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IndustryArena Forum > CNC Electronics > General CNC Machine Related Electronics > Switching power or Toroidal power supply?
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  1. #1
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    Switching power or Toroidal power supply?

    I'm installing 3 x Nema 34s. 5A 60vdc drivers.

    Rough numbers without knowing what peak currents my drivers might pull, well I am looking at 900w huh if all three are maxed out which is plausible.

    I've read that a non filtered power supply is the better way to go for steppers? To not cut out at peak current demands. Is this correct?

    I already have a 1200w switching power supply now. Is there an advantage by purchasing a decent transformer, put it through a rectifier and feed that into my drivers? I guess it sounds a bit rough but keen to hear thoughts. Actually a driver that might accept ac might be an advantage too I have seen those around. B

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  2. #2
    Community Moderator ger21's Avatar
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    Re: Switching power or Toroidal power supply?

    If you already have the switching supply, go ahead and use it, as it shouldn't really have any effect at all on performance.
    If you didn't have one, then I'd say get a toroidal supply. Or, if you don't have the drives yet, get AC drives. Those usually run at very high DC voltages, and would likely provide the best performance.

    With any decent modern drive, the drives usually won't draw more than 2/3 the motors rated current, so a 700w power supply should be sufficient. Personally, I'd still go with the 900w, as the prices would usually be similar.
    Gerry

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  3. #3
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    Re: Switching power or Toroidal power supply?

    And inputting DC as opposed to AC is better? I guess the AC drives must have their own rectifier inside - I haven't seen a driver like that before.

    They are not much more I will order them. B

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  4. #4
    Community Moderator ger21's Avatar
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    Re: Switching power or Toroidal power supply?

    Not better, just different.
    I've seen two types of AC drives.
    One type aceepts both DC and AC, with the AC requiring a transformer to proves a lower voltage than your mains voltage.

    The other type takes 240V directly. These typically supply much higher voltage to the motor, and will give higher speeds. They also tend to cost a bit more.
    Gerry

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  5. #5
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    Re: Switching power or Toroidal power supply?

    Attachment 460648

    What stepper drivers do u use for NEMA34 ? There are some stepper drivers NEMA34 that have input voltage ac or dc (VAC: 18-80V, VDC: 24-110V) such as DM860H, so you can use toroid PS directly. I think it will be stable since you do not need bridge rectifier and cap. I will use toroid PS on this type stepper driver.

  6. #6
    Community Moderator Al_The_Man's Avatar
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    Re: Switching power or Toroidal power supply?

    Many still using NEMA size as a power rating!
    This is a mounting standard, you can have many sizes of motor power rating for a given NEMA size!
    CNC, Mechatronics Integration and Custom Machine Design

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  7. #7
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    Re: Switching power or Toroidal power supply?

    I run with a toroid and AC drives from Lam Technologies. Cheaper, simpler fewer failure points. 64V output form the Torid gives the motors around 90 volts so the motors scream along!
    Rod Webster
    www.vehiclemods.net.au

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    Re: Switching power or Toroidal power supply?

    Good reading. I am probably a bit guilty of comparing motor power by size. Although the 34s I am buying seem to start with a holding torque that the 24s top out with. And I do appreciate holding torque is not the rotating torque.

    It must be apparent though with the size of the motor also comes the size of the lever it has to push around. I remember replacing a servo in the back of a commercial aircraft once. It was about 50mm thick with a diameter of about 250mm. And it was pushing a considerably large force.

    Here in NZ, unless we want to pay massive freight costs out of the USA I normally go Chinese for gear. I've chosen a set of 2HSS86H drivers to go with 6.0A 34s for a decent direct drive system. They will accept AC and DC.

    My Nema 24s are running just at their limit. So the 34s will be great.

    I don't know about you guys, but seem to be constantly looking for closer to commercial? Actually, I might be a tad bold here. But I reckon, my machine, is possibly a bit better than a few on the market today (low range of course ha)

    But man it's running well. Cost a few bucks tho....

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    Re: Switching power or Toroidal power supply?

    Hi,
    I'm using Vexta 23 size 5 phase steppers in my mini-mill. They are paired with Vexta drivers which have 230VAC input.

    I have pulled them to bits to have a look inside, all good quality Japanese stuff. There is a rectifier and DCLink filter followed by a buck regulator. The buck regulator
    outputs 150VDC, and this is the voltage consumed by the driver.

