Talk:Brushed DC electric motor

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Graphic Incorrect?[edit]

I am by no means an expert on electrical physics or engineering, but I am fairly certain that the three-part diagram provided near the top of the article is incorrect; the third panel shows, or is implied by the description to show, a stage immediately after the commutator has re-contacted the brushes; however, the color of the field windings (implied to mean a given magnetic pole) has not switched, as it should have at this point (i.e. in the third diagram, the red and blue colors of the rotor SHOULD have switched, but they have not). This would not provide a working motor and is the entire reason DC motors need a commutator.Hamiltondaniel (talk) 01:15, 28 December 2010 (UTC)

EDIT: On further inspection, the graphic IS correct, but it is less explanatory than it could be; it does not show the motor at a point after the commutator has flipped the magnetic field, which seems to me essential to the way a motor like this works.Hamiltondaniel (talk) 01:15, 28 December 2010 (UTC)

I think you are right that the graphic fail to clearly show on of the most important points. If anyone can take on this fix, it would be a significant improvement.ike9898 (talk) 00:45, 30 May 2011 (UTC)

ANOTHER POSSIBLE ERROR?: Sorry if I am being complete stupid here but are not all the graphics in this row incorrect in how the poles on the electromagnet/armature are labeled? Should they not be the other way around? Indeed, with dirction of (conventional) current as drawn on the diagrams, Fleming's left hand rule would say that the rotation would be the other way around no? Please do correct me if I am wrong here. — Preceding unsigned comment added by Oblongn (talkcontribs) 12:16, 28 April 2014 (UTC)

This is a Dynamo, not a "Brushed DC Electric Motor"[edit]

Generally this page needs to be changes to a different title that involves the word dynamo.

A Dynamo is a brushed commutated DC device, that can be either a motor or a generator, depending on whether electrical power is applied or if mechanical force is applied to the rotor.

The distinction line between DC motor and DC generator is extremely blurry, and two dynamos can be interconnected across two circuits physically acting against each other, to balance current across the two circuits.

If this article is kept as it is now, about 90% of the information in this article will be duplicated an any article that attempts to discuss brushed DC generators.

DMahalko 03:05, 15 September 2007 (UTC)

I agree that a DC motor and DC generator are, physically, very similar but I have never heard a motor described as a dynamo. Biscuittin (talk) 11:06, 20 January 2010 (UTC)
I think the "Dynamo" heading on one of the sections was confusing, so I have changed it to "Motor". Biscuittin (talk) 11:09, 20 January 2010 (UTC)


See Talk:Stepper_motor#Spam. - Mdsummermsw (talk) 19:55, 28 December 2007 (UTC)

Simplest model direct current machine[edit]

From this: F/I = E/V = Bl
so that: FV = EI (mechanical power equals electrical power)
Martin Segers (talk) 13:32, 4 January 2008 (UTC)

Diagram Error[edit]

The diagram (Image:3ptMotorStarter.gif)shown on the Wiki page concerning Brushed DC Electric Motor is incorrect. The diagram shows the electromagnet coil shorted out and could not possibly work in this wired configuration. Here is a link to the incorrect diagram [1] —Preceding unsigned comment added by (talk) 04:13, 20 January 2008 (UTC)

Poor understanding of why the field is skewed[edit]

"Gets dragged round" indeed! Explanation obviously gleaned from textbooks but is completely wrong. Motors and dynamos have inductance. The build-up and decay of a magnetic field takes time hence the full effect happens some time AFTER the time when an electrical circuit is made via the commutator segments, by which time the rotor has turned some more. Nothing to do with 'dragging' or even phlogiston. Looks like the best that could happen to this page is it gets deleted.

