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 ?

On Wed, 28 Mar 2012 15:07:03 +0100, "N_Cook" put
finger to keyboard and composed:

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
--
Please remove one 'i' from my address when replying by email.

On 3/28/2012 9:07 AM, N_Cook wrote:
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

"amdx" wrote in message
...
On 3/28/2012 9:07 AM, N_Cook wrote:
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



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.

"N_Cook" wrote in message
...
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 ?





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

I have no idea whether they specifically chose a fan that would always start
though.



Gareth.

"Gareth Magennis"

Some Studiomaster Powered Mixers used to adopt this method - the fan would
sit there shaking like a ****eting 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

Gareth Magennis wrote in message
...


"amdx" wrote in message
...
On 3/28/2012 9:07 AM, N_Cook wrote:
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



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