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  1. #1
    Hi i want to build my own Toroidal power supply. I have 3 50v max drivers i need it to power , So im thinking it needs to be about 42v . But i have no idea what parts to by. This will be my first toroidal supply So any pointers towards what parts i need to get would be cool? Im a heating engineer so know my way around a multimeter so i should be ok with the build. I just need to know what to get and where to get it from ?


    thanks Mick

  2. #2
    Quote Originally Posted by amxen View Post
    Hi i want to build my own Toroidal power supply. I have 3 50v max drivers i need it to power , So im thinking it needs to be about 42v . But i have no idea what parts to by. This will be my first toroidal supply So any pointers towards what parts i need to get would be cool? Im a heating engineer so know my way around a multimeter so i should be ok with the build. I just need to know what to get and where to get it from ?

    thanks Mick
    I answered this here http://www.mycncuk.com/threads/7871-...6040-problems? post 58. ..Clive

  3. Don't forget input side fuses, mains connection socket, a bleed resistor across the capacitors, some sort of 'mains on' and/or 'volts out' indicator and relays etc to tie it into your eStop arrangement.

  4. #4
    Hi Clive the links don't work any more they changed the site. Also I don't need 50v that's a bit much for my drivers.

  5. #5
    Hi,

    there are no big price differences between toroid and switched-mode power supplies anymore.

    I'd always use a switched-mode power supply for CNC machines because they offer some advantages:
    • You get a finished, reliable product - no need to choose components and solder them together.
    • It won't blow your fuses from time to time like many large toroids do if you don't use a current limiter.
    • Most Important: Load and idle voltage is constant. With a toroid you have to take care to keep idle voltage below the drivers maximum voltage rating - but once the machine starts running this voltage will drop and you won't get the maximum speed and dynamics you'd get if you use a switched-mode power supply.


    Christian
    2D / 3D CAM Software and CNC controller: http://www.estlcam.com

  6. #6
    silly question but dose it matter what bob you use. Seems to be loads about but dose it matter what you use
    Last edited by amxen; 26-09-2014 at 11:34 PM.

  7. #7
    Quote Originally Posted by Christian Knuell View Post
    Hi,

    there are no big price differences between toroid and switched-mode power supplies anymore.

    I'd always use a switched-mode power supply for CNC machines because they offer some advantages:
    • You get a finished, reliable product - no need to choose components and solder them together.
    • It won't blow your fuses from time to time like many large toroids do if you don't use a current limiter.
    • Most Important: Load and idle voltage is constant. With a toroid you have to take care to keep idle voltage below the drivers maximum voltage rating - but once the machine starts running this voltage will drop and you won't get the maximum speed and dynamics you'd get if you use a switched-mode power supply.


    Christian
    This is taken from the Leadshine drive manual:
    Regulated or Unregulated Power Supply

    Both regulated and unregulated power supplies can be used to supply the drive. However, unregulated power supplies are preferred due to their ability to withstand current surge. If regulated power supplies (such as most switching supplies.) are indeed used, it is important to have large current output rating to avoid problems like current clamp, for example using 4A supply for 3A motor-drive operation. On the other hand, if unregulated supply is used, one may use a power supply of lower current rating than that of motor (typically 50%
    70% of motor current). The reason is that the drive draws current from the power supply capacitor of the unregulated supply only during the ON duration of the PWM cycle, but not during the OFF duration. Therefore, the average current withdrawn from power supply is considerably less than motor current. For example, two 3A motors can be well supplied by one power supply of 4A rating.

    It is generaly accepted that unregulated power supplies handle back emf better than regulated.

    Hi Clive the links don't work any more they changed the site. Also I don't need 50v that's a bit much for my drivers.
    The links still take you to the company and with the part No's. in the link they still work if you do a search on the site. Also I did point out that you had to pick a transformer to suite the voltage you require. Not forgetting to times the voltage of the TX by about 1.4 to get the DC voltage you will get. ..Clive


  8. #8
    Hi,

    regulated power supply usually refers to linear regulators with typically small output capacitors.
    Industrial switch mode supplies on the other side have quite large output capacitors or inductors and are perfectly suitable for stepper drives.

