# motor dc control

#### neiji

Joined Jul 25, 2007
19
this is a question that i have been asked recently. if you have a small dc motor(Vrated=1.5V) and it is connected to battery (1.5v), the motor is supposed to run. however if you hold/blocked the rotating part it stops even though it is still connected to the battery.I know that voltage determine the rotating speed but in this case even with the 1.5V battery it stop rotating. the answer i came with is that the power delivered by the battery is not sufficient to overcome the blocking force. is this a valid reason or do you have another answer.

#### beenthere

Joined Apr 20, 2004
15,819
The battery drives current through the armature windings. The resulting magnetic fields generate a torque on the shaft, alternatingly pulling towards and pushing away from the fixed magnets inside the case.

If you hold the shaft locked, there will be a point where the armature will overheat and fail without being able to turn the shaft. It probably won't happen with a 1.5 volt motor, unless you try to run it on a higher voltage. 12 volts might cause an immediate failure even if the motor is free to spin.

#### thingmaker3

Joined May 16, 2005
5,084
The current still creates the magnetic fields, and they still exert force. In this instance, the force of one's fingers is simply greater.

#### recca02

Joined Apr 2, 2007
1,214
another way to look at it wud be power =torque*speed
since power is quite low and torque is comparatively very high speed is negligible (practically zero)

#### thingmaker3

Joined May 16, 2005
5,084
Indeed. Approximate Ounce-Inches of torque = 1,000,000 * horsepower / r.p.m.