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Timer For Fans And Lights

This simple circuit provides a turn-off delay for a 230VAC light or a fan. It can be used to make a bathroom fan run for a set period after the switch has been turned off or it can be used with a pushbutton to turn a light on for a specific time. The timer circuit consumes no standby power when the load is off.

By Nicholas Vinen

Bathrooms and toilets need an exhaust fan to vent humid air or odours outside. It’s a good idea to have the fan running while you shower and then for a little while afterwards, to prevent condensation and mould. This unit makes it easy, by automatically running the fan for a preset period after the wall switch has been turned off and then switching itself off.

And while this timer was designed specifically with bathroom or toilet fans in mind, it is equally applicable to exhaust fans in kitchens where cooking odours need to vented outside. Of course, cooking also produces large amounts of water vapour so a fan is desirable to avoid condensation on the walls which can lead to mould.

It has other applications too. For example, many apartment buildings have lights in the foyer or stairwell with pushbuttons to turn them on. This allows people on any level to turn the lights on for long enough to get into or out of the building without the possibility of them being left on for long periods. This unit can perform that task too, when combined with mains-rated momentary pushbuttons or spring-loaded switches.

Or do you forget to turn off outdoor lights after visitors have departed? This timer will avoid that problem.

You can easily set the time-out from five seconds to one hour by changing an on-board link and possibly a capacitor. The whole thing fits in a standard junction box (Arlec 9071 or equivalent) for ease of installation. And as noted above, it has no standby power so it’s quite “green” (well, the PCB is anyway).

Commercial units to do these jobs are available but can be hard to get and expensive. This SILICON CHIP design has relatively few parts and it can handle loads of up to 5A/1250VA.

Warning!

This circuit is directly connected to the mains and all parts operate at 230VAC. As such, contact with ANY part of the circuit could be fatal!

DO NOT operate this circuit unless it is fully enclosed in the specified junction box and DO NOT touch any part of the circuit while it is connected to the mains.

Note that, in most states, a licensed electrician must be used to connect this unit to fixed electrical wiring.

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