Synchronous Motor

ToneWheel Hammonds use a *synchronous motor* to turn the ToneGenerator. A synchronous motor is a electric motor whose rotational SynchronousSpeed is locked to the AC line frequency. A motor consists of the *armature* built into the frame of the motor and the rotor* which turns inside the *armature.

The *armature* consists of copper windings that convert the incoming alternating current into a pulsating magnetic field. Organs used on 60Hz power systems use a six winding or "six-pole" armature. On a 50Hz power system, the *armature* has four-poles. A two-pole *rotor* turns inside the armature. The rotational speed of a synchronous motor is equal to (120 x Power Frequency) / No. of Poles in the Armature. So the *rotor* inside the six-pole *armature* turns at (120 x 60) / 6 = 1200 RPM. On a 50Hz organ, the *rotor* turns at (120 x 50) / 4 = 1500 RPM.

Before organs, Hammond made HammondClocks --- the first clocks to use the AC line frequency for a time reference. The AC line frequency was not very stable in the early days of electrification. Laurens Hammond reportedly sent free clocks to upper level managers of various power companies to encourage them to hold the line frequency at a steady 60Hz (or 50Hz). Line frequency stability is, of course, critical to keeping a Hammond clock "on time" or organ "in tune."

As of July 2011 there is a active proposal by the Federal Energy Regulatory Commission to test allowing the AC line frequency to "drift" within a wider range around 60Hz. A great deal of energy goes into keeping the line frequency constant, so the rational for this test is to explore possible energy savings. Most likely, the line frequency will increase "slightly" making all Hammond organs sharper in pitch. Joe ~?McClelland, head of electric reliability for the Federal Energy Regulatory Commission asks “Is anyone using the grid to keep track of time?” ~?McClelland said. “Let’s see if anyone complains if we eliminate it.”

Synchronous motors are not self starting: the HammondClocks have a knob in the back that one has to spin to start the clock. The Hammond organ patent application showed a hand crank on the side of the organ to start the motor! Wisely, Hammond added a separate inductive StartMotor which is used to get the ToneGenerator up to speed. See HowToStartAHammond.