fans on a switch

Gavin

Good god. Sticky overload.
Anyway.


I got a 19" rack mountable atx case the other day. Nice case, with a ridiculously large fan, that sounds like a wind tunnel. ( I'd imagine ) The case also has a nice little switch for keyboard lock. Small on off flicky switch. I don't have support for this on my motherboard, but I figure that I can use it to turn on and off the fan as I need to.

I was planning on taking the earth wire going to the fan and cuutting in it two. Then attach the two wires to the small jumper like connector on the end of the switch. Turning the switch on would of course close the circuit and then wooohoo ! fan action !

Is this stupid ?

Gav

Inspector Gadget

Verb, is that case using an AC (mains) fan???? (I ask because you referred to an "earth" wire)

If you have an AC device of any kind, cutting the earth to switch it is the worst possible idea you could try for two reasons:

• The earth is there to save people from dangerous short circuits - if you live in a house with ELCBs (earth leakage circuit breakers), they sense a voltage in the earth (where there shouldn't be any, all going well) and shut off power to the socket within a few milliseconds to help prevent electrocution.
• It won't actually switch the fan on and off - the power comes in on the Live and Neutral anyway :rolleyes:

If you're switching an AC fan, the best solution is a double-pole switch that can switch both the live and the neutral at the same time; if you can't manage that, switch the live with the one switch you have. However, if your fan is large, and your switch is small, it might burn (read: arc weld) the contacts and fry your switch prematurely.

For what it's worth, the colour codes work like this (IEC colour codes are used in Ireland/UK):

Conductor     IEC      US      Alternative 
=========     ===      ==      ===========
Active/Live   Brown    Black   Red 

Neutral       Blue     White   Black 

Earth         Green    Green   Green 
              /Yellow

If, on the other hand, it's a DC fan (usually this means it's supplied with a red wire (positive) and a black wire (negative)), then it's okay to put the switch on either, although convention suggests that the positive (red) wire be switched. However, a large DC fan is bound to draw more than enough power to burn out a switch intended for a keylock - you might want to consider something beefier.

Hope this helps,
Gadget

Gavin

Gadget,
thanks for the reply. My electronic stupidity reveals itself.
You are correct, it's a DC connection. I see red as positive and black as earth/negative. Confusing thinking eh !

anyway. I might try the keylock and if it goes kablamo, just buy a larger switch. There's even 3 holes cut in the case already for spare led's / switches. These cases are great !

thanks again,

Gav

Inspector Gadget

(You're welcome, by the way )

A DC fan is likely to burn that little switch out, so I'd contemplate getting a new one now for when that happens. Does it have a rating written on the side of it, by the way?

Gadget
P.S.> For what it's worth, calling the negative "earth" is accurate when dealing with car electronics, at least in Europe, as the negative pole of the battery is tied to the car's body so that only half the wiring is needed to most of the heavy stuff (as the body acts as the other half). Everywhere else, though, (for the techies, assuming we're not using a so-called "split supply"), people may refer to it as "ground". Confusing, eh?