Has experience shown NEED to eliminate batteries before each competition through load-testing? (assumption: new batteries each season)
What do powerhouse teams do/use?
IF needed, what load-testing devices are recommended… make/model?
THANKS for your help!
CBAIII is a must have for every team.
After we purchased ours three years a go (due to many recommendations from CD) we have not had a single battery related failure.
Purchase one, you won’t regret it. We load test every battery before every competition.
We also use it to load test our Vex batteries.
Not sure what powerhouse teams do, but I second Indy Sam’s recommendation above.
The CBAIII won’t tell you a battery’s state of charge, but it will tell you whether it is healthy or not. What it does is discharge the battery at a relatively low current (a few Amperes for a 12 volt battery - it is limited to 100 Watts continuous discharge) and tracks the battery voltage over time, until it reaches a ‘safe’ voltage (maybe 9 volts?), all automatically. You then compare the discharge curve to your other batteries, and the health of a given battery will become apparent.
It also gives you the battery capacity in Amp-hours, but use this carefully, because capacity is very dependent upon discharge current.
Team 217 has used the CBA load tester in the past. It has worked well for us. However we have a significant amount of batteries +40 that we have acquired over the years so testing all of them has become time consuming as the CBA testers apply a load over a long period of time to determine Amphours. This has been the tried and true method for many years. We have found a faster and equally reliable method through measuring the internal resistance of each battery. The test provides instant results and may be performed in or out of circuit. We named the device the Battery Beak. If you are going to IRI we will have a couple beaks to demo.
With lead acid batteries the internal resistance increases as the plates inside the battery age. This resistance also increases as the battery discharges, the ability to measure this resistance is the key to determining battery health and even state of charge. The problem with traditional load testers is that they must completely discharge the battery in order to determine capacity. This can cause the internal resistance of the battery to increase to the point of failure. Charging also ages the plates although a small amount depending on charge rate. We have had batteries that tested well at the beginning of the season only to have them fail halfway through. The bottom line is the battery can fail at any time. The need for a test that could be administered quickly just before the match begins became obvious.
Mike, I was planning on flying to IRI to observe/learn… but we’re preparing to compete in the Inaugural Texas Robot Round-Up that runs less than a week after IRI…
Could you post info here on the Battery Beak? THANK YOU for your help!
I also recommend the CBAIII, I have used it both with 294 and other robotics projects. 294 has used that to go through all our batteries in the lab. Time consuming, yes, but totally worth it to identify good batteries.
For at site competition, this year we utilized a load tester that we purchased with recommendations from our friends from 1114. In 2010 we had shipped 8 batteries only to find that several of them were no longer keeping charge. 1114 helped us identify our best batteries all the way through the finals that year! This year before the batteries got put into the crate they were all checked out and tested
Here is the product info: Midtronics SCP-100 SCP 6/12
While in St. Louise this year, I stopped by the AndyMark booth. One of the new toys I saw there really made me happy. They said they should be offering it some time this fall.
What is it? A small battery health tester that had a LCD display on it as a read out. It tested the current charge state as well as load test results of the battery. It used a connector that plugs right into the Anderson Power connector. This thing was about half the size of a deck of cards.
It uses a PIC to control the testing process and drive the display. Testing is performed at a precisely controlled 1A and 10A. It then calculates the internal resistance of the battery and determines the overall health of the battery. All this is performed in about 5 seconds.
Granted, the unit I saw demonstrated was a demo version, thus some changes may take place for the production versions. Regardless, I believe it will be a great addition to any teams tool set.
What you saw was the Battery Beak and it will be available this fall through www.crosstheroadelectronics.com and most likely AM.
Any idea on pricing?
Around $100.
Buying a product like this is a great idea if you have the money. But, with our team being on a shoe string budget we decided to build our own battery tester out of scrap parts. Initially it was not much more than some homemade high power resistors that could be used to load the battery while you read the voltage with a hand held voltmeter.
The resistors for our tester were just lengths of coiled nichrome wire salvaged from a scrap electric heater. We cut the length of the coils to give us the highest current draw that did not overheat the wire, and then doubled up several lengths in parallel to provide a heavy load test. We wanted to draw enough current for a long enough period that we adequately simulated a real match.
Later we added some fans, and a solenoid controlled by digital I/O and an analog input so we could start and stop the test and read voltages from a computer. Not exactly portable, and not constant current, but most of the parts were already in hand. Also, our software team wrote a program to control the test and plot out the voltage drop over time. We can run tests of varying length to give a quick analysis of a battery, to watch for a sudden drop off in voltage during a longer test to simulate a real competition. The plot shows unloaded voltage, loaded voltage, voltage drop over time, and voltage recovery.
If we did not have some of the parts around already, building something like this would probably be more expensive than just buying a ready made unit.
And after seeing the comments here, we should probably try to buy a real load tester next season. But for now the home brew one works for us and seems to impress the kids with what you can do yourself without a lot of parts when you have to. Remember the old Yankee saying.
Use it up, wear it out,
Make it do, or do without.
Tom
The CBAII and now the CBAIII have the ability to chart and compare battery Amp/Hr ratings with the manufacturer’s specifications. One thing that is invaluable is the ability to store curves for batteries from each test, even if years apart. This type of testing allows you to track battery trends, cell capacity and internal defects due to misuse, manufacturing, and end of life. While we do not test every battery prior to each competition, we do make some comparisons each year and certainly check all new batteries when they arrive. It is not possible to predict battery life for a specific robot in any match as there are far too many variables within a match. The battery testers do a fine job of checking suspect batteries and can specifically show when one or more cells have reduced capacity or are damaged in some way. The end of my electrical presentations show a family of curves comparing healthy and defective batteries. If your battery meets or exceeds the manufacturer specification then at least you know that the battery is capable of providing the same amount of power as the other guy’s.
While gel cell batteries had certain indicators that they were aging (weight for instance), the AGM cells we now use do not. Often AGM cells will fail due to mis-handling such as dropping on a corner or lifting by the wiring. As the batteries age, non-conductive material will build up on the plates in the normal course of charge/discharge. This is the cause of gentle reduction in the capacity. However, our use is often times destructive in that high currents are demanded over short periods of time. I believe this causes distortion of the plate material due to the high temperatures encountered during the discharge. some teams have experienced actual cell shorts that cause high heat without load and distortion of the case.
This is great info… THANK YOU all for your help!!
