On Saturday 28 March 2015 19:36:09 [email protected] wrote: > On Sat, 28 Mar 2015, Bertho Stultiens wrote: > > On 03/28/2015 08:37 PM, [email protected] wrote: > >> I have a question about the voltage to drive a stepper motor > >> 12 volts works but higher voltages make the motor weaker > >> I am building a simple stepper driver > >> A nema 23 2.7 amp stepper motor and 36 volt power supply > >> The controls are hand held, forward ,reverse, stop, and speed > >> I built the controls and driver using a 12 volt battery to test > >> Now I completed the project and am using the 36 volt supply > >> The motor runs at the same speed but it is so weak I can hold the > >> shaft and stall the motor This is also the same with 36 and 24 volt > >> batteries > >> With a 12 volt battery I can not stall the motor > >> I am using http://piclist.com/techref/io/stepper/SLAm/SLAm_bld.htm > >> and an Arduino I would be happy if someone would point out my > >> stupidity > > > > The chip uses a constant current setup using PWM. When you raise the > > supply voltage then the trip-current is reached sooner and recovery > > may take too long for the next PWM cycle. > > > > The datasheet says that the off-time is between 7 and 12 > > microseconds. Your high voltage level may cause a feed-through on > > the current-limiter because of the increased rising flank of the > > current. This decreases the on-time vs off-time and the effective > > current to the motor is reduced which results in a lower torque. > > > > The problem may be in the physical setup, where too much noise is > > propagated. You should check the wiring and use an oscilloscope to > > check the signals for spikes etc.. > > I do not have an oscilloscope
You may have to cultivate a friend who does have one. As a scope user myself since 1951, there is no other way to measure things where time vs voltage or amperage needs to be measured. > and I don't think noise is the problem > I am single and it is usually pretty quiet around here :) The noise being refered to is electrical, not acoustical and steppers, with their built in PWM modulation in a decent driver that does regulate current to maintain the average, is one noisy puppy electrically, which is the sort of noise being referred to. One more question though. After half an hour powered up on 12 volts, how does the motors temp (its gonna be hot, use an IR thermometer) compare with 1/2 hour powered up on 36 volts? If its smell it hot in 10 minutes, pull the plug, your drivers are not regulating the current adequately and the motor is saturated, possibly damaging the rotors magnetism forever If its many degrees cooler, then the driver may be turning itself down to protect the driver. If its smart enough, most of the lower cost drivers aren't. I have let the magic smoke out and broke the mirrors on quite a few allegro A-3977 based drivers. I switched to 2M542's off fleabay about 5 or 6 years back, buying enough to switch them all out with one spare for the parts drawer. Its still there, has not been needed. 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
