Batteries and Chargers

Harding is wondering if an automotive battery tester will work for the FRC batteries. Are there any cheaper options than the Battery Beak from AndyMark.

Thanks!

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The Battery Beak (and other CTRE gadgets) are built specifically for FRC, and are tuned for their uses specifically. Other options will work given you put the research behind it, and build off of other teams’ research.

For example, Team 1736 made code that uses the PDP’s built in current and voltage measurements to estimate the percentage of the battery.
The code can be found here:

and to use it, you can supply it values from the PDP here:
https://wpilib.screenstepslive.com/s/4485/m/13809/l/219414-power-distribution-panel

Make sure your PDP is connected to CAN.

Our team has a battery beak, so we don’t use this, but the battery beak is not perfect either. A fully charged battery registers as 120% - 130% full according to it.

Have fun researching and learning about electronics. That’s what’s great about FRC when you’re building your own systems.

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As former auto mechanic, when a lead-acid battery is fully charged, it will register over 12V, sometimes up to 14V. This might explain. the over 100% readings. Another factor here is discharge rate . Depending on discharge rate, a lead-acid battery will not just hold a steady voltage and then die quickly. See graphs here.
https://www.eetimes.com/author.asp?section_id=36&doc_id=1320644#
A traditional automotive battery tester puts a load on the battery and measures the battery’s ability to supply current at a fairly high rate (basically a big heating element). That’s all it really does. This is designed to mimic an automotive starter, which pulls a large amount of current (250A @ 12V!)

I suck at coding, but you should be able to pull voltage values from the CAN bus as mentioned above and store them in memory as you use your robot. You can then make a plot of V vs. time. You might also be able to pull amperage data as well to see if the battery is supplying the needed current (compare to a plot using a new battery). A battery can register a good voltage, but then fail to provide when a large current demand is made of it. It’s complicated.

Edit 1: To my knowledge, you could look into doing something like pdp.getCurrent(1);. I do not know the pdp import in java off the top of my head but you could look at the https://first.wpi.edu/FRC/roborio/release/docs/java/.

This seems to indicate you can log both current and voltage, but maybe would have to sum current for connected devices
https://wpilib.screenstepslive.com/s/currentCS/m/java/l/219414-power-distribution-panel