Decent priced proper dusk-dawn time switches

[James Salisbury]

Hi,

I am looking for some proper dusk dawn time switches such as the Sangamo range, what are the proper prices and suppliers rather than Farnell?

Thanks

[Andrew Gabriel]

Any reason you want timed ones rather than photocell operation?

[Dave Plowman (News)]

Mechanical solar day switches have always cost an arm and a leg. Any reason not to use a light sensing one?

[James Salisbury]

The building is currently wired with timers, I suspect they are standard

24hr rather than dusk dawn, wanted to do a cost benefit calculation.

[Andrew Gabriel]

Photocells are likely to be very much cheaper. They tell you when it gets dark, rather than telling you what time sunrise/set is. They don't go out of sync after a power cut (although clocks typically have 24h spring reserve backup). They allow for different areas of a building getting dark at different times. They are available for switching at different lux levels.

OTOH, the dusk/dawn timers were available second-hand some 30+ years ago as large numbers were stripped out of streetlamps. Places like Proops, J Bull Electrical, The Shop on the Bridge (Reading), etc had loads of them (and might still be worth trying). They still weren't cheap though. They are a marvel of clockwork engineering if you get the opportunity to play with one.

[Owain]

Sangamo timer £116 + VAT

offence to clockwork, but they date from an era when skilled labour was cheap and a man on a bicycle checked the streetlights every six months.

Photocell £16 + VAT

the photocell is only 5A rather than 20A switching capacity you might also need a contactor from c. £16 if you can mount in an enclosure be honest I would fit photocells even if the costs were reversed. You know the lights will be on when they are needed and off when they are not, regardless of the season or weather, and if it saves even one call-out cost for resetting a timer the photocell pays for itself.

Photocells don't last for ever though. so mount it somewhere reasonably accessible so swapping it is an easy job.

Owain

[Andrew Gabriel]

the dusk to dawn version of it. Note that you should in theory use different dials at different latitude (2nd page shows there are 4 dials covering the UK latitudes). Using the wrong one will simply mean the light over or under shoots dusk by some minutes on either side.

Oh, and I just found the instructions for it...

No offence to clockwork, but they date from an era when skilled labour

[dennis]

I like the way it says it can be left unattended for years.. then states an accuracy of 5 mins per year. How far out does it need to be before it needs attending to?

[Owain]

The TLC page does say however that the product has a "Solar Dial". Anyway, it's useful as an indication of the sort of price these things go for.

Yes.

Owain

[Owain]

If it loses 5 mins in the first year then gains 5 mins in the second and third years, then loses 5 mins in the fourth year, it'll never be more than 5 mins out.

That's probably a lot less than the natural variation of twilight due to local weather conditions .

Owain

[dennis]

That's a big if.

[Dave Plowman (News)]

I'd imagine it uses a synchronous motor so isn't actually losing time. It just can't adjust for the variations of the solar cycle year on year.

[dennis]

That makes it worse doesn't it?

Anyway toolstation item #44224 looks like a simple solution. LE buld with built in dusk to dawn sensor so you throw it away with the lamp.