. The bugger is $150, but well worth it. It tests the battery at various power draws, and can show you what the REAL level of the battery is.

(5) If your battery doesn't seem to be charging properly and you've ruled out a bad charger, check the terminals going to the battery. I've seen WAY too many batteries that didn't have a SOLID connection between the wires and the battery terminals, and that can lead to loss of power in charging. I've even seen the connection corroded (rust), that's never good!

(6) Last but not least, never leave a battery on a charger unattended. I've been witness to too many batteries exploding while on charge. Fortunately none of them at FIRST events, but unfortunately the worse ones were at various robotics competitions (mainly BEST Robotics).

Happy Trails.
-Danny

Re: Best way to charge batteries
 

You should test the batteries to see if they're shot.

The best way to do this is with a CBA tester. If your team is low-budget there are simple and inexpensive but manual home-brew ways to do the test.

The quickest way to kill an FRC battery (other than dropping it) is to discharge it too completely. The recommended depth of discharge is no greater than 50%. If stored improperly during the off-season, the battery will die a slow but inexorable death.

Re: Best way to charge batteries
 

If the CBA is out of your price range, take your batteries to AutoZone (or similar auto parts store). They will usually test them for free and let you know if the battery is usable anymore, especially if you tell them what you are doing.

Re: Best way to charge batteries
 

Not. Autozone does a short-duration high-load test. This does not reliably test the battery capacity, and may damage the battery if done improperly.

http://www.chiefdelphi.com/forums/sh....php?p=1286958

http://www.chiefdelphi.com/forums/sh....php?p=1287478

Re: Best way to charge batteries
 

No it will not damage the battery as it does not apply as much load as the typical FRC drive train and it does so for a much shorter duration.

Re: Best way to charge batteries
 

"It" depends on the load tester and who is operating it.

Re: Best way to charge batteries
 

Generally, AutoZone uses a conductance tester such as a Midtronics, and not like a carbon pile of the olden days. In other words, a LOT like the battery beak. These are very fast, lightweight, and accurate, and do not rely upon the user's skill.

Thhat being said, even a 150A load for 10 seconds will NOT damage an FRC battery. It's not good for this to be done on a regular basis, but 2 or 3 times a year is not harmful.

Re: Best way to charge batteries
 

We always charge at 2amp unless we are doing a demonstration where we know we will drain enough batteries to have to reuse them quickly.

I've posted this before and I'm not sure if it's still true, but we were able to get West Mountain to send us an old CBA III for free just by telling them it was for a high school project.

The CBA and Battery Beak allow for you to actually know you have good batteries. Also make sure you have good contacts at the battery terminals, Al recommends star washers between the ring terminal and batter lug and we have been using them with great success the last few seasons. They don't let the connection come loose. Also common sense, never carry or lift a battery by it's leads.

Check the SB50 connections them selves, they can get damaged and hinder battery performance.

Re: Best way to charge batteries
 

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.


Yuasa NP18-2 datasheet: Maximum discharge: 112 amps.

MK ES17-12 datasheet: Maximum discharge current for 30 seconds: 360 amps.

Go figure.

Re: Best way to charge batteries
 

We've been having some issues with batteries this season as well. We use the Battery Beak, check our batteries with the CBA before and after every regional, and try to conserve battery life as much as possible. What I've found, in doing this, is that batteries that are old, and especially have been dropped in any way, are noticeably less reliable, with less charging capacity and amp hours. We get around this by using brand-new (2013+) batteries, and removing them from the roster if they get dropped, until we can test them to find out if they're usable.
<EDIT>
After reading the OP, we charge all our batteries at around 3~3.5 amps. I'll have my captain check me on this, but I do know that we don't like to charge on the maximum amp. </EDIT>

Re: Best way to charge batteries
 

How many regionals do you attend in a typical season?

Re: Best way to charge batteries
 

Typically two, so at least: once before Utah, once after Utah, which is typically coupled with before Las Vegas. Then, if we're lucky, after Las Vegas/ before Saint Louis, or if we're not so lucky, then after Las Vegas. At least 3 times, maybe 4~5 if we're lucky.

Re: Best way to charge batteries
 

+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...

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

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?:)

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

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.

Re: Best way to charge batteries
 

+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.

Re: Best way to charge batteries
 

I charge batteries at the lowest setting that the charger allows, which in this case is 2 amps. It takes longer to charge them, but the life of the battery itself is extended. We only increase the charging rate during elimination matches if we happen to be running low.

Re: Best way to charge batteries
 

One way to help with the cycling of your batteries is to name them. If you haven't seen "Judy" for a while or "Grace" or "Hermione" then your battery usage cycle is faulty. Part of reducing maltreatment is ease of identification.

Re: Best way to charge batteries
 

I agree, but the only problem with that is remembering who comes after "Judy," was it "Grace" or "Hermione?"

Numbering or lettering is unambiguous.

Overuse of a particular battery, either at random or by choice, increases the chance that the battery will become damaged by heat, or just get used up and reach it's end of life sooner than other batteries of the same "vintage."

I've found our team saying things like "We drove really well that last match. What battery did we use? Can we use it again?" You need a person in charge of your battery charging that can say "No, it's not ready yet. Use the next one in the rotation. Number 3 is up next."

I think giving batteries names would increase the chance of unbalanced use, either by confusion, or by favoritism: "I like Grace, it's my dog's name."

But, if it works for your team, go for it. as long as it achieves the goal of balancing use and giving time to charge/cool equally.

Re: Best way to charge batteries
 

2014-1, 2014-2, 2014-3 works well.

Re: Best way to charge batteries
 

What is your experience for battery life? Most of our batteries are from 2011, and they still work well. I've seen batteries last only a year or two, these ones are pleasantly surprising me. And we don't maintain them nearly well enough, they sit over the summer with no charging, and use/maintenance in the fall is sporadic.

edit: we have our batteries identified by year and letter, 2011-A, 2011-B, 2014-J, etc and try to keep them in rotation

Re: Best way to charge batteries
 

Well Hermione would come after Grace and would be followed by Izzy and then Judy. Same as using A, B, C ect.