Not transistor and weak electromagnet

[Ilija]

Hello. On these picture I provide is my circuit that uses Arduino to give a signal on the transistor so I can operate with the electromagnet. The problem is that I give 12V on the transistor, but the electromagnet have just 2V, and after 4-5 min the transistor becomes very hot. I will be happy if someone help me fix these problem. Thanks, Ilija.

 

[kellys_eye]

The transistor is not being driven into full saturation but using a MOSFET would improve the situation dramatically. Use a logic-level MOSFET for best compatibility.

 

[Ratch]

Hello. On these picture I provide is my circuit that uses Arduino to give a signal on the transistor so I can operate with the electromagnet. The problem is that I give 12V on the transistor, but the electromagnet have just 2V, and after 4-5 min the transistor becomes very hot. I will be happy if someone help me fix these problem. Thanks, Ilija.View attachment 37742

Twelve volts and two volts equals fourteen volts., How can that be? Scope the base and collector leads to the transistor and see if there is an oscillation present. That solenoid provides plenty of inductance and the capacity of the leads could support an oscillation. Especially if the leads are long. An oscillation will confuse your voltmeter into giving an erroneous reading. If no oscillation is present, what is the DC voltage of the base lead?

Ratch

 

[kellys_eye]

Twelve volts and two volts equals fourteen volts., How can that be?

I think the OP is referrring to the 12V supply to the solenoid and the voltage at the collector of the transistor when it is switched on - ideally it should be 0V to get the full supply across the solenoid but because the transistor isn't being driven hard enough (isn't the Arduino digital output 3.3V??) the transistor can't reach saturation, or anywhere near, therefore is dropping the full 2V at 1A (2 watts) across the transistor.
The solenoid SHOULD have a back emf protection diode across it but it won't be causing oscillation.

 

[Harald Kapp]

The TIP120 is a darlington transistor with Vcesat 2 V ... 4 V depending on collector current. This is a principal feature of Darlingtons, there is nothing you can do about it - except use another transistor. Kelly's recommendation in post #2 is a good one.

 

[Ilija]

As first thank you for the help an for the late response. I order an MOSFET transistor and as you all said me, it helps and the situation is fixed. It do the job. But, not appears one new problem. As you can see, the transistor is connected to the arduino on the 9pin which is PWM. So, I am expecting the electromagnet slowly to go in one direction and then slowly back, but here happens something strange. The electromagnet do what I explain and that is my idea also, but it also scream and has a very disturbing and loud noise from him. I know that it is not familiar and I dont know what is the problem. Some idea and possible solution?

 

[Bluejets]

Solenoids are not normally driven by pwm. They are essentially a "turn fully on....turn fully off " device.

 

[Harald Kapp]

The "scream" is due to the coil's wires moving ever so slightly with the frequency of the pwm. Follow Bluejet's suggestion.