Electronic – Can a DC motor with obstructed movement be damaged

control systemdc motormicrocontrollermovement

I am trying to build shades, which should roll up or down, controlled by a DC motor. This motor can only be turned on or off (1/0 to turn it on/off). Also, it should be noted that the microcontroller behind this is a NI-SPEEDY with a daughter board that provides relay switches (not a range from -1 to 1).

The first thought was that when given a 1, it should roll it up then stop. And when given 0, it should be turned off and let gravity pull it down.

The problem is with stopping: I can't figure out a way to make it stop when it reaches the top. So I thought I should leave it on. But since it won't be able to rotate, I guess it might be damaged. How critical can such a thing be?

UPDATE:

This is the datasheet of the DC motor:

Matsushita Electric, Japan
13.2V DC
MYT-5AC8

Similar to this one and that one.

A 12V battery is plugged to the daughter board of the microcontroller. The motor gets 12V DC, but I'm not sure about the current that is drawn to it.

The battery specs: 12V 7.5Ah/20hr

I tried keeping it plugged to the battery for a minute, and the heat produced was negligible, but I guess keeping it for more than that will fry it.

UPDATE 2:

After trying almost all of the technically possible solutions provided, it turns out all the sensors we put were mechanically not possible to set up. They either were never activated or not reliable. Also, the circuitry involved seemed too complex (you might have noticed I'm a beginner) for two states (0/1). And since the controller is a requirement, it was not possible to use PWM or any other technique to control it via software.

All in all, this was very helpful, I learned a lot. Now let's just hope the motor will not be damaged by the time it is presented to the jury.

Best Answer

Yes, leaving it running will stall the motor and thus draw a lot of current and eventually overheat it. A few possible solutions, sorted roughly by increasing cost:

  • Figure out how long it takes to roll them up and program the controller to run the motor for a set time (dead reckoning).
  • Measure the current being drawn by the motor and immediately stop when the current goes over a certain threshold that indicates a stall. If it stops promptly enough the motor won't have a chance to heat up too badly.
  • Add a limit switch at the end of the range of motion. Given that you're rolling up shades, I'm not sure if you could position the switch to do that.
  • Mount a distance sensor of some sort (probably IR) just below the top of the shade so that it becomes exposed once the shade is fully rolled up. This will effectively work like the limit switch idea.
  • Closed-loop speed control of the motor with a shaft encoder.
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