AC and DC Motor Drives: Is One the Clear Choice?

When engineers are looking to buy a motor, the question most often asked:  Is AC or DC technology better? The answer isn’t that one is better than the other. Rather it is application and cost dependent.  Here we will discuss the options and specifically the advantages and disadvantages of each. Furthermore, it is often a matter of personal preference, and as such we encourage you to let us know your thoughts on the subject.

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10 Responses to AC and DC Motor Drives: Is One the Clear Choice?

  1. Jean November 6, 2014 at 7:13 pm #

    I think that you are right on your argument. I would like to say there is no pressure on the technical ability of maintenance and operations personnel.I think industries should employ graduate electrical engineers who have studied electric drives to deal with electric drives maintenance. It is very exciting field of electrical engineering and uses vector control for AC drives.the output voltage could be fixed or variable at fixed or variable frequency.A variable output voltage can be obtained by varying the input DC voltage and maintaining the gain of the power converter constant.On the other hand, if the DC input voltage is constant (fixed) and it is not controllable , a variable output voltage can be obtained by varying the gain of the inverter, which is accomplished by pulse width modulation control with the power converter.we do not use PLC but we use programmable microchip implementing C program language.Without power converter you cannot achieve speed control within electric drives such as PMSM, PMDC,INDUCTION MACHINE…

  2. Mark Lewis November 7, 2014 at 9:01 am #

    Thank you Jean for your thoughtful comments. Regarding the technical ability of personnel, it would be nice if companies decided they should employ degree’d engineers as you suggest, but many don’t or can’t afford to.

  3. Dave C. October 9, 2015 at 5:41 pm #

    I have been researching this question for a few weeks. In particular I was trying to find a way (VFD) to convert a Midi-lathe to variable speed to eliminate belt changes to alter speed. I get conflicting information and I did find a vendor that sold a device to do this. However, using it on a capacitor start (induction motor) is in question. Some say when the motor slows down the motor switches between the start and run windings. Many people feel there is a power experience between AC and DC motors. (DC being more than bigger AC????) Many have converted their lathe to a DC motor and added some controls to get variable speed. You can buy variable speed lathes but many feel they are underpowered for anything but small work like pens etc. I don’t want to count on someone throwing away a treadmill to get a motor and then have to jury rig a controller. So is it possible to buy something to backfit an AC lathe and make it variable speed? Some kinf of VFD drive controller etcf?

  4. Gary June 16, 2016 at 1:42 am #

    Induction appliances is a somewhat new appliance brought to the home. If AC motors can be adjusted by frequency, then why not make AC appliances like air conditioners work like an inverter appliance? They make solar power inverters that can conform to the grid so adjusting the frequency seems to be an easy feat. I don’t think it would be a cost issue.

  5. Mark Lewis June 16, 2016 at 7:17 am #

    Induction appliances use multi-zones (coils) and ‘on-off’ control to vary temperature. More zones on for longer time = more magnetic flux = higher temperature. Appliance OEM’s would not spend the money to buy a VFD for each cooking zone, so from their perspective it is a cost issue.

  6. Mark Lewis June 16, 2016 at 7:22 am #

    Capacitor start motors are not designed for variable speed operation. So you are looking at changing both the motor and adding a control to have a variable speed lathe. DC motors inherently offer higher torque at lower speeds; an AC induction motor can be made to do the same but a vector drive may be required. Vectors drives are more sophisticated and more costly. So the application / what you are turning on the lathe is an important factor – higher speeds may opt for induction motor / basic VFD; lower speeds probably go DC.

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  9. Benjamin October 1, 2016 at 12:46 pm #

    Interesting comparison.I want to use battery to start ac motor by the help of inverter or should i use dc motor for simplicity?Help.Thanks

  10. Mark Lewis October 3, 2016 at 7:39 am #

    You can do either, however, the voltage output of the inverter needs to match the motor voltage you use. If you use a DC motor, you can run directly from a battery but again, the motor voltage needs to match the battery voltage. Both options will produce a fixed speed on the motor. The DC motor option will provide significantly more starting torque, if that is a consideration/concern for you.

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