Battery Best Practices
 

I have a few questions about batteries at competitions.
1) How many batteries do you take?
2) How many chargers?
3) How do you test, charge or otherwise prepare your batteries for competition?
4) Do you do anything special between matches to keep your batteries ready?
5) Any other advice?

Re: Battery Best Practices
 

Our team usually takes 4 batteries, and that gets us through usually pretty well. As far as chargers, I would suggest at least one per battery, but you could get away with just 2 or 3 chargers if you must. For testing the batteries at competition, we have a device (I think it's an old automotive battery tester) that puts the battery under load and reads it as good or weak. To charge the batteries, we charge them over night before and during competitions, and during the day on Fridays and Saturdays, we change it to the full 6AMP charging rate and try to always keep one full charged battery on hand. We also separate full charged batteries from batteries that need to be plugged in. If there is ever an open charger, we plug in a battery unless the battery is >95%.
If it comes down to elims, you can always ask other teams if you can borrow batteries/chargers. They'll be happy to loan you for the afternoon.
Hope it helps!

Re: Battery Best Practices
 

For testing, we have a voltmeter with the tips of the cables cut off and soldered to a battery connector. We normally bring one charger per battery, and about seven to the competition (though this is probably a bit overkill). Some major advice: if the battery drops below 10.5 volts, it will get damaged! :ahh: I would advise to check the batteries pretty frequently, and make sure they don't go below 11v. Also, when they charge, their max is 14.4v, but it will drop to 13.8v (its max rest charge) afterwards, so don't freak out if they seem to charge and then drop again!

Re: Battery Best Practices
 

The Andymark Battery Plugs provided in the KOP are an excellent way to indicate that a battery is charged.

Re: Battery Best Practices
 

Both the teams I mentor use these: http://www.tecmate.com/u_accumate_pro5.php

They are an affordable, compact and brain-dead solution to battery charging. We have them wired up to battery connectors so all you do is plug your batteries in and when the light turns green you're good to go. If you have five batteries which are always plugged into one of these and take them home at the end of the competition day to charge you should never be left without a battery. If for some reason you need to charge a battery at a higher rate, you can connect multiple terminals to one battery to boost the charge rate.

An important note about the batteries we use. The ONLY way to reliably test if a battery is indeed good is to use a load tester. This is a fancy voltmeter with a large resistor (heating element) inside it which loads the battery heavily to check that it is still capable of supplying sufficient voltage under heavy load. Last year Cybergnomes went to 6 motor drive and we found that the performance was extremely different between the new batteries that we had obtained that year vs the old ones. After load-testing them it was found that nearly half of the older batteries were incapable of supplying the same power as new when under load. The "failures" were attributed to storing the batteries at the end of the year and leaving them in a depleated state. With a lead acid battery it is very important to exercise it during the offseason. If you simply store it and forget it, the charge level can deplete. If these batteries are left in a depleted state they are prone to sulfation which is a formation of sulphides internally. These crystals can severely degrade the battery's performance. The best solution to avoid this problem is to charge your batteries or even better, cycle them (discharge, charge) regularily during the offseason. The phrase "use it or lose it" applies here. This type of failure can be very difficult to diagnose because the battery will test full voltage and without a loaded tester will show charged however, as soon as you apply a load the voltage nose-dives and you realize the battery can only store a fraction of what it should.

Re: Battery Best Practices
 

Brandon,
These batteries can and do regularly drop down below 7 volts without damage. Testing with simply a voltmeter is not enough to determine if a battery is good enough for competition. Only a load tester of some type will give you an indication that the battery can actually supply power. A voltmeter reading of 13 to 14.5 volts is normal for a battery that has just been removed from the charger. This battery, however, is nominally 12 volts under load and that is the reading that will show on your dashboard when communicating with the robot. That reading comes from the battery connection on the analog module of the Crio through the jumper to port one. That is actual battery volts as measured at the PD. Without a true load tester, using the robot and dashboard while running the drivetrain may give you a pretty good idea of battery health. You can expect to see a voltage drop when starting but it should return to near 12 volts after one second. I highly recommend the West Mountain Radio CBAII or III USB battery tester. These devices will fully test batteries for AMP HR ratings taking an hour or two to perform the test. The results are available in graph form and can be saved in order to perform annual tests on batteries and compare the results. Please remember that our batteries are specified for about 400 charge/discharge cycles maximum. Our use causes that number to drop as a match will draw far more current than the battery was designed to deliver. I would expect life to be in the 300-350 cycle range.

