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I'm attempting to make a simple PWM speed controller for a fan motor.

I am powering the circuit with a 12V 10A PSU and have successfully tested the motor directly connected to it. When connecting the motor to the circuit output though it fails to turn on.

I have tried to disconnect the MOSFET portion of the circuit and use a simple led with a resistor to check the 555 timer works. It seems to be functioning properly as it dims as I turn the potentiometer.

I am unsure as to why the the motor won't spin but I think it might be due to the low voltage from the output wires that connect to the motor.

It displays only ~2V on my multimeter. Maybe due to a faulty MOSFET?

I would appreciate any suggestions or information on the subject. Thanks! enter image description here enter image description here

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  • \$\begingroup\$ What MOSFET are you using? \$\endgroup\$
    – JRE
    Jul 1, 2022 at 11:08
  • \$\begingroup\$ Hi, I am using the IRFZ44N mosfet \$\endgroup\$ Jul 1, 2022 at 11:09
  • \$\begingroup\$ Missing decoupling on your IC. \$\endgroup\$
    – winny
    Jul 1, 2022 at 12:30

1 Answer 1

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Sometime I really need to look instead of just reading.

You are trying to push high current through a breadboard. You can't do that.

Breadboards are great for prototyping low voltage digital circuits - and that's about it.

You are trying to squeeze amperes of current throuhg tiny little spring connectors in the breadboard sockets. The resistance of the contacts will prevent any real amount of current from flowing through the motor.

Anything that needs to carry current will have to be wired around the breadboard. You ought to solder the connections to the MOSFET and the flyback diode. The wires to the battery (including ground,) the source and drain of the MOSFET, and the motor connections must all carry high current - they need to be solid connections.

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  • \$\begingroup\$ Oh I see, thanks for the advice I'll try it and see what happens. Thank you \$\endgroup\$ Jul 1, 2022 at 11:21

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