Replace LED with Brushless Fan in Circuit and then Doesn’t Work

Hi All,

I created a timer circuit (per below link) with a 555 chip, resistors, and capacitor which works fine when powering an LED. If I swap out the LED with a brushless DC fan, it doesn’t work. Is there some reason for this?


by molerat16
December 02, 2021

A possible reason is that the output of the 555 is not rail-to-rail (not to ground and not to Vcc). Check the minimum required voltage for your motor.

by vanderghast
December 02, 2021

I suspect the motor requires more current than your circuit can supply; however, it is very difficult to do any sort of analysis without a schematic diagram and motor data.

by Foxx
December 04, 2021

Did you also take out the LED series resistor? If this is still in I doubt that the motor would run.

by Foxx
December 04, 2021

I tried removing 2 of the resistors (except the one paired with the capacitor to set the timing) and still did not work. I will check the voltage and current reaching the fan to see what’s happening.

by molerat16
December 04, 2021

Don't forget you must replace the LED series resistor with a wire jumper to get a continuous circuit to the motor. Don't go randomly changing things without some plan of action and understanding of expected results.

by Foxx
December 05, 2021

Hi Foxx, thank you, that worked and the fan runs now. It runs much slower, however, then when connected directly to a battery. Per my DC supply, its only pulling about 150 mA but is rated for 300 mA. Based on franrungo's feedback, I did some googling and seems like the 555 may be limiting the current. Am I on the right track with article below?

by molerat16
December 08, 2021

Preferable to place the load on the high side, with an NPN BJT. In the supplied example, the resistors R1 and R2 represent the "load", your DC motor and V555out, the possible output of a 555. You may get different current with different transistor, though, but the comparaison will likely hold for any NPN. Check the power dissipation for the transistor. Add a flyback diode for you motor.

(R3 represents the internal resistance of the source, and like the Amperemeter, they are not strictly part of the circuit.)

by vanderghast
December 08, 2021

And note that a MOSFET canal N, or NMOS, is probably preferable. A little bit more expensive to buy, but more economical energetically.

by vanderghast
December 08, 2021

1 Answer

Answer by franrungo

Es probable que la salida del 555 no tenga suficiente potencia como para mover ese motor, si conecta un buffer mediante transitor y resistencia es probable que funcione

+1 vote
by franrungo
December 05, 2021

Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account

Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers

Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.

About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.