Fan Speed Control

2112 wrote:

The PWM things have big heat sinks, so are producing heat.

Most everything electrical dissipates some wattage in the form of heat, even if it's 1/10th of a watt. There is no free lunch here. It can be such a small amount that the properly designed component in a properly designed circuit doesn't heat up enough to notice, if at all.

The MOSFET transistors have heat sinks because they are capable of passing 15A at 95% duty cycle. That's probably about 8 watts. The controller is designed to handle worse case. But you are only drawing 3 amps or less. The transistors might dissipate a watt or less with the fan running full speed. When you slow it down that wattage dissipation goes down. That's the beauty of a PWM controller. If your knob is turned down half way you are using 50% power, creating less heat.

Thanks for the answer... This is more the discussion I am interested in. So, the heat sink on a PWM is to keep the electronics cool, not to burn off heat in any way to reduce fan speed...

Sounds like the pwm is the way to go for efficiency at least.
The one I had did make noise, and I have heard others mention the ringing noise from the pulses, so might not be a bedtime item... At night I can just use a clip fan.


Also, a heating element is a resistor, thats why it works. The FF uses these "things" to waste electricity. I don't have an amp meter to test how much though.