Re: [CAD_CAM_EDM_DRO] Re: mill servo conversion ?'s

Roy J. Tellason wrote:

>On Thursday 05 August 2004 11:57 am, Jon Elson wrote:
>
>
>>>If they are, where is there a better deal? And why
>>>isn't it more widely publicized? Also, why do you recommend a 80-120V
>>>power supply for the Ameteks when camtronics only sells a 36V for them?
>>>
>>>
>>For performance. To get full peak torque, you need to deliver 12 A
>>to the motor. With a 36 V power supply, you can't deliver 12 A to a 4 Ohm
>>motor, even standing still. At 900 RPM, the back EMF of the motor is
>>approximately 36 V, so you can produce zero torque! This severely
>>limits performance. I have a client in town who has an 800 Lb Grizzly
>>style machine with these motors and a 36 V supply, and the performance is
>>pretty weak. To get full peak torque at rated speed, you need 36 + 12 * 4=
>>84 V minimum, appled to the MOTOR itself. You need some margin for the
>>modulation scheme of the servo amp. too. So, a 120 V supply sounds good,
>>but if using Gecko 320 drives, 75 V or so is the limit. With a 5 TPI screw
>>driven directly, you get 180 IPM, which should be plenty for most users.
>>But, if belt reduction is used, or if the screw is finer than 5 TPI,
>>then the max rapid rate goes down, even with the higher voltage.
>>
>>
>This part of your post I don't quite follow. How are you figuring out what
>the back EMF of a motor will be? I feel like I'm missing something here...
>
>

That's a rating that usually appears on the label of the motor as Ke.
It will be in Volts per Radian/Sec or Volts/kRPM.

- Steve