Hey Guys,
I’m a fairly new member here and of my FRC team but I have been charged with finding a way to test our batteries that will tell us, simply, if they have gone bad or not.
I just wanted to ask if anybody on any team here has done this before what they did, and if their solution worked.
Thanks!
https://www.ctr-electronics.com/battery-beak.html
Buy one, and it’s about as plug-n-play of a solution as you’ll ever get.
The easy way? https://www.andymark.com/battery-beak-p/am-batterybeak.htm
Make sure you’re using a tester (like the beak) that puts a load on the battery - not just a voltage tester. This will help you weed out batteries that suffer large voltage drops under high current draw. Those batteries aren’t quite dead, but will severely impact your robot performance.
-Dan
This. So much better than anything else we have tried.
Another way other than the beak from my experience is to see how long it takes to charge. If it holds less current it will seem to charge faster. Its more subjective but is a basic solution.
I would definitely vouch for the Battery Beak, but it’s not the end-all of battery testing. We use it during competitions to make sure batteries are charged before going into the robot, and to take readings after taking them out.
There are a couple other steps that we take during our big annual battery roundup to get a baseline ranking of batteries:
-Short duration, high current discharge, with voltage measured before, during, and after. I think we use a tester like this.
-Long duration, low current discharge, with voltage measured before, during, and after, and time to “low voltage” recorded. We use a 12v power inverter, like you would use in a car, hooked up to a load like a light bulb, and run until the inverter trips, measuring the total time to tripping and taking voltage readings along the way. We don’t have automatic data logging (yet!).
In the past we’ve also tracked internal resistance using the Battery Beak to check for cell failures, but those have been so rare and obvious from other signs that we stopped recording that data.
As a rule of thumb, we don’t use batteries more than three years old in a match, even if they’re still good for practicing.
Yes, again!
Also don’t forget the simplest test of all - visual inspection! If parts of your battery look like they have moved, swollen, melted or been burned, retire and recycle it.::safety::
Also, to make FRC and other lead-acid batteries last longer: when doing demos or practice, do not wait for the battery to stop performing to pull it out and make a swap. Change batteries every match at competition. Put discharged batteries back on the charger as soon as possible - keep them in a charged state as much as possible. Float chargers are your friend here, especially if your team takes a long break for some part of the year.
The battery beak is a quick and easy hardware solution… but won’t push your skills or knowledge that much. If you’re interested in exploring a bit, you don’t need to buy anything… you’ve already got all the tools you need right on the robot.
The PDP monitors battery voltage, and current use on each of the channels. https://wpilib.screenstepslive.com/s/4485/m/13809/l/219414-power-distribution-panel You can set your software up to have the robot perform a pre-determined series of tasks and monitor the battery voltage (and current draw, if you want) while the robot performs those tasks.
Graphing how each battery responds will show you which batteries maintain a higher voltage during the series of tasks. The higher voltage under load indicates a lower battery internal resistance and thus a “better” battery.
This will help you become familiar with typical battery voltages and motor current draws during the off-season, and help improve your coding so that you can include this feature in your robot for testing next season. It may help you in optimizing your gear ratios, or diagnosing performance issues when you’re testing your new robot.
Learning to monitor robot performance for later analysis can be a useful tool, not just to improve robot performance but to show the judges that you are following a logical, engineering-based approach to optimizing your designs.
Jason
We do routine discharge testing and voltage plotting over time to qualify our batteries. We use a West Mountain Radio CBA IV with discharge amplifier. It’s not cheap.
CBA IV is best for really determining if your battery is healthy. Check out this battery discharge plot from one of our batteries: https://imgur.com/4dgND1b This battery tested “Fair” on the Battery Beak and when measuring the open circuit voltage with a meter registered as >13V. Yet, this battery is severely unhealthy and completely unusable in competition. For reference, this is what a “healthy” battery is supposed to look like. https://imgur.com/a/WyRMq
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I’ll also recommend the CBA IV. We use the Battery Beak for quick checks.
Make sure that the fasteners holding the two cables to the battery terminals are tight. You should not be able to cause the lugs crimped onto the cables to rotate relative to the battery terminals by pushing on them with your fingers.
If the lugs are loose on the battery, the high contact resistance will make a good battery look bad to a tester such as the Beak and the CBA. It can also cause the radio or Roborio to reset while you are in the middle of a match.