Re: Battery Best Practices
 

1) We generally take as many batteries to a competition that we can. In previous years this number has ranged from 4-6 'competition' batteries and 2-3 'Practice/Testing' batteries.

2) Recently, we've taken 3 Chargers to most competitions, this is usually enough at most regional events until later in eliminations when battery changes happen more frequently.

3) In previous years we never had a scientific method of testing batteries, we've usually just relied on pre-season robot testing to find out what batteries are the best.

4) After a match ends and the robot is brought back to the pits that battery is immediately put on the charger and one of the charged batteries is staged to go into the robot for the next match.

5) Sometimes you'll come across an older battery or two that won't quite make it through an entire match but will hold enough of a charge to run the robot for some period of time. We usually set these batteries aside for pre-match testing and practice field use. In years that we've used the compressor, we'll often use these batteries to initially charge the pneumatic system. If you don't have enough batteries to do this, then you can always leave the battery from your previous match in your bot up until it's time to go into que for your next match and use that battery for testing and pneumatic charging. No reason to drain a fresh battery before a match just to see if everything's working, IMO.

Re: Battery Best Practices
 

Team 612 takes 9 batteries and usually 4 to 5 chargers. Our logic is that with 9 batteries, that is normally the maximum amount of matches a team would play in the playoffs. 3 QF matches, 3 SF matches, 3 Finals matches. Its also nice to have extra batteries just in case an alliance partner needs one.

Re: Battery Best Practices
 

1640 brings around 9 batteries and 7 chargers to competition. This lasts us through finals if none break, and usually gives us one to loan to an alliance partner or opponent.

My number one recommendation is to clearly number all your batteries and chargers. We also test all the batteries beforehand with a CBA III and test any questionable chargers as well.

At competition, we use a comprehensive match chart which includes the match number, battery and charger numbers, and battery performance (namely actual starting and final voltage from the dashboard if they're abnormal). We also keep them all carefully sorted in the pit, using a standard sequence as well as checking the charge lights on the SC-600A (highest amperage). We've also purchased a Battery Beak, which we've been using in the shop and plan to use in the pits. We looking to build a battery cart in the off-season, as the current setup is sort of table-space intensive.

Re: Battery Best Practices
 

You want to keep up with your batteries. Buy this http://www.crosstheroadelectronics.com/Beak.html

Re: Battery Best Practices
 

I'm using one of these this year. We only have four batteries at present, so knowing the capabilities of each is critical. I have recorded measurements of all batteries at well-defined points. E.g. after each use in a testing session, after each charge session, after each idle period. I expect to use the information as evidence that we need more batteries for competition.

My only objection to the device so far is that it comes with a lanyard (around the neck) that doesn't split. Safety hazard in a mechanical environment. ::safety::

Re: Battery Best Practices
 

I second this. We ordered one through AndyMark and have found it very useful to give a quick charge rate and reasonable idea of battery health.

Re: Battery Best Practices
 

We bought a battery beak this year and think it’s great. If we monitor the internal resistance of our batteries over time using the beak, is that a fair substitute for a CBA III for a team on a budget?

Re: Battery Best Practices
 

We are a team on a bit of a tight budget looking into a load tester. Does anyone have any experience with the attached relatively cheap tester from Harbor Freight?


http://www.harborfreight.com/100-amp...ter-90636.html

Re: Battery Best Practices
 

Chad,
I would recommend that no team use the linked battery checker. The minimum load is 100 amps. While FRC robots can draw that much, the battery will likely show up deficient on this tester. In the hands of an inexperienced user this tester could cause some internal damage to the battery. The CBA can run a duplicate test to the manufacturer printed test to calculate amp hour rating. The CBA tests can be stored on the host computer and compared over time with the same battery or with all batteries. The Battery Beak is a quick tester that determines battery condition at 1 amp and at 15 amp and makes calculations to determine internal impedance and battery condition. The Beak is a good quick tester while the CBA tests over a two hour period. The Beak fits in your pocket and requires no special cable, the CBA does not fit in your pocket and requires a USB connection to a computer.

Re: Battery Best Practices
 

1) - 7 or 8 competition batteries, 1 "pit test" battery for testing code, charging pneumatics in the pits, etc.

2) - One triple charger and two single chargers (5 batteries max charging at once).

3) - Our EE mentor spends about a week discharging and recharging batteries before competitions start. He reconditions the batteries, and then load tests them. Those which do not pass the competition load test become "pit test" batteries, and they are replaced with brand new batteries for competition use. All passing batteries are then labeled "Competition OK 2012"

4) - We label our batteries by number, and keep a running list of how often they're used during a competition, and what their individual voltages are when they're finished charging. We put 1 charged battery in the robot, take 1 extra charged battery on our cart to the field just in case, and have at least 2 charged batteries ready to replace them in the pits.

