Ray Henry wrote: > I guess we must be looking at or thinking about different things. > Perhaps I did not say it well. The DRAW on the power supply is what I'm > saying is greatest at zero speed. After all the comment in the earlier > post was that the DRAW on the power supply would be greater during > acceleration. That statement would be true of a servo motor but is NOT > true of a stepper. At least that is my understanding of the meaning of > life. That is certainly true of the ghastly old L-R drives, may they all rest in peace (or in pieces!)
Newer drives, like Geckos, Xylotex, etc. limit the current like a switching power supply, and so at standstill and low speeds, very little voltage appears across the windings, and so very little power is drawn from the power supply. For instance, assume a mid-size motor, with a 4 A 2 V rating (that would be 1/2 Ohm per winding). Idling with one coil at full current, it would be dissipating 4 * 2 = 8 W in that coil. But, with a 50 V power supply, it would only need to draw 4 * ( 2/50) = 0.16 A from the supply. So, a Gecko 201 drive would draw about 1/5 Amp to keep such a motor idle, WITHOUT the idle current reduction. (It may be slightly higher depending on the phase of the microstepping, as it may be feeding partial current to both windings.) At very low speed, the current won't be a lot higher, but then it climbs as the drive needs more transistor on time to fight the rising back-EMF of the motor. At some speed the current peaks, and then the motor's inductance takes over and the current falls back again as the combination of back-EMF and inductance make it impossible for the DC supply voltage to charge the windings each cycle of the waveform. Load on the motor does affect the phase angle of the current, so a loaded motor will cause the drive to draw more current from the supply. With modest-sized motors this is a pretty small effect, but with size 42 and larger, it can be quite significant. Jon ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
