On demand 12V fan control

[N_Cook]

Under therrmistor control. If at power up the DC voltage is too low to start
the fan can you always rely on the fan starting at some point with a slowly
increasing voltage or does it depend on the make/design of fan ?

 

[Franc Zabkar]

Under therrmistor control. If at power up the DC voltage is too low to start
the fan can you always rely on the fan starting at some point with a slowly
increasing voltage or does it depend on the make/design of fan ?

FWIW, here is an article that shows the innards of a typical
thermistor controlled CPU fan:
http://www.pavouk.org/hw/fan/en_fan4wire.html

- Franc Zabkar

 

[amdx]

Under thermistor control. If at power up the DC voltage is too low to start
the fan can you always rely on the fan starting at some point with a slowly
increasing voltage or does it depend on the make/design of fan ?

Different fans will start at different voltages.

Your circuit is NOT a thermistor and a fan in series, right?
Mikek

 

[Phil Allison]

"Gareth Magennis"

Some Studiomaster Powered Mixers used to adopt this method - the fan would
sit there shaking like a shiteting dog, often making various squeeks,
before finally getting going.
It was driven by a TIP32.

** A great many power amplifiers have the same kind of circuit.

BLDC fans start reliably when the applied DC voltage is about 33% of
ated - no matter how slowly the voltage rises.

IOW there is no need for a kick start.


.... Phil

 

[N_Cook]

I think the question is will the fan ALWAYS start with a slowly ramping
voltage, rather than perhaps sit there in a stalled state.



Gareth.

3 fans fed from the same varying supply. 2 large , one small, all nominally
12V. The 2 large start with the applied "cold" voltage and eventually the
small one starts with warming of the amp . Checked by slowly powering from
a bench ps a few tmes . But I randomly picked up another new fan that I had
about and once out of 10 or so times it did not start by the time it had
reached 12V. I decided as this amp was never used for low power use that I
would disable the ramping and set it on maximum drive always, not worth the
risk/inconvenience of stressed components/mid-performance chance of a cut
out