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Is The CNC Electronics Bundle Dangerous?

Discussion in 'General Talk' started by Eclectic Hobbyist, Mar 21, 2021.

  1. Eclectic Hobbyist

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    I was doing some quick math on the CNC Electronics Bundle in the part store. CNC Electronics Bundle

    The kit comes with the 24v 14.6A power supply, which runs at 85% efficiency. This means you can get about 297W safely from the supply. However if you get the kit with the NEMA 23's, which are 2 phase 2.8A/phase, I math out that they individually draw about 134W each. Four of them calls for 536W.

    So, this leads me to wonder if this is actually okay? Could this be hazardous?
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Reread the motor datasheets. 2.8A at 3V coil rating. Stepper motors are constant current devices when controlled by a modern stepper driver. Factor in some driver inefficiency and you are well under 30w per motor.
     
  3. Eclectic Hobbyist

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    Where does it say that on the motor data sheets? I don't see anything in the pic of the data sheet provided that shows 3V coil rating. NEMA 23 Stepper Motor.

    Are you talking about Stepper Drivers?
     
    #3 Eclectic Hobbyist, Mar 21, 2021
    Last edited: Mar 21, 2021
  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Oh right yes, the datasheet doesnt list it directly anymore (it lists the recommended driver input voltage to make it easier for people who doesnt care about the math and just want to know the recommended PSU)

    But the datasheet does list the Resistance and Max Current though, so some simple Ohms Law calculations will give you the voltage rating:

    1.1ohm per coil, and max of 2.8A current setting.

    V=I*R
    V= 1.1*2.8
    V=3.08v

    so recalcalulating the wattage:

    V*A
    3.08*2.8 = 8.624w per coil *2 coils = 17.248w.

    Factor in some losses for the driver, you are still well below 30w per motor

    Input voltage to the driver (24v) gets chopped by the microstepping driver and delivered to the motor at a far lower voltage to maintain the current setpoint to avoid overheating the motor.
     
    David the swarfer likes this.
  5. Eclectic Hobbyist

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    I know this is late, but thank you for clarifying this. I was getting really confused and over thinking it I see. Thanks!
     
    Peter Van Der Walt likes this.
  6. David the swarfer

    David the swarfer OpenBuilds Team
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    "Is The CNC Electronics Bundle Dangerous?"
    (voice of Dr House) "Absolutely, if you drop it on your foot, or your friends foot, or head, but they won't miss that"
    (-:

    but seriously, it is working for thousands of people, and has been chosen and put together by real engineers, so no, it is not dangerous or more correctly, it is not specified incorrectly.
     
  7. AceSwiftShooter

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    Hi. new here.... just an observation.

    85% efficiency means the PSU will give you 350W, but will need about 410W from the wall to do so.
     

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