-2
\$\begingroup\$

Forgive me if I am asking something absurd, I really do not understand much about electric motors.

After reading the answers of Why does a Tesla car use an AC motor instead of a DC one? , I got curious:

Is it possible a DC induction motor? At least theoretically?

\$\endgroup\$
2
  • 2
    \$\begingroup\$ Induction requires a change in magnetic field which in turn requires a change in current which in turn implies an alternating current. \$\endgroup\$
    – Andy aka
    Feb 8 '15 at 9:36
  • \$\begingroup\$ Supplying DC input for induction causes the coil to burn out. This is because of the low/zero frequency of DC. This results in no induction of EMF to oppose the current flow and it increases to unimaginable levels and ends up burning out the coil. That is why commutators are used to reverse the direction of current every half cycle thus creating the back EMF. \$\endgroup\$
    – Sâu
    Jun 13 '18 at 10:41
5
\$\begingroup\$

No, a DC induction motor is not possible. Induction implies causing current thru a magnetic field. Only varying magnetic fields can do that. This is also the same reason that transformers don't pass DC. There is no on-going power associated with a fixed magnetic field, just some fixed energy to hold it there. If this weren't true, you could get ongoing power from a fixed permanent magnet.

However, true DC motors are possible. In fact, the first real continuously running electric motor was DC. You can also make a disk spin by pushing DC current thru the disk radially, with a fixed magnetic field perpendicular to the disk. The reason this is not usually done is because of the difficulty of electrically connecting to the outside edge of a spinning disk. However, it can be done and has been done.

The reverse also works. A spinning disk with a fixed magnetic field perpendicular to it will develop a radial potential (between axis and outer edge). There have been tachometers based on this principle.

\$\endgroup\$
3
  • \$\begingroup\$ Thanks. Derived from this I now want to ask if it is possible a DC motor without magnets. \$\endgroup\$
    – sergiol
    Feb 8 '15 at 1:29
  • \$\begingroup\$ sure it is. series and shunt wound brushed DC motors \$\endgroup\$
    – JonRB
    Feb 8 '15 at 1:42
  • \$\begingroup\$ @JonRB technically, coils "are magnets" when energised. I think that sergiol wanted to know if DC motors could exist without magnetic field generation. But that's just me guessing. \$\endgroup\$
    – user42875
    Sep 14 '15 at 16:33
2
\$\begingroup\$

No (well ... sort of but it is a waste)

All electrical machines need an AC flux to couple the magnetic energy. DC brushed machines produce this via commutators. Basically these are also AC, just expose a DC accepting connection.

So why can't you have a "DC induction machine" Well the defining characteristics of an induction machine are: AC stator & AC rotor & torque generated at any other speed but synchronous.

If you were to feed the machine with DC you would need some form of commutator to take that DC and alternate it to produce the required AC. Could this AC be enough to excite the rotor with an AC field? ... sure something would be coupled across, but it would not be efficient as the airgap field of a DCmachine is more squarewave.

Imagine a mains transformer being excited with a squarewave, some energy does get transformed but not as much as if it was AC

\$\endgroup\$
0
\$\begingroup\$

Yes: but qualified. There is a class of induction motor called "Electrically Commuted Motor" or "ECM" for short. If you pound the string "ECM motor" into Google, you can learn how it's done and what the benefits are.

\$\endgroup\$
3
  • \$\begingroup\$ Isn't that a DC brushless motor? \$\endgroup\$
    – sergiol
    Feb 8 '15 at 1:45
  • \$\begingroup\$ which is closer to a sync machine \$\endgroup\$
    – JonRB
    Feb 8 '15 at 2:13
  • \$\begingroup\$ I searched the Internet for 'sync machine' but the results where not pertinent to this discussion. What's that really? \$\endgroup\$
    – sergiol
    Feb 8 '15 at 13:47
0
\$\begingroup\$

Yes,It's Possible,but not so efficient.You need two commutators to build such a motor.The first commutator receive current from source supply it to the rotating coil and second commutator.And the second commutator supply current to the stationary coil.The impression of this kind of motor is given in this image.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.