
I know that the answer to the question "What is the difference in motors?" is in "Operating at normal power line frequencies, universal motors are often found in a range less than 1000 watts. Universal motors also formed the basis of the traditional railway traction motor in electric railways. In this application, the use of AC to power a motor originally designed to run on DC would lead to efficiency losses due to eddy current heating of their magnetic components, particularly the motor field pole-pieces that, for DC, would have used solid (un-laminated) iron and they are now rarely used.". Can you tell me what it is? 


the use of AC to power a motor originally designed to run on DC would lead to efficiency losses
