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October 4, 2006

How can I get higher starting torque out of an AC motor?

Filed under: AC Gearmotors — mota @ 3:38 am

Use a reversible motor. They have higher starting torque than their Induction an Synchronous counterparts. Don’t forget about inertia. The permissible inertial loads (p. A-12) will not change. www.motadistribution.com

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Will Induction motors have a higher in-rush current when starting up?

Filed under: AC Gearmotors — mota @ 3:20 am

In-rush current = 2-3x rated current, and duration is 100 ms.

Click this link to choose Induction motors. Or if you already know your part number (eg: 5IK60A-AWU), use mota search: www.motadistribution.com

Are the cooling fans of AC motors using Loctite?

Filed under: AC Gearmotors — mota @ 3:18 am

No, Loctite is not used on the cooling fan cover screws of the 5IK60 type. The factory can put the Loctite on the screw as special product if the customer wants. In such a case, a technical inquiry needs to be submitted through the manufacturer, and there will be an extra charge to the customer. Please contact us to start the technical inquiry: www.motadistribution.com.

In the past, there was a case of the fan cover coming loose, but this machine had a lot of vibration.

Can we lower the capacitance value to allow a reversible motor to run at continuous duty?

Filed under: AC Gearmotors — mota @ 3:16 am

Yes, but only on the World K and V Series (3 wire reversible motors).

Advantages: Runs cooler, allowing for continuous duty.

Disadvantages: Less starting and rated torque.  May affect reverse-on-the-fly capability.  Motor loses UL certification.

Can I use the same capacitor of an AC motor rated for 115VAC/60Hz overseas at 120VAC/50Hz?

Filed under: AC Gearmotors — mota @ 3:16 am

The same capacitor might be fine at 120VAC/50Hz. But, we can’t give the customer any guarantee, nor is there any UL certification.  If the motor case temperature is less than 90°C after saturation, we can expect the same life time with using at 115VAC/60Hz.

If the temperature is higher than 90°C, we should recommend a different capacitor.  If the customer wants a guarantee to meet certain specifications, we have to evaluate it and then make it as a special product.

Using a three-phase voltage input type eliminates the need for the capacitor and there’s no need to consider the above issue.

How can I test an AC motor to see if it’s still good or if it’s been shorted?

Filed under: AC Gearmotors — mota @ 3:14 am

One way to do this is to measure the resistance in the windings.  If using a single phase motor, remove the capacitor and measure the resistance between the black and red leads.  Now measure between the black and white.  The two resistance values should be about the same.  This indicates that the motor is fine.  If either value is zero or close to zero, then the motor has been shorted.

For a 3 phase motor, measure between any 2 wires.  Measure all 3 combinations and compare.

3-Phase motors vs. 1-Phase motors.

Filed under: AC Gearmotors — mota @ 3:13 am

Since 3-phase motors operate on 3-phases, there is no need to use a capacitor to obtain a shift in phases.  One characteristic of 3-phase motors is that they have a much higher starting torque than 1-phase motors.  When there are not any negative torque elements, there is no need for a reversible motor.

How does the tachogenerator on the back of an AC motor work?

Filed under: AC Gearmotors — mota @ 3:11 am

The tachogenerator creates a single phase, AC voltage out of the 2 wires.  The output signal of the tacho-generator motor has 2 components: voltage amplitude and frequency. The amplitude represents the speed of the motor. This amplitude is subject to other variations besides the motor speed. The primary factors are the tolerances of the winding resistance and the magnetic flux density of the magnet.  Also, as each motor heats up, the resistance will change and the magnetic flux density can also change. 

The frequency of the signal can be easily calculated by the formula: (N/60) x 12 = Hz where: N = speed of the motor in rpm, Hz = frequency of the voltage signal, the 60 is used to convert the units from minutes to seconds, and the 12 comes from the fact that the generator uses a 24 pole magnet , which will give you 12 cycles per revolution.  Temperature of the generator itself will not affect the motor speed.  Keep in mind that as the motor heats up, the torque that it produces will reduce, which will cause the motor speed to decrease, assuming a constant friction load. This is normal.

Capacitor start motor vs. Permanent Split Capacitance (PSC) motors.

Filed under: AC Gearmotors — mota @ 3:10 am

Smaller motors will typically have a permanent split capacitor (psc) design, and is more efficient that way.  Larger motors will usually have a capacitor to start.  Capacitor start motors tend to overheat with a lot of starts and stops.

October 3, 2006

Can I use a Variable Frequency Driver (VFD) / Inverter to control the speed of the AC Motors?

Filed under: AC Gearmotors — mota @ 10:51 pm

Yes.  AC motors can be controlled via frequency.  The permissible frequency range is 10-80 Hz.  Only Three-phase, 230VAC motors can be used. 

Calculating the synchronous speed of the motor is accomplished with the following formula: Ns= 120*frequency / Number of poles. 

Limitations on maximum frequency include the permissible torque of the gearheads being able to handle high speeds, and the outside temperature of the motor not rising above 90 degrees.  Click this link for other technical information regarding AC gearmotors’ speed related issues.

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