Problem with dc motor
Problem with dc motor
(OP)
Hello.
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.
PS: Atached are the schematic hand made and a picture of the circuit.
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.
PS: Atached are the schematic hand made and a picture of the circuit.





RE: Problem with dc motor
RE: Problem with dc motor
A MOSFET is a better choice of switch than a BJT at low voltage, and easier to drive unless you're running at very high frequency.
You need a freewheel diode across the load, otherwise you will destroy the transistor.
Buy a book on the fundamentals of power electronics.
RE: Problem with dc motor
From what i understood of your reply the base current is not enough?
I based my calculations on the atached datasheet. Could u have a look and tell me if 0,5 mA in base is not enough for saturation?
I don t know the meaning of "freewhel" but i have a 1N4007 diode across the motor, i just forgot to draw on the schematic.
The PWM frequency is 430 Hz.
I based this project on another person's, he uses a 2n222 NPN and it works great.
Thanks again. Have to buy on book of these.
RE: Problem with dc motor
RE: Problem with dc motor
RE: Problem with dc motor
I will try to lower resistance in base to 1 K.
Thanks.
RE: Problem with dc motor
I put a 1K pot in base and moved it to lower resistance till the motor spin. Voltage source was 6 volts, the same as colector.
The motor decreases speed till the max pot value that corresponds to more or less 4,7 mA in base, VCE is around 2,6 V and Icolector is around 170 mA. I have one more litle problem, sometimes the motor doesn t start when the pot is at its max resistance, and i have to lower ir for the motor to start spining. Could this be connection problems or is this normal?
Thnaks to everyone.
PS: Tomorrow will try with PWM from arduino.
RE: Problem with dc motor
That same problem is why a lot of house fans and ceiling fans that are multi-speed, always have the highest speed immediately adjacent to OFF. This means the fan will always be jerked into motion.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Problem with dc motor
By the way, allready tried with arduino and it works ok.
Next task is connect a tooted ring to motor axle and read rpm with a inductive sensor. Lets see if i can do this.
Thanks guys.