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October 7, 2006

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).

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October 4, 2006

Should I use a zero-crossing type solid state relay (SSR), or a random phase type to operate the motor?

Filed under: AC Gearmotors, Speed Control Motors — mota @ 3:44 am

Zero-crossing type SSR’s cost more and lasts longer, but is safer in that it reduces sparks since it waits for the AC voltage to become zero before turning on. However, since current is delayed (due to coil inductance), there is still a small chance of sparking. Drawbacks: Delay in starting (waiting for zero crossing) and delay in stopping (due to residual current). ES controllers have a zero-crossing SSR built into them.

When designing a circuit with SSR’s, which reverses a reversible motor on-the-fly, make sure that there is at least a 30ms delay between the CW turning off and CCW turning on. This is because the residual current makes the motor continue CW, while the CCW command will make the motor try to start in the CCW direction. Without a 30ms delay, this could cause a problem in operation. The ES Series already has this 30ms delay built in.

Can I use an electromechanical card relay between the PLC and the DC Brushless driver?

Filed under: Speed Control Motors — mota @ 3:04 am

The solid-state relays (SSR) are more expensive than the electromechanical. Would the motor driver have a problem with the bounce created from the electromechanical relay?

Using an electromechanical relay is no problem. The AXH driver accepts both dry contact switches as well as solid state relays. All it needs is a path to ground. The bounce created from an electromechanical relay will not create a problem because the system is not fast enough to where any bounce would make a difference. Please see pages 20 and 21 from the AXH manual. www.motadistribution.com

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