How To? Thermally Controlled Variable Rate Fan? Plans?

[MEXICOWANDERER]

I'm lazy. Rather than go online, make a fool out of myself purchasing something expensive and megadeath overkill, I'll ask the experts here on this forum for advice.

Are there shortcuts, meaning cheater's tricks purchasing and installing components to make a variable speed thermally controlled fan(s)?

I resolved the issue of general, several unit cooling (area fans) by buying an HVAC mechanical A/C thermostat. Off came the cover, and the bi-metallic screw adjustment, now triggers at around 40C. This is going to power a 33 watt AC fan that is guaranteed to keep the CHEAPOWATTS hip deep in cooler fresh air.

Yeah I got designs on buying several more CHEAPOWATTS. Even with the warts landyacht pointed out (overcomeable nuisance). I would like to take the MOSLER SAFE size ferroresonant charger off-line and series parallel (don't ask) CHEAPOWATTS for my 24 volt system. The big charger snacks on 135 watts just sitting there grinning at me. it'll make a nice back-up.

But besides new ball bearing quiet fans, I would love to incorporate thermal fan control.

[landyacht318]

How about a fan which is designed to adjust itself for the temperature it sees?

http://www.frozencpu.com/products/10352/fan-677/Akasa_120mm_x_25mm_Auto_Thermal_Fan_-_800_-_2300_RPM...

[ken_white]

MEXICOWANDERER wrote:
Got a favorite comparator? Assuming a 7805 would offer stable voltage.

Basic comparator is an LM 106/306, and adjustable reference comparator is an LM 615, both configured using a Schmitt Trigger topology.

[MEXICOWANDERER]

Got a favorite comparator? Assuming a 7805 would offer stable voltage.

[ken_white]

MEXICOWANDERER wrote:
Sadly I have the fans already and getting new ones means waiting until Feb or March. Logistics problems in pickup and transportation. Got circuit boards and MOSFETS and optocouplers. Need thermistors and a way to set hysteresis, even for on off control. Looks like variable speed is a dream for now.

A simple rectifier diode can be used as a temperature measuring device. Si diodes have an approximate -2.2 mV per degree Celsius change in forward bias.

Epoxy it to a hot device, feed it a constant or nearly constant bias current, signal condition the voltage to an acceptable range, and you can feed it to a comparator with hysteresis since you want on/off control.

[MEXICOWANDERER]

Sadly I have the fans already and getting new ones means waiting until Feb or March. Logistics problems in pickup and transportation. Got circuit boards and MOSFETS and optocouplers. Need thermistors and a way to set hysteresis, even for on off control. Looks like variable speed is a dream for now.

[time2roll]

Google has computer fans that adjust to temperature for under $10.
Not sure they shut off, just the rpm changes.

Google shopping

[ken_white]

MEXICOWANDERER wrote:
I'm lazy. Rather than go online, make a fool out of myself purchasing something expensive and megadeath overkill, I'll ask the experts here on this forum for advice.

Are there shortcuts, meaning cheater's tricks purchasing and installing components to make a variable speed thermally controlled fan(s)?

I resolved the issue of general, several unit cooling (area fans) by buying an HVAC mechanical A/C thermostat. Off came the cover, and the bi-metallic screw adjustment, now triggers at around 40C. This is going to power a 33 watt AC fan that is guaranteed to keep the CHEAPOWATTS hip deep in cooler fresh air.

Yeah I got designs on buying several more CHEAPOWATTS. Even with the warts landyacht pointed out (overcomeable nuisance). I would like to take the MOSLER SAFE size ferroresonant charger off-line and series parallel (don't ask) CHEAPOWATTS for my 24 volt system. The big charger snacks on 135 watts just sitting there grinning at me. it'll make a nice back-up.

But besides new ball bearing quiet fans, I would love to incorporate thermal fan control.

Depends how sophisticated you want to get.

For a DC fan, a simple temperature measuring device (T-V) mounted on or near the component that will be temperature controlled will be in the feedback loop.

This signal will feed an op-amp circuit that has a user defined set-point and it will drive either a MOSFET or BJT that is connected in series between the fans power and source leads.

A better design would use a PWM scheme since it would be more efficient but a little harder to implement...

[MrWizard]

The ones used in computers are voltage controlled on the third wire
Which in a pc application comes from a sensor on the mother board

I remember buying some for industrial applications, that had a thermistor mounted on the back of the fan in the intake air stream

A thermistor attached between the main plus and the third wire might provide a workable solution