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Hello.

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?

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

Thanks.
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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.

Thanks.

You're welcome.
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Here is the schematic hand made.

I will post a picture of the circuit i made.

Thanks.


* schematic.JPG (10.51 KB, 640x512 - viewed 28 times.)
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Here is the picture of the circuit.


* pic1.JPG (143.49 KB, 1280x1024 - viewed 16 times.)
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Anyone please...
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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.

Thanks.
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I don't think you connected the grounds, Dave.
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The maximum collector current for that part is 100mA, but your circuit shows 130mA.

Quote
I don t have any resistance in base
Do you think that is wise?
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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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