Electrical – How is power divided from a wall outlet? Powering multiple motors with PSUs, extension cord

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My project involves powering 7 motors from a wall outlet, using switching power supply units. I am a little over-budget on possible output power, but it is very unlikely that all motors will run max power at the same time. Below is the architecture:
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EDIT – Sorry folks, typo in my "infographic". Should be 1700W from the PSUs.

My questions are below. I'm a bit of a newbie so please excuse 🙂

1) Can the wall outlet, plus a generic extension cord, really transmit up to ~1800W ? Like is it safe, would anything melt, etc. I've only used extension cords for small electronic devices like laptops.

2) The amperage requested by the motors may be in the 30-50 A range in total, but the wall outlet provides 15A. Just to confirm, the PSUs take care of the power conversion to the amps/volts required, right?

3) What will happen when the system requests more than 1800W ? E.g. if all motors are on and at their highest torque requirements.

4) Similar to above, but for an individual PSU with 400W. What happens if both the 288W motors are trying to request their max power, will power be split evenly at 200W per motor? What if one starts 'working hard' first (taking the max 288W), then after a few seconds the other starts requesting as much power as possible, does it get stuck with only 400-288 = 112W ?

EDIT – one more important question:

My motors are using motor drivers with adjustable current settings (so I can control max #s) and overcurrent protection. Can I leverage these current settings to operate at lower power and ensure I generally don't go over e.g. 1700W?
example product: http://www.omc-stepperonline.com/24-phase-nema-23-stepper-motor-driver-2450vdc-15a45a-256-microstep-m542t-p-293.html
(I am using Stepper Motors)

Thanks for any insights, as well feel free to suggest improvements to the setup. It's based mostly on available parts and physical space constraints, but could change. What's fixed is using the wall outlet as a source, and having those particular motors.

Best Answer

I am a little over-budget on possible output power…

No, you are way over budget on power.

  • You've added something up wrong. Your four power supplies sum to 1700W, not 1900W. They are completely inadequate for the aggregate load of your motors.

  • You cannot assume that it is "unlikely that all motors will run max power at the same time". Electric motors draw the most power under stall torque, which will occur when the motor first starts turning from a dead stop.

    In the case of PSU1, this means that it will probably overload the power supply every time motor 1 starts up. You need a larger power supply for that motor.

    In the case of PSU2/3, the only way this configuration would be safe would be if you had interlocks in place to make it impossible for both motors to be powered at the same time. 288W x 2 is well in excess of the capacity of those power supplies.

  • Power supplies are not 100% efficient. The wattage ratings you are quoting are for the output of the power supplies; the input will require more power. Read the specifications on your power supplies for details.

  • With regard to the extension cord… read its specifications. Any reputable cord will have its power ratings marked on it. Do not chain extension cords under this type of load.

  • With regard to the outlet, you absolutely cannot draw more power from the outlet than it's rated for. At best, you will trip a circuit breaker. At worst, you may cause an electrical fire.