On Thursday 15 October 2020 23:03:00 Jon Elson wrote: > On 10/15/2020 09:49 PM, John Dammeyer wrote: > > The theory is that if the PWM signal is high the H-Bridge is > > switched to say turn the motor clockwise. If the PWM signal is low > > the H-Bridge is switch to turn the motor counter clockwise. > > Therefore with 50% the motor is first asked to turn one way and then > > the other. That results in the motor essentially being locked in > > place. Change the PWM on either side of 50% and the turns in the > > subsequent direction. >
> This is called synchronous antiphase. The advantage is > there is no dead zone around zero. > The DISadvantage is it causes a triangle-wave current in the > motor which can be quite substantial, > and causes excessive heating of the motor and power transistors. > > Jon But, given fast enough switching fets, can this disadvantage not be addressed with a combo of near the high limit for pwm frequency, and a suitable, non-saturating toroid in series with the motor? Currently I appear to have a mess in my G0704's hal file, leftovers I didn't clean up after converting it from a 5i25 and 2 bobs, to a 5i25, a bob on the 5i25's p2, and a 7i76D on p3. I have a pair of the VNH3SP30 based boards coming, which I think can be driven with a pwmgen in mode 2, but the other one in that lashup is currently running in pdm+dir, or mode 1 to drive the spindle output of the 7i76. So, 2 questions for Peter CW: Can I run the 5i25's pwm-gens in different modes? If so, how? If I use the VNH-based boards for an axis A, driving this BS-1 clone, I'll need mode 2 for that. If that won't fly, then: If I use the 150 watt rated class-D audio amp board I'll also have 2 of in about 5 days, I'll need to short its input caps in order to establish a DC path, but with the available hal modules to add the 50% offset, that doesn't appear to be more than a config problem. But the power supply is 24 volts, and the audio board says 27 volts max. Thats rather close to breaking the mirror and letting all the smoke out. >From my reading between the lines, the audio boards pwm can run at 500 Khz max. I think thats well above what the 5i25's pwmgens can run at, requiring more inductance to control the ripple current. Maybe I'll kill them, but at $13/copy, its worth a try if only because its 50x faster than the 10 Khz max of the VNH based board. At 86, I can't really hear it, but it can still give me a headache rather quickly. BTDT fairly recently. And looking over that hal file, I need to move the outputs on the encoder.1 pins, a std bob to someplace on the 7i76, as enabling the 2nd encoder steals those last 3 p2 pins. Fun and games if I can recall the rules. Discussion? > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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
