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What kind of connection is there betweeen Amp Turns and Motor Torque Constant?

  1. Mar 23, 2008 #1
    I have a question concerning a range of simple electromagnets I have been building for motors. It seems that for a given gauge of wire (I used 28AWG), the larger I make the coil, the more torque I get (change of angular momentum / time) for the amount of amperage I am using. In my latest easy-to-build electromagnets, one of them has 1300 feet of wire about 1000 turns and the other has 4000 feet of wire and about 2400 turns. When I operate them using 16 double AA batteries connected in series, the first one runs for 50 hours at 1800 rpm (using two regular domino shaped magnets as my rotor) at 20 volts. The other one I have just built uses about the third of the current and runs on the same battery which I have tested at 22 volts and have observed to be running at 1350 rpm. I used the same rechargeable batteries in each case. What I observed is that my newest electromagnet with 2400 turns, which is more than three times heavier, has considerably more torque at low speeds than the one with about 1000 turns. Why then do I not observe a significant increase in amp-turns while I do observe significantly less amperage in my larger coil (using an TrueRMS Multimeter) even when I tested it at a higher voltage?

    I believe it has to do with the torque constant of the motor. But what is the theoretical maximum torque constant of the motor? I know torque is angular momentum transfer per unit time, and that it is also work done per angle. I have observed my 4000 foot coil to have considerably more torque against the rotor I try to stop with my hand even at lower revolutions per minute. I know the relative motion of charges in the coil, produced by their acceleration due to electrical potential (due to proximity of charges) being consumed when overcoming a resistance, generates magnetic field which has its own energy. But what is the theoretical maximum torque constant of the motor?
    Last edited: Mar 23, 2008
  2. jcsd
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