Any fan going at 2000 RPM doesn't like a piece of metal stopping it almost instantly. If the blade doesn't break entirely, it will probably crack. (I used to experiment with old computer fans. They go really fast on 30V.)Takes a heavy duty fan to be able to lose a blade! Wouldn't stick my finger in that one...
Sorry - this isn't the case.Most solid state fans (brushless) are constant speed. Varying voltage does not speed them up or down.
Generally, 3 wire fans are PWM capable, while some 2 wire small fans aren't good at variable speed or reversal.CPU fans nowdays yes, but not standard units like what is in a power supply. PWM will not work on a fan that uses the arrangement I just described (the RC oscillator). The chip sequences between the 6 coils.
Bill, I'm sorry, but I have to disagree with your assertion that an RC oscillator keeps a stable frequency over voltage. That feature is unique to 555's and some forms of relaxation oscillators built around comparators. It is likely just using a Schmitt inverter internal to the chip to generate the oscillations; and the frequency increases as voltage increases. I have found 90% of modern power supplies include a fan regulator which runs the fan slowly under low load and fast under high load. It is done using PWM.CPU fans nowdays yes, but not standard units like what is in a power supply. PWM will not work on a fan that uses the arrangement I just described (the RC oscillator). The chip sequences between the 6 coils.
As Wookie just mentioned, there are other methods. As for RC circuits being stable, look again. The charge curves are in percentages. Where the variations come in are from fixed voltages from junctions. Stable is relative. You will not get a 50% change from a simple RC circuit.Bill, I'm sorry, but I have to disagree with your assertion that an RC oscillator keeps a stable frequency over voltage. That feature is unique to 555's and some forms of relaxation oscillators built around comparators. It is likely just using a Schmitt inverter internal to the chip to generate the oscillations; and the frequency increases as voltage increases. I have found 90% of modern power supplies include a fan regulator which runs the fan slowly under low load and fast under high load. It is done using PWM.
But it's not just ratios - for most simple oscillators, the on and off thresholds are not ratiometric to the supply voltage. So they may be 2.8V and 2.0V at 5V, but 1.5V and 1.2V at 3.3V. Try it - you'll find that a Schmitt oscillator will vary considerably. In my case, from 2V to 6V, I got it to go from a few kHz to about 40 kHz - that's a massive variation.As Wookie just mentioned, there are other methods. As for RC circuits being stable, look again. The charge curves are in percentages. Where the variations come in are from fixed voltages from junctions. Stable is relative. You will not get a 50% change from a simple RC circuit.
So, after all this, is there an answer to my question?I have a 12vdc computer fan. It is being turned on for about 5 seconds every 25 seconds, so the duty cycle is about 17%. Is the fan's life expectancy longer or shorter than if it ran continuously?
Thanks.
Two sides to the issue.So, after all this, is there an answer to my question?