Our electrical team has gotten around to connecting and charging up the 2 Genesis batteries we got from FIRST Choice and the 1 battery we received from the KOP.
Have you load tested these batteries?
Generally we will cycle out batteries that fail our team specification. Our tester is a standard low-man’s automotive 100-AMP load tester, that will load a battery for 10 seconds with a heat resistor and check for weakness using a CCA (cold crank amps) scale, we don’t have a computerized load tester yet…this might be the year we purchase one…Typically the automotive 12V standard is 500 CCA for cars.
There will be someone that will probably argue CCA is not a good way to determine battery capacity. But we are establishing a base line with the automotive tester across our batteries and the new ones are the lowest numbers we have ever seen.
Anyway, after charging up the new Genesis batteries from 2013, they are posting about CCA 300 AMPs. Our team spec is no less than CCA 500 AMPs. Generally when we get new batteries, we see about CCA 700 AMPs to CCA 800 AMPs. We have seen this in both EnerSys and MK Batteries in the years past.
However this year…it’s different…all three new 2013 batteries…CCA 300 AMPs…
I reference CCA because that is the tester we have, an automotive one.
While we appreciate the donation and are most thankful, we may not use these batteries on the robot this year. We might just repurchase some others. Unless there would be someone that could give us some insight into why we are only seeing CCA 300 AMPs on the 2013 batteries and maybe recommend a better more proven method to measuring battery capacity. Traditionally, we have seen the robot voltage drop below 11 Volts at the end of a 2.5 minute match with a CCA less than 500 AMP battery. Anything higher than that and the battery is generally good enough to even play a second match back-to-back. (Pending how many motors we have that particular year…)
So my questions are:
Do you load test batteries?
Did you load test the EnerSys Genesis NP18-12B 2013 KOP and FIRST Choice Batteries?
What was your results?
Can you confirm if your batteries meet your team spec?
Being that 2 batteries came from one source, and 1 battery came from another source…I am wondering if we are an isolated case or not.
We do have a Battery Beak Tester as well, we use for a spot check right before the battery goes in the robot.
But so far it seems a basic CCA rating from our “cheap” automotive tester seems to be a good gauge based on what we see on the field. I am mostly interested in “capacity” of the battery. How long can I run a robot on a fully charged robot before it dies completely.
At 500 CCA - we might get 6-7 minutes
At 800 CCA - we will get 10-15 minutes
That’s about some rough numbers we’ve seen over the years.
Quick summary to your questions is immediately below. Details farther along
Do you load test batteries?
Yes.
Did you load test the EnerSys Genesis NP18-12B 2013 KOP and FIRST Choice Batteries?
Yes, but we only have the 1 KOP battery
What was your results?
Our new 2013 EnerSys KoP battery gave comparable performance as prior years, with a capacity (in our test setup) of around 12Ah to 14 Ah (I can provide more detail tonight.)
Can you confirm if your batteries meet your team spec?
Yes, our 2013 KoP battery seemed to have performance typical of prior year’s new batteries.
More details follow…
First off, we started load testing our batteries a few years ago. We used to make use of an automotive load tester like you describe, drawing a high-current load of 150 amps for 15 seconds, similar to what you describe.
Our automotive load tester wasn’t very good and didn’t have a good CCA read out, however. We were also concerned about the possible battery damage from doing such a harsh test on our batteries.
So, a few years ago we switched to using a West Mountain Radio CBA III. (See Computerized Battery Analyzer - West Mountain Radio - the current model is now a CBA IV). With that tester, we now “slow discharge” the battery with a continuous load of 7.0 Amps until the battery voltage drops to 11.0 volts. This is much more benign to the battery and is a test we feel we can do without risking battery damage. When doing this test, the CBA III produces a nice plot, which can be very informative, especially when compared with plots from other batteries and/or the same battery from prior tests. The key metric we use from this test is how many Amp-Hours is sourced from the battery before dropping to 11.0 volts.
However, neither of the above tests really reproduces “FRC Match Conditions.” The first case is way too much current too quickly, and the second case is much less current than in a typical match.
We did test our 2013 KoP battery, and I can provide the plot tonight. My recollection is that our test methodology gave a capacity of about 12Ah to 14Ah, which is right in line with what we have seen with brand new batteries in past years. We typically see between 12Ah and 14Ah for a “good battery” with our test methodology. I believe the 18Ah rating from the manufacturer is for an even slower discharge rate (less than 7.0A) to a lower voltage (less than 11.0V), which will successfully extract even more charge from the battery.
From your tests, it seems like the 2013 batteries you have did not do as well with high-load (100A) test, but the one that I tested was fine in the low-load (7A) test that we did.
I would note that in the past with the test that we’ve been doing, we haven’t seen a difference between the Enersys and MK batteries. (We have a mix of both, as FIRST has been putting Enersys ones in the kit, but all our purchases have been MK batteries.)
OK, I found the summary plot I made for our team’s batteries as of the 2011 build season, which did not include tests of our then-new 2011 batteries. I’ll still have to wait until tonight to check to see our 2013 test results, as those results are on a computer which is only at our build location.
This plots shows that “new” batteries were giving a range of about 14Ah to 16Ah with our test methodology (I didn’t remember that quite right, apparently).
To understand the plot, we give each battery an identifier (e.g. 2010-A indicating the year of purchase and a letter for the year). The plots are labeled with the battery name and the date of the test.
