On Wed, 2011-12-28 at 12:03 -0500, gene heskett wrote: > There are hall effect based ammeters
A while back, I mooched a Tek Hall-effect current probe from my buddy Eks to take some interesting pix: http://softsolder.com/2011/06/20/stepper-sync-wheel-current-waveform-first-light/ http://softsolder.com/2011/06/27/stepper-motor-winding-current-rise-time/ The winding current stays within a skosh of the setpoint for each microstep, which the driver determines by applying the sine & cosine of the microstep (electrical) angle to the overall peak current setpoint. That may also contribute to the mystical 70% derating factor, because in full-step mode the driver (well, Allegro drivers, anyway) applies 1/sqrt(2) = 0.71 of the peak current setpoint to *each* winding. That keeps the overall motor power dissipation the same, but the total current into both windings is 2*(1/sqrt(2))*peak = 1.4*peak. Perhaps the person who first stated that factor, back in the dim past, forgot about the current in the *other* winding? While I was doing that, I managed to stoke a mechanical resonance that back-drove the winding current something awful: http://softsolder.com/2011/09/12/stepper-dynamometer-mechanical-resonance/ Keeps me off the streets at night... [grin] -- Ed http://softsolder.com ------------------------------------------------------------------------------ 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
