[SOLVED] Faulty fan caught fire - why didn't PSU short circuit protection kick in?

[PeteZapollo]

Hi all,

So a low-quality fan in my PC decided to stop spinning and eventually burnt out. With it, it burnt the cable all the way down to the molex connector.

What I want to know is why the PC continued to stay on? The PSU is a Thermaltake 750W 80+ Gold so I don't believe the quality is at fault.

Will be grateful for any answers as would prefer not die as a result of a house fire.

Thank you!

 

[JohnBonhamsGhost]

Faulty fan caught fire - why didn't PSU short circuit protection kick in?

the PSU has no way to read what is happening with this fan.
short circuit protection is to provide protection from outside currents, not individually connected hardware.

if a surge had come from your building's wiring or from a faulty surge protector, UPS, etc then it likely would have.

 

[PeteZapollo]

the PSU has no way to read what is happening with this fan.
short circuit protection is to provide protection from outside currents, not individually connected hardware.

if a surge had come from your building's wiring or from a faulty surge protector, UPS, etc then it likely would have.

So is there no way to prevent this from happening?

 

[JohnBonhamsGhost]

So is there no way to prevent this from happening?

use better fans.

 

[PeteZapollo]

use better fans.

i meant preventing fires in general

 

[USAFRet]

i meant preventing fires in general

Don't use crappy parts.

In this instance, there is nothing the PSU could have done to prevent the fan from dying and lighting itself on fire.

 

[Lafong]

There is a non-zero risk of fire from any connected electrical device.

Some people unplug their radios when leaving town for a few days.

Most don't. Take your pick depending on your anxiety level.

 

[deesider]

What I want to know is why the PC continued to stay on? The PSU is a Thermaltake 750W 80+ Gold so I don't believe the quality is at fault.

For a faulty fan the short protection would need to be on the motherboard rather than the power supply.

Short protection works the same way as a fuse; when too much power is drawn it shuts the circuit down. So for a fan plugged into the motherboard to trigger the short protection it would need to draw more power from the 12V rail than what the power supply would expect the motherboard to use - this includes power to the CPU and peripherals such as multiple GPUs at 75W each - probably more than 20 amps.

Those thin wires powering a fan can't handle 20amps, so unlikely to trip the short protection, even when enough current is being drawn to light the fan on fire.

 

[t0rxe]

With it, it burnt the cable all the way down to the molex connector.

Luckily it wasn't so cheap that they used non-self extinguishing insulation on the wiring. The whole cable would have ignited in that case.

All in all, there was no fuse on that fan power rail so the power supply kept pumping out current and it did its job as intended. I'm sure there was current limitation in place but the wiring in the fan couldn't handle the current. Don't use cheap parts when building stuff. Spend the money and always get high quality components.

 

[jonnyguru]

i meant preventing fires in general

Not if you use <Mod Edit> parts. No.

The PSU won't shut off until it senses a short. Since the fan isn't directly connected to the PSU in any way, the only short it's going to sense is when all of the insulation is melted off the fan wires and the + and - touch.