Spark Attack

[5614]

I have a 3" x 3" computer fan which I thought I'd add to my computer, however my computer uses the standard 4-pin power leads and the fan just had a red and a black wire (postivite/negative)... I don't know for certain which way around to put the wires in, I asked a few people and no one knew, couldn't find it on the net, so I just took the red lead and put in into the 4-pin power socket into the hole which had a red lead going into it.

 

Incidently the computer was on so I could see if the fan worked, so the HDDs where whirring and there was a CD going too... as I put the red lead into the 4-pin thing at first nothing happened, then SPARK.... power failure.

 

OK, crap, my computer had just sparked and now all power had died.

 

So I took the fan lead out and pressed the power button... nothing... repeated that a few times... nothing.

 

So I thought, a spark has high current, so maybe it was the RCCB, maybe a fuse, maybe the whole PSU (power supply unit) had gone, maybe I'd just melted part of my motherboard or something.

 

I took out the main power lead to it (the black 3 pin thing which plugs into the PSU) and put it back in again, pressed the power button and it all works.

 

Conclusion:

It must have been an RCCB or some kind of over-current-circuit-killer (not the fuse, that would have needed replacing).

And also dont stick wires into those 4-pin power leads!

 

I don't know why it sparked, those things are low voltage and there must have been a thread of wire (multi thread wire) that went near the negative pin or something, not sure.

[Lance]

http://xtronics.com/reference/atx_pinout.htm

 

It sounds like there was a short. Computer power supplies will turn off if you short them and turn back on after a few minutes.

[5614]

That's not the lead I was talking about, I meant these:

I put the red wire from the fan into the far pin hole with a red lead input... I think they are 12V, which is quite small and it was a reasonable sized spark, I'd say kinda 30V AC size spark.

 

What causes the computer to cut when there's a short? Is it an RCCB?

[Lance]

I don't know exactly what causes the shut off. I only have two computer PSUs and I would rather not take either apart, one is used by a computer and the other is used for testing circuits.

 

The size of a low voltage spark is determined by the current, not the voltage. I have seen a picture of a 1v, 800a arc that was over an inch long. Also, red is +5v which depending on your power supply could supply around 50 amps.

 

Anyway, I hope that helps.

[5614]

1V and 800A.... the resistance must have been massive!

 

I have a PSU open on my floor, however it is 10 years old and I don't think I'd recognise a RCCB if i saw one!

[Silencer]

What did the fan lead look like? Was it a little dinky thing with tiny pins? If so, it's supposed to go on the mobo, not the power supply.

 

however, you can get an adapter to run your fans off of the power supply.

 

At least there was no permanent damage!

[5614]

The fan was literally just a standard black computer fan with two wires coming out, red and black (+/-), it was just the basics, no 3 pin mobo thingy.

 

"At least there was no permanent damage!" YES (as in I totaly agree)

 

[edit] looking for a pic, didnt find one but:

http://www.cybersalt.org/cleanlaugh/images/c/computerfan.jpg

that looks cool.

[RICHARDBATTY]

I think there is a minus volt wire in the four pin plugs but I'm not sure as its a while since I looked at one. Maybe you got +12 and -12v.