On Monday 26 October 2020 22:33:36 Chris Albertson wrote: > Gene, I've got a ton of these chips driving motors. They work fine. > Just write the software to the datasheet spec. If the chip is getting > hot and the motor is not mechanically stalled then you are doing > something wrong. For debug/development replace the motor with a 100R > power resister and then you know 100% no more then 1/4 amp is flowing > through it.
I don't think my junk box has such a critter. And the motor runs just fine when connected to the 24 volt supply. > Place a volt meter on the resister and watch the voltage > change with PWM duty cycle Put an amp meter on the power supply. A > motor not under load running at 50% PWM shouldn't use even one amp. > The chip will not be even warm > > One of the best investment you can make is a $10 logic analyzer. The > they can collect data on 8 pins at once. Put on on every pin > > When I do a direction change I ALWAYS go through a "brake" mode on the > way. That is not possible withing hacking up something in hal which would soon run out of gpio. I am using the complimentary capability's of the 7i76 to extract the dir- and dir+ signals, which change state simultaneously. > I've never once seen a car with a 150 audio amp driving the > wind shield wipers. But it could be done. > The problem is you are trying to futz with both a new-to-you chip and > LCC at the same time. This is true. > I keep an Arduino around for leaning how > controller chips work. Arduino is a very simple and clean environment > for experiments. In fact there is an example program in the IDE for > testing PWM controlled motor where you control the speed with a three > terminal pot. > > On Mon, Oct 26, 2020 at 6:56 PM Gene Heskett <ghesk...@shentel.net> wrote: > > On Monday 26 October 2020 20:33:40 Jon Elson wrote: > > > On 10/26/2020 06:48 PM, Gene Heskett wrote: > > > > 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. So, I need a d2a to > > > > drive one of the 150 watt class D audio boards after > > > > shorting the inputs hi-pass filters caps. And I have the > > > > feeling that even as sweet as the SpinX1 is for knocking > > > > around a vfd, that it won't be fast enough for this, so > > > > I'll need a real d2a that I can shove fresh data thru at > > > > servo-thread speeds. Looking for likely suspects I might > > > > be able to drive from the 7i76D sserial extension bus. > > > > Suggestions? > > > > > > I'm guessing the thing was designed for 50 Hz PWM or > > > thereabouts. That might actually be OK for a spindle motor. > > > Clearly NOT OK for a positioning servo. > > > > Jon, Its a car seat positioner driver, claims very low milliohm on > > r's. $13 on fleabay. Looks promising, but writes checks it can't > > cover even with a 1 kilohertz pwm. Rated up to 10 kilohertz. Either > > that or the first one is fubared. I bought two, and its not hard to > > change. I'll measure the rise and fall times being delivered to it > > tomorrow too on the chance the Sainsmart bob is slow. Manual claims > > up to 10 Mbits/S at any output. For driving switches, thats > > bordering on cook it slow. 10ns rise and fall would be a heck of a > > lot better. Designed for car seats, in cmos circuits, rated on time > > delay is 100 to 300us, off time is 85 to 255us. > > > > And change of direction is 600 to 1800us. In polite language, that > > explains it all. For starters, there is no measureable lag coming > > out of the 7i76 for a direction reversal. So with our drive, this > > thing probably has 150us of shoot thru time for any dir signal > > change. I could probably design an interfacing circuit that would > > fix that, but IMNSHO that is the semi designers job. And STM > > failed, miserably. Thats not a problem in this particular circuit, > > but that geological rise and fall times for the pwm are a killer, > > even at 1 kilohertz. At 50 hz, maybe. At 10KHz, nearly instant > > overtemp shut down at 170C. Sigh... These last two paragraphs are also true. If you are driving one of these with linuxcnc, show me some .hal code and schematics. I am always open to learning something that "gets around" the limitations the semi stuff imposes on us. > > Thanks Jon. > > > > > _______________________________________________ > > > 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 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
