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October 7, 2006

How far away can I wire the capacitor from the motor?

Filed under: AC Gearmotors — mota @ 2:20 am

There is not a published maximum distance. However, anything within 1m or so should be fine. Much farther than that, and we get away from the designed 90 degree electrical phase shift that the capacitor was sized for, since the wire itself has inductance and capacitance. As a result, the AC motor runs less efficiently, and therefore hotter.

Long wire runs also results in voltage drops. That would mean that the capacitor phase would have less torque (proportional to the square, or up to 2.5 power, of the voltage drop).

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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.

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

How do I protect against in-rush current?

Filed under: Stepper Motors — mota @ 3:20 am

Looking to size a fuse when the maximum input current is 5.0A. You will need a 5.0A slow blow fuse. This will protect against possible in-rush current.

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.

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