    The 150VDC sure makes these wee steppers sing! My G0 rapids require that they spin at 2400rpm.....and I have at various times had them running at 3000rpm, but
    they get hotter than I like so I backed off a bit, back to 2400rpm.

    So I can concur that AC input drives have the potential to use much higher DC voltage for their drives than you might otherwise encounter.

    Craig

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    Re: Switching power or Toroidal power supply?

    Hi,
    just as an aside, if you shop around you can get some reasonable freight deals from the US.

    I imported (from Virginia) a great big kick-arse servo, about 25lb, and it cost 110USD to fly it to New Zealand, which I thought was pretty good.
    Another time I got a low lash AtlantaDrive worm reduction box weighing 35lb and it cost $130 to fly it out here.....not too bad.

    I don't know whether you've checked out the service by NZPost. You can set up an account with them and have your items delivered by your US supplier to an address in Oregon,
    and then NZPost take over and ship it to you, handle GST and customs, the whole works. Its not cheap but very fair.

    Craig

  11. #11
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    Re: Switching power or Toroidal power supply?

    Quote Originally Posted by joeavaerage View Post
    Hi,
    and I have at various times had them running at 3000rpm, but
    they get hotter than I like so I backed off a bit, back to 2400rpm.
    If your motion controller supports it, this is where the Lam Technologies boost function comes in. The motor is only working hard during accelleration and Decelleration. While at constant velocity, it might only require 30% of the power needed to accellerate/decellerate. So by reducing the current to the motor when this power is not required to 30-50%, the motor gets a chance to cool down and I'd wager your drives will run all day at 3000 rpm.

    There are plenty of high quality Stepper motor manufacturers in China. Motion King (rebadged by Lam Technologies) and Moons Industries come to mind. Moons do sell in small quantities, not by the carton.... China is so close to AU and NZ, its a lot cheaper to source from there..
    https://www.moonsindustries.com/
    Rod Webster
    www.vehiclemods.net.au

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    Re: Switching power or Toroidal power supply?

    Hi rodw,
    the Vexta drives I use are not quite that sophisticated. They do reduce current at idle but to my knowledge do not reduce current when spinning at constant speed.
    I already run the steppers at somewhat reduced current, about 1A per phase as opposed to 1.4A per phase rated. 1A may sound a little measley but a 5phase stepper has
    four phases powered at any one time so the total current into the stepper is closer to 4A.

    As it turns out the motors get hot, really hot, I'd guess 75C, when doing long continuous jobs but they have been doing that for six years without demur so I haven't
    bothered trying to fix something that's not broken.

    My new build mill has 750W servos and I'm spinning them up to 5000rpm and they don't even seem to get warm. In fact the ballscrews start to warm up when they
    are subjected to repeated and prolonged G0 moves. I've read about ballscrew heating but this is the first machine I've ever had where it happens!

    Craig

  13. #13
    Community Moderator Al_The_Man's Avatar
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    Re: Switching power or Toroidal power supply?

    Stepper motors are designed to run at Exactly their rated plate current right throughout their rpm range, it should never be exceeded, the job of a stepper driver is to monitor this current and provide the Exact plate current at all speeds.
    This is done by using a supply that is quite a bit higher voltage than what the motor is rated for, this is in order to maintain the current as the motor inductive reactance increases with RPM.
    The old original method before PWM was a simple series resistor scheme.
    CNC, Mechatronics Integration and Custom Machine Design

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  14. #14
    Community Moderator Al_The_Man's Avatar
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    Re: Switching power or Toroidal power supply?

    CNC, Mechatronics Integration and Custom Machine Design

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    Re: Switching power or Toroidal power supply?

    Good reading. Hey the funny thing is I started with 23s. Real dirt cheap ones. And a floppy frame with an old Makita router screwed into a Z on a board.

    I am now with 34s and 2HSS86H drivers. The frame and gantry are at build 5 good enough for some great alloy machining results.

    New control box for the 5.5kw VFD and 4.5kw spindle.

    All this. With a $5 BOB. Haha.

    Far out. Do I go for a better controller?

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  16. #16
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    Re: Switching power or Toroidal power supply?

    Quote Originally Posted by boydage View Post
    All this. With a $5 BOB. Haha.

    Far out. Do I go for a better controller?
    Is your 5-dollar board limiting you in any way? Will a new controller let you do something you are not able to do now? If yes, then go for it. If not, might as well leave it alone. Just my two cents. :wave:

  17. #17
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    Re: Switching power or Toroidal power supply?

