What happens to DC motors when they are connected to AC current?
Most DC machines will not operate successfully on AC unless they are rewired to operate similarly to the AC/DC Universal motors used in hand tools. You probably have already operated a DC motor on AC if you have a drill. Hope this helps, Newton1Law
IT STAYS STILL AND VIBRATION WITHOUT ANY ROTATION, MAKES NO HARM TO DC MOTOR IF THE AC VOLTAGE IS THE SAME AS DC VOLTAGE RATE MARKED ON MOTOR.
None of these people answered your question fully, so I will. A DC motor that uses permanent magnets will vibrate at the rate of the AC line frequency, which for the USA is 60 Hertz. However, if the DC motor is a shunt wound motor or series wound DC motor aka field wound motors, then it will rotate. These motors use copper wingdings in the field instead of permanent magnets to produce a magnetic field when current passes through the copper conductors. In fact the universal motors you find in power tools, vacuum cleaners, and blenders use series-wound DC motors that are using AC power to run. If want to know how it is possible for a field wound DC motor to run on AC then let me know and I will tell you.
Vibration at the frequency of the AC and higher current draw, meaning the voltage will have to be lower for the same amount of power and heat. That's because a spinning motor creatures back-voltage which reduces the current, a still or oscillating/vibrating motor does not. Most AC sources are higher voltage than DC rather than lower. If you connected a cordless drill motor to wall power you'd blow a fuse. And, if the fuse doesn't pop fast enough, you'd permanently fry the motor with a bang/pop and the smell of burnt plastic.
akm 69 is correct this is beoz dc motors have commutator ring whereas AC one's has slip rings,now when AC is supplied to DC motor the direction of coil movement wil change very rapidly as becoz magnets in motor are repeling it but repelling in different direction very rapidly will act as huge resistance to electrons and they will loose energy in form of heat letting it to burn!
