Raspberry Pi Cooling system? :D

[zeeteex]

Before I receive a barrage of messages telling me that it isn't necessary, it doesn't get hot enough blah blah... I am doing this because i want to! I want to try and connect a 5V 25mm fan to the GPIO headers and incorporate this into an acrylic/card case.

So, I just want to know your opinions on it and if you think it is even possible.

I plan to buy this 25mm 5V fan http://uk.rs-online.com/web/p/axial-fans/5440481/

And mount it just above the processor on a piece of acrylic with a hole in to fit the fan size. How can i connect it to the GPIO, or cant i? I know the GPIO is 3.3V but will that just mean it cannot spin as fast?

I just want to see if this will work because if it does, it would look very cool, just like a desktop pc with heatsink and all

[__Miguel_]

Hmm, I predict two possible problems with that setup (besides noise, but that's a given, since the Pi doesn't actually give out any, and whatever fan you put there will increase the noise output of the build, and that fan seems particularly LOUD from the spec sheet):

1) Power requirements. I don't have the GPIO max output available right now, but please make sure both the GPIO and the power supply can handle the power draw.

2) Fan not spinning up. That fan is, as you already pointed out, designed to run with a 5V input. Having only a 3.3V input will at the very least make the fan spin much slower than what it's rated for (which is not that bad, really, as I said that fan seems like a screamer) or, on a worst-case scenario, it won't even spin up. PC modders have had this kind of issue for years: most PC fans can run on voltages lower than 12V (now PWM is the norm, but that wasn't the case a few years ago, if you wanted to slow down the fans you had to lower the fan's voltage). However, every fan's spin-up voltage is different. On PC fans, there are a few that can actually spin up with a 5V input, but most of them need at least 6V or 7V. The vast majority of them will still spin at 5V, but there are not that many that start up at that voltage.

In short, try to check out that fan's spin-up voltage. If it's higher than 3.3V, it will probably fail to work on your build.

Good luck!

Miguel

[zeeteex]

In short, try to check out that fan's spin-up voltage. If it's higher than 3.3V, it will probably fail to work on your build.

Found this site: http://www.digikey.com/product-detail/e ... ND/1021172

Says voltage required is 3-6V DC

Sounds good! I ordered the fan and parts needed, will try as soon as it comes!

[__Miguel_]

Yikes, that will be a tight fit indeed... Spinning up a 3-6V fan from a 3.3V source will be a hoot and a half

Make sure your power supply can handle the extra load without dropping the voltage too much, or else the fan will either not power up or look like someone learning to drive stick for the first time

And again, good luck!

Miguel

[mahjongg]

A GPIO pin will not deliver the current needed to power a fan directly, you will at the very least need a transistor and a base resistor as a switch, and in that case you can just as well power the fan from 5V.

The picture below is an example (source wikipedia).

transistor used as switch

200px-Transistor_as_switch.svg.png (5.63 KiB) Viewed 3623 times

[johnbeetem]

A GPIO pin will not deliver the current needed to power a fan directly, you will at the very least need a transistor and a base resistor as a switch, and in that case you can just as well power the fan from 5V.

The picture below is an example (source wikipedia).

I strongly recommend putting in a flyback diode across the fan, with anode connected to the transistor collector and the cathode connected to 5V. Otherwise when the transistor turns off, the inductance of the fan may produce a voltage spike that will turn the transistor into a fuse.

For more info, see: http://en.wikipedia.org/wiki/Flyback_diode

[johnbeetem]

Before I receive a barrage of messages telling me that it isn't necessary, it doesn't get hot enough blah blah...

IMO, RasPi gets pretty hot, especially if you've got Ethernet connected and the CPU is working -- for example, trying to render a web site.

I've found that mounting RasPi vertically seems to help a lot. A lot of the heat from the SoC and USB/Ethernet chips is conducted through the board's power and ground planes, so the whole board gets quite warm on both sides. By mounting the board vertically and giving it lots of ventilation, both sides act as radiators and natural air convection (i.e., heat rises) keeps the air moving without needing a fan.

[__Miguel_]

I've found that mounting RasPi vertically seems to help a lot. A lot of the heat from the SoC and USB/Ethernet chips is conducted through the board's power and ground planes, so the whole board gets quite warm on both sides.

While the OP clearly stated he wants to do it because he can, not because he actually needs it, I have also observed that the whole board gets quite hot. The CPU can even get hot to the point it hurts to touch it on those occasions you described. And having the whole board sit on the large block of foam that comes in the case for testing purposes can't help, I assume.

