benhewitt97 wrote:Hi all,
I'm working on a small project involving making a case for my pi, including a fan and LEDS, out of an old PSU case. I'd like for the fan to come on when the Pi goes over 45 degrees c, but if i plug it straight into GPIO, it's very slow due to the 3.3v GPIO outputs. Is there any way i can boost the output voltage to say 12v? maybe using a UL2003 chip?
If you boost the voltage you drop the current. With the inefficiencys of boosting you will end up with a slower fan than you started with.
Also, YOU SHOULD NEVER RUN ANY MOTOR DIRECT FROM THE GPIO! Motors draw more current than the GPIO can supply (and this is the real reason your fan is so slow, it has no current to get it turning at any decent speed). Attempting to draw more than the GPIO can supply CAN PERMANENTLY DAMAGE YOUR PI!
You have to use a higher current power source for the motor alone and then use either a motor driver or transistor to control it from the pi GPIO, but not power it.
If you are using a powered USB hub then you may be able to tap power from one of the USB ports for that (which will give 0.5A at 5V), alternately the 5V pin on the pi GPIO can be used as a supply, not a huge one still. The current on this port is approx: [input power]-[approx 500-700mA/0.5-0.75A]-[power drain from USB devices]. It is not recommended to use this pin either really. External supply or nothing.