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Old 24th September 2013, 09:39 AM   #11
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by cliffforrest View Post
.................... heat ................ 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.
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Old 24th September 2013, 09:50 AM   #12
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by richie00boy View Post
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?
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.
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Old 24th September 2013, 12:52 PM   #13
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Quote:
Originally Posted by AndrewT View Post
The temperature of the coolant rises.
The hotter parts of the engine COOL after switch off.
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.
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Old 24th September 2013, 06:16 PM   #14
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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.
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Old 25th September 2013, 08:42 PM   #15
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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.
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Old 25th September 2013, 09:08 PM   #16
dmills is online now dmills  United Kingdom
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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.
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Old 26th September 2013, 03:51 PM   #17
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I don't say it is mandatory to have fans run after switching the amps off.
but allso, it does not hurt to be honest.

the question was how to achieve it, not why.
I did show how.
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Old 3rd October 2013, 09:57 AM   #18
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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.
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Old 3rd October 2013, 02:14 PM   #19
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Quote:
Originally Posted by honeycomb0 View Post


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)
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Old 3rd October 2013, 02:38 PM   #20
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Quote:
Originally Posted by cliffforrest View Post
.. a hangover from automobile technology.
I was thinking of the so called 'courtesy lights', when the lights wait for 10 seconds before turning off.
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