Motor speed help

[Patrick Morrison]

Hey,

Complete novice to electronics here, and I was wondering if I could get some help. I'm trying to rig up a dc motor to a 9v battery and use a potentiometer to adjust its speed. I thought I calculated proper resistances, but so far I've either had a motor that didn't move, or pots that caught on fire. I measured the motor as drawing 62 miliamps, with of course 9v in the circuit, when there is no resistance.

Any help would be appreciated!

 

[Minder]

A simple PWM controller designed around a 555 is a simple approach, there are many designs out there and $5.00 ones on ebay.
M.

 

[(*steve*)]

Motors are a type of load that is not easily controlled by a potentiometer. They require higher currents to start than the do to continue rotating. A resistor will limit this peak current far more than the operating current. This means that you may have trouble starting the motor. In addition, when in this state, most of the voltage appears across what may be a small section of the pot which will be called on to dissipate more energy than it is capable. At this point it lets out the smoke.

All of this is to say that your experience with a pot is not at all unusual.

Minder's solution is far better.

 

[Patrick Morrison]

A simple PWM controller designed around a 555 is a simple approach, there are many designs out there and $5.00 ones on ebay.
M.

sorry, should have said that integrated circuits aren't allowed.

 

[(*steve*)]

Please post your homework in the homework section.

 

[Audioguru]

sorry, should have said that integrated circuits aren't allowed.

We might not find anybody who remembers how it was done 55 years ago without integrated circuits.
Can your teacher remember how it was done? Why doesn't your teacher teach how it is done today?