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Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Hi,
I have just put together a very crude temperature sensing fan speed controller using an LM317 adjustable voltage regulator and have got the resistor values just right so that it will adjust the voltage from around 2.9 to around 10v depending on the temperature of a 4.7k NTC thermistor.
Edit: There is a 2.2k resistor in parallel with the NTC thermistor since 4.7k was the smallest Maplin stocked.
However my question relates to allowing the fan to be in a stalled state, as I measured 50mA still being drawn by the fan when the NTC presents its highest resistance at room temperature (which is when the fan should not be spinning).
Can this damage the fans internal electronics at all being in this stalled state? I am just using a regular 12v computer case fan here.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've built several similar circuits. They've run for years and none has ever blown up a fan. In particular I remember one audio amp that would start up with the fan stalled, and 5 minutes later it would start to make a funny squeaking noise and then burst into life. The fan in that one outlived the rest of the unit.
So no, I don't think undervoltage is bad for the fan. Nowadays I like to add a capacitor to the circuit to give the fan a kick at power-on and get it spinning at a low speed.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I'm going to go against what has been said, and say that under-volting fans can completely obliterate them.
Down to zero volts is probably ok, but as you go lower, -1, -10, etc... you will eventually get to the point where not only the fan stops working, but some kind of vapourisation of anything conductive will occur, along with a large flash of plasma.
If you're lucky, the fan rotor will start spinning mid air as it is ejected from the fireball.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
I've heard of this problem, usually only a problem (on mains fans) if the start capacitor goes dead short. Result is humming and burnination of motor coils.
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Can under-volting fans to the point of stalling damage them?
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