I have in the past simply dished out the reddies and bought an off the shelf solution, but I figure there must be a cheaper way to contruct something that will switch my pump on when the PC is switched on. Ideally I am looking for a 'numnutz' guide with regards to which relay to purchase as I am completely baffled by the various types on offer. Other than that I get the idea and am competent enough with a soldering to get the job done without sending myself across the room. Any help gratefully appreciated!
any relay with 12v coil and contact rating of 240v at your pumps amprage will work. check out http://www.maplin.co.uk/Mproduct.asp?oc=JM67X for an example here is how to hook it up
Thats great - thanks. Only one question - I'm sure it should be obvious but with regards to UK wiring which is Earth/Live/Neutral. The diagram suggests to me that only one of the three cores is switched, whilst the others pass straight through to the pump. So is grey live?
grey = hot (switched) red = netrual (passthru) green = earth (passthru) sorry if that wasnt clear there usaly is no diffrence between switching hot and netural
If you do this, the wiring is still 'live' even when the relay is off, and it's just good practice to switch the active/live and NOT the neutral. I think these are the colour codes, correct me if i'm wrong: UK / Aus: Active = Brown, Neutral = Blue, Earth = Green/Yellow stripe US: Active = Black, Neutral = White, Earth = Green
If you have space you can put it inside your PSU than you can tap the AC/DC directly from the apropriate plugs direct, all you will need is the output socket, placed on the PSU casing depending on pump location of whatever type to suit your pump, and of course the relay. Always switch the live, or both live and neutral, just because your house isn't up to code is no excuse for further careless workmanship.
now what you really want is a system where the relay sticks 0n for a couple of mins after power off to cool things down.. and the cooling fan..
If the pump follows electrical guidelines, there is no real need to switch more than one wire since you wouldn't open the electrical parts of the pump without unpluging it anyway. Switching only the live wire becomes impossible in many countries since the wall outlet is reversible in most standards, as far as i know, only the UK, Chinese and US standard grounded plug is irreversible. Swedish wiring standards: live: black or brown. zero: blue. ground: green/yellow.
I assume you mean the plug is reversible, like our old 2-pin 5A system. But the outlet itself should be switched on the live side, isolating anything plugged into it. Same with lighting switches. South Africa has a 3-pin plug, round pins. Actually, a lot of places use polarised plugs, some shown here.
