On Tuesday 27 October 2020 00:42:28 Thaddeus Waldner wrote: > Hazarding a guess here so... > > It appears as if you are switching the direction signals at pwm > frequency. This would switch the high side fets and those are slow and > do have high switching losses. The intended design is for the low side > fets (controlled by the PWM input) to be off until the switching is > complete, and only then to resume current. Why did they choose those > transistors for that application? Who knows.. maybe to eliminate the > need for external bootstrap circuitry...
The direction signals aren't being switched or gated by the pwm. They are determined by the sign of the applied .value applied to the pwmgen. But there is zero both low or both high time, defined as braking. So they are basicly a dc signal. They Only see heavy activity when the spindles Pgain is high enough its actually oscillating at the pwm frequency. And that applies only to the Pico pwm-servo I use for the spindle, not to this olimex board. But since the motor isn't running, its moot that there is no feedback, so the current pid config is as a lowgain dc amplifier only. FF0=1, everything else is zeroed. The board as a whole is acting as if the motor is shorted, but the motor runs normally if connected directly to the 24 volt 350 watt supply, at probably about an amp no load. This 40 volt, 30 amp rated board has NEVER moved the motor, connected to that same supply it just does a thermal shutdown long before the on time of the pwm has reached 20%. With the motor connected to the 150 watt class D audio amp, and powered by this same 24 volt supply, and the 150 watt amp driven by a 20 Hz sine wave from a function generator, it makes a great, will numb your hand in a minute or two, hand massager. I don't dare let go of it as it will dance right off the kitchen counter. The 420 watt amp won't move it, and generates no heat sink temp rise, apparently it needs an AC supply to make a bipolar on-board DC. I have some suitable toroids to power it with, took them out of the Sheldon kit when I switched the steppers out for 3 phase stepper-servo's. But no d to a to drive it with from LCNC. > >>> But the switching losses in the olimex board, even at only > >>> a 1 kilohertz pwm are killers, getting it hot enough to > >>> burn a finger in just 2 or 3 seconds. Thanks Thaddeus. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
