slowing electrical motors

[jonnythesurfer]

hey,

I have a small electrical motor running off 9v batteries and want to reduce its speed. At the moment it runs at around 5000 rpm I want to reduce it to 3600rpm is there a way I can do this exactly? Is it as simple as increasing the resistance by 30% (the difference between the two?) or decreasing the voltage by that 30%? is there a equation i can use?

any help would be much appreciated!

 

[Reloadron]

If you want to remain with the 9 volt supply then you can try a pot in series with the motor or the best option would likely be a small PWM circuit to drive the motor. You really don't say much about the motor as to power rating, torque, anything important like what it does so it is hard to give a good answer.

Is it as simple as increasing the resistance by 30% (the difference between the two?) or decreasing the voltage by that 30%? is there a equation i can use?

Again, hard to say without more info on the motor. How important is the speed control?

Ron

 

[jonnythesurfer]

sorry I don't really no any more information.. its just a small 9v motor I got from school so don't know.

I'm asking for a friends product but am intrigued myself, it is important because cant gear down due to no space. and am trying to make a clock off it so need to be perfect... ish

 

[crutschow]

sorry I don't really no any more information.. its just a small 9v motor I got from school so don't know.

I'm asking for a friends product but am intrigued myself, it is important because cant gear down due to no space. and am trying to make a clock off it so need to be perfect... ish

Just reducing the voltage to a fixed value would not give good speed regulation. For that you would need a pickoff from the motor to measure speed and use that in a feedback loop to adjust the motor voltage.

What type of clock uses a 3600 RPM motor?

 

[4pyros]

5000 rpm

Is that loaded or not, The speed will change do to load on the motor. Andy

 

[Reloadron]

sorry I don't really no any more information.. its just a small 9v motor I got from school so don't know.

I'm asking for a friends product but am intrigued myself, it is important because cant gear down due to no space. and am trying to make a clock off it so need to be perfect... ish

Not to dissuade you but I doubt you will get this to work. Making a clock involves using a synchronous AC motor generally designed for 50 or 60 Hz. operation using an internal gear network to gear the speed down. The speed is a function of the line frequency.

The big problem is you will not get a good constant speed from a small DC motor short of getting pretty elaborate using feedback and just more than it is worth.

Now the good news is that if you really want to build a simple good old electric clock there are plenty of motors out there much like these.

I just don't see what you want to do with what you have as being very viable. If you could find an old working electric clock in a thrift store you could take it apart for the learning experience.

Ron