DC Motor Speed Controller





Introduction: DC Motor Speed Controller


today I’m gonna show you how to make a really simple DC motor speed controller.

Step 1: Watch the Video

the video is in my Youtube channel Chris' Project

Step 2: The Schematic

Step 3: Buy All of the Components

The components for this project are:

1pc IRF3205 mosfet

1pc 100k ohm potentiometer

1pc potentiometer knob

some wires

1pc old credit card

1pc DC motor

1pc heatsink

1pc skrew

1pc 9V battery clip and a 9V battery.

Step 4: Put the Heatsink on the Mosfet

Put the heat sink on the mosfet with the skrew

Step 5: Glue the Components to the Credit Card

Glue the mosfet and the potentiometer to the credit card

Step 6: Connect the Battery Clip

Connect the positive wire of the 9V battery clip to the drain pin of the mosfet and the negative wire to the dc motor.

Step 7: Connect the Potentiometer

Connect the left pin of the potentiometer to the drain pin of the mosfet, the middle pin to the gate pin of the mosfet, and the right pin to the negative wire of the 9V battery clip.

Step 8: The Last Connection

Finally connect the source pin of the mosfet to the other pin of the dc motor. Now just plug in the 9V battery and we are done.

Step 9: Testing

If you connect everything correctly than if you turn the potentiometer anticlockwise the motor will spin faster and if I turn the potentiometer anti clockwise the motor will slow down.

2 People Made This Project!


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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 or mofset ? any suggestion ? and don't you think that 100k potentio is to much??

would this work with 12 volts and higher?

can i use 12v DC power supply and a dc 12v motor



I have a motor that runs 9-12v (from a hobby shop-it's actually a motor to turn a propeller for a model airplane); tried to hook up a potentiometer to it (twice!) and both times the pot got really hot, then started smoking. Hoping this instructable will help solve my problem.

I like your enthusiasm but I think the reason why the potentiometer got hot and eventualy smoke because you connect the potentiometer in series with the motort and in that case it acts as a voltage divider. The pot can't handle the current load that the battery or your power supply delivers. Based on the above circuit, the pot controls the frequency or the width not the voltage. I hope I answers your doubt.

This circuit is a far from an optimal solution. This circuit is more suitable as mosfet test fixture (with modifications like adding a snubber) than as a real world motor controller. May I ask what your intended application is, what your motor's specs are, and those sorts of nitty-gritty details?

Not sure. The data sheet of IR is missleading. Important is how much current your motor can draw. According to current and voltage your are driving the MOSFET in the linear Mode with this circuit and MOSFET then often die because of a thermal runaway in the so called Spirito region. Some manufacturers show that region on their datasheets in the Save Operation Area, but IR does not and they don't even show the DC rating.

So if you want to figure out if it blows up, look for a data sheet where the linear mode performance for DC currents is shown in the datasheet together with the spirito region. I found this document explaining linear mode performance in more detail:


If you read the question carefully, it asks if this setup will work with a 12 v motor. Yes it will work with a twelve volt motor. It's not complicated. Its a 55v, 110a mosfet controlling a nine volt battery. Typically nine volt batteries can't supply 110a for very long, so barring the improbably ridiculous, and assuming it is properly snubbed for higher currents, it will work albeit inefficiently. Also I'm not the op.