Two small fan motors one rotates faster when other is jammed

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Discussion Overview

The discussion revolves around the behavior of two small fan motors connected in a circuit, particularly focusing on why one motor rotates faster when the other is jammed. Participants explore the implications of circuit design and motor dynamics, as well as a theoretical question regarding coaxial helicopter motor configurations.

Discussion Character

  • Technical explanation
  • Exploratory
  • Conceptual clarification

Main Points Raised

  • One participant describes a setup with two fan motors connected to a single switch and battery, noting that when one motor jams, the other rotates faster.
  • Another participant suggests that the power supply may not be strong enough, indicating that the motor with lower power demand is functioning while the other is jammed.
  • A third participant explains that the motors are likely connected in series, detailing how the current and voltage distribution affects their operation. They note that when one motor is loaded, its resistance decreases, which alters the voltage across the other motor, resulting in increased speed for the unjammed motor.
  • A later reply thanks the third participant for their detailed explanation.
  • Another participant poses a theoretical question about applying coaxial helicopter theory to motors, suggesting that if two motors rotate in opposite directions, they could provide anti-torque to each other, and inquires if this concept makes sense.

Areas of Agreement / Disagreement

Participants present various viewpoints regarding the behavior of the motors and the implications of their connection. There is no consensus on the theoretical application of coaxial helicopter principles to motor configurations, as it remains an open question.

Contextual Notes

The discussion does not resolve the assumptions regarding the circuit configuration or the theoretical implications of the coaxial motor concept. The effects of motor loading and power supply limitations are also not fully explored.

ahmed11
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i made a small thing for my nephew, i connected two small fan motors with one switch and one battery but everytime one of the motors jams or he grabs the fan the other fan rotates faster. why is that?
also tried to increase number of batteries but same thing
 
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It sounds like the power supply is not strong enough.
So only the fan with lower power demand is working.
You should check that both fan motors work with separate batteries first.
 
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Your fans seem to be connected in series. That is, for the current to get to one fan from the battery, it must flow through the other fan.

General Rules
  1. For DC motors, motor speed is proportional to applied voltage
  2. For all motors, available torque (shaft twisting force) is proportional to the current flowing thru the motor
When a fan, or any motor, is heavily loaded its resistance (impedance) decreases. Normally it would be connected directly across the battery, and the reduced resistance would cause more current to flow, supporting the increased loading.

In your situation of a series connection, resistance of the loaded fan (Fan #1) decreases as expected, but Fan #2 is in the circuit. Fan #2 allows only its 'normal' current to flow. The decreased resistance of Fan #1 with the 'normal' current of Fan #2, causes a reduced voltage across Fan #1. Consequently. more of the battery voltage appears across Fan #2, increasing its speed.

In a your series connection, you can see the same effect by shorting the terminals of one fan. The other fan will speed up. (keep the battery voltage within the rating of one fan.)

For some images of series and parallel circuits, see: https://www.google.com/search?hl=en&tbm=isch&source=hp&biw=986&bih=649&q=series+vs+parallel

Have Fun!
 
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thank you for the detailed info!
 
another question, can coaxial helicopter theory be applied on motors to give anti torque to each other, like two huge motors attached together vertically but each one rotates in opposite direction so the anti torque or thrust applied on motor from each side will give anti torque to the other. does that make any sense. like if one motor rotates right and other to the left, if first doesn't rotate then motor must rotate left and second one doesn't rotate then it's motor rotates right so each anti torque will apply as a fixed frame for motors right?
 

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