Restart delay switch? - Advice needed

[drbob]

Hello,

I'm installing a socket in my living room ceiling for a projector (it currently trails an ugly cable down the wall to the floor), I'd also like to install a wall switch to turn off the projector when not in use, rather than leave it in standby the whole time. Projectors need at least 5 minutes to cool down before being switched back on after switch off, I'd like a switch that will enforce this delay. I've been unable to find any such "restart delay" switch from rs components, maplin or farnell.

The closest thing I've found is this industrial relay, which I guess I could use with a standard wall switch, but it's probably expensive and will take much more effort to install (needing a wall box etc):

http://www.ferret.com.au/articles/1c/0c00ef1c.asp
http://www.comat.ch/zeitrelais/e/det...p?EDV_Nr=12893

Is such a relay my only option or is there a cheaper domestic option which does the same thing?

Thanks in advance for any help or advice.

--
drbob

[Dominic]

i guess this sort of thing isnt an off the shelve item, sounds like you need a timer circuit connected to a 240v relay which is controlled by the wall mounted switch.
So the wall mounted switch controls the timer which will then fire the relay after the preset time.
have a look around on maplins in their projects section for timers.

[Rob100]

Hi m8,

A circuit like this would do you. The timer is a delay off timer (could be a true delay off, but I've shown a delay off with aux supply and control input).

Typical examples would be a Crouzet MUR1 (mode C) or a Foxtam/Nortonic YRC.M.

Circuit works as follows:

1) With power on and switch off, relay R is de-energised

2) Switch on, will energise R (through N/C contact of T) and R will then latch it's own supply. The other contact of R (21/24) will activate the control input on the timer and provide power to the PJ. Activating the control input of T will energise T, therefore opening the N/C (15/16) contact of T.

3) When you switch off, R will immediately de-energise cutting supply to PJ and initiating timer (timer will start timing).

4) If you switch back on before the set time period, as T is still be energised, R cannot energise (and thefore latch or supply PJ).

Hope this makes sense. It's getting late and I'm not explaining too well!

The timer should cost approx £15 and the relay £5. Make sure the relay can handle the current of the PJ and fuse accordinly.

I don't have a PJ (yet), so correct me if wrong but don't you need to leave the power to the PJ to allow the bulb to cool?

Rob.