Aftercooler problems using NE556

[Sceadwian]

No properly designed system should ever heat up to the point to where an additional cooling source is required, if it does then the initial engineering is at fault, no tack on solution will ever replace that. For the vast majority of systems it's paranoia not practicality which defines the need for these extra cooling devices. A couple of early version of a few console systems and some PCs have had systematic problems with overheating, this isn't even a recognizable percentage of the PC market. Laptops are a different story but thanks to lower power chips coming out will be less of a problem in the coming years.

 

[mgeno216]

Well, it seems that Microsoft has acknowledged a reliability issue on the mobo. Most notably that the CPU bga device loses connectivity of some pads due to rapid temp changes after CPU is turned off resulting from board warpage, so I wonder if adding a cooling fan would only hasten the warpage due to a rapid cooling.

Other questions I have are; Is not that cpu fan rated for 250ma @ 12vdc, how well will it run at 5vdc and how much current will it draw? Secondly, what is the power sequence timing? That is when is 12v de asserted in relation to when 5vdc standby is asserted, and lastly what is the current drive of the standby 5vdc ?
These are issues that I think should be addressed prior to any tinkering or your red button of death, or whatever it is called may occur sooner than if left alone.

Sorry I forgot to keep checking this thread, I have been spending more time in General chat. I hadn't thought about that actually, I think it will be fine. Each of the two fans are rated for 400ma at 12vdc. They will both run fine on 5vdc, I know this because the CPU adjusts the volts going to the fans based on the temperature sensors in both the GPU and CPU. The fans start at 5v, but ofcourse that only lasts for 30seconds, tops. The fans will eventually pick up to 9v, during a heavy gaming session. The only time you see the full 12v is for 5 seconds, once the chips overheat, before the console shuts itself off. I am not sure that this will lead to rapid cooling. I consider this to be fairly slow cooling in comparision to what could be done. Given the options: Let the xbox sit in its heat for an hour or cool it down in 5 mins, I feel the second option is better.

On a side note what do you think of the new 360 Microsoft announced at E3:
**broken link removed**

Mike

 

[Mikebits]

Given the options: Let the xbox sit in its heat for an hour or cool it down in 5 mins, I feel the second option is better.

I am willing to explore this further but, as food for thought, consider a glass bottle heated to extreme heat but not melted, then suddenly water is poured on the bottle. What do you suppose happens?

 

[mgeno216]

Ya, I understand the argument. But that is also quite an extreme comparison. Consider the same scenario, but with a fan blowing on the near molten glass bottle. What happens to the glass now. What I think I am proposing lies somewhere in the middle of both scenarios.

Mike

 

[xxxxxxxxxxxxxx]

I remember reading somewhere that laptops generally have a shorter lifespan than desktops because of the many heat/cool cycles the components undergo. It said that it was often better to let the computer idle at a warm temp (ie: dont put it to sleep) than let it cool down so often. This isn't very environmentally friendly, of course, but I would have to agree that letting it cool down gradually would be better.

I understand its a 'must-finish' project, so good luck, but I would be questioning if the rapid cooling would be beneficial, as from what I understand, it could be detrimental.

Best wishes.

 

[mgeno216]

So regardless if this is a good idea or not. How does my schematic look. Anyone see anything obviously wrong

Mike

 

[mneary]

In your schematic post #18, I don't see any circumstance that would turn either transistor on. D1 can't provide current from the 555, and D2 blocks the 3.3V.

 

[mgeno216]

I don't know if you knew this, but the 3.3v turns off when the console turns off, whereas the 5v is always on so long as the console is plugged in. D1 is there because I wasn't sure if the 555 would be damaged or affected by current following into the 555 output while the timer was off. I can remove it if nothing will happen.

Mike

 

[mneary]

I understand how it's supposed to work. I have simulated the circuit from post #18 and confirmed that the fan never, ever, turns on. Both D1 and D2 are always reverse biased for all possible input conditions. Q1 and Q2 never get any base current.

With no base current, Q1 never turns on the fan and Q2 never powers the 555.

[edit] At a minimum, I think one or more diodes are backwards, but it is more than that, since reversing D1 would cause unlimited base current in Q1.

