Okay heres the deal, for classroom use of the vex kit for demos or development, the students often need to keep changing and charging batteries.
One possible solution I thought of is to drive the remote and vex microcontroller off an 8-8.5v power supply, with the microcontroller side current limited to 5A and the remote current limited to 1A.
Anyone made such a supply before, or is there any COTS solution? :o
i made a thing once with an AC to DC converter that was 6 volts but when you hooked it to a volt meter it was 7.2 volts i pluged it right into the battery cord port thing
Any power supply that supplies 7.2 volts to around 9.6 volts should work (you can go higher but its not a good idea.) Also make sure to have a good amp rating to draw from say like 4 amps.
Actually I will be doing a presentation at a school this Wednesday and what I have done is just parallel 2 batteries together to give me longer run time. You can get the connectors from a hobby shop or from Radio Shack.
I’m gonna try using a bunch of the LM338 (sister of the LM317, but 5A rating) with an ATX PSU to supply like 5 to 6 rails of 8+v, and allow adjusting from 7 to 8.5V. With digital voltage meter (switchable). Each rail ends with a connector to plug into vex controller or remote. No current limitation at the moment, though I may add a thermistor to reduce voltage when the 338s heat up excessively or something else innovative. No fuses, as I don’t want to run around replacing fuses.
As mentioned above, the Vex Controller can output a MAX of 4 Amps for ALL the Motors, so the 7.2 Volt supply will need to provide a little more than that. The Vex Transmitter you will have to make an “educated guess” on its power requirements at 9.6 Volts.
For “working on a bench”, I think this is a real good idea. I also place my Vex on “blocks”, so that the motors can run, and not have it drive around the table.
thanks for the heads up… yeah the 338K are rated to supply up to 5A constant and 8A peak. Probably hook up a 12v fan and heatsink to it too.
Another 338K set to provide 9.6v will supply the required power to all remotes used, I estimate about 4 to 5 remotes can be powered.
if you want a longer run time, just put multiple batteries in a parrallel.
I believe you intended to say “parallel”, which sums the available current from all the packs.
Wiring batteries in series will sum the voltage across all the battery packs. This won’t help with runtime and may damage the microcontroller and/or motors.
Cheers,
i was pretty sure i said parrallel… well that’s what i meant anyway. thanks for catching that! in a series would be useless, it only increases the voltage, resulting in no longer run.