Crazy idea I just had

[Tom41]

When summer comes round again, I would like my PCs to cool down quickly after shutting down. Thing is, the CPU and case fans cut off when the PSU goes into 'standby' mode after shutting down.

I had an idea that I could wire a rechargeable battery or large capacitor in parallel with each fan, so that the fans remain spinning for a couple of minutes after shutting down - while still spinning as normal while the power is on.

Is that something I could do easily with wires and solder, or would I need some kind of special circuit to detect the power on/off and switch power over? I am concerned about the power from the battery flowing back up into the PSU, powering the regulator backwards and causing all sorts of problems - would a diode help?

[arneson]

Re: Crazy idea I just had

Tom,
Not a bad idea, I used to time delay relays with a large cap and an isolator diode.
Your idea is simple and effective.

[gonzo0815]

Re: Crazy idea I just had

Ok, if you want a more sophisticall circuit, you can use the 5v SB line for aftercooling. IMHO there are some devices ready to buy, wich do thatbkind of aftercooling. AFAIR it wasn`t that expensive.

For your initial idear, you should use one diode to protect the battery from the supply (to avoid that it would accidentaly be charged and blow up) and one diode into the + line of the fan to avoide that other things could source power from it. Then i guess you have to ad a switch or timer circuit to avoid a empty battery each time you power the system of.

[willawake]

Re: Crazy idea I just had

http://www.ioss.com.tw/web/English/RD7%20CA.htm

[arneson]

Re: Crazy idea I just had

My DVD R runs the fan for a full minute after shutdown and the front projectors keep the fan on the bulb going for at least a minute.
I have to run the air conditioning to keep the living room cool while watching movies.

[willawake]

Re: Crazy idea I just had

i was on a yacht and in the wheelhouse there was a switch which was labelled "plasma fan" i asked what it was for and its because they have two saloons each with a plasma tv on either side of the same wall. so when both are watching tv have to switch on a fan in the wall

[arneson]

Re: Crazy idea I just had

I could use a fan that comes on when I sit on toilet.
It should pretty much stay on after that.

[willawake]

Re: Crazy idea I just had

we could use that for the office toilet.

some of these playing something also for those monday morning beer shits

[999999999]

Re: Crazy idea I just had

I don't mean to be offensive but there is no reason to cool down an "off" system faster, no benefit to it. On different devices where there is a direct correlation between hours on at elevanted temp to lifespan, it would save some of that lifespan, but it is negligable on a PC/computer in any case, even that much less so to have it cooled for a couple mintues versus the substantially longer on-time.

Regardless, it might be prohibitively expensive to parallel enough massive capacitors to be able to run a fan for a couple minutes. Perhaps some surplus electronics websites have good deals on super capacitors and you could parallel enough of them to get the needed runtime, but it seems unnecessary when you already have a live 5VSB rail on an ATX system that you could tap instead.

If you had a fan in mind that could run reliably from 5V (5VSB PSU rail), you could tap into that rail and use a NE555 /similar timer IC to drive a transistor-switch, solid state or mechanical relay, etc, to run the fan for the required period then switch off.

You could use batteries, but I don't see a gain in doing so instead of off the 5VSB, since any typical brushless DC fan spec'd for typical 12V will use a pretty small amount of current at 5V, within the margin of what you'd expect to have still available on a 5VSB rail if the PSU is decent, and with a battery you have the other factors of what happens when the voltage drops too much, if the fan then goes into an instable mode or pulsating behavior for quite a long time, or otherwise needing to add a cutout circuit when the battery reaches too low a voltage else you'd be draining the batteries quite a bit which will be hard on them in the longer term. I mean that idealy it would seem this circuit should remain working without having to replace batteries for the life of the system and draining rechargables too low, perpetually won't be very good for them.

Considering the time to do any of these, it could be as worthwhile to just get that "Cooling After" product alreadylinked but as I mentioned above, there isn't any need to cool a PC after it has ceased to produce heat (but a minor level, lower than the passive radiation rate acceptible from 5VSB powered circuits).