# Effective Speed Control Circuit for a DC Motor (Blades Fly) :

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## Introduction: Effective Speed Control Circuit for a DC Motor (Blades Fly) :

Hi!

In the instructable you will be taught how to make a variable speed control circuit for your DC motor.

The potentiometer used in the circuit enables us to obtain infinite number of speeds.

Go through the steps to learn how to make one yourself.

To see how the circuit actually performs, watch the video

## Step 1: DC Motor & Bottle Cap:

Stuff Needed:

1. a bottle cap
2. a paper cutter
3. a 12 volt DC motor
4. a fan to connect to the shaft of the motor (optional).
5. a silicone gun
6. a 12 volt battery
8. a power transistor 1351
9. a 100 k-ohm variable resistor
10. double sided paper tape
11. I heavy base stand for mounting the DC motor
12. some wires
13. scissors

Take the bottle cap and cut the side of the cap with the paper cutter as shown in the picture.Now stick the motor to the cap with the help of the Glue gun as your in the pictures.

FULL length video!

## Step 2: Placing the Components:

Place the motor on the base stand with the help of the double sided tape as shown in the picture.

In a variable resistor, you will see three terminals but you have to use only two terminals.The middle one and any of the side ones.Now connect the wires to these two terminal and stick the variable resistor on the breadboard with the help of the double sided tap as shown.Connect the power transistor to the breadboard.

Full length video

## Step 3: Circuit Diagram:

Connect the wires exactly as shown in the schematic. the base and the collector of the power transistor will be connected to the variable resistor terminals.

(The schematic shows that the positive terminal of the battery is connected to the collector of the power transistor while the actual circuit shows that the collector terminal of the power transistor is connected to one of the motor wires).

Follow any of the two ways and you are done.

Full length video

## Step 4: Testing:

Slowly, rotate the nob of the variable resistor and you should see that the DC motor starts rotating with low speed and as you keep on rotating the knob the speed keeps on increasing until it reaches its full speed.

So that was all about the instructable guys.

Full length video

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## 7 Discussions

Hi, I like simplicity of the speed controller. I m trying to do a speed controller for PC fans, so 12V.
can I use any power transistor ? any suggestion ? and don't you think that 100k potentio is to much??

Which one of these transistors would work?

http://www.robotistan.com/arama?B=Arama&Kid=T%C3%9CM+KATEGOR%C4%B0LERDE&q=npn

Hello, I am a rookie.

I got all the components , except "a power transistor 1351 NPN" I dont know what it is. We have tons of transistors here in the market. What can I use instead of it? Something equivelant? Or specs would be appreciated.

This is not serious to drive a transistor that way. It won't work with any NPN transistor and can burn it, as there's no base current limit. It isn't even an emitter follower as there's no clear reference on the base. Don't do that or you will destroy both transistor and potentiometer. Can you imagine the current between plus and the base when the potentiometer value is close to zero ? Try to measure it, but fastly before the pot burns.

Apart from theory.. This circuit will actually work nice as long as the total circuit current does not exceeds 2amp.Base current is low since the potentiometer is like 100k-ohm.. so no device burning possibility.

And when the pot resistor is closed to 0 ?

Yes,the base current will increase indeed but thats a power transistor and the motor that is used here is operated at less than 0.5A which can never be a problem for a power transistor.

Your point would be correct had i been using an 8W motor or above.