Glad to know I'm not the only one experiencing it, and that there is a quick fix available. Now, to figure out a way to prop it up... Oh, I got! A small photo stand Hopefully it will hold, every cable wants to throw the RasPi around... lol

That being said, can someone please explain to my why the extra bits are necessary? I come from the non-engineering-savvy modding world, where we can just plug a fan to a power source and not even thing about it (there are even Molex adapters for plugging the fans directly to the PSU, on 12V, 7V or 5V). Is it because of the simplified electrical paths on the RasPi? Or just because it's a better practice (and, if so, why don't we need that sort of extra stuff on PCs)?

Cheers.

Miguel

[jamesh]

The Raspi was never designed to drive a fan, which is why you would need to add extra bits. Broadcom testing has shown a fan is not necessary - these chips or similar ones are in millions of mobile phones - none of which have a fan!

[bredman]

can someone please explain to my why the extra bits are necessary?

The extra bits are only needed in some cases, it depends on what you are talking about.

If you are talking about the 3.3v or 5v pins on the GPIO header, nothing extra is needed. These pins provide constant voltage, so they would be useful if you want the fan to run permanently.

If you are talking about the input/output pins on the GPIO header, you need a transistor. The input/output pins can only supply a couple of mA, and they would probably be destroyed if you connected them directly to a fan. These pins are useful if you want the ability to turn on and off the fan.

[__Miguel_]

Ah, I got it now. We're trying not to fry the thing

I'm guessing some sort of a relay might be a more suitable solution then, no? From the little knowledge I have on the area of electricity (I'm a law major, so... ), that sounds about right: you get one circuit to power up another, independent one, less prone to catastrophic failure when overtaxed and capable of handling higher voltages and/or currents.

Did I actually get that one right? And, if I DID get that right, TIFL (Today I Finally Learned) what a relay actually is, and how it works. I had the concept, I just never got around to understand it...

Anyway, good luck to the OP, and thanks for teaching me something new

Cheers

Miguel

[bredman]

I'm guessing some sort of a relay might be a more suitable solution then, no?

Yes, a relay would be perfect. Unfortunately, the GPIO output pins can only provide 5mA, and this is not enough current to drive the coil in a normal relay. You may be able to find specialist relays that could switch at 3.3v 5mA, but these would be very rare.

Your best bet is a transistor, see the diagram from mahjongg. Remove the switch and connect the GPIO output to the resistor.

[johnbeetem]

Broadcom testing has shown a fan is not necessary - these chips or similar ones are in millions of mobile phones - none of which have a fan!

That's because in normal operation a mobile phone is held vertically

They also don't have hot USB/Ethernet chips and linear regulators. OTOH, they do have RF modules.

[johnbeetem]

I'm guessing some sort of a relay might be a more suitable solution then, no?

Yes, a relay would be perfect. Unfortunately, the GPIO output pins can only provide 5mA, and this is not enough current to drive the coil in a normal relay. You may be able to find specialist relays that could switch at 3.3v 5mA, but these would be very rare.

Your best bet is a transistor, see the diagram from mahjongg. Remove the switch and connect the GPIO output to the resistor.

You can get solid state relays, but they're a lot more expensive than a transistor + flyback diode.

[mahjongg]

Broadcom testing has shown a fan is not necessary - these chips or similar ones are in millions of mobile phones - none of which have a fan!

That's because in normal operation a mobile phone is held vertically

They also don't have hot USB/Ethernet chips and linear regulators. OTOH, they do have RF modules.

I hope, and believe, you are kidding.

The whole PI uses about 2 Watt only, that there is a tiny part of it that consumes most of that energy and is getting warm to the touch means nothing, its temperature, even when its "painful to touch", is far below a value that brings it in any danger.

The OP said he is only doing it because it looks cool, not because he wanted to cool it down.

[zeeteex]

Thank you all for your responses. Today the fan arrived, along with a 12mm heatsink I ordered and some thermal tape. Placed the heatsink on easy with the tape, and wired up the + wire of the fan, to the 5V GPIO pin, and the - wire to the ground pin. Plugged in the pi and bingo, fan starts up and works like an absolute charm.

Havent yet built/found the case that i can mount it to, but if you want to have a look, here is the picture album.

https://plus.google.com/photos/11123183 ... 1860267489

Feel free to let me know what you think!

Also, see post: http://www.raspberrypi.org/phpBB3/viewt ... =63&t=8554
Jake