    Christian
    2D / 3D CAM Software and CNC controller: http://www.estlcam.com

  9. Quick tutorial using simple rule of thumb calcs:

    V(DC) =1.4 x V(AC) so for 42v DC you need 42/1.4 = 30v AC transformer. Ideally you should add 2v for the drop in the rectifier but 32v transformer is non-standard size, so you'll actually get 30 x 1.4 - 2v = 40v out.

    Now calculate the current needed as 60% of the total motor current, e.g. for 3 axis @ 4A each you need 3 x 4 x 60% = 7A.

    Now calculate the size of the transformer, simply multiply V x A. 30 x 7 = 210 so a 250VA transformer will do the job, going bigger won't hurt, just costs more but gives you flexibility for the future. This could have either one 30v @ 8A secondary winding, two 15v @ 8A secondary windings (wire in series to give 30v) or two 30v @ 4A secondary windings (wire in parallel).

    The capacitors you need can be roughly calculated using C (in uF) = 100000 x current/voltage = 100000 x 7/42 = 16666uF. For this application the exact value isn't critical so within 20% is good enough. 3 x 4700uF wired in parallel would do, rated at 1.5 or 2 times your working voltage, in this case 45 - 60v or higher (don't go too high as price get silly).

    Below 50v a bleed resistor across the capacitors isn't necessary but it's good practice to have one, R (ohm) = 5000000/C(uF). Here 5000000/(3x4700) = 350 so use 330ohm rated at 2 x v^2/R watts or in this case 2 x 30 x 30/330 = 5.5w so use 5w or higher. These can get expensive so either use multiple parallel resistors e.g. 8 x 2700ohm 1w (equivalent to 2700/8 = 338ohm 8w) or it's common practice to use a relay to switch them out of circuit when power is applied, in which case a v^2/(2 x R) rating is ok (in this case a 330ohm 2w or two 680ohm 1w in parallel)

    Hope that helps.
    Last edited by irving2008; 27-09-2014 at 06:14 AM.

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  11. #10
    Quote Originally Posted by Christian Knuell View Post
    Industrial switch mode supplies
    Industrial thats the key word here.!! . . . . . The problem with Unregulated switch mode supply with correct voltage and amp's is the cost. Industrial supplies that you can trust are very expensive and the Cheap chinese ones blow up for fun and are a lottery what you actually get out of them dispite what the ratings say.!
    So Compared to Torodial built supply which you can taylor exactly to your needs regards V & A Good Switch modes are very expensive. Every machine I build use's custom built toroidal supply and I don't get any issues with blowing fuses. Only one time did I have any problem with a sensitive fuse tripping and changing the B rated fuse for a C rated eliminated the issue. Plus if this happens it's mostly on larger Va transformers not small ones.

    Amxen Man:

    You need 30Vac 2 x 15 transformer like this. Wire it in series as it's easier and neater IMO. If your not sure what we mean by series or parallel just ask it's simple.
    http://www.airlinktransformers.com/c...nge/CM0300215/

    3 x 4700 Caps rated 63V this will be the most common to find. Wire them in parallel so + to + to + to fuse rail and same for negative side. What you pay will depend on if you don't mind soldering or not. Clamp ones are expensive. See here.
    http://uk.rs-online.com/web/c/passiv...984,4294466590

    Then Simple 25A Bridge Rectifier. Something like this will do it's OTT but better that way.
    Mount it on a piece of aluminium or heat sink. I find best thing to do is to mount the whole lot on piece of 3mm aluminium plate which then acts as a heat sink for the Bridge Rec.
    http://uk.rs-online.com/web/p/bridge...fiers/8023240/

    Regards Resistors to drain cap's then I use the NC contact of the relay which I use for E-stop circuit which then pulls in a Resistor to drain the Caps quickly.
    That said you can get away without one if you like because the drives tend to drain the caps for you. Best to make use of the enable signal thou if your using this technique to avoid any chance of motors running on slightly while drives drain.

    Other thing to be aware of with these supplies is that what you get out depends what you put in.? So if your mains supply is on the lower or higher side then you might not get exactly 42Vdc could be slightly lower or higher but you have enough safety margin so it's not an issue but don't be surprised or think you have done anything wrong if don't get exactly 42vdc.! (Little more wouldn't hurt anyway, your well safe @ 42v).
    Last edited by JAZZCNC; 27-09-2014 at 11:49 AM.

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