Hi
Wantai drivers want anything from 18-50v and wants 4A is that 4A at 18v which would mean less at higher voltage? I’m trying to size the wattage for the psu I need. I’m thinking 24v so will work on 4A for each of the 2 drivers. Then I have drv8825 for the Z Axiz. So I’ll work 9-10A
Am I right that it would want 240w so 300-500w depending on price should be good?
The power supply current requirements is dependent on the current rating of the stepper motors and not necessarily the maximum output of the stepper driver. You don’t set the stepper driver current higher than what the motor datasheet says.
For pwm/chopper type stepper drivers, the minimum supply current can be calculated by adding up all the stepper motor nameplate current times 2/3 (Geckodrives white paper on power supply requirements. Formula can be used for most modern chopper stepper drivers )
For example three stepper motors with 2amp rating.
(2+2+2)*2/3=4amps.
Can’t hurt to have more power supply current capacity but no need to buy something much more expensive such as a 20amp supply.
The drv8825 maximum voltage rating is 45volts. Most recommend no more than 36volts. I use only 24volts with mine since they get pretty hot without good heat sink cooling. I run my Geckodrives with 45volts for higher motor rpm performance.
I would probably not use more than 36volts for the wantia drivers to play it safe.
Modern stepper drives are PWM constant current power sources. So they limit drive current at all voltages to a constant value. That’s what they do. The reason for why they do it is a bit more complicated. But for that same reason you should probably run a bit higher voltage. Or you’re going to suffer from premature torque failure. No one wants to come up short in this life either.
@Jim_Fong
Your Gecko drives should be able to handle 80V input. Mariss builds those things right. He uses 160V MOSFETs in them. So his ratings aren’t maximum, but rather run ratings. He does all of the hard figuring out for users. Because there is a bit of bass ackwardness going on with stepper driving.
@Paul_Frederick yes they will accept 80v. They are good drives, I probably have about a dozen of them. I get 1500rpm (300ipm) with my stepper motors at 45volts on my gantry cnc. Rather not spin the ballscrews to much more. Also higher voltage supplies do get expensive.
I’ve spun stepper motors over 9000rpm with a gecko before on my test bench. It takes low inductance motor with high voltage to do that. No practical use since the torque is so low but it is kinda neat to see. I should post a video of a motor doing that someday.
Edit.
I should add that Gecko does make a 4 drive “hobby” g540 version that is conservatively rated at 50volts@3.5amps. You can use a standard 48volt power supply just fine. I like to use the single drive version that are rated at 80v@7amps.
@Jim_Fong
High RPM is difficult to use effectively in CNC machines. You must have really good support bearings to be able to run at 1,500 RPM. I ran my machine briefly to 2,000 RPM but managed to damage my HDPE acme lead nut in the process. That may have been down to the acceleration I was using then too?
I ended up limiting my machine to 900 RPM to reduce the wear, and tear on it. In use the rapid travel I get at that speed is sufficient for me. My machine has a pretty small work envelope.
But in another iteration a 50% reduction in speed did leave me wanting a bit more. There’s certainly a happy medium to be struck with everything.
@Paul_Frederick I’m using NSK ground ballscrews. I think they are good for 3000rpm but there really isn’t to much torque left in the stepper motors past 1500rpm anyway. I have some high performance brushless servo motors/drives that I plan on installing one day. Machine works so well now that I don’t want to mess with it. I get lazy about upgrading too.
@Jim_Fong
3,000 RPM is a theoretical value based on optimal installation. Which is fixed at both ends with a preload. Or basically the lead stretched taut between two bearings. Are your leads 10mm in diameter?
@Jim_Fong thank you. Now if the motor is rated 2A per phase do you treat that as a 2A motor or a 4A motor
@Paul_Frederick No way I would attempt to spin it at 3000tpm. It’s 5tpi and around 1" diameter.
@Jim_Fong
Hmm an inch in diameter should be able to withstand far higher than 3,000 RPM before centripetal forces distort it. But yeah, it just isn’t very practical.
@Michael_Scholtz 2amp, a microstepping drive never fully energizes both windings simultaneously. There is a whole lot going on inside a stepper driver.
https://www.geckodrive.com/gecko/images/cms_files/Step%20Motor%20Basics%20Guide.pdf
The gecko step motor basics paper better explains it than I can.
Thank you everyone. It’s alive!
@Michael_Scholtz
congratulations. Did you set your drive current?
Yes I’ve got the y axiz with 2 steppers running in opposite direction (hence the rookie mistake) running higher than the single motor on x at this point I’ve got them running cool to the touch so current may be low but I’d rather have them skip steps for now than force and break something. If you see the stepper wired are colour coded to the stepper yellow for x white for y and black for z. Other than that cable management will need to be cleaned up but I’m still going to get a enclosure for everything to go into.
@Michael_Scholtz
I looked up the drives you have online and you have a switch table arrangement to set the current on the drives you have. So you do not have a trimmer pot to adjust. As long as you have your DIP switches set right you should be OK.
I used a defunct PC case as an enclosure for my electronics. The price was right. I never took a picture of the electronics with the last drive changed in it, but it is not much different than this http://i.imgur.com/2frKz9O.jpg