Re: Battery Best Practices
 

We tested our batteries this year as follows:

1. Acquire battery
2. Plug battery into dc to ac converter
3. Attach volt meter to leads
4. Plug Halogen bulb into converter
5. Turn on converter
6. Turn on bulb
7. Record Battery start voltage
8. Wait for battery to drop below 10 volts
9. Record time taken
10. Label battery accordingly

It took awhile, but worked fairly well for reheating pizza.


Also,

What are the approximate dimensions of this battery charger? We're considering building a new battery cart (wooden box containing chargers, slots for batteries, and AndyMark battery plugs. On wheels.) and this seems almost perfect.

Re: Battery Best Practices
 

The Genesis NP18-12R battery (2012 FRC KoP) datasheet¹ indicates that it is rated up to 150 amps, so in theory you could measure it with a 100amp load tester, but:

1. The datasheet does not list any manufacturer specs at that high discharge rate, so any assessment based on testing done at that rate could only be relative to other batteries tested the same way.
   
   
2. In the wrong hands, testing at 100amps could damage the battery or be a real safety hazard.

Use something else.

¹ http://www.batteryplex.com/sheets/NP18-12R.pdf

Re: Battery Best Practices
 

FWIW you can buy 300 watt 12 volt bulbs at a pool supply store. Not the safest thing to do either.

Re: Battery Best Practices
 

We just used a shop light that we had lying around.

Re: Battery Best Practices
 

Was the DC to AC inverter lying around too? Or did you have to purchase that for this use?

Re: Battery Best Practices
 

yes ours is still going strong after 2 years and an anderson connector soldered to it

Re: Battery Best Practices
 

How long do you leave the 100amp load on, and what is your voltage criterion for pass/fail?

Re: Battery Best Practices
 

FRC Team 2949 PWNAGE just finished building a new battery cart. It consists of 12 batteries, 9 charger banks, a BatteryBeak, Spill Kit, 2 DeWalt chargers, extra AndyMark Battery Clips, and a removable lid. Some pictures below show the setup.






The DeWalt chargers and spill kit still needed to be added since these pictures were taken. The DeWalt chargers are mounted on the plate on the top middle of the cart (in-between the chargers). The spill kit goes under the 2 3-Bank chargers. Eventually with some more fundraising done we will switch out the 3 1-Bank chargers for 2 more 3-Bank chargers.

I would be happy to answer any questions about it. I had just uploaded a couple of pictures of it to CD a couple of days ago, but apparently hey still haven't been approved... anyway let me know what you think.

More pictures can be found at our fb page (Like us!):
http://www.facebook.com/pages/pwnage...09248172427910

-Nick

Re: Battery Best Practices
 

1. All of them (we only have 4)
2. 2, maybe? (we only have 1 right now)
3. We plug them into the charger to see it they're charged (no Beak yet)
4. Nope
5. Charge them always. They run out of juice super fast.

Re: Battery Best Practices
 

Nick,
Can't wait to see it.

Re: Battery Best Practices
 

1) My team takes all of our batteries from the last 3 years to competitions
2) My team takes a "battery cart" that has 4 chargers connected to a single wall outlet
3) My team puts each battery through a cycle of discharges over decreasing loads using the incandescent lightbulbs also on the battery cart. this conditions the battery and can restore some lost capacity. The battery cart is fully automated with an Arduino microcontroller and can condition 2 batteries at once. for electrical schematics and datasheets and eventually source code for the Arduino, search "team 955 battery cart" on google and select the first option.
4) besides charge them?
5) don't store batteries partially discharged for long periods of time.

Re: Battery Best Practices
 

Can you provide a link to an authoritative source for a technical discussion of this phenomenon?

Re: Battery Best Practices
 

I suspect the attempt here is to remove some sulfation on batteries that have sat around for a long (many months) time. Batteries self discharge over time so it is impossible to store partially stored batteries. (see battery sheet on self discharge specifications) However, it is best to charge batteries before storage and keep them in a temperature controlled environment. i.e. Don't allow them to winter in an unheated garage or to sit in an closed shed during the heat of summer.

Re: Battery Best Practices
 

I have also known of some people doing this with brand new batteries since SLA batteries reach top performance after a few proper charge discharge cycles. A friend of mine actually holds a world record for an electric vehicle race, and does things like this. The random discharge cycles a new battery might experience are not likely to be ideal in conditioning a new battery if left to chance. I have never tried this though because from what I understand the benefit is modest at best, and doing this to incorrectly can actually increase sulfation and other battery problems. I might try it someday, but right now it has not made it very high up on the priority list.

