I have a little hobby motor, a small one from radio shack. I want to make a variable speed control on it from very very slow to as fast as it will go.

I used a 10v/700ma output walwart for a device I have here at a home and a connector from radio shack so I could connect it to the motor.

In between one of the terminals I soldered a mini volume control pot #271-215 from radio shack to the #1 terminal and the middle terminal. The other terminal (3) I just left unused.

I plugged it in and it adjusted the speed as planned but within a few seconds the pot started smoking an emitted a bright light so i quickly unplugged the walwart.

The pot says Rated Power .05 watts. Switch rating 3amps at 30vdc. It is a 10k ohms with audio taper.


Question:

What am I doing wrong? I am trying to make a variable speed control on the motor from 0v to 2v. The motor is from an device that used two AA batteries for power.

Do I need a different power supply or a different pot?

Thanks for any help you can give me.

Timmy

 

Timmy,

First...which motor? :

http://www.radioshack.com/search/index.jsp?kwCatId=&kw=motor&origkw=motor&sr=1

Ken

 

You have been officially initiated into the electronic world. Everyone has to release some smoke from a component at some time. Get use to the smell. You will need that smell memory in the future when you encounter another pending smoke release.

The current drawn by the motor was too great for the poor little potentiometer to endure.

It is generally not a good thing to use a resistor in series with a motor to control the speed. The series resistor has the effect of robbing current from the motor when the motor is loaded. The result is a loss of torque.

hgmjr

 

Timmy,

First...which motor? :

http://www.radioshack.com/search/index.jsp?kwCatId=&kw=motor&origkw=motor&sr=1

Ken

Its a little smaller than this one
http://www.radioshack.com/product/i...&sr=1&origkw=motor&kw=motor&parentPage=search

 

You have been officially initiated into the electronic world. Everyone has to release some smoke from a component at some time. Get use to the smell. You will need that smell memory in the future when you encounter another pending smoke release.

The current drawn by the motor was too great for the poor little potentiometer to endure.

It is generally not a good thing to use a resistor in series with a motor to control the speed. The series resistor has the effect of robbing current from the motor when the motor is loaded. The result is a loss of torque.

hgmjr

Thanks for the initiation. If not a pot then what would be best for variable speed from 0 to maximum?

 

To handle the motor speed control properly requires the use of a technique referred to as PWM (Pulse Width Modulation).

If you are interested in this approach, I would suggest you google search for the phrase pulse-width-modulation with keywords motor and speed-control.

hgmjr

 

Here for example is just one of the many documents I located when I googled on the subject of pulse width modulation.

hgmjr

 

I saw your article and I appreciate your showing it to me and respect your extreme intellect but i do not have even the aptitude to grasp that stuff without making it my full time occupation and even then.... anyway.. is there an easy way for me to simply put some kind of speed control on this little motor? from 0 speed to maximum?

Thanks again much appreciated

Timmy

 

Another approach that would work would involve the use of a 3-terminal regulator such as an LM317 or equivalent. These devices can be obtained from a Radio-Shack or on-line from Digikey, Mouser, or Jameco. The price is a couple of dollars.

In effect what you would be doing is building a variable voltage source. This would provide the low-impedance drive to the motor and permit you to use a standard potentiometer to adjust the output voltage. The input voltage would come from your wall-wart.

Is that something you would be interested in?

hgmjr

 

hgmjr: LM317s don´t regulate from zero in usual connection, it would need something better than regulated voltage source.

 

Do you know how to solder and read a schematic? If not, it will be difficult for you to make your own speed control. If you do, we can give you a circuit for a simple PWM.

 

i am not positive if it will work, but i would try a rheostat rather then a pot. a standard wall control light dimmer.

 

i am not positive if it will work, but i would try a rheostat rather then a pot. a standard wall control light dimmer.

I think most wall control dimmers will only work with AC, and only on voltages much higher than 3V.

 

...I used a 10v/700ma output walwart for a device I have here at a home and a connector from radio shack so I could connect it to the motor.
...

hgmjr: LM317s don´t regulate from zero in usual connection, it would need something better than regulated voltage source.

Based on the availability of the 10V DC power supply, I thought that Timmy could use the LM317 as an adjustable power source for powering his motor. Granted an LM317 would provide an adjustable voltage that would range between a low of 2 volts and a high of 8 volts but I thought that would be a simpler approach than to tangle him up in the design of a PWM circuit. Specially since he had expressed a reluctance to tackle the PWM approach which is clearly the superior of these two methods.

hgmjr

 

RadioShack doesn't have a clue about electronics.
Their spec's are useless.
Max current?
Average current?
RadioShack doesn't know anything about current.

Even for an LED they don't say its brightness. Duh!

RadioShack has kids stealing discarded junk from the floor of factories then sells it with a huge profit.
No wonder they are gone from Canada. Their replacements are called. "The Source by Circuit City" (good American ripper-offer store)
I think they are called Maplin in the UK.

 

Radio Shack DOES sell a small rheostat; I don't recall it's rating offhand, but it was several Watts. Wouldn't be very efficient, but it would work to control the motor's speed - right up until the batteries got tired of fighting that rheostat

 

How about a simple power opamp? It isn't as efficient as PWM, but you can rig one up very easily and it is more intuitive for the beginner.

You can get a sample of one from Fairchild semi.
http://www.fairchildsemi.com/pf/KA/KA334.html

or the L272 from ST, you can get through digikey.. Save your time and energy and stay away from radioshack, they're awful...

Steve

 

Radio Shack DOES sell a small rheostat; I don't recall it's rating offhand, but it was several Watts. Wouldn't be very efficient, but it would work to control the motor's speed - right up until the batteries got tired of fighting that rheostat

A rheostat won't increase the load on the battery. A pot would.