Pi-FAN for RPi4 with 4 (instead of 3) cables?

Usually 4-wire computer fans use the 4th wire as a speed control input, to be driven by a PWM signal. If you don't connect the wire it'll run at full speed, which is probably what you want here. The 3rd wire is a tachometer output so the computer can sense if the fan is spinning at the correct speed.

Normal PC wiring colours are:

1. GND: black
2. 12V: yellow
3. Tach (sense): green
4. PWM (control): blue

but this is a 5V fan so it looks like they've swapped yellow (12V) for red (5V).

I'm guessing that the blue pin is actually the speed control PWM, and the green is to report spin speed back to the Pi. If you don't care about that you don't need it.

If you're unsure, you can just wire red and black and ignore the other two wires - the fan should spin at full speed and you won't be able to sense the spin speed, but maybe that's ok.

Theo

Tnx for the follow-up. According to the shop I could just snip the green wire, so I've done that. I've set it to run at 60°C and the fan's not turning (CPU temperature is 48°C).

My Pi 4B runs about that with no fan

That's what I'm saying: it's 48°C when the fan is not running. Software only allows to set a minimum temperature of 60°C before the fan starts running, so I unchecked the setting and now the fan is turning all the time. A fan with only 2 cables (red & black) should have been enough. I don't know if there's a way to set that minimum temperature to 40°C...

But yes, it's not really necessary and I shouldn't have bought it. But it was fun setting it up. I use RPi4 for Pi-Hole and PiVPN. I've played a little with RetroPie, so maybe I'll give that another go, because I have two RPi4 now.

I used a Pimoroni Heatsink Case for the first one I bought:

Temperature is around 40°C.

The Unity V2 comes with a fan:

Temperature is between 30° and 35°C. (There's a real peak when I open Fx.)

It's an interesting thought as to why one would use a fan at all. If its such a high compute task that you need one, maybe a bigger Pi or an Intel based machine is indicated.

I dislike fans. They fail.

Heat is often about continuous utilisation, like CCTV. On my Pi4 I have a heavy aluminium case that serves as a heat sink, it is fine without a fan.

On my Pi5, I use the official active cooler heat sink, which has a fan. But a good fan, in that it only comes on during the hottest days of summer.

In a moment of stupidity I also bought a metal case for the Pi5 which messes up my USB keyboard/mouse dongle (reflection?), I haven't checked to see what it does to Bluetooth and WiFi.

They do, but they normally last for years.

Not IME

Repaired several computers with failed fans. If you were lucky the fan itself just needed replacing, If you were unlucky it took the processor with it.

The trouble is the environment in which they run. In a clean machine room, OK. In an office full of people some of whom must have had pets and some of whom smoked, it could be a very common failure...

I know I don't really need it, but some people claim it's better to have the CPU at (for instance) 35°C than 48°C. It can't hurt, can it?

Well, if this one fails I won't be in trouble, because it does fine without it. ;-)

I think it will probably extend the chip lifetime from about 150 years to a couple of thousand.

Well that's true!

håhå

Point well taken.

Does your experience come from this millennium?

I remember that type of thing happening, but it was a long time ago. Modern fans are good, I have CPU fans still running after 10 + years. Stunning reliability.

Plus, CPUs shut down without a running fan, and have thermal shutdown too.

Admittedly no, 1990s

They didnt use to!

PC fans run pretty much all the time. A fan on a RasPi is likely to run less of the time, and could well last longer overall.

Fans fail. Disc drives fail. SSDs fail. Batteries fail. Reservoir capacitors fail. But before they do, they are very useful.

David

Fans which are spun up and down frequently tend not to last as long as one which are on all the time.

However, quality has a much bigger impact, and a well made PWM fan designed for variable speed will last far longer than a normal cheap fan which is being switched on and off.

---druck

Such an ArtStudent™ view of life.

Do you know what MTBF means?

I was surprised you'd use MTBF for a component which is expected to steadily deteriorate due to wear and tear.

I though MTBF was more a random failure thing.

For some relatively reliable components, such as people, you initially see a relatively low failure rate, but come 80 or 90 years they start dropping like flies, due to wear and tear.

For some things like atomic an atomic nucleus, the failure does seem random, so MTBF seems applicable.

I don't know which it is for PC fans, but would assume it is more wear and tear than random.

No it isnt that at all.

Yup. MTBF of peole is about 70 years.

Never used.

In general fans fail for one reason only. Bearing failure. The cheapos use phosphor bronze plain bushes and these dry out and seize up, wear out and get noisy and start slowing down or get clogged with people's cruft.

You can go for sealed ball races if you like, as in hard drives, but the price goes up.

In terms of drying out, its time elapsed, not time spent running. Same for cruft. Only bearing wear is time dependent.

None of these are random., All if them are however dependent on conditions and maintenance

MTBF is an attempt to get a handle on how long a collection of parts should stay operational given the spreads of failures in a spread of conditions of the individual parts

There will always be variations in conditions and manufacturing quality

My experience of cheap fans is that 5 years was about the MTBF.

Well yes and no. There is no guarantee that the failures will be (economically) repairable. MTBF is a stochastic emergent property of a bunch of items all of which have a lifetime.

A fan has items inside it, like its bearings.

"According to the information provided earlier, the primary distinction lies in one encompassing the failure rate of all components, while the other exclusively focuses on the lifespan of electrolytic capacitors."

This is full of bullshit

"MTBF estimates the lifespan of a fan’s electronic components, expressed in millions of hours. In contrast, L10 Service Life, measured in thousands of hours, is based on the durability of the bearings and lubrication grease."

So a fan with no electronic components has no MTBF?

"Furthermore, MTBF specifically excludes wear-out factors"

Total crap.

"Mean time between failures (MTBF) describes the expected time between two failures for a repairable system. For example, three identical systems starting to function properly at time 0 are working until all of them fail. The first system fails after 100 hours, the second after 120 hours and the third after 130 hours. The MTBF of the systems is the average of the three failure times, which is 116.667 hours. If the systems were non-repairable, then their MTTF would be 116.667 hours."

"In general, MTBF is the "up-time" between two failure states of a repairable system during operation "

It is an academic nicety to make a distinction between repairable and irreparable subsystems.

In a Triggers broom sort of way a replacement is simply a repair of all components

I could for example clean the cruft out of a seized fan Or oil its bearings. Or completely replace it.

What matters is how long the repair or the new fan will last. Not splitting hairs over MTTF versus MTBF

Yes. Something I don't understand, though, is why so many people use the term MTBF when the appropriate one would be MTTF, since so few of the things referred to are repaired.

David