Driving fan using transistor

Using Arduino Motors, Mechanics, Power and CNC
1

Hi everyone,

I'm using an 8.4V battery pack to power an Attwood Turbo 3000 fan and a TIP41C to drive it. The circuit I'm using basically looks like this (except the diode is reversed and the Arduino ground is connected to the battery ground): http://i.imgur.com/dYAa5.png

However, I need to be able to use code to power the fan on and off at various times. This is what I wrote, but the fan is perpetually turned on, regardless:

int fanPin = 7;

void setup() {
  Serial.begin(9600);
  pinMode(fanPin, OUTPUT);
}

void loop() {
  digitalWrite(fanPin, HIGH);
  Serial.println("high");
  delay(2000);
  digitalWrite(fanPin, LOW);
  Serial.println("low");
  delay(2000);
}

Any ideas on what I might need to do? Thanks!

2

If you have a diode across the transistor's c-e, reversed from the one in the pic, aren't you effectively shorting across there so there's always a path?

The diode should be across the fan, pointing up.

Edit.... like this.

3

ahhreeyell:
(except the diode is reversed and the Arduino ground is connected to the battery ground)

Just a guess because I'm rusty on my electronics, but if your diode is in the wrong direction it could be shorting around your transistor thus keeping the fan on.

4

I tried reversing the diode direction and it didn't do anything. Could I have damaged the diode or the transistor with the short?

5

Do you have a meter that can check the diode? I'd suggest ANYONE playing with this stuff gets at least an inexpensive meter and learns how to use it. One of the first things I did before sending my son off to college was to get him a meter and teach him to use it.