Maker Pro
Maker Pro

Why connecting a brush motor to voltage divider doesn't work?

9905mi

Jul 5, 2018
8
Joined
Jul 5, 2018
Messages
8
Hello everyone, I have connected a brush motor to a simple voltage devider made from a 9v battery and two- 10k ohm resistors as it is shown in the image but the motor doesn't work althought it gets enough voltage (4.2v). However when I connect the motor directly to the battery the motor spins and if I insert a led to the sircuit, instead of the motor, it glows. What is the problem then?
 

Attachments

  • ArtBoard Image (2).jpg
    ArtBoard Image (2).jpg
    26.3 KB · Views: 38

Minder

Apr 24, 2015
3,478
Joined
Apr 24, 2015
Messages
3,478
The 10K resistor is Way too high for a series resistor, even on a small motor.
You would be better off using a simple PWM circuit.
M.
 

73's de Edd

Aug 21, 2015
3,613
Joined
Aug 21, 2015
Messages
3,613
Sir 9905mi . . . . .

Equating your presently initially perceived aspects of electricity / electronics . . .cross field to mechanics instead . . . perchance . . . .even earlier in your life.
Did your childhood observations of the WILD activity of your hamster on its exercise wheel, then create a visualization of the feasibility of mechanical cross adaption and having it power your bike.
Same concepts . . . .

motor doesn't work althought (sic) it gets enough voltage (4.2v).
( Not 4.5 ? . . . . you must be using a slightly depleted battery . . . )

That would be the voltage out of the center of the voltage divider . . .when NOT being connected to its motor load.
The CONNECTED motor is then asking for hundreds of milliamperes . . . if not amperes . . . of current supply demand.
Your series 10k limits that motor supply current down to the 400 microamperes range. (0.0004 amperes)

That back up test of the use the LED, results in its meager demands of current of ~20ma or less is fooling you, due to its MEAGER current demands.



73's de Edd
.....
 
Last edited:

9905mi

Jul 5, 2018
8
Joined
Jul 5, 2018
Messages
8
Sir 9905mi . . . . .

Equating your presently initially perceived aspects of electricity / electronics . . .cross field to mechanics instead . . . perchance . . . .even earlier in your life.
Did your childhood observations of the WILD activity of your hamster on its exercise wheel, then create a visualization of the feasibility of mechanical cross adaption and having it power your bike.
Same concepts . . . .

motor doesn't work althought (sic) it gets enough voltage (4.2v).
( Not 4.5 ? . . . . you must be using a slightly depleted battery . . . )

That would be the voltage out of the center of the voltage divider . . .when NOT being connected to its motor load.
The CONNECTED motor is then asking for hundreds of milliamperes . . . if not amperes . . . of current supply demand.
Your series 10k limits that motor supply current down to the 400 microamperes range. (0.0004 amperes)

That back up test of the use the LED, results in its meager demands of current of ~20ma or less is fooling you, due to its MEAGER current demands.



73's de Edd
.....
Ok, I didn't know that dc motors require that amounts of current.
 

Minder

Apr 24, 2015
3,478
Joined
Apr 24, 2015
Messages
3,478
Ok, I didn't know that dc motors require that amounts of current.
Measure the current with a low voltage using a locked rotor, test a couple of locations and calculate initial start current. As the rpm increases the current decreases, relative to load.
M.
 
Top