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October 7, 2006

How is CN3, the regeneration unit connector, to be used?

Filed under: Stepper Motors — mota @ 3:01 am

In occasional cases where the AS motor is driving very large inertial loads, a regeneration unit supplied by OM can be used. P/N: RGA50-A (100V), and RGA50-C (200V). CN3 on the driver is actually connected direclty to the rectified DC power from the driver, and is around 164VDC. The regeneration unit from OM connects to CN3 and, by using a current controlling circuit, absorbs any surges in current caused by back emf. Therefore, customers should not design their own regeneration unit for this purpose.

How do I apply power to the electromagnetic brake wires?

Filed under: Stepper Motors — mota @ 2:59 am

For the AS46 (size 17), apply 24VDC, 0.3Amin. to the red and black wires that come off directly from the magnetic brake unit. For the AS66, AS69, and AS98, you must use an extension cable, which is designed to have the power wires pigtail from the cable. Apply +24VDC to the orange/black wire (orange for flexible cable), and GND to the gray wire.

Can I use the END output signal as a trigger to turn on/off the magnetic brake via a relay?

Filed under: Stepper Motors — mota @ 2:57 am

Yes, but you need to have a programmed delay before the motion starts and after the motion ends. You can do this through the PLC’s timer function, or if using the SC8800, feed the END output signal from the AlphaStep driver into one of the SC8800’s inputs. From there, you can use conditional statements, e.g., If IN1=1, DELAY=0.2, MI, etc. Remember, the END signal comes on only when the deviation counter (the difference between the pulse counter and rotor position counter) is within +/- 1.8° of the commanded position. So pulses may have stopped, but the rotor is lagging due to inertia, velocity filter setting, etc. If you didn’t compensate for this slight delay, the brake would come on right after the pulse train stops, and that would lead to premature brake wear and possibly inaccurate positioning.

Are the commons on the AlphaStep inputs & outputs on the same node, i.e., is there a possibility of grounding loops occurring?

Filed under: Stepper Motors — mota @ 2:54 am

The common grounds for the AlphaStep inputs & outputs (Pins 2, 14, 16, 24) are all on the node, so that regardless of which voltage you use (5V or up to 30V), you have the same DC ground. The cathodes for the inputs & outputs (Pins 10, 12, 22, 32, 34 on the inputs and pins 24, 26, 30 on the outputs), however, are not on the same node since it relies on the grounding on the customer’s side. Our driver relies on photocoupled signals.

Why do some of the OM motors have Class E (248F) insulation class windings, but UL only recognizes them as Class A (221F)?

Filed under: AC Gearmotors — mota @ 2:51 am

Class A (221F), Class E (248F), Class B (266F).

UL does not have a category for Class E, so we have to be recognized using the next lower class.

Replacing 220/240 VAC motors.

Filed under: AC Gearmotors — mota @ 2:49 am

These p/n’s are older K Series motors designed for the European market. When these were designed for 220/240, the stator targeted around 230V (middle of 220 and 240). Movex show these are “D” ranked, so now obsolete.

With the -CW motor, the stator design targets around 215V (middle of 200 and 230). This is a different design that one targeted for 230 (middle of 220 and 240). Today, OM only supplies World K type motors to Europe, as there have not been any “new designs” of 220/240 motors. Therefore the customer has these options:
1. Order a special motor for 240VAC or,
2. Use a transformer and a -CW motor or,
3. Use the -CW and test for temperature rise.

2 other important points:
1. Make sure the capacitor’s voltage is rated at about 2x that of the applied voltage. (e.g., 220VAC needs 450V cap., and 250VAC needs 500V cap.)
2. At high voltages, there will be much more torque (torque is proportional to the square of the voltage), so the gearhead will receive more shock during accel. and decel.

What is the service factor of OM’s AC motors?

Filed under: AC Gearmotors — mota @ 2:45 am

Service factor (a NEMA term) represents how much over the “nameplate rating” an AC motor can by driven without overheating. The OM catalog states rated torque which represents 100% of the load that should be applied to the motor, at the specified ambient temperature range. We don’t recommend any value over the rated torque, and have not tested for loads which will result in overheating. Therefore, our service factor is unity, or 1.0.

If the overloading is a result of the acceleration. and deceleration of the load to the motor, then the sizing of the motor needs to be considered. The starting torque would have to be greater than the total of acceleration torque and constant torque, multiplied by some safety factor.

Reversible motor duty cycle.

Filed under: AC Gearmotors — mota @ 2:40 am

Reversible motors have a higher starting torque compared to normal Induction motors to help it reverse directions quickly. This, in addition to the heat caused by the brake mechanism of the Reversible motor, makes the motor very hot and hence a 30 min. “ON” time (regardless of direction) rating. The key factors are the ambient temperature and duty cycle %. As long as the motor case temp. is below 90°C, you can safely increase the duty cycle % and/or the 30 minute rating.

What does the safe operation line mean for AC speed control motors?

Filed under: Speed Control Motors — mota @ 2:35 am

Input power to thep AC speed control motor varies with the load and the speed. The greater the load, and the lower the speed, the higher the motor’s temperature will rise (due to operation at less than peak efficiency). The safe operation line (p. F-22) is a representation of how much heat the motor can safely dissipate through its casing. Therefore, you should only apply a torque load to the motor which is at or below the safe operation line. The motor is capable of continuous operation as long as the case is below 194°F (90°C).

Induction vs. Reversible motors.

Filed under: AC Gearmotors — mota @ 2:26 am

World K Series Induction and Reversible motors have the same stator design with balanced windings (primary and secondary coils wound the same), and the same rotor. The only difference is the capacitor. The higher capacitance value for the Reversible generates a higher starting torque for reversing, and eliminates the negative torque area in the speed-torque curve. The higher capacitance results in higher temperatures, which is why we have a limited duty cycle.

K Series Induction motors have 4 wires, and the Reversible has 3 wires. In the Induction motor, the primary is wound differently than the secondary, and is a more efficient motor. The Reversible motor has balanced windings. Sometimes, the rotor on the reversible will incorporate a lower head height, which increases the resistance in that area, resulting in a higher starting torque.

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