Choosing the power supply.



  • I'm so happy with my DuetWifi Delta printer that I'm going to build another printer with this fantastic board.
    It's going to be CoreXY type with a build area of 300x300x325mm. I'm thinking of going 24v.

    The problem is that these numbers don't seem right:

    • Heated Bed will be 220vAC +SSR. No power draw here.
    • Heater Cartridge 24v 40w
    • 24v Fans x4. 2w each? = 8w
    • Extruder: Nema17 Pancake. (Rated Voltage * Rated Current) 2.7v * 1.4a = 3.78w
    • X and Y: Nema17 Wantai. 3,1v * 2.5a = 7.75w // x2 = 15.5w
    • Z Dual TR8*8: Nema17 from Robotdigg. 2.3v * 1.2a = 2.76w // x2 = 5.25w
    • DuetWifi: 2w
    • PanelDue: I've the 4.3" version. 3w? less?

    TOTAL: 77.53w

    So a 24v 5a 120w is ok? It feels wrong :S
    Am I missing something here?

    Also, the wiki recommends motors with an inductance lower than 4mH.
    The two I’m going to buy for the Z axis have 4,5mH https://www.robotdigg.com/product/31/NEMA17-Threaded-Rod-Stepper-350-or-400-Tr8*8-Leadscrew
    Should I source for different ones?

    Any help is much appreciated.
    Martin


  • administrators

    24V 5A is what I have in my 1m high delta printer.

    Those motors should be OK for your Z axis if they provide enough torque to lift the bed (which depends on how heavy it is). The slightly high inductance will limit the maximum speed, but the Z axis doesn't normally need to move very fast. If you wanted high speed, motors wound for higher current and lower inductance would be better.

    Three Z leadscrews instead of two would allow you to do automatic bed levelling - but then of course you would need to add a DueX2 or external driver to drive the 6th motor.



  • @Martin_S:

    ….....................................................The two I’m going to buy for the Z axis have 4,5mH https://www.robotdigg.com/product/31/NEMA17-Threaded-Rod-Stepper-350-or-400-Tr8*8-Leadscrew

    Should I source for different ones?
    …...................................

    Martin

    Yes. But not because of the motor itself. It's the lead screws you need to ditch. 8mm lead is far too course for the Z axis IMO. You'll need a lot of torque to drive them, you'll have to rely on micro stepping for positional accuracy and you'll run the risk that the bed may drop when you remove power from the motor due to the steep angle of the helix. It's a pet hate of mine and one that I went into a bit more detail on my blog https://somei3deas.wordpress.com/2017/01/31/z-axis-lead-screws/



  • @dc42:

    24V 5A is what I have in my 1m high delta printer.

    Those motors should be OK for your Z axis if they provide enough torque to lift the bed (which depends on how heavy it is). The slightly high inductance will limit the maximum speed, but the Z axis doesn't normally need to move very fast. If you wanted high speed, motors wound for higher current and lower inductance would be better.

    Three Z leadscrews instead of two would allow you to do automatic bed levelling - but then of course you would need to add a DueX2 or external driver to drive the 6th motor.

    Thank you David, I'm happy to hear that. I might go for a 10a 24v PSU in case I will add lights or another extruder in the future. The price is almost the same.
    Regarding the maximum speed… approx how much? for a bed that weights let say 2kg?
    With my current printer I normally print at very conservative speeds, 60mm/s and 200mm/s moves. It just makes me wonder how low the maximum speed of these steppers would be.

    @deckingman:

    Yes. But not because of the motor itself. It's the lead screws you need to ditch. 8mm lead is far too course for the Z axis IMO. You'll need a lot of torque to drive them, you'll have to rely on micro stepping for positional accuracy and you'll run the risk that the bed may drop when you remove power from the motor due to the steep angle of the helix. It's a pet hate of mine and one that I went into a bit more detail on my blog https://somei3deas.wordpress.com/2017/01/31/z-axis-lead-screws/

    Oh boy… I'm even more confused than before.
    My first and only 3d printer is a Rostock Max variant, so when talking about lead screws, pitch, turns and everything related to that, I'm lost.

