If i increase the voltage say 12v 5A do i need to change materials used in the circuit?. the 1k resistor?, the diode? and potentiometer?. because when i tried it with 12v 5A the tip120 quickly becomes hot and suddenly motor stops and after 3-4 secs the motor start again but can't control it anymore with the potentiometer the motor goes on rampage.. i need to turn off the arduino to make it work again.
Do i need a higher potentiometer say 50k or change the 1k resistor or the diode?
5 A is absolute maximum continuous current for TIP120, symptoms as you described say transistor damaged, if you run it w/o heat think - overheated. MOSFET is better in this manner, as dissipate a lot less power. Look for logic level type, you can't drive IRF510 from arduino, need additional voltage amplifier stage.
Magician:
10 k pot regulates voltage at the analog input, you free to change , it doesn't change much as input impedance arduino 100 M.
ok thanks how abou the 1k resistor and diode should i use a higher wattage for the resistor say 1 watt? and for the diode higher current say 3Amps?.. thanks
It's unfortunate that "luckylarry" shows his work as pictures, no schematics.
I haven't the patience to read through a verbal account when a schematic conveys the point "instantly".
*** "I’m using the TIP120 because its emitter pin uses no more than 5 Volts which is what you’re looking for with the Arduino...", luckylarry notes. I'm speechless. ***
If you change transistor to MOSFET, resistors would be different. Have a look: http://ruggedcircuits.com/html/circuit__7.html
There is no pot, but you can introduce one ( 10 k is optimum value ), connecting middle pin to analog input of arduino, two others
to +5V and Gnd on the arduino board. Reading a voltage value with analogRead, you could vary motor speed by pot.