# Universal motor DC vs AC which will give more speed and torque

I have shortlisted a universal motor for a DIY project requiring High speed and torque of the motor.

Motor looks like below and some characteristics.

DC Motor : Washing Machine
Input Power: 750 Watt
Voltage: 230 V 50 Hz
Current: 0.95 – 1.1 A
Speed: 16500 - 20000 rpm (3 speed)
Rating: 30 Minutes
Insulation: Class B

I see it being a universal motor can be powered by 230v AC or 230v DC supply.
Will AC or DC give more speed and torque for a 30 min continuous operation ?

• Is there a data sheet for the motor? Is there a manufacturer's site that can be read? Commented Jan 20, 2021 at 11:09
• Trying to get datasheet, what ever information I had from manufacturer's website I have put in question. Commented Jan 20, 2021 at 11:51

A universal motor operating with DC power at a voltage equal to the motor's RMS AC voltage rating will have speed vs. torque capability curves that show both higher speed and higher torque capability when operating with DC as shown below. The actual operating speed and torque will be determined by the load's speed vs. torque demand torque. At steady-state, operation will be at the intersection of the curves.

The safe continuous operation point or the safe operation for a given load vs. time duty cycle will be determine by the motor's efficiency and its capability to dissipate heat due to losses. The motor will be more efficient with DC power because of iron loss reduction. However the copper losses will be higher at a higher torque or speed since the motor's output power is proportional to torque multiplied by speed.

Will AC or DC give more speed and torque for a 30 min continuous operation ?

Yes. However how much more speed and and torque and how long it will be safe to operate will be determined by the load's torque vs. speed demand curve and the motor's efficiency and cooling capability.

Image from Fitzgerald, Kingsley, Umans, Electric Machinery, 4th ed

Here are some findings.

R. Garg, "Behavioral Analysis of a Universal Motor When Operated On DC and AC Supply," 2019 International Conference on Intelligent Computing and Control Systems (ICCS), Madurai, India, 2019, pp. 705-710, doi: 10.1109/ICCS45141.2019.9065475.

Abstract:

In this paper, a universal motor which is actually a modification of dc series motor is made to run on a particular voltage level of DC supply and on same RMS value of AC supply. DC series motor with certain modification for the purpose of reducing losses when run on AC supply is called AC series motor or Universal motor. Analysis of behavior of Universal motor is done through a SIMULINK model. Various scopes have been used to monitor the value of current, voltage and speed of the motor. Comparison between speed characteristics of the motor when made to operate on same voltage AC and DC conclude that motor runs on a higher speed on dc supply, thus proving that although motor is universal but performance on dc supply is better than that on ac. Also other parameters are better in dc as compared to that in ac supply.

https://ieeexplore.ieee.org/document/9065475