Re: [CAD_CAM_EDM_DRO] Re: CNC newbie questions

john_haddy wrote:

>>>-----Original Message-----
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>>>2/ I'm having trouble understanding the power supply
>>>requirements that I've seen documented (e.g. in Gecko Drives'
>>>white paper). Assuming the motor is at rest in the 45 degree
>>>step position, where the motor will need the maximum current,
>>>each winding needs to be powered with Iwinding =
>>>Imax/sqrt(2). From this, it would appear to me that the drive
>>>power supply needs to provide an average current of 2 x
>>>Iwinding = 1.4 x Imax This conclusion doesn't gel at all with
>>>the requirements in the white paper (in that my calcs show a
>>>MUCH gruntier supply is needed), so I'm confused as to where
>>>I've got it wrong.
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>Tim,
>
>Is this 4 amps per motor? If so, then this is even larger than
>my calculation (being a peak current of 2.83A for a 2A Imax
>motor). Or is it 4A for the 4 axis drive DenverCNC box (i.e.
>driving 4 steppers)?
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This is the highest current the driver can draw, with the motor running at
maximum speed, and accelerating or driving a load. The motor would
almost certainly stall under these conditions. And, you just can't keep
this
up on most positioning systems. The idle and low-speed power draw
will be dramatically less. At idle, the power draw would be 1.4 * Imax *
winding voltage. Winding voltage is usually between 2 and 4 V at rest.
So, that is 1.4 * 2 * 4 = 11.2 W. If the power supply is 50 V, it will draw
11.2/50 = .224 A at rest. Actually, due to losses in the drive and motor,
it will be a little higher. A current of 2 Amps average over a long time
is a good guess, for continuous movement.

Jon