Just on the off-chance someone may have done this before.
My Comms cabinet get quite warm in summer, mainly from PSU and the ADSL modem & Ethernet switch.
Maybe if I use a 3 lead variable speed DC brushless fan (as in PC cases) and a tenp sensor I could get a simple fan that kicks in above a set temp and varies it's speed dependent of how hot it is above threshold.
Seen one such cct:
(option 3 )
Anybody got anything easier.
The 3rd wire is just a tacho output. 4 wire introduces a dedicated PWM speed control wire. 2 and 3 wire fans are happy, within limits, with direct PWM, provided you aren't interested in a sensible tacho signal from a 3 wire.
There is a chip, MIC502, that does all the grunt work for PWM control. Just add a few minor components, can't be any easier. B-)
I simply use a on/off thermostat (needs to be changeover or designed for cooling, so you can switch *on* when it gets hot).
Well, I say *simply* - mine is actually done by software rather than a crude bi-metallic stat, but the latter should work just fine.
I used to run a minicomputer at home, and did the same for that, although I used a Maplin min-max temperature module (FP64U, no longer sold, but still references on the web). You could set a min and max threshold, and when it went over the min, it switched the fan on, and when it went over the max, it cut the computer power (which remained latched off by an external circuit until manually reset). FP64U was an extremely useful and cheap building block module, and it's a shame nothing similar seems to exist anymore.
Proportional fan speed control wasn't really required - nothing in either the minicomputer or my PC today is that temperature sensitive.
In article , Rick Hughes writes
If you don't mind something ticking over slowly all the time then they do already make self contained PC fans with temperature based speed control.
Here's an example (not used, just found on a search):
That one has a temp sensor on a 40cm lead but an example I have used (Coolermaster I think) just had a thermistor directly in the fan airflow so that when used as an exhaust fan it would monitor the exhaust temp.
opamp measures Vbe, compares it to R divider on regulated line. Small power tr output, voila, Vout depends on temp. A small cap cuses it to come on fu ll V at power up. A 2nd opa zeroes base drive when Vout is too low.
With a 3rd opa you could pwm it.
NT
It does because that's how I did it for the charger cabinet in my motorhome. The two chargers abd the 24/12 converter have their own stats and fans but it was also necessary to ventilate the cabinet. A large diameter flexi tube allows air to enter from under the vehicle, and a fan pushes air out of the cabinet. The stat is set to 30C. Any lower and the fan runs due to the ambient temp, even when the chargers aren't active.
Bill
I just looked at what my PC does ,,, it has variable speed cooling fan on processor heatsink stack and also 3 x 4" fans again all variable speed. Does mean computer is very quiet unless doing significant video coding and then fans speed up accordingly (as to GPU fans)
Sort of assumed as this is now common place there may be simple way to build a free-standing version.
want to get one that is 'off' below a set temp (30 deg probably) as hopefully means most of time I'm not paying to run fan.
I have coolermaster psu on my PC's good kit.
A fan doesn't take a lot but "from little acorns do oak trees grow".
Just wire a stat in series with a fan with built in temperature speed control if you don't want to build the MIC502 circuit.
I can understand that but the one I linked to is just 2.16W at full whack (1300rpm). At min speed (400rpm) I doubt it will be more than a watt, possibly as low as a half so 50p to £1pa and I don't get out of bed for those kind of savings.
Processor fan is done in software. It's done by the BIOS in SMM (System Management Mode), although some BIOSes will allow the operating system to take over control if the OS knows how to.
Variable power supply fans are sometimes done by measuring temperature of a heatsink in the PSU or exhaust temperature, and in smarter PSU's which provide power consumption data for the powerating system, it can be based on the consumption of the system as a whole (depends if the PSU fans are also cooling the whole system, or just the PSU).
My case fans are also variable speed - and that is what I think would suit the task ... 4" fan speed variable by temp.
BTW ... the cct I gave link to does use the MIC502 chip
Missed smilely?
Apart from the stat and fan with built in temperature speed control you can't get much simpler than using the MIC502.
Easier: 2 bimetal stats, 1 feeding half power
NT
sorry missed that .... They are only £2.50 as well so might as well try one out.
He was probably referring more to the price of enduring the discomfort of a noisy fan rather than its modest annual energy cost.
There's more than one way to 'pay a price' beyond that measured purely in monetary terms. It's the main reason why I'm not tempted to employ spin down power saving on my 4 disk NAS box.
I regard the potential 30 quid a year saving I'm eschewing as an 'insurance premium' to minimise the risk of catastrophic disk failure (and data loss). It's a strategy that seems to have worked ok for the past 2 1/2 decades thus far (fingers crossed).
"The ARCTIC F Pro TC is completely inaudible (0.05 sone) at low temperatures a much quieter level than generic TC fans."
There is that but the cure is easy: Bigger slower fan. Shifts the same amount of air but gently so far far less noise. The HP microserver has a large slow fan, 120 mm, almost inaudible, unlike the 80 mm PSU fan in the PC.
anybody know of a good make quiet & reasonably cheap 120mm fan ...
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