Sorry, but a different opinion here.... Gecko publishes the 67% number based on real world experience with a large number of motors and power supplies tested.
The reality of calculating the current needed is daunting. First you start by looking at power, which is what is really being delivered. The Gecko drivers are modern chopping drivers which behave somewhat like a switching power supply. They convert a high voltage moderate current into a lower voltage at a higher, but regulated, current to drive the motor. For the same driver and motor the current drawn from the power supply will be different (lower current) for a higher voltage power supply than for a lower voltage one. Indeed, I have seen drivers overheat simply because the power supply voltage was too low. This is a natural result of the driver delivering a mostly constant amount of power, but having to draw more current to do so. Heating in the driver is dominated by I squared R when the MOSFETs are fully turned on, and twice the current results in four times the heat losses. Things get complicated because the power required is the sum of: 1) mechanical power delivered by the motor 2) mechanical losses within the motor (bearing and air drag) 3) resistive losses ( I squared R ) 4) hystersis losses in the iron (this is often the main cause of motor heating) 5) efficiency of the driver itself Modeling all of the above is a lot of work, even if you do have accurate data to start from. Gecko has stated that the 67% is the most you are going to need assuming you have selected a reasonable power supply voltage and are driving the motor to deliver its maximum mechanical power output. The fact that most machines only move two axes at a time for most operations will mean that the mechanical part of the power is less, but the other factors are not much effected by the mechanical power output. I generally tell my customers that 50% is good enough for typical machines, 67% will provide for anything you can ever hope to achieve, and anything more is purely for bragging rights. Regards, Steve Stallings PMDX > -----Original Message----- > From: Dave Caroline [mailto:dave.thearchiv...@gmail.com] > Sent: Wednesday, December 28, 2011 1:27 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] stepper power supply > > The reason they state 67% is because they are not getting the full > torque from the motor > They are not fully powering both windings and there is an > assumption that > the motors are not all in the same phase so some windings are > partially powered. > for full step and full power you power both windings fully. > > > see half step and microstep sections > http://en.wikipedia.org/wiki/Stepper_motor > > Dave Caroline > > -------------------------------------------------------------- > ---------------- > Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't > need a complex > infrastructure or vast IT resources to deliver seamless, > secure access to > virtual desktops. With this all-in-one solution, easily > deploy virtual > desktops for less than the cost of PCs and save 60% on VDI > infrastructure > costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Ridiculously easy VDI. With Citrix VDI-in-a-Box, you don't need a complex infrastructure or vast IT resources to deliver seamless, secure access to virtual desktops. With this all-in-one solution, easily deploy virtual desktops for less than the cost of PCs and save 60% on VDI infrastructure costs. Try it free! http://p.sf.net/sfu/Citrix-VDIinabox _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
