Hi guys,
I have very strange problem using 2A motor and TIP122 transistor.
I want to control the motor using pin 9.
The motor starts but it does not have enought power-as If I connect it directly to the battery.
I am using the same schematic as this one: http://www.instructables.com/files/deriv/F9L/KDFG/GU7FXUMH/F9LKDFGGU7FXUMH.LARGE.jpgI just dont have the cap and I am using 1N4007 instead of 1N4001.
I am using 1.2kOhm resistor and I am giving ~2ma current to the transistors base.
hfe of tip122 is 1000 so with ~2ma I should be able to drive the motor(2A - when I connect it to free run directly on the battery its drawing 1.3A).I tried with less resistor values but the problem is the same.
The motor starts but its not so powerful like when I direclt connect it to the battery.Its runs half the power when it runs throught the transistor
The motor is RS380S 4.8V.
I tried with 2 different TIP122 and this didn't solve the problem.
The code is very simple:
int motor = 9;
void setup() {
pinMode(motor, OUTPUT);
}
void loop() {
analogWrite(motor, 255);
delay(1000); // wait for a second
}
i might be wrong but i see that the schematic that you give have some problem. first The emmiter must go to ground, second collector go to one of the motor leg, while the second motor leg go to the power V+. and the base well go to your signal. your resistor is ok. But the other thing that you need to change is the diode. the diode is ok but the connection is not. in that connection it just limit the supply. you need to change that put the diode in parallel to the motor leg, just make it in reverse polarity
ash901226:
whats the purppose of the transitor if you just short out the collector and ground?
why you think that I am shorting collector with ground?
there is a diode between them so the current will not flow from collector to ground.
Sorry If I am asking stupid question
If the motor and battery are only 4.8V then the problem is the voltage drop in the TIP122. Darlington power transistors such as that device should be consigned to history, they are obsolete now that we have inexpensive power mosfets. Throw that device away and get a good logic level mosfet instead. For example, an IRLU8726PBF will have a voltage drop of 0.016V max @ 2A, whereas a TIP122 has a voltage drop of up to about 2V @ 2A.
dc42:
If the motor and battery are only 4.8V then the problem is the voltage drop in the TIP122. Darlington power transistors such as that device should be consigned to history, they are obsolete now that we have inexpensive power mosfets. Throw that device away and get a good logic level mosfet instead. For example, an IRLU8726PBF will have a voltage drop of 0.016V max @ 2A, whereas a TIP122 has a voltage drop of up to about 2V @ 2A.
I was thinking about the voltage drop but I was thinking that all transistors have voltage drop around ~0.7V and that should not be so big problem.
But after you post I really think that this may be the problem.I am using 4 x1.2V batteries to power up the motor.
Can I compansate the voltage drop by just adding 1 additon battery 1.2Volts.Is there any reason why I can't do this?
I want to successfuly understand and test the regular transistors and then jump to mosfet.
Thats why I want to continue the task with tip122 and not just buy motor driver or mosfet.
Thanks again
Thanks again,
since I drive few motors with few transistors how can I know I if all transistor can be attached to the same heatsink?
When I am looking at the transistors datasheet what tells me if I can connect multiple transistors to the same heatsink?
Thanks
The datasheet doesn't say, but I think you will find that the tab is connected to the collector. So you can't share a heatsink between several of them unless you use mica washers etc.
It's much simpler to use mosfets, if you choose them correctly then they won't need heatsinks at all.
Hi again,
it seems that if I add two more 1.2V cells is not fixing my problem.I am compensating the voltage drop in the transistor with the additional cells, but that doest fix the problem.Is there any chance that the diode is somehow shorting and is limiting the current to the motor.
Thanks
tonko_lonko:
it seems that if I add two more 1.2V cells is not fixing my problem.I am compensating the voltage drop in the transistor with the additional cells, but that doest fix the problem.Is there any chance that the diode is somehow shorting and is limiting the current to the motor.
Only if you have connected it the wrong way round. The cathode (the end with the stripe) should be connected to to the positive supply, the other end to the TIP122 collector.
Its connected exactly as on the image.
Its as you describe.
Now I am thinking that maybe my wires or breadboard cannot carry more then 1A.
Also the output to the gate is giving 2ma that should be enought to drive 2A.(Yesterday another wire was shorting the output pin to the gate and arduiino was giving 80ma from the output pin but its seems its still working :))
Can the reason be that I am not using cap?
OK I made everything on another board soldered etc... And the problem still exists.I have less power when I use the transistor . I have added additional cells to handle the voltage drop across the transistor with no luck - its better but not as when directly connect the battery to the motor.
I just get l298 h bridge and I have the same problem.
I connected the bridge as on this link:
