Is it possible to equip your robot to legally be capable of using power from an off-board source (i.e. a charger or something) for testing purposes? The power would not be used during competition, just to save batteries for practice.
I was thinking about putting 2 Anderson connectors on the PD board, 1 for the battery, one for the external power. Would it work continuously if I disconnected the external and switch immediately to the battery? or would it run off of both or something?
If my understanding of what you want is correct, having both plugged in would fry just about every circuit on the robot, and the battery and charger. I’m not sure if the charger plugged directly to the robot would work or not, but I know i have used a power covertor before to power the robot from a wall socket. Don’t know if its legal in the pits or not though, and having two anderson connections seems not needed to me, since you would never want to have both plugged in at once.
A standard 6-amp charger would not be capable of running the robot.
A single CIM, stalled at 12 volts, will draw 133 amps.
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DO NOT DO THIS. First, don’t put 2 Anderson connectors on your robot. The second one only introduces a perfect place for a short during the match. Second, the battery chargers we have in the KoP are designed to charge batteries, not power robots. They can only put out 6A max, which isn’t enough to drive your robot around (40-60A would be more appropriate for running a robot, but even that isn’t enough when you start talking about stalling CIM motors). They also don’t put out a straight 12V - in order to charge a 12V battery, it needs to put out more than 12V… Having 14 or 16V going into the robot might damage something.
Also, please consider the possible safety implications of running a robot off an extension cord. How do you manage that cord across a practice field? What happens if the cord gets caught in a moving mechanism and is crushed/cut? The risk of electrocution or other serious, damaging accidents is much greater. Do you want to be the one to explain to a dozen other teams why their pits suddenly lost power at competition? Do you want to have to explain to the rest of your team why the expensive electronics on the robot are burned out from a sudden 120V short?
Your best bet is to have your older batteries used for testing, and save the new ones for competition.
this is now sounding like a bad idea. it seems that off-board power isn’t strong enough + and it would be dangerous and complex to wire properly=not worth it. also old batteries are easier to use.
For what it is worth, I did a lot of the PD testing using a giant programmable power supply so that I could easily push the voltage around and test corner cases.
As long as you don’t need to move motors (or only move them unloaded/on blocks), you might be able to use a high power computer power supply.
As everyone else has already said, do not attempt to use a battery charger for this.
In the past we’ve wired a charger in parrallel with the battery.
Make an anderson “extension” cable using proper gauge wire a few inches long. Plug the battery in using this. Inline on the extension cable, hook up the charger.
If you’re average current draw over time is low, this will work. It’s great for programming.
In general, using a battery charger in parallel with the battery while connected to a load, is a bad idea for the electronics that are connected as part of the load. The charger (even smart chargers) are confused by the varying load/battery combined and will on occasion produce the maximum voltage the charger is capable of generating. This condition is bad for both the electronics and battery. A high current power supply as Erik has suggested might be available from your mentoring organization but these items are rare for most businesses. You can substitute a larger battery, i.e. a automotive battery, for testing purposes if you need extended battery times. Please be sure to insulate any wiring you choose to make. With the battery disconnected from the robot, you can then charge the larger battery with an appropriate rated charger.
I was going to suggest the same, if you need a battery to last an extended period of time for a workbench time scenario go for a marine or car battery (The robot batteries are 18Amp-Hours so choose accordingly). If you don’t need a lot of current, a deep cycle battery should allow you to run even longer between chargings (correct me if I am wrong but deep cycles have less cold cranking amps at the cost of greater capacity)
Al, I was under the impression that even with no load on the battery chargers aren’t a very clean source of power, is this true?