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What happens if a motor is not supplied required amps?

  1. Jul 5, 2012 #1
    Hi everyone,

    I am in a situation where I need to run two 3000RPM, 24V, 15A DC motors from one 24V, 23A switching DC power supply, rated at 600W.

    Firstly, the power supply has three sets of DC outputs and one set of AC inputs. By sets I mean one positive and one negative. This means I can power three different circuits from it. What I am confused about is how much power each of the motors can receive if they are connected to separate ports. Will I get 24V, 23A at each port? Or will the voltage be same but the current shared across the motors?

    The second thing is, if each motor receives only half the current (11.5 amps), and 24V, what effect will that have on the performance of the motors? Will it decrease their max RPM or torque or both, and by estimated how much?

    I am a complete beginner in electrical engineering so please go easy on me...
    Thank you very much for all your time!
     
  2. jcsd
  3. Jul 5, 2012 #2

    psparky

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    Gold Member

    I'll just take some guesses for fun......I have learned to enjoy being wrong. Take this advice with a grain of salt and wait till great minds prevail. Still, just for fun....

    Have you tested the 4 outputs with a volt meter....or at least a small light bulb?

    Does it have voltage at each port all the time....or only one at a time as "switched" implies?

    If it is only one at a time, you should be able to still run two motors in parallel. AC motors hate drops in voltage...but a DC motor should run at just slightly less RPM and torque. Why do I say this? Because I remember playing with tyco trains as a youngster and watching the train speed change with the change in the throttle....voltage I presume.

    24 volts X 15 amps = 360 watts...X 2 (motors)= 720 watts. 600/720 = 83%

    But I think you might burn up your power supply if you are constantly running it maxed out at 600 watts all the time.
    You can safely run one motor off of it.....I think everyone will agree with that.
     
    Last edited: Jul 5, 2012
  4. Jul 5, 2012 #3
    You really should contact your suppler about this question. You risk damaging the power supply and possibly the motor if you are wrong about how the power supply works. Find the manufacturer on the tag attached to the power supply and look it up on the internet to get the phone number. When you call ask for technical assistance about [model number] power supply.

    The max RPM is determined by the voltage across the motor and the current determines the torque.

    As long as the load doesn't require more torque or current than the power supply can deliver you should be alright. What happens when you exceed the max current of the power supply depends on the power supply. It may blow a fuse or it may lower the voltage, and therefore the speed of the motor until its current is sufficient to drive the motor at a lower speed. If that speed is zero RPM or a stalled motor, the motor will heat up and you could destroy the motor. If the power supply has no internal protection it could also blow the transistors in the supply.
     
    Last edited: Jul 5, 2012
  5. Jul 5, 2012 #4
    Your 24 v, 23 A is 552 W - 600 W is the nominal rating.

    If the three DC outputs do not have seperate ratings of volts, amps, watts then they are most likely not seperate circuits, but internally connected and the outputs are just supplied to you for your convenience. Check the ratings tag on a standard swithced PC power supply to compare.
     
  6. Jul 6, 2012 #5
    Judging from all your answers, it is clearly not a good idea to attach the two motors at once to this power supply.

    Does anyone know of a power supply with a greater amp rating but the same voltage?
     
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