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Old 03-22-2020, 09:19 PM   #1
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Default Dahlander motor control

I have to convert a lathe that has a Dahlander switch for two speeds. straight delta for low and a double star for high. Customer wants a VFD. I think I can figure out all the safeties but would like some opinions on which motor method would be best the star or delta.
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Old 03-22-2020, 10:23 PM   #2
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The vast majority of 2 speed motors I've installed VFDs on, I use high speed. It gives the greatest speed range.
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Old 03-23-2020, 01:03 PM   #3
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A "Dahlander" motor is the IEC term for what we call a 2 speed 1 winding motor.

There are 3 types of 2S1W motor designs, so what you do in hooking up a VFD is going to depend on which type you have and what you need from the machine.

2S1W Variable Torque motors will list two different HP values on the nameplate, and the slow speed will be 1/4 of the high speed. In this case, you want to use the High speed connection to get the maximum torque using the VFD.

2S1W Constant Torque motors provide the same torque at either speed, so the HP values on the nameplate will match the ratio of the speeds, i.e. if the Low speed is 1/2 of the Hi speed, the Low HP is 1/2 of the Hi HP. In that case it really doesn't matter which speed you connect the VFD to, but if you connect to low speed, you will not be able to go faster than that(without losing torque).

2S1W Constant HP motors will only show one HP value even though it has 2 speeds. In that case, the motor torque at the low speed is HIGHER than it is at the high speed, so which speed you use with the VFD will affect the motor shaft torque.
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Old 03-23-2020, 02:10 PM   #4
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Wire the motor for high speed and if you are going to use another motor connect it for "Run" which would be delta on most 3 phase motors.
Also, if the lathe has pulleys used for speed control, use the highest speed. This will give you full speed range.
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Old 03-24-2020, 11:00 AM   #5
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thanks much.
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