    Quote Originally Posted by Al_The_Man View Post
    Stepper motors are designed to run at Exactly their rated plate current right throughout their rpm range, it should never be exceeded, the job of a stepper driver is to monitor this current and provide the Exact plate current at all speeds.
    This is done by using a supply that is quite a bit higher voltage than what the motor is rated for, this is in order to maintain the current as the motor inductive reactance increases with RPM.
    The old original method before PWM was a simple series resistor scheme.
    A very simplistic view, The role of the motion system is to provide sufficient power (in watts) to meet requirements for a given motion profile having regard for the forces to overcome and the required velocity, acceleration and performance at a given moment in time. Watts can be calculated from the volts, amps and motor spec. Generally, the motors are rated at RMS amps which overstates their true capability. Often the torque curves are quoted at 48 volts and we insist on using higher voltages (72, 90, 150 or whatever). Complex laws of Physics allows us to calculate the required voltage and amps from the motor's plate to achieve this performance. If the calculated amps exceeds the motors plated amps, then you need to find another motor. If the calculations shows the motor runs too hot and is at risk of an internal melt down, we need to find another motor. In our motor profiling it was not uncommon for say a 7 amp motor to only need 5 amps. In this case, there is no need to run the motor at plated amps which will just add unnecessary heat.

    But back to our motion profile. Once the axis is at a constant velocity (lets work on rapids as that the maximum velocity we require), those laws of physics show that the power in watts can be as much as 30% less than that required when accelerating. If we reduce the power available at the motor when its not required, the heat output is reduced and the motor will achieve a lower maximum operating temperature. This is a good thing becasue in our performance testing, missed steps occurred when a motor gets too hot.

    To vary the power output Its not easy to vary the volts but it is easy to vary the current supplied to the motor. This is where smart stepper drives from Lam Technologies come in if your motion controller can tell when constant velocity has been reached on a given joint. The motion controller can then tell the drive when to reduce the current to reduce the motors power output.

    So in my case I have my 7 amp RMS rated motor receiving 5 amps when accelerating or decelerating and 2.5 amps (50%) when at constant velocity using Lam's boost feature. I've been meaning to test if the motor will still perform with a 70% current reduction. I think from the maths it should.

    So the end result is that we can push the acceleration up to 0.5 G for the 30 milliseconds it takes to get to rapids of 35 metres/min (1378 ipm) and idle for the rest of the time. At a more normal cutting speed of 2 m/min, the drive is only working hard for 7 ms.

    So the end result is a super high performance stepper based system that uses the motors low down torque to get to speed quickly without loosing steps.

    In my testing, motors got hot and lost steps. We implemented the boost feature and due to poor physical layout in the control box, one of the drives faulted with an over temperature error. So we arranged the drives to be side by side as recommended by Lam (and enabled a cooling fan for good luck). After we did this, our 120 amp plasma cutter overheated when only cutting at 40 amps. So at this point , we felt that our torture test nest was taking things to the limit without the motors failing or loosing steps. (eg. the plasma cutter was the weakest link).

    Without the boost feature, our only options would have been to reduce current or reduce the maximum acceleration and possibly rapid velocity which was not desirable.
    Rod Webster
    www.vehiclemods.net.au

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    Re: Switching power or Toroidal power supply?

    Quote Originally Posted by CitizenOfDreams View Post
    Is your 5-dollar board limiting you in any way? Will a new controller let you do something you are not able to do now? If yes, then go for it. If not, might as well leave it alone. Just my two cents. :wave:
    Good read in the last post.

    In response to this quotation. I actually don't know because I have not tried anything better. And I don't feel limited. Well, I do know the screws are at the top of the mass range for the stepper motors I have - and this is true to calculation on a previous post. So I am putting some larger motors in. But that is not related to my bob.

    But I do tend to think my $5 BOB will be staying put ha. Oh, I am a bit limited with inputs. Currently I have had to use a ssr (chip form) to assist in the multiple probe inputs. Some are NC some NO. To get all that working on a single NO input took a bit.

    I guess the question is, what do I have to gain by upgrading a $5 bob to a $80 bob? Because that's about what I would spend.

    Unless of course someone here told me not to be such a dork and showed me why. Lol Regards

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  19. #19
    Community Moderator ger21's Avatar
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    Re: Switching power or Toroidal power supply?

    I guess the question is, what do I have to gain by upgrading a $5 bob to a $80 bob?
    Unless the $80 board offers additional features, then most likely nothing.
    Gerry

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