Re: [CAD_CAM_EDM_DRO] Stepper motor voltage VS amps.

sriddle68 wrote:

>I am looking and making a small 3 axis CNC mill for wood routing and
>such. I have been surfing through Ebay and it's endless supply of
>varied stepper motors. The question I have is this. I see several
>postings that say for the power source to use 20-25 times the motors
>rated voltage. So if the motor says 2V you should use 40-50V. I
>understand this is done for responce and such but what about the
>amperage? If it says 2V 3A should you supply 40-50 Volts and 3 amps?
>Or do you supply it the same wattage as the motor plate adds up to?
>2V x 3A = 6Watts. This seems to low.
>
>

Yes, it is too low. The motor and a chopping-type driver WILL draw
something near
2 (windings) x 2 V x 3 A = 12 Watts when not moving. But, when
accelerating, it will
draw considerably more, as the back-EMF (self-generated voltage) created
by the motor's
rotation increases the voltage that needs to be applied to the windings.
On the other hand,
when moving, the current in the two windings are never at full strength
at the same time,
therefore, the current can be considered to be .667 times 2 x the rated
winding current.
Most unregulated power supplies can deliver 2 x the rated current for a
brief surge,
and in most home-use machines, the bursts of acceleration will not be
happening that
frequently. (A router is probably more demanding in this regard than a
milling machine.)
The worst case would be 3 axes x 2 windings x 3 A x .667 = 12 A. I
think a 6 A power
supply would work fine in most cases.

Jon