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  1. #81
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    Quote Originally Posted by arizonavideo View Post
    You guys are way over rating the current needed for the steppers.

    The maxim value that a stepper can draw may be 3A but at any RPM over resonance it will draw less current, a lot less.

    A 9A transformer supply can deliver 13A for 30% of the duty cycle with no problem. It is almost imposable for a stepper system to draw max current for any amount of time unless all the steppers are going the same speed. Most of the time the Z will be parked and drawing 60% less power.

    You might want to see a 15A PS in real life and ask yourself if you want a 25 pound PS.

    The ratings of the PS is for a 100% duty cycle so it is OK to run them that way. If you have a fan in the box you can run them even harder.

    For two 3A and a 4.5A stepper a 7A or 8A coil PS is fine.

    I like the Gecko's because the are made in the USA even the outputs are US products. All the Keling products are China made.
    So if I have a 5A stepper and adjust the controller for a 5A output then it will not consume 5A? Only about 3A?

    I thought it will consume 5A if still or low speed. And depending on half or microsteps it can consume over 5A. If you have enough speed then the coils will not reach the max current before next step.

    I'm a newbie on this and try to figure out what PS to buy. The steppers will be the Keling 570oz model (5A 50V).



  2. #82
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    A rule of thumb when selecting power supply for steppers is to add up all the phase currents and multiply by 0.6

    So for instance say your using three 5A steppers

    3*5A = 15A

    15A * 0.6 = 9A

    So a 9A power supply would be the one you want to use. You never want to under rate a power supply though. If the closest you can get is 10A like the Keling KL- 5010, this is still okay.

    Hope this helps...

    ~Scott



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    Question

    This goes off topic but...

    I have read about this rule but what is the theory behind it?
    If I have one PS per 5A stepper should it be a 5A PS?
    If I have a shared PS for three steppers maybe the 2/3 rule works then because most probably only two steppers are used at once.

    If I use micro stepping is the maximum current total 5A (3,54A max per phase)? Or 5A per phase so total is 7,1A?



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    Registered mwood3's Avatar
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    not that it clears up anything but...why not just stick with what is already proven to work? once you get a better understanding of the nature of a cnc system then try some experimenting.

    http://www.g0704.blogspot.com/


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    The Keling 6050 stepper controller does not seem to have current reduction mode while not in use. So with these controllers the steppers take up to 5A. The 570oz model is quite low inductance so it does take high current to a higher speed than high inductance models.

    So why would not the XYZ motors take 15A when in use and in low speed?

    Some other controllers seem to have an option for 40-50% reduction in current while not in use. This reduction kick in after the motor being idle for 1-2s.

    I have a BF20L clone coming and want to make sure I buy a proper PS.

    Hoss: have you tested your PS with all steppers in use? If you have a multimeter can you measure the current taken from the PS?



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    If in doubt just get a power supply that can handle 15A and be done.

    Here is a 50VDC 800Watt Power Supply.



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    Quote Originally Posted by daman View Post
    The Keling 6050 stepper controller does not seem to have current reduction mode while not in use. So with these controllers the steppers take up to 5A. The 570oz model is quite low inductance so it does take high current to a higher speed than high inductance models.

    So why would not the XYZ motors take 15A when in use and in low speed?

    Some other controllers seem to have an option for 40-50% reduction in current while not in use. This reduction kick in after the motor being idle for 1-2s.

    I have a BF20L clone coming and want to make sure I buy a proper PS.

    Hoss: have you tested your PS with all steppers in use? If you have a multimeter can you measure the current taken from the PS?


    So that makes me wonder if the Gecko 201X drivers would be fine with the 12A power supply but the Keling might be better with the 20A power supply which makes the Geckos a little more attractive.



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    I have a probably stupid question on the thrust bearing arrangement on the Y axis. Is the rear bearing loaded against the mill base or against a shoulder on the leadscrew shaft? I'm thinking it must be a shoulder on the shaft that pinches the bearings together against the inside of the spacer block and thus the pockets can be a little deep without it being a problem. I can't pry the last race off the Y shaft to look behind it. It's on there like it was glued.

    My other question. On the threaded hub of the oldham, am I supposed to also use the setscrews there too? If I try to reverse the table it of course wants to try to screw itself off the end of the shaft but if the motor is in place the opposing coupler would be there to prevent that, however, I was thinking the plastic would compress and induce backlash like that, but if I use the set screws then I'm almost certain to booger up the threads.

    My hat's off to you folks that know this stuff inside and out. The electronics are easy to me but my newb-ism really shines in this arena



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    I'll put a meter on my supply tonight with the motor holding and see what is really being drawn from the supply. Right now I only have a 9.5A supply which was intended for an X2 conversion not the 5A big-boys being talked about for this. Should be easy to see if the current draw is double or not. I'm doubting it.

    I had a unipolar design I built myself and the chip was rated to handle 3A motor output but there is no way that chip could have handled passing 6A in half-step mode where I tested it most often nor were my traces sized for that. What I can't explain outright is why it wouldn't be that way but I think it has to do with the nature of the chopper.



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    Quote Originally Posted by photomankc View Post
    I have a probably stupid question on the thrust bearing arrangement on the Y axis. Is the rear bearing loaded against the mill base or against a shoulder on the leadscrew shaft? I'm thinking it must be a shoulder on the shaft that pinches the bearings together against the inside of the spacer block and thus the pockets can be a little deep without it being a problem. I can't pry the last race off the Y shaft to look behind it. It's on there like it was glued.
    That's how mine is set up. This is my X axis but the Y is the same way. One pocket on each side. The ballscrew shoulder buts up against the inner race on the backside and the bearing retainer locknut buts up against it on the outside.




