I want to keep my 5v (x2) heatsink fans running after all power is disconnected.
Maybe for 60 seconds or-so.
Would this chip + the super-capacitors work ?
http://www.linear.com/docs/41966
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Maybe for 60 seconds or-so.
Would this chip + the super-capacitors work ?
An externally hosted image should be here but it was not working when we last tested it.
http://www.linear.com/docs/41966
.
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Far too complicated. I would use a 3.6v Lithium Ion rechargeable battery and a blocking diode from you fan supply. If you use the blocking diode in series with your fan, feed the battery with a 3k3 resistor, from the diode blocked fan feed, then feed the fan through another diode linked from the fan supply, that will give you your fan timer.
So when you power up your amp, the fan works normally and the battery receives a charge through the resistor. When the power is off, the battery feeds the fan with 3volts, (place the other diode reverse bias across the resistor} allowing cooling at a slightly slower speed for the duration of the batteries charge. The voltage from the battery does not feed anything else because of the blocking diode placed before the fan feed.
So when you power up your amp, the fan works normally and the battery receives a charge through the resistor. When the power is off, the battery feeds the fan with 3volts, (place the other diode reverse bias across the resistor} allowing cooling at a slightly slower speed for the duration of the batteries charge. The voltage from the battery does not feed anything else because of the blocking diode placed before the fan feed.
Aren't lithium-ion batteries destroyed if you fully discharge them? And dangerous to leave them charging for hours on end via a simple series resistor?
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Perhaps it is not necesary.
I may be thinking too much in engine (auto) theory....where the fan keeps running (or in some engines the oil keeps circulating after shut-off).
Some digital projectors also keep the fan running onto the bulb even if it accidentally get unplugged.
The above cases must be that...it's the movement of air that is the main heat sink.
I have enough mass in my hsinks.
I'm over-designing again.
thx.
I may be thinking too much in engine (auto) theory....where the fan keeps running (or in some engines the oil keeps circulating after shut-off).
Some digital projectors also keep the fan running onto the bulb even if it accidentally get unplugged.
The above cases must be that...it's the movement of air that is the main heat sink.
I have enough mass in my hsinks.
I'm over-designing again.
thx.
I think it is a misunderstanding, a hangover from automobile technology.
With a water cooled car, thrashing the engine then suddenly switching off CAN cause the water to boil and escape. Even worse with belt driven mechanical fans (do they still exist?) since the cooling effect at idle is very poor.
This happens because the heat from combustion stored in the block does not instantly transfer to the coolant fluid, so temperature can actually RISE after switch off!
With a water cooled car, thrashing the engine then suddenly switching off CAN cause the water to boil and escape. Even worse with belt driven mechanical fans (do they still exist?) since the cooling effect at idle is very poor.
This happens because the heat from combustion stored in the block does not instantly transfer to the coolant fluid, so temperature can actually RISE after switch off!
The temperature of the coolant rises.
The hotter parts of the engine COOL after switch off.
Yes. Li-on cells should never be trickle charged. The chemistry doesn't support that mode of operation and the cell is destroyed quickly.
As to the original question, well I think its a non-problem to tbh.
That is what I said! What is measured in the car is the water temperature, and that can rise to boiling because of the heat dumped into it from the block.
'not sure what your point was? But, peu-importe.
temperature controlled fan, and a separate power supply for it.
will switch on at say... 50 celsius and stay on till it does not drop under 50 c.
seems far more intelligent no ?
2455R-01000074 HONEYWELL | Érzékel?: termosztát; Kim.konfig: NC; Topen:70°C; Tclos:55°C; 10A | BT-L-070/H | termosztátok // TME
one of these should work flawlessly.
btw, i support the idea.
after the equipment had been pushed hard and it gets a fast shutdown, and the fans stop,
naturaly the air around the heatsink will get hotter. so the heat transfer is less efficient etween the heatsink and the air. since delta T is less.
naturally between the semiconductor/chip/whatever and the heatsink the delta T allso drops.
and so on.
probably any decent size heatsink will be able to deal with it, but if i persoanly would like to go for suuuuuure, i would use some methood to keep them fans running a bit after switching off the stuff.
will switch on at say... 50 celsius and stay on till it does not drop under 50 c.
seems far more intelligent no ?
