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Topic: Problem with dc motor (Read 1 time) previous topic - next topic



I am newbie, i am trying to put a small dc motor working and regulate speed with PWM generated by arduino. The transistor i am using is a bc547c.

The problem is that the motor make a strange noise but doesn t spin (no its not damaged). Connected an amp to see the colector current and it increases as i increase duty cycle, but the voltage between colector and emiter stays more or less the same. Shouldn t that decrease as current increase? There is no voltage across the motor as it stays in the transistor.

Motor is a mabuchi from a car toy;

As external motor source i used 4 1,5 V batteries;

I calculated resistor base to have enough current to feed the motor according to transistor and motor datasheets.

Do you have any idea for wath is happening?



Try wider pwm pulse(analogWrite() 100-250 )  or maybe try more powerfull transistor


Thanks for reply.

Already tried TIP31C that is a power amplifier transistor. By the way it was the first i tried, before bc547c. It does exactly the same, What do you mean aboute wider PWM? Bigger than 100 DutyCycle? (Sorry if i think something absurd)



Do you have any idea for wath is happening?

Because we are mind readers and can see your circuit...

HINT: Post a schematic and/or picture of your circuit, then maybe we can begin to help you - code might also be helpful, but maybe at a later stage.


You're welcome.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


Here is the schematic hand made.

I will post a picture of the circuit i made.



Here is the picture of the circuit.



Problem solved.

It was not enough current in base to achieve saturation of transistor.

Now it works ok. I don t have any resistance in base, the rest remains the same.



The maximum collector current for that part is 100mA, but your circuit shows 130mA.

I don t have any resistance in base

Do you think that is wise?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.


I consulted several that sheets in the last days for BC547c, there is one, http://www.datasheetcatalog.org/datasheets/150/128380_DS.pdf,
that is 200 mA max amp on colector, and 0,5 W heat dissipation. I think the transistor i have is equivalent to this.

In saturation i have 240 mA in collector times 0,5 V voltage drop in the transistor equals 0,12 W. I think its safe and goes even more as i tried it.

The least current, for this circuit i made, for the motor to spin is 123 mA and 4,58 V voltage drop on transistor and equals to 0,56 W, a litle more than 0,5 V. Let the motor spin a couple of minutes at this condition, touched the transistor and it was not hot.

I think its more or less ok.

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