USB hub power adapter exploded cuz of too much power consumption

[koko0]

small intro -
Hi!
1. new here, but very not new in the eevblog video series. i'm addicted to it.
2. English is not my main language, feel free to correct me so i can learn more than just electronics.
 - end of intro

I've built a usb fan to absorb fumes when im soldering.
i didn't put any resistor there, cuz i thought nothing too bad should happen (small motor of a dead quadcopter). i've connected it to a USB hub outside of my compter so i couldn't damage it.
well, the fan started to slow down after a few seconds so i've turned it off. then the power adapter (that thing that is connected to the wall) flashed few times and powered down my home.

my questions are -
shouldn't it be protected from happening? it's just cuz it's a cheap adapter?
why would it explode after i turned it off?

some post-magic-smoke pictures added for your pleasure.

[elgonzo]

That wall wart is as cheap as it can get. Zero protection whatsoever.
I guess the same is true for the USB hub itself. Did you purchase it from ebay or one of the Chinese online shops like Alibaba?

What was the power or current rating for this wall wart, and what is the current rating of the fan/motor?

From the pictures it's hard to tell what went up in smoke. There is no visible damage to the components, and the charring is on the bottom side of the PCB. Thus, my guess is that the fan drew more current than the traces on the PCB of the wall wart could handle, causing one or more of the PCB traces to heat up until charring occurred. The charring (perhaps mixed with some displaced copper from molten traces) established an electrically conductive path with sufficiently low resistance between the two mains terminals which eventually tripped the mains fuse...

[Brumby]

(small motor of a dead quadcopter)

That was not the best move, IMO.  Those motors are designed to deliver POWER - enough to lift themselves, an airframe, battery and electronics.  You just needed to move air.

The overload was inevitable and, obviously, severe.  It is not inconceivable that once there was damage in the wall-wart, it entered upon its own destructive path.

[IanB]

The best kind of fan to use would be a small case fan from a PC. Although designed for 12 V these will usually run quite happily on 5 V.

[koko0]

Yeah that was a very cheap one from ebay.
Nothing was written on it as far as i remember.
I bought some 5v fans from ebay to try to build another one.
Funny thing - the seller offered me a new one... Not sure if i want it.

Thanks!