    A TR84 would be a good choice? If I got it right, that would have 2 starts and the motor will need to turn faster than a TR88, but with a better accuracy right?
    FYI, the lower print height that I do is 0.15mm

    Thanks for the patience.
    Martin



  • I bought a laptop power supply for my delta (similar to Davids) which has a mains powered bed so 5A is plenty and I never see any voltage drop. As it was going to live under the bed, I removed the top casing and printed one with lots of ventilation in it.

    Rostock max is a delta, and its belt driven, the bed is fixed so no leadscrews to worry about go for low inductance motors.



  • @Martin_S:

    Oh boy… I'm even more confused than before.
    My first and only 3d printer is a Rostock Max variant, so when talking about lead screws, pitch, turns and everything related to that, I'm lost.

    A TR84 would be a good choice? If I got it right, that would have 2 starts and the motor will need to turn faster than a TR88, but with a better accuracy right?
    FYI, the lower print height that I do is 0.15mm

    Thanks for the patience.
    Martin

    Martin,

    I think I explained it all in my blog post but …........

    4mm lead instead of 8 means 1 turn moves the bed 4mm instead of 8mm. I turn with a 1.8 degree stepper is 200 steps so 200 steps is 4mm. So 0.15 layer height would be 200/4*0.15 = 7.5 steps. Not a whole number so not good. You could choose layer heights that are multiples of 1/50 (0.02) so 0.10, 0.12, 0.14, 0.16 etc. Or you could use 2mm lead screws which means that 1 full step would be 0.01mm of travel so 0.15mm would be 15 full steps. Or you could stick with the courser pitch but use 2:1 or 4:1 gearing which gives that added advantage that you only need half or a quarter of the torque but you run the risk of introducing backlash which might be an issue if you intend to use baby stepping. Or you could use 0.9 degree steppers which give you 400 steps per mm but tend to have less torque. Or you could simply ignore everything I've said - most people do (especially my wife) 🙂



  • @DjDemonD:

    I bought a laptop power supply for my delta (similar to Davids) which has a mains powered bed so 5A is plenty and I never see any voltage drop. As it was going to live under the bed, I removed the top casing and printed one with lots of ventilation in it.

    Rostock max is a delta, and its belt driven, the bed is fixed so no leadscrews to worry about go for low inductance motors.

    Indeed my good sir, but the lead screw is for a future to be CoreXY.

    @deckingman:

    Martin,

    I think I explained it all in my blog post but …........

    4mm lead instead of 8 means 1 turn moves the bed 4mm instead of 8mm. I turn with a 1.8 degree stepper is 200 steps so 200 steps is 4mm. So 0.15 layer height would be 200/4*0.15 = 7.5 steps. Not a whole number so not good. You could choose layer heights that are multiples of 1/50 (0.02) so 0.10, 0.12, 0.14, 0.16 etc. Or you could use 2mm lead screws which means that 1 full step would be 0.01mm of travel so 0.15mm would be 15 full steps. Or you could stick with the courser pitch but use 2:1 or 4:1 gearing which gives that added advantage that you only need half or a quarter of the torque but you run the risk of introducing backlash which might be an issue if you intend to use baby stepping. Or you could use 0.9 degree steppers which give you 400 steps per mm but tend to have less torque. Or you could simply ignore everything I've said - most people do (especially my wife) 🙂

    Sorry, you did, and I read it. The thing is… slow learner here 🙂
    I think I might get a leadscrew with 2mm lead / 2mm pitch and use 1/16 microstepping. If it takes way too long for Z to move, then play with the micro-step values.

    Thanks for the help.


  • administrators

    A 2mm pitch leadscrew sounds good to me. My SCARA printer has one for the Z axis and it manages 1000mm/min Z speed easily. It would probably do more if I increased the motor current.


 

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