Gallery, Projects and General > How do I??
Power supply for Nema 23 Stepper ?
Johnny Bravo:
This is a very interesting thread,with evidently some very experienced people responding. I don't want to hijack this thread,but I think my questions would be relevant. There seems to be a myriad of considerations when choosing stepper motors and drives. Unfortunately,for the newbie,some of these considerations are very difficult to quantify. So here is what I want to do....
I have a couple of Longs motors Nema 23 steppers, 425oz with an inductance of 6.8mH per phase.
Drivers can handle up to 50v.
Psu is 36v 9.6A
Ballscrews have a 5mm pitch.
Now, lf I use that formula used earlier in the thread,these motors "should" be fed about 80v... More than the drivers can handle. However....
I want to use it with a laser welder. My feed rate will be dictated by the frequency at which I can fire the laser,in my case, 40 times a minute. Assuming a maximum spot diameter of 2 mm and 50% step over,this would give me a maximum feed rate of 40mm a minute. Obviously it's not like a lathe or a milling machine where the load goes up exponentially with regards to the depth of cut. The load will be constant. So.... I would still need to rapid occasionally, but it's not really a major issue. So, what would the best route to go be? Should I uprate the psu to 48v? Would I be better off say using a 3 to 1 reduction on the stepper motors? That would lend itself to a more compact set up, and more controllablility with finer work with say a 0,3mm spot weld and 50% step over.
Enlighten me !
philf:
Johnny,
A 5mm pitch ballscrew directly driven from a half-stepping 200 ppr motor would give you a step of 0.0125mm. Is this not fine enough resolution for your welding job? A 1:3 reduction would obviously improve the resolution but if you don't need it why add it.
40mm/ minute is pretty pedestrian even by stepper standards. I'm sure your 36v supply will be more than OK at the low speeds (8 rpm) you're talking about with a decent margin for rapid moves.
Phil.
Johnny Bravo:
Thanks Phil
If I had to add the extra 3-1 reduction,I could tuck the stepper motors in between the linear rails and make the whole set up more compact. The reason I asked, was, with such pedestrian feed rates, as you correctly point out, would it not be better to use the reduction and use full steps instead of micro stepping? Surely these stepper motors have a sweet spot where they run really nicely? I know with the servo motors on my cnc lathe,they are definitely happier not running at really low rpm. Surely here must be a certain rpm where they deliver maximum torque?
philf:
Hi Johnny,
Running a stepper in full stepping mode can cause resonance problems. Half stepping or particularly microstepping helps to get around the problems.
On my CNC mill I use Nema 23 4N-m motors in 1/8 microstepping mode with no problems.
Phil.
Johnny Bravo:
Having messed around with one of the stepper motors already, I have noticed 1/2 steps seemed smoother than full steps. Still think I will run the 3-1 toothed belt reduction, as it makes for a tidier install. Jury still out on running 48v psu or possibly swopping out Chinese stepper drivers for Geckodrives and running 80v. I have a nice toroidal transformer that would give me 80v dc with the necessary gubbins...
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