Driving tip110 with Arduino Mega

[normad]

Hey guys im trying to drive a solenoid(electro-magnet) at around 1.5-2Amps with a TIP110 transistor which is switched by an arduino. I have 130Ω resistor between the duino output and the transistor base. transistor emitter is connected to the ground of the arduino and the ground of the seperate power supply for the solenoid. The solenoid is connected at the collector with a seperate supply.
When i switch the arduino output i can see that voltage goes upto 4.3V at the output and (0.8V at the base) its sourcing a current of about 25mA (which i assumed is safe because the specs say it can source upto 40mA) but still the transistor doesnt appear to turn on. the current through the solenoid is 0A.
what could i be doing wrong?
I can see the secondary supply voltage between the emitter and collector continuously regardless of the base voltage.
please help.. thanks

 

[normad]

well the solenoid has practically no resistance.. and if the current gain is 500 according to the datasheet it should draw about 10A :/ could i have burnt the transistor?

 

[dr pepper]

Maybe, the maximum base current for the '110 is 50mA so that shouldnt have fried it.
From what you describe the tranny is open collector emitter.
Does your circuit have a back emf proection diode accross the coil?(even though there is one built in the '110), if not you'll fry the tranny, but that usually makes them go short collector emitter not open.
You are switching to the negative rail (low side)?

 

[normad]

hmm... yup im switching low side and no back emf protection. ill put one now. and yes the transistor appears to be open collector emitter. so can i assume its not fried? this is strange. ill look into it a bit more. thanks a lot for the quick response.
please let me know if you can think of any other possible reasons

 

[MikeMl]

Is the transistor on a BIG heatsink? It should be.

 

[normad]

oh.. it wasnt.. ill get to it