On Sat, 4 May 2013, Viesturs L?cis wrote: > Date: Sat, 4 May 2013 23:27:13 +0300 > From: "[UTF-8] Viesturs L?cis" <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] Blown fuses on 7i39 cards > > 2013/5/4 Peter C. Wallace <[email protected]> >> >> >> Both motors should draw 16 A only if they are both at full torque and full >> speed simultaneouly. I suspect some of your troubles are due to trying to >> run >> high speed motors with 1 KHz commutation (for the 7I39 and > a few thousand >> RPM I would suggest a minimum of 4 KHz). >> > > Motors are coupled coupled to pinion through 6:1 belt drive. There is > something wrong in mechanics, it gets really loud, if I spin the motor > above 1000 RPM, so 1K RPM is where I have set my limit. > Motor has 8 poles, so drive should do 4000 electrical revolutions per > minute. Is that considered high-speed? > > Do I understand correctly that by commutation frequency You mean servo > period update rate? > > Could You, please, explain in more detail, what exactly is happening there, > what makes those fuses to give up? > I somehow do not get, how increasing servo period update rate can affect, > how much power/current is drawn from motor PSU? >
At 1000 RPM you are probably ok but its still an issue with a 8 pole motor. This is 66.6 Hz AC drive frequency with an 8 pole motor at 1000 RPM so the maximum phase difference between the motors BEMF and the 7I39s supplied voltage caused by the 1 KHz commutation rate is 24 degrees (66 Hz is 15 ms period, 1 ms servo thread = 24 degrees at this period. This represents a small difference between the 7I39 output voltage and the motor BEMF (~8% peak). Because both the motor and the 7I39 are fairly stiff voltage sources, this voltage error causes AC currents flowing between the 7I39 and the motor that contribute no actual torque but draw power. Note that the magnitude of the problem diminishes very rapidly as the maximum phase error decreases (at 24 degrees error its ~8% at, at 12 degrees error its ~2%) Possible remediations: reduce servo thread period, or adjust BLDCs lead angle dynamically with velocity so the peak error at 1 KHz is 12 degrees rather than 24 (that is make the electrical angle lead the encoder angle by 12 degrees at 1000 RPM and 0 degrees at 0 RPM) It may also be that your fuse issue is simple caused by a mismatch with the motors. If the motors are rated 8A peak, they are a good match to the 7I39 but if they are rated 8A continous they are much too large to be driven by the 7I39. > >> You can of course disable the fuses. The problem at that point is if you do >> manage to blow a MOSFET (or bypass capacitor), Instead of a fixable card >> you >> have a fire. >> > > Ok, thanks, this perspective does not sound really tempting. > > -- > Viesturs > > If you can't fix it, you don't own it. > http://www.ifixit.com/Manifesto > ------------------------------------------------------------------------------ > Get 100% visibility into Java/.NET code with AppDynamics Lite > It's a free troubleshooting tool designed for production > Get down to code-level detail for bottlenecks, with <2% overhead. > Download for free and get started troubleshooting in minutes. > http://p.sf.net/sfu/appdyn_d2d_ap2 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
