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Registered Member #8
Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214
Hey folks. It's been a long time since I've posted here with any of my endeavors, but I have been doing alright in general.
I have picked up on my old electric mini-dragster project (I will be using it as a demo for one of my college courses), with a few differences. Rather than an external source as I had planned before, I will be running the car from an 11.1V 2200mAh lithium polymer battery and an adjustable constant current regulator at around 20-30A for now, but may move to a higher current later with larger batteries. By using a constant current, I can ensure that the torque is constant (and maximal) throughout the run, until maximum voltage is reached and the torque begins to diminish with further acceleration. Besides giving the best acceleration, this scheme also makes the performance of the vehicle highly predictable; I can calculate pretty much exactly how far it will be and how fast it will be going at a certain time.
To regulate the current I have come up simple with a PWM regulator controlled by a hall effect current sensor (thanks Steve Ward for the advice!) based on the TL494 and a single MOSFET. The current through the hall effect sensor induces an output voltage which is compared to a selectable reference voltage by the TL494, and the pulse width is adjusted accordingly to equate them.
I intend to enable to vehicle either with an overhead wire which closes a switch, or with a 555 timer that simply runs the vehicle for a calculated amount of time. The enable relay switches the controller input from ground to the reference voltage, so that the circuitry can be powered up beforehand. When the vehicle is not enabled, the motor will connected across a low resistance of a few turns of nichrome wire, which will act as an electric brake.
Below is the schematic and PCB layout as they are so far. More to come after it is tested, including pictures of the car. I am not very familiar with the TL494; this will be my first time actually using it. I'm looking for any additional help or comments before this gets underway.
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Constant Current Motor Controller
