Thread: PSU question

  1. #1
    Hi

    I need to drive 4 x 1090 oz-in motors. The motor is rated as follows:
    NEMA34, Current = 5.6A/phase, Inductance = 4.1 mH/phase. Using the Leadshine AM882 driver.
    So the optimum power required to drive this configuration would be 65-70V and 16Amp.

    I have a SMPS that produces an output of 48vdc and 24amp, which would be way under on voltage to get the best out of this motor/driver combination.

    Would using one of these 1x 1500W 30A DC Boost Converter Step-up Power Supply Module In10~60V Out 12~90V to boost my SMPS to 70Vdc at 17Amp be an acceptable solution?

    Thanks
    Ian

  2. #2
    I'd not be keen on it - at the 92% efficiency at 1kW (wet finger approximation to your 70V x 16A), that's 160W it needs to dissipate - the heatsink looks a bit weedy for that, so immediately I'm worrying about the duty cycle / overheating of the regulator. £20, though - might be an interesting experiment.

    I'm curious that you claim you require 16A, I'm assuming 2-phase motors, so 2x5.6=11.2A/motor(x3)?, so >30A requirement, or is my understanding wrong? (I thought steppers excite both phases).

  3. #3
    Hi

    I worked it out as 70% of 4x5.6=15.68A for 4 motors. It looks like forgot to add in the 2 phases Thanks for catching that! So it should be a requirement of 31.6 Amps correct?

  4. #4
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 9-10 years. Has a total post count of 2,011. Received thanks 221 times, giving thanks to others 5 times.
    Steppers use both phases, however only 1 is ever fully energised, so you only need to use the basic amp figure for PSU calculations.

    Plus with modern drives, it's very rare for the drive to draw the full rated current anyway, and it's even less likely you'd be able to run at motors to meet the condition where the full power/current would be needed.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  5. #5
    Hi

    Yes, I was thinking about this and went to check the detail in the Gekodrive STEP MOTOR BASICS GUIDE, This is a extract from Section 6: Power Supplies

    The easiest factor in choosing a power supply is its current rating, which is based on your motor
    ratings. A motor control will always draw less than 2/3 of the motorís rated current when it is parallel
    (or half-winding) connected and 1/3 of the motorís rated current when it is series (or full-winding)
    connected. That is to say, a 6 amp per phase motor will require a 4 amp power supply when wired in
    parallel and a 2 amp power supply when wired in series. If multiple motors and drives are used, add the
    current requirements of each to arrive at the total power supply current rating.


    With that in mind it looks like my original estimate of Approx 16 amp would be correct.

  6. #6
    Quote Originally Posted by iforeman View Post
    Hi

    Yes, I was thinking about this and went to check the detail in the Gekodrive STEP MOTOR BASICS GUIDE, This is a extract from Section 6: Power Supplies

    The easiest factor in choosing a power supply is its current rating, which is based on your motor
    ratings. A motor control will always draw less than 2/3 of the motorís rated current when it is parallel
    (or half-winding) connected and 1/3 of the motorís rated current when it is series (or full-winding)
    connected. That is to say, a 6 amp per phase motor will require a 4 amp power supply when wired in
    parallel and a 2 amp power supply when wired in series. If multiple motors and drives are used, add the
    current requirements of each to arrive at the total power supply current rating.


    With that in mind it looks like my original estimate of Approx 16 amp would be correct.
    Depends if the Motors are 4 wire or 8 wire.? If 4 wire which most large motors are then high chance they'll be series wound not parallel. In which case you won't need so much.

    Regards PSU then I wouldn't mess around and just build Toroidal PSU to meet your exact requirements.

  7. #7
    I suspect that the Gecko recommendations are based on linear power supplies. The trouble with switch-mode supplies is that they can hard-limit at max current which gives stepper drivers a problem when they demand short but high-current pulses. Linear supplies with their big smoothing capacitors will handle this with no problem - it doesn't matter in this situation if the output voltage drops a few volts when you demand higher than rated current for a few milliseconds. If you are looking at cascading a switch-mode inverter off the back of a switch-mode power supply, it might not handle this kind of load very well. Linear supplies needed to be rated for average demand, switch-mode for peak demand, as a general guide.

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