    Quote Originally Posted by photomankc View Post
    My other question. On the threaded hub of the oldham, am I supposed to also use the setscrews there too? If I try to reverse the table it of course wants to try to screw itself off the end of the shaft but if the motor is in place the opposing coupler would be there to prevent that, however, I was thinking the plastic would compress and induce backlash like that, but if I use the set screws then I'm almost certain to booger up the threads.
    You got me there. Why did you thread the hub of the oldham coupler?


    Edited to add:

    I just realized you are talking about Hoss' Phase 1 conversion with the leadscrews so nothing I said may be accurate. I imagine you threaded the hub to go on the stock leadscrew. I am using bearing locknuts for my ballscrews and they have a cool little mechanism to lock onto the threads. It is basically a setscrew but the setscrew pushes down on a tiny brass piece that has threads on it instead of directly onto the threaded shaft. It would be pretty easy to make - I can take some pictures if you aren't familiar with what I am talking about.



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    Sorry, should have said that. Yes, phase 1. The oldham is threaded to act as a jamb nut against a collar that takes up the space between the hub and the front bearing.

    The little brass plugs make sense, I guess one could make them and then run a tap through with them protruding a bit and get the thread pattern cut into them. Not losing them might be a challenge though.



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    photomankc:

    Go to McMaster.com and type in set screws. You can buy set screws with different tips, brass, nylon, polyurethane etc.. I prefer the polyurethane tips. It won't mar your threads.

    Another tip I found useful is to make the end of the set screw flat with a belt sander or even face it on the lathe. Most set screws are cupped/pointed which is going to inflict a lot more damage to the threads then if the tip was flat which applies even pressure instead of concentrating the pressure to the point. You still don't want to get crazy when tightening it, but if you use thread locker and just snug them you'll be good to go.

    Hope this helps..

    ~Scott



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    Yes, that helps. I do face the screws I use to clamp tools in the lathe to avoid dimpling all my tools so it would be easy enough to do that to the set screws here too.



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    My meter is showing about 0.3A draw from the power supply when the stepper is holding and about 1.1A peak at around the halfway mark for speed. The driver is set for 4A and the motor is rated for 4.2A bipolar so that suggests the current is very spikey and the meter is probably not fast enough to catch it all.

    When I measured a single coil the current would vary from none to about 2.0A every other 0.0005" increment. Again I think the switching nature of the power is probably fooling the meter a bit but it does demonstrate that there are times, even in a microstepping mode when the coil current is not the maximum and this is likey where the rule of thumb comes from. All the coils of all the motors are not going to full on and even so they are not sucking in full rated amps solid over time.



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    Quote Originally Posted by photomankc View Post
    My meter is showing about 0.3A draw from the power supply when the stepper is holding and about 1.1A peak at around the halfway mark for speed. The driver is set for 4A and the motor is rated for 4.2A bipolar so that suggests the current is very spikey and the meter is probably not fast enough to catch it all.

    When I measured a single coil the current would vary from none to about 2.0A every other 0.0005" increment. Again I think the switching nature of the power is probably fooling the meter a bit but it does demonstrate that there are times, even in a microstepping mode when the coil current is not the maximum and this is likey where the rule of thumb comes from. All the coils of all the motors are not going to full on and even so they are not sucking in full rated amps solid over time.
    good to know. Same goes for servos or is that apples and oranges?



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    Not sure. Never looked at servo much but I think they are usually a PWM type arrangement and would tend to draw more current at the high end of thier operation when the signal duty cycle is highest.

    http://www.solarbotics.net/library/pdflib/pdf/drive.pdf

    The document there has a good graphic illistration on page 7. The drive is setting the maximum current by sensing a voltage developed across a resistor as the current flows through and when the voltage reaches the threshold that indicates that the max current is flowing it turns off and the current decays away slowly till the next chopper pulse. this is repeated over and over again. So if you look at it the current would spend nearly all it's time at some average less than the max level.

    The larger microstepping modes vary the current in a 90 degree phase shift across the coils so when one coil is balls-to-the-wall the other coil is on the down slope or up slope and they alternate in that way.



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    Lightbulb 3000W power supply for few dollars!!!

    Someone on some forum suggested using HP server power supplies.

    Well, I searched the eBay and found this:
    http://cgi.ebay.com/ws/eBayISAPI.dll...#ht_500wt_1154

    51,4V 57A power supply for a few dollars!!!!



  18. #98
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    Thats interesting, electronics is my weak point, wonder if it has all the correct outputs, Id be interested to hear more...

    http://www.g0704.blogspot.com/


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    Quote Originally Posted by daman View Post
    Someone on some forum suggested using HP server power supplies.

    Well, I searched the eBay and found this:
    http://cgi.ebay.com/ws/eBayISAPI.dll...#ht_500wt_1154

    51,4V 57A power supply for a few dollars!!!!
    Holy crap! 3000 watts! That must be a monster @ 18 pounds. That would be a steal if it did work.



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    Quote Originally Posted by mwood3 View Post
    Thats interesting, electronics is my weak point, wonder if it has all the correct outputs, Id be interested to hear more...
    Quote Originally Posted by diyengineer View Post
    Holy crap! 3000 watts! That must be a monster @ 18 pounds. That would be a steal if it did work.
    I ordered one. I'll test it as soon as I get it. The seller I bought from even gives 12 month warranty. This is probably worth its own topic if it works.



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