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[SOLVED] Using TIP41C to turn on and turn off Motor

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AnimaSolo

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I'm new to motors so here's my question:

Power supply:
12V 4.5A Battery
Motor current = 2.5A
Transistor : TIP41C

Here's the circuit diagram:

**broken link removed**

I just want to test if the 12V supply can turn on the TIP41C transistor. When I turn on the switch, the transistor gets REALLY hot (hurt my finger when I touched it :oops:), and the motor turns VERY slowly.

Is the problem here because the base current is not enough to fully turn on the TIP41C transistor and thus the motor is not getting enough current to spin at it's maximum speed?

And is that amount of heat normal? When it became hot I immediately turned off the power.

Transistor Datasheet:
www.electro-tech-online.com/attachm...7194d1202307690-transistor-current-tip41c.pdf


*sry that you guys hv to copy and paste the links, I don't hv enough post counts to put them :(
 
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Your circuit doesn't make sense. Ignoring the fact that the base resistor won't supply enough base current to turn the transistor ON with 2.5A, if you have a switcher in series with the motor why bother with a transistor at all?

Keith
 

I just want to test if I can turn on the transistor that's all. The full circuit will incorporate an optocoupler which will be connected to a microcontroller pin, and its output to the motor power supply and the base of the TIP41C.

Yes I know at the moment, the 1k ohm resistor won't supply enough current to the TIP41C base, as I calculated I need roughly 50-100ohms, but I don't have that with me at the moment, so I tested with a 1k ohm.

I'm more worried about the heat of the transistor. Is it normal? Or is it because the transistor is not fully turned on that causes it to be extra hot.

edit: I realized that it is silly that the switcher is in series with the motor, I changed the diagram already.
 
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You are right - because the base resistor is too high the transistor doesn't turn on properly and most of the power ends up in the transistor not the motor.

You are probably right in the sort of resistor value you need, but you may find your driving circuit cannot supply enough current to the base. In that case you will need to add an extra transistor.

Keith

---------- Post added at 07:15 ---------- Previous post was at 07:13 ----------

By the way, it is normal to put a resistor across the base-emitter to help the transistor turn off when the switch is open.

Keith
 
Alright I'll try it out. Thanks loads.

---------- Post added at 13:21 ---------- Previous post was at 13:18 ----------



But why won't the driving circuit be able to supply enough current?
 

You haven't made it clear where the transistor base drive will come from but you need maybe 100mA. A microcontroller pin won't be able to supply that.

Keith
 

This would be what I plan to do, once I get my parts:

**broken link removed**
 

Two possible problems. The optocoupler output probably won't be able to supply enough base current and even if it could, the current transfer ratio of the opto coupler would probably need more LED current than the micro could supply.

I am pretty sure you will need an extra transistor. It doesn't need to be huge - just to supply the base current.

Keith
 

What if I were to swap the TIP41C for TIP102, a darlington pair transistor.

Datasheet:
https://www.fairchildsemi.com/ds/TI/TIP102.pdf

I'm not sure if I am reading the datasheet correctly, but I would only need approximately 6mA to turn on the transistor to allow 3A. (I read this from the VCE(sat) section of the datasheet)

Just want to make sure before I go buy the components, it's a long drive from where I live :(
 

Yes, a darlington would be fine. If you have two NPN transistors you can make your own darlington configuration without having to buy the TIP102. I think you need to look at mail order :)

Keith.
 

Hi.. Thanks for your help. I've managed to turn on and turn off my motor already using the TIP102 transistor.
 

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