Two small fan motors one rotates faster when other is jammed

  • Topic: Automotive 
  • Thread starter Thread starter ahmed11
  • Start date Start date
  • Tags Tags
    Fan Motors
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
4 replies · 2K views
ahmed11
Messages
83
Reaction score
0
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
 
Physics news on Phys.org

Discussion

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.
 
  • Like
Likes   Reactions: ahmed11
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!
 
  • Like
Likes   Reactions: CWatters, russ_watters and ahmed11
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?