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Electrical switch for DAYLIGHT not night

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Lathe User

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Hello
I wish to turn a 30 watt fan “on” only in daylight. Simple! Well no actually all the photo cell switches I can find want to do the reverse. Power lights at dusk.
Just to add to the requirements I need to make it weatherproof as it will be located in a greenhouse ( of sorts) Alpine House.
So buying an off the shelf sensor and taking it apart and trying to reverse NC/NO isn’t a great idea.

Does anyone know where I can buy one or externally adapt one or repurpose a unit?
 

Garden Shed Projects

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The smart sockets have a setting that will allow it to be switched at dusk and dawn based on time. Very cheap and easy to install but you may need WiFi nearby although I understand there are systems that use the power cable to transmit the signal if it is connected to the power in the house but I haven’t used them.

for the weather proofing it could be in a sealed box.
 

sometimewoodworker

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Hello
I wish to turn a 30 watt fan “on” only in daylight. Simple! Well no actually all the photo cell switches I can find want to do the reverse. Power lights at dusk.
Just to add to the requirements I need to make it weatherproof as it will be located in a greenhouse ( of sorts) Alpine House.
So buying an off the shelf sensor and taking it apart and trying to reverse NC/NO isn’t a great idea.

Does anyone know where I can buy one or externally adapt one or repurpose a unit?
It’s really simple. Just get any of the photocell switches and a normally on relay. This will mean that when there is no power to the relay current will flow (daytime use) when the relay is activated the current is cutoff (nighttime).
There you are and Bob is your mothers brother
 

paulrbarnard

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The smart sockets have a setting that will allow it to be switched at dusk and dawn based on time. Very cheap and easy to install but you may need WiFi nearby although I understand there are systems that use the power cable to transmit the signal if it is connected to the power in the house but I haven’t used them.

for the weather proofing it could be in a sealed box.
Yes they work great. I have one for my pond pump. I have it turn on an hour after dawn and off an hour after dusk.
 

Lathe User

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Thank you chaps. As this is not my area - some extra detail on the relay needed would be appreciated. Smaller in size the better.
 

Gerry

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The relay already built into your dusk to dawn sensor will already have a normally closed contact (N/C). You just need to solder the feed to the lights to that one instead of the normally open one (N/O). No other components needed or the introduction of extra points of failure.

Gerry
 

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Lathe User

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😁 The thick cable sounds ideal!
Phil -Plants respond to day light hours much more than appreciated so I would be forever changing the timer throughout the year and life’s far too short for that,
Gerry - thanks for that I will ponder it for an hour or 2 cheers
 

Old.bodger

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Where are you / can any of us do the alteration for you? Gerry might be right but the contacts you want may be missing just to save the manufacturer a fraction of a penny on each unit of production. What you need is indeed simple - if you know what you are doing / understand it !
 

Phil Pascoe

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😁 The thick cable sounds ideal!
Phil -Plants respond to day light hours much more than appreciated so I would be forever changing the timer throughout the year and life’s far too short for that,
Gerry - thanks for that I will ponder it for an hour or 2 cheers
It's a 30w fan. What real difference does it make if it runs a while before or after dawn/dusk?
 

Spectric

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Hello
I wish to turn a 30 watt fan “on” only in daylight.
Only in daylight, hot houses and the like normaly control ventilation on humidity and temperature, use a PLC and you could have multiple inputs to give precise control based on several input parameters.
 

Sandyn

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The relay already built into your dusk to dawn sensor will already have a normally closed contact (N/C).
Unfortunately this cannot be guaranteed. Manufacturers will not use a change over relay when a make/break is all that is required. It would cost more and normally cost is critical in this type of device.
These relays will normally be UL recognised because it's easier to get CE certification on the finished item. Having an additional contact on the relay will drive the cost of achieving UL recognition up.

I'm not saying that you will never get one which uses a change over, but probably the only way to find out is to get one and open it up, or find a unit where someone has already done it and made the information public. The danger of course is that there may be different revisions of the item where they used/didn't use the change over relay.
It would make sense to offer the option of dawn to dusk or dusk to dawn, but the lack of a suitable unit suggests there is little demand in the 'consumer' market.
 

Sandyn

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I use the LAP unit from screwfix, just as a dawn to dusk. I have several of them, they have been very reliable.

There are different ways of adding a normally closed relay. The sensor could be mounted on a small sealed box where the NC relay is housed. OR with a bit 'redesign' of the cable clamping, it would release a lot of space inside the unit for fitting a suitable relay. The cables can come in from the base of the unit, so the cable clamping could be done external to the unit. OR there is also a volume 13X30X20 inside the unit which could hold a relay, but a suitable one would have to be sourced and it would be really tight wiring. All that subject to usual stuff about wiring mains stuff etc. etc. :)
I think the WiFi switch is a good simple solution, you could use a Power line adaptor/access point to deliver WiFi into the greenhouse if it's too far from the house, or you could use a separate mains feed to the greenhouse, switched by the WiFi switch inside the house.

The connection will probably fail at some point, so if that would cause loss of produce, you would need to make it fail safe, so if the WiFi failed, the fans would remain on permanently, possibly incorporate that into the dawn to dusk system if it is critical. That could also fail.
Lap_5498.jpg
 

the great waldo

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Hello
I wish to turn a 30 watt fan “on” only in daylight. Simple! Well no actually all the photo cell switches I can find want to do the reverse. Power lights at dusk.
Just to add to the requirements I need to make it weatherproof as it will be located in a greenhouse ( of sorts) Alpine House.
So buying an off the shelf sensor and taking it apart and trying to reverse NC/NO isn’t a great idea.

Does anyone know where I can buy one or externally adapt one or repurpose a unit?
I just fitted a solar panel about 40cm square onto the roof of my greenhouse used a car cigar lighter usb adapter and ran some usb fans. I also got a larger fan with a lithium power pack that charges ok with a sloar panel /usb connection but that one is manually switched when it gets really hot. The little usb fans are fine with the solar panel (depending how big it is) and are cheap to buy. As soon as the