 

[mgeno216]

Well you are probley right about the diode being backwards. So my understanding of diodes are that they let current flow freely in one direction, and resist current flowing in the opposite, right? Now here is the part where I think my understanding is failing. I thought all diodes resist current flowing from their cathode to the their anode, and freely pass current from their anode to their cathode. A diodes symbol is like this correct:
**broken link removed**

Assuming this is correct, I think the diodes are fine. Could it be the resistors from the 3.3v source (R2, and R3+R4).


Thanks for your help so far,
Mike

 

[mneary]

Your understanding of the diode is correct. Can you load LTSPice (might be called Swcad III) from Linear.com?

Here's the simulation. I decreased the time to make it run faster.

 

[Mikebits]

One more thing. Don't you want your 555 timer set up as a mono stable one shot mode? Your set up looks more like astable mode.

 

[Reloadron]

Backwards, current flow is into the arrow. Isn't it?

Ron

 

[Sceadwian]

Conventional current flow is in the direction the arrow points. Electron flow is opposite that. If you ever see the word 'current' used anywhere without specifically saying conventional vs electron flow, assume conventional. It's called conventional current flow for a reason =) Unless you happen to work with physicists a lot, in which case electron flow is the direction of 'current' flow typically. It's a lot of linguistic dodginess. Hole's can't accumulate beyond the gaps in the valence bands they stand for, electrons can exist independantly, have doubt? Try to find a 'hole gun' rather than an electron gun. I've always been a fan of reversing conventional current flow terminology, but it's been taught in schools since probably before I was born, I'm gonna get nowhere with THAT real fast.

 

[mgeno216]

Ya I want monostable, and it is set in monostable.

Thank you very much for taking the time to make the LTSpice drawing. I have used LTSpice before, but I am still a noob. I think the problem is the current going to the transistors to begin with. I probed the collector lead of both transistors and this is what I got:

**broken link removed**

As you can see the collectors are only getting a few hundred nano amps. I think that is the problem because the fan is never getting more than that.

Mike

 

[mgeno216]

Conventional current flow is in the direction the arrow points. Electron flow is opposite that. If you ever see the word 'current' used anywhere without specifically saying conventional vs electron flow, assume conventional. It's called conventional current flow for a reason =) Unless you happen to work with physicists a lot, in which case electron flow is the direction of 'current' flow typically. It's a lot of linguistic dodginess. Hole's can't accumulate beyond the gaps in the valence bands they stand for, electrons can exist independantly, have doubt? Try to find a 'hole gun' rather than an electron gun. I've always been a fan of reversing conventional current flow terminology, but it's been taught in schools since probably before I was born, I'm gonna get nowhere with THAT real fast.

Now you have just blown my mind. I thought electrcity was the movement of electrons, so to say that current flows one way and electrons flow the opposite, just made my mind **** itself. Could you tell me if my diodes are causing a problem in my circut.

Thanks,
Mike

 

[Sceadwian]

Try basic semi conductor theory if you want to blow your mind out your arse =)
SCIENCE HOBBYIST: how transistor works, an alternate viewpoint

In semi conductors and ionic fluids it's a VERY VERY complex story. Chemistry will probably fry every neuron in your brain if you look at it electrically.

Post the .ASC file I can barely read the image posted.

 

[mgeno216]

@Sceadwian
Post #31

I will read up on that.

Mike

 

[rocket8080]

Im glad to see that this thread hasnt died and some help is on hand. As Im probably going to get no where with the original design i was using Im going to scrap it and go with Mikes idea. After thinking about everyones comments on heating and cooling cycles youve all slightly changed my mind. Although my intentions were not to rapid cool the xbox , more like just to take the edge off to help with heat soak from the residual heat.

Mike hope you get working, will have to keep a eye on this but im busy at the mo fixing microsofts cock ups for a few people.

Good luck

 

[Reloadron]

This is a good read on the subject. Do electrons flow or do holes flow is the classic. My first experience was with vacuum tubes like the 5U4 and 5Y3 and my initial learning was current flows from Negative to Positive and made sense to me at the time. Thus when I look at a symbol of a diode (or transistor) I see current flow into the arrow. The link is a bit of a long read but interesting as to the origins with enough humor to keep it interesting.

Ron