On Sunday, February 08, 2015 11:40:19 AM Dean Posekany wrote: > A little background : > > About six years ago, as I was just starting to design my shop-built > gantry machine, I came across a SUPER deal on Ebay for six sets of drive > components. Each set included a line filter, Parker OEM300 75V, 7.5A > power supply, Parker OEM750 stepper driver and a stepper motor. I didn't > know a whole lot about this stuff a the time, but I knew it was a deal I > couldn't pass up. So, they became the drive system for my CNC build. As > it turned out, only five of the six drivers worked. Thas wasn't a > problem (especially for what I'd paid for them) because my gantry is > only (at least for now) a 3-axis machine. But, six years later I've lost > two additional OEM750's and I'm now running on my last three. Another > failure and I'm down and its decision time. > > Here's my question for the worldly experience of the group. I'm retired > and this is a serious hobby machine and I don't have a great deal of > money that I can throw that this. So when the inevitable failure of the > next stepper driver occurs, what would you do? Repair the OEM750 > (~$280)? Or would you look at replacing the Parker hardware with > something else like Gecko or maybe go the Mesa route? I've really been > pleased with the stepper performance I get from the Parkers and the > software stepper generation that Linuxcnc gives me is more than fast > enough for the work I do. The repair is expensive and the drives were > released in 1997. So they're 18 years old. I just don't have enough real > world experience with this stuff to feel like I can make a good decision. > > If it was your problem, what direction would you go? > > Thanks in advance for your thoughts. > > Dean
Stepper Electronics 101 is in session. ;-) Drive designs and dependability have come a long long way since 1997. I personally have 6 of the 2M542 drivers running my stuff and they seem to be bulletproof, withstanding motor shorts or opens by responding with an instant shut down that you must power cycle them to recover from. These drives have a big brother, for not too much more money, rated at 80 volts and 6+ amps to the motors. There will be an 860 in the part number for those drives. I am running my lathe, an early early 7x12 with a 1 hp spindle motor, with a 425oz nema 23 geared down 2/1 on the carriage screw, now a now 16mmx5 ball screw, and a 262 oz on the rear of the carriage, direct drive to a small ball screw to run the y. All this running on a surplus tranny/rectifier and a couple 10,000 uf caps caps putting out about 37 to 38 volts. Rock solid and 60+ ipm on the Z. My mill was the first conversion, an X1 with the LMS big table kit, but only a 28 volt supply so its not super dependable north of 10 ipm. Power supplies in the 40 to 50 volt range are hard to find and I wound up buying a 5 pack of 48 volt, 3.3 amp switchers off ebay for a $95 bill, all will be paralleled thru .5 ohm wirewound resistors to insure enough load sharing that the overcurrents will not easily cascade. Tested laying on the table with one 425 oz 8 wire motor wired series so it runs on about 2.5 amps, and driving my spare 2M542 driver with a function generator, I can get, with lots of torque, better than 2000 revs, and did see over 3500 several times before it locked. That speed also disclosed that the opto-isolators in the 2m542 inputs weren't all that fast as it was quite sensitive to the applied duty cycle. That was a bit north of 375 kilohertz from the generator with the drive set at /8 microstepping. For your bigger setup, this looks like the best deal on ebay ATM: <http://www.ebay.com/itm/DM860-2-4-phase-Nema34-Stepper-motor-driver-256micsteps-7-8A-24-50VDC- CE-/251522680246?pt=LH_DefaultDomain_0&hash=item3a8feb85b6> He has 7 left ATM. And despite his claim of a 50 volt rating, all the other DM860's listed are rated at 80 volts. Immediately above that listing is a 3 pack of them for $159. Rated at 80 volts. Typo? Check with the vendor to be sure they aren't 2nds or? And I see suitable 60 volt power supplies, use one per motor, at similar prices. But I expect your 70 volt Parkers are not switchers but analog, and barring transformer failures, are fixable on your own workbench. At their age, I would replace all the electrolytic caps in them if there is any problem. If you have an oscilloscope, bad/old caps will be obvious because of the 20 volt or more noise spikes from the motor drivers at the supply outputs. A digital DVM may not show that noise as its way to high a frequency to register on a DVM. Their AC voltage ranges loose any semblance of accuracy when the AC they are measuring is not 50 to 60 Hz. And the comment goes triple for any DVM claiming to be RMS accurate, that log amplifier that does that is very slow. So the HF noise is ignored. Yes, I am a Certified Electronics Technician. And I like to teach. And being both 80 yo, and long retired myself, I do consider the costs in the long view if I can. They will be happier, with the drivers running cooler, and the motors may have much better high speed torque when those caps are big enough and fresh. Be aware that some switching supplies are not at all happy driving a stepper due to the high recirculating currents causing what the switcher thinks is an overvoltage, tripping it off, so its recommended by great-grandpa Gene here, to isolate the switcher from the load a wee bit with a small power resistor, .5 ohms or less, and a large, low ESR capacitor which will serve as the recycle currant container for most of the voltage spikes that are part and parcel of todays stepper drivers. All of my drivers are looking at 10,000 uf or more at their input terminals, and the switchers then seem to behave well with the extra cap to gobble up much of that noise. 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> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