2455R-01000074 HONEYWELL | Érzékel?: termosztát; Kim.konfig: NC; Topen:70°C; Tclos:55°C; 10A | BT-L-070/H | termosztátok // TME
one of these should work flawlessly.
btw, i support the idea.
after the equipment had been pushed hard and it gets a fast shutdown, and the fans stop,
naturaly the air around the heatsink will get hotter. so the heat transfer is less efficient etween the heatsink and the air. since delta T is less.
naturally between the semiconductor/chip/whatever and the heatsink the delta T allso drops.
and so on.
probably any decent size heatsink will be able to deal with it, but if i persoanly would like to go for suuuuuure, i would use some methood to keep them fans running a bit after switching off the stuff.
I'll try to explain why it is useless to run fans after turn off.
Lets say you use the amp for 2 hours, everything is warmed up. Ideally chip is not hotter than 60, heat sink is 50-55 celsius. You turn off the amp, the chip cools down to the temp of the heat sink in about 10-20 seconds. So what problem can cause a 55 celsius heatsink? Maybe warm up the air slightly? Everything can hadle easily 100 c.
Engine is different thing as the block is hotter than other parts can handle (water / oil). This is never true in an amp. Only if was designed badly.
Lets say you use the amp for 2 hours, everything is warmed up. Ideally chip is not hotter than 60, heat sink is 50-55 celsius. You turn off the amp, the chip cools down to the temp of the heat sink in about 10-20 seconds. So what problem can cause a 55 celsius heatsink? Maybe warm up the air slightly? Everything can hadle easily 100 c.
Engine is different thing as the block is hotter than other parts can handle (water / oil). This is never true in an amp. Only if was designed badly.
Arc sources also sometimes need a period of blowdown, in that case the issue is that the electrodes inside the envelope have significant thermal mass and the glass metal seals have an upper temperature limit.
If the cooling is shutown too soon the heat stored in the electrode mass can raise the glass/metal seals above their transition temperature and they will be damaged (In a xenon short arc source, the damage shows up at next strike and sounds like a grenade going off inside the lamphouse)..
None of this however applies in the case of a simple power device on a heatsink, but you can have issues where thermoelectric coolers are used as in something like a video projector where the DMD can have a temperature limit below the operating point of the heatsink....
Regards, Dan.
If the cooling is shutown too soon the heat stored in the electrode mass can raise the glass/metal seals above their transition temperature and they will be damaged (In a xenon short arc source, the damage shows up at next strike and sounds like a grenade going off inside the lamphouse)..
None of this however applies in the case of a simple power device on a heatsink, but you can have issues where thermoelectric coolers are used as in something like a video projector where the DMD can have a temperature limit below the operating point of the heatsink....
Regards, Dan.
If I would really want to keep my fan working until the certain temperature drop, I would built a simple analog fan controller with LM324N(4 opamps in single package, costs peanuts) and sensor LM335Z (costs little less than nothing) overnight. Two opamps will do me a triangle signal, one opamp will amplify the analog signal from sensor, and finally fourth opamp will act as comparator, which compares the triangle with amplified temperature sensor output. Why triagle, someone may ask? Well, bacause the output of the this comparator would be a basic PWM, which's pulse width is propotional to output of the temperature sensor. The PWM drives the fan: more temperature on chip -> longer PWM pulse width - more power on driving fan, and vice versa 
BUT, I must say all of this as well the idea of the fan for amp, is a big big OVERKILL. I don't want to exaggerate, but the next step would be a popping-in the ice on the chip My biggest advice is to spend some time on looking for the right heatsink - it works perfectly when it is designed properly.
Hope that helps.
BUT, I must say all of this as well the idea of the fan for amp, is a big big OVERKILL. I don't want to exaggerate, but the next step would be a popping-in the ice on the chip
My biggest advice is to spend some time on looking for the right heatsink - it works perfectly when it is designed properly. Hope that helps.
Big big OVERKILL, a fan is nothing, check this out (grin)
BUT, I must say all of this as well the idea of the fan for amp, is a big big OVERKILL. I don't want to exaggerate, but the next step would be a popping-in the ice on the chip
Hope that helps.
http://www.diyaudio.com/forums/chip-amps/222718-liquid-cooling-build.html
I was thinking of the so called 'courtesy lights', when the lights wait for 10 seconds before turning off.
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