What we do right now is to never deeply discharge any battery. We try to always get a battery onto the charger immediately after use to avoid sulfation. We also store the batteries in a cool but not cold location and top up the charge regularly (at least monthly, preferably weekly) on any unused batteries. And our newest competition batteries do not get used for driver testing or software development where they can easily be over stressed before anyone notices. Someday we will try to increase our knowledge of and attention to proper battery care. But for now just a few basics seem to have made a significant difference for us.

Re: Battery Best Practices
 

Hey Al,
Thanks for your informative post about the West Mountain Radio unit. We bought one awhile back and have yet to really understand how best to use the thing. We can't seem to test a load with more than 7.2 amps and even then the results are hard to interpret (for us).

Would you mind laying out a few steps and settings you use to test it?

Thanks very much in advance.

Re: Battery Best Practices
 

Aaron,
The 7.2 amps is sufficient. set your cutoff voltage to 7-8 volts, which is the cutoff for most of the battery spec sheets. It will take more than a hour to run the test. After a few minutes the battery voltage should fall a slight amount. This is due to any remaining surface charge and the all of the components reaching a set temperature. After that the voltage should remain relatively constant until the end of the test when the curves start to drop off to the 8 volt limit. The program runs constant amp hour calculations and should match the battery curve very nicely on a good battery. What you are looking for is a drop of 2 volts during any part of the test. This is one of the cells giving up. I have a had a few batteries where one gives up and then a second gives up a little later. The cell loses capacity if the electrolyte is not full in that cell or if one or more plates have broken within the cell. On a rare occasion a battery will start off at 10 volts indicating a cell is shorted. Once the test is complete, save it with a unique ID that you also mark on the battery. That way you can track the same battery from year to year and watch for end of life when the battery no longer can ~18 amp hours. The program also allows you to overlay several curves so you can look at the same battery annual curves or you can compare batteries you want to use for competition. The 7 amp discharge is nowhere near what the robots will pull during a match but remember you are testing to manufacturer spec in this test and that is really the only valid test to determine if the battery meets spec. I also recommend that if you are testing a suspect battery, try moving the cables around and tap on the battery to see if you turn up any intermittent voltage dips. We added an Anderson connector to our CBA II to make it easy and all of our chargers are also so equipped with the APP connectors. We do not use alligator clips and neither should you.
If you search, I put up some curves a long time ago to demonstrate all the possibilities.

Re: Battery Best Practices
 

Is this the one?
http://www.chiefdelphi.com/forums/showpost.php?p=766746

Here's one from Hugh Meyer:
http://www.chiefdelphi.com/forums/showpost.php?p=916447

Re: Battery Best Practices
 

Yep, but I didn't want to make it that easy.

Re: Battery Best Practices
 

I am also a proponent of the West Mountain Radio CBA III. I agree at first, you will not know how to interpret the results, especially since the graphs auto-scale to fill the screen.

The real value of the results shows up when you overlay the test results. Then you see the differences between tests. I test each battery at the beginning of the season and do an overlay of all the batteries. It becomes easy to see which batteries are the strongest and which are getting weak.

The other use is when a battery is suspected of getting weak. Test it again and overlay the results with the test you did at the beginning of the season.

Bad cells and broken internal connections are quickly spotted with the CBA III.

If a team was short on money and can't afford the Battery Beak and a CBA III, I'd take the CBA III. It's only shortcoming is it can't be used quickly in the pits. You must be disciplined enough to test all your batteries ahead of time.

Another recommendation I make is (and I think some of the posters here were alluding to it) is to number your competition batteries and use them in sequence. Don't fall into the trap of saying "Battery 3 was strong that last match, let's use it again." Pretty soon, you have overused battery 3 and it's your weakest one.

Batteries need to be given time to charge, as well as time to cool after charging. Having more batteries than you need and rotating them in sequence allows them to be used equally and be given the best operating conditions.

A two minute match along with a few minutes of power on before a match should not come anywhere near depleting these batteries. If you run a match, then charge them, they should be able to be charged back to full capacity fairly quickly. You don't need one charger per battery. A 1-2 or 1-3 ratio should be enough.

I find that the most damaging thing to the batteries is practice and demos. We get playing with the robot and run it for 10-15 minutes until someone notices the battery won't drive the robot anymore. By then you've severely depleted the battery. They only can take so much of that.