Robots42 (talk) 10:29, 22 December 2008 (UTC)

Don't like the way it is written? WP:SOFIXIT -- DMahalko (talk) 12:56, 31 December 2010 (UTC)

Dead link in references[edit]

The references section at the bottom of the page contains the following line:

Indented line^ Hawkins Electrical Guide, p.359
Indented line^ Hawkins Electrical Guide

It is marked blue like a link, but it refers to the wikipedia page for 'brushed dc motor' (this page) —Preceding unsigned comment added by (talk) 07:56, 6 April 2011 (UTC)

Fixed. Wizard191 (talk) 19:58, 6 April 2011 (UTC)

Merge from Torque and speed of a DC Motor[edit]

I'd like to propose merging Torque and speed of a DC motor into this article. There is no information on that page pertinent to Brushless DC electric motors, and the additional detail on different windings is relevant to the subject as a whole. I would imagine that speed and torque of a motor would be merged into the relevant section for that winding on this article. — Preceding unsigned comment added by Hypergeek14 (talkcontribs) 13:16, 30 November 2011 (UTC)

  • I have now blanked that page and moved it into this page. (talk) 01:55, 5 April 2013 (UTC)

Position of zero torque and of maximum torque on a two-pole armature.[edit]

This is in regards to caption2 for "Electric motor cycle 2.png", where the armature is vertical.

Electric motor cycle 2.png

If you treat the armature as if it was a rod-shaped permanent magnet, the upper end is being repulsed by the N stator pole and attracted to the S stator pole. Likewise the lower end is being repulsed by the S stator pole and attracted to the N stator pole. This is the point of maximum torque on a small permanent magnet positioned between the poles of a larger permanent magnet. Once the armature has rotated 90 degrees, making it horizontal, the rotational torque drops to zero.

If the diameter of the armature coils are increased to the point where they nearly touched the stator poles, the result would be very much like [Figure 1.12] in Electric Motors and Drives: Fundamentals, Types and Applications by Austin Hughes, Bill Drury. That shows "Current-carrying conductors on rotor, positioned to maximize torque."

This was my reasoning for revision 569981088. The phrase "due to inertia" is not appropriate when the armature is in this position. Joeinwap (talk) 07:48, 27 August 2013 (UTC)

Polarity of Electrical Connections Incorrect on graphic?[edit]

In the multi-stage diagram that demonstrates basic motor operation, the polarity of the electrical connections and the direction of rotation of the rotor doesn't appear to be consistent with the direction of windings of the blue and red wires. This could be corrected by reversing the polarity of the electrical connections. Zeneca248 (talk) 02:45, 4 February 2014 (UTC)

Incorrect statement on mechanical power[edit]

Towards the end of the section titled "Simple two-Pole DC motor" there is an incorrect statement/formula: "The mechanical power produced by the motor is given by: P = I \cdot V_{cemf}"

This formula is not for mechanical power, but rather it is electrical power. To elaborate further: Electrical power is P = IV, whereas mechanical power is P = Tw, where T is the output torque of the motor and w is the angular velocity of the motor (note that while I am typing w, the symbol typically used is a lower-case omega). When using units of N-m for torque and s^-1 for angular velocity, the resulting power term will be in watts. The difference between these two terms is the heat loss in the windings and will be equal to i^2*R, where i is the winding current and R is the winding resistance. The ratio of the mechanical power out to the electrical power in, (Tw)/(IV), is the motor's efficiency.

Note also that the above relationships are idealized and will not be exact for real world applications, where friction and eddy currents and the like also contribute to inefficiencies in motor operation. (talk) 14:06, 30 April 2014 (UTC)A. Latour

Simpler motor[edit]

Instead of a Solenoid based dc motor (the one in the article) couldn't we have a diagram for a plain coil dc motor like This one? RetΔrtist (разговор) 05:40, 21 January 2015 (UTC)

It's impossible to see the splits in the commutator in the proposed illustration. It's also more schematic, the illustration now in the article somewhat better resembles a real motor. --Wtshymanski (talk) 14:25, 21 January 2015 (UTC)
Time for a visit to your optician, because I can see them perfectly. (talk) 17:31, 21 January 2015 (UTC)