On Wednesday 28 October 2020 14:30:39 Chris Albertson wrote: > I bit of information from Polulu's web site. They say.. > > "*While VNH3SP30’s over-voltage shutoff doesn’t activate until 36 V, > in our experience, shoot-through currents make PWM operation > impractical above 16 V.*"
Which pretty well explains my problems. > This seems reasonable for the intended automotive use case where a > lead/acid battery is supplying the power. but there may be transient > up to 3X the nominal battery voltage. > > I've never run these using more than the nominal 15.7 volts I get from > a fully charged LiPo battery and when bench testing I use a 12 volt > power supply that does about 13.5 volts. Try running your motor on > 12 volts > > I think the way to go is to just buy from Polulu and not try to sav $2 > on eBay. Polulu actually offers support Here is one that seems to > actually handle higher volts https://www.pololu.com/product/1457 Which reads much like the ones I bought two of, for less that half of polulu's asking for that board @$60/copy. > Or you just buy four MOSFETS and build you own switch > > Another one I was not going to recommend because of the cost is really > excellent and again their support os excellent. I had a problem and > they offered to replace the unit. They will also talk with you about > software. But you pay for the support in the product price. Obviously. > This unit has input from the quadrature encoders and runs the PID loop > itself. The computer (That would be some HAL component in LCNC) > sends only the desired position or the desired velocity of one of the > interfaces. There are a few to choose from, RS232, USB, PWM and > analog. ThePID has an autotune feature that can get you in the > ball-park > > I use one of these to drive a mobile robot's traction motors. It > pushes a lot of complexity out of my control computer because this > controller does the encoder processing and PID control . But these > are $90 devices and I've switched to using these > > https://protosupplies.com/product/vnh2sp30-dual-monster-motor-shield/ > > The above is the EXCELLENT tutorial on using the VNH3SP30 chip and the > dual-chip version attached to an Arduino-like board with zero wires or > solder. It just plugs in. But I buy the dual-chip boards from China > for $7 each. Much cheaper than the 90 Roboclaw units. > > These dual-chip drivers are widely cloned because the design is Open > Sourced. The Egle design files are available > > So my now-standard motion control setup is one of these: > ebay.com/itm/Dual-VNH3ASP30-... > <https://www.ebay.com/itm/Dual-VNH3ASP30-replace-VNH2SP30-Stepper-Driv >er-Module-30A-Monster-Moto-Shield/291549918162?hash=item43e1bab3d2:g:14 >wAAOSwVb5d8guN> plugged into one of these you can get for about $14. > www.st.com/en/evaluation-tools/nucleo-f446re.html > > My experience is that I can drive this with a lipo battery for hours > and the chips are not even warm. That may change as my current > project is a Kidie car conversion. It is the kind of toy car that > hold two 6-year old kids and goes up to 6 MPH on the sidewalk. > Fisher-price sells them > www.target.com/p/power-wheels-tough-talking-jeep-powered-ride-on-black >-red > <https://www.target.com/p/power-wheels-tough-talking-jeep-powered-ride >-on-black-red/-/A-53016862#lnk=sametab> The car is being adapted to > autonomous self-drive and will do laps around the block with no > driver. > These VNH3SP30 chips (and the nucleo-f446re) will power the rear drive > wheels. The car's total weight (including a lead/acid marine > battery) is about 100 pounds. The driver chips really can handle > maybe 100W per chip or 50W continuous Given their admitted NOW maximum voltage, good deal. But 12 volts might not even start this 24 volt motor. :( Thank you for finding that bit of data that is NOT in their docs on the STM site. But I'll also stand by my comments re the poor internal gate drivers, way too small to drive a high current device as the gate capacitance in some of those can be a major piece of a microfarad. It takes higher powered drivers to charge and discharge that level of gate capacitance in a timely manner when it is comeing on it is essentially a miller run-up, the gate capacitance is multiplied by the devices gain forming a huge negative feedback loop while the drain voltage is falling. A higher drain=worse effect. And the effect is there again when its turning off, the rising drainvoltage feed back thru that capacitance, slowing the off transition by the same feedback mechanism. Needs about 100x what they actually built in an oxide lined tub on the same die, to do the job right. Plainly, the chips layout designer should have been fired, along with the prof that supposedly taught that coarse. Thanks Chris. 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