I would note that as of last season, we were still using 2 of our original 4 batteries from 2005 (our rookie year) as they still held over 12Ah of charge, although we were using these batteries only for practice as they were no longer competition-legal. (I still need to test these batteries to see if they are worth keeping, but I think last season is likely to have finally killed them - 8 years of competition use including many off-season events isn’t too bad!)
I’ll try to remember to update this thread tonight with a plot of our test results for our 2013 KoP battery.
Battery manufacturers will measure the capacity at 1 amp or less. MK does it at 0.9 amps. There’s a nice chart on the data sheet. http://www.mkbattery.com/images/ES17-12.pdf
These times I posted are actual driving practice matches non-stop driving, collecting, shooting, etc… Demo hardly use any juice. We have lasted about an hour as well on one battery sitting still shooting or something easy to do.
You mentioned that 100 Amps might be too harsh and your test at 7 Amps might be too light. But reading the manual on the CBA tester, doesn’t it do higher than 7 Amps? I thought I read that it can load up to 40 Amps?
This is a perfect example of marketing literature stretching the truth a little!
Yes, the CBA III can draw up to 40 Amps of current, but there is also a 100 watt limit. So, up to 40 Amps can be used for a test, but only if the battery being tested is less than 2.5 volts. (40 Amps at 2.5 volts = 100 watts)
For a robot battery (6 cells, 13.2 volts peak, 12.0 volts nominal), 7 Amps is the limit the CBA III will allow. (7 Amps at 13.2 volts = 92.4 watts). There are lots of safety controls in the software to avoid users setting up dangerous tests, and 7 amps is the maximum the software will allow for batteries of the voltage and capacity of our FRC robot batteries.
Chris,
The specification on both batteries is a peak current (for a short period) over 500 amps for a new fully charged battery. I highly recommend you stop using the CCA tester. It produces significant currents internally for the small batteries. Even at 10 second duration, it may weaken inter-cell wiring or cause damage to the plate and glass mat internal to a cell. If you really need to use the big load, and you can get 500+ amps or better when you first pull the trigger, I think the battery may be OK. Just don’t leave it on for 10 seconds.
We have been using the CBAIII for many years and to match manufacturer specs. We set for 7 amps and 8 volts terminal voltage which is the MK graphs cutoff. I tried to test batteries last week only to find that the CBAIII is not supported for Vista but West Mountain will take it back and refurb to correct the problem. If you own one, see the West Mountain site for details and RMA info.
I should add that high resistance connections may also be giving you false readings. Improper crimps or loose hardware on the battery terminals could show up as low CCA numbers. We use a #10 external tooth star washer between the battery and the wire terminal. This will cut through any surface crud on either terminal and prevent the two terminals from sliding around and loosening the hardware.
West Mountain does sell a higher load device if you need to check larger batteries but the extra load is six times more than a CBA.
Thank you for your information, you always have good advice for everyone. The CCA tester is only loading the battery at 100 Amps, but it produces the “CCA” reading based on resistance inside is basically what I understand. It’s not loading it up to 500 Amps. I wasn’t sure if that was what you meant or not, but I just wanted to clarify. When I mentioned computerize, that is the one I was eye-balling, sounds like the CBA is something we should check into.
When you call West Mountain, mention my name and FIRST. I have been trying to get them to sponsor teams or discount. I haven’t been able to talk to anybody this year yet. I may miss the DuPage hamfest on Sunday. they sometimes have a booth.
Do you load test batteries?
2012 was the first year we load tested.
Did you load test the EnerSys Genesis NP18-12B 2013 KOP and FIRST Choice Batteries?
Not yet, we plan to.
What was your results?
See attached spreadsheet (some batteries listed not tournament legal). We have found some batteries were not manufactured correctly, this may explain the lower CCA you are experiencing. For measuring capacity, our batteries were discharged at a 10A constant current rate. The equipment used was an aviation battery tester we have access to. Looking at the resulting voltage plots, we could identify bad cells and other problems.
When we had a battery with a bad or weak cell, we would quickly recharge the battery in an attempt to recover capacity. I’d have to check what the fast recharge rate used was, but it was at least 10A. By the way, in case anyone thinks this was dangerous, we the facility we had access to was capable of handling any issue which could arise.
Can you confirm if your batteries meet your team spec?
We’ll let you know when they are tested. At this point our “spec” is no bad cells and >12Ah. We’ve found new batteries come in at 14-17Ah typically.
Over the years, Team Fusion has received a few defective EnerSys Genesis batteries. Enough defective ones that we don’t even consider using them now.
By defective, I mean the internal resistance is too high to run a motor. They read a good voltage powering the cRIO and other small loads, but as soon as a heavy load is applied, our robot would reset.
Our number’s aren’t that high though. Maybe 3 or so defective ones? We also had problems with them splitting open on year, while the MK batteries seemed to not split open at all. (2010, side mounted cradle… it was a bad design).
Guys,
We chose the 7.5 amp/0.4C discharge rate as it gave an fairly accurate calculation of the design AH rating for the battery while using a test that lasts a little over two hours. We experimented with adding a shunt load to increase the discharge current and as expected the AH rating went down nearly identical to published curves from the manufacturer for the higher discharge rate. Remember that the 18 AH rating is generally accepted for discharge rates in 0.1 C range. Discharge rates above 0.4C will give quicker results but will not display anywhere near the rated AH.
Our new KOP battery tested at 15.3 AmpHours. The Battery Beak Rint was 0.018 ohms and the charge % was 105. This is on the low side of normal. Most of our batteries test in the 14 - 17 range. This was the first test. Sometimes we see a subsequent test of a new battery measure higher.
Attached is the data from the CBA tester. You should get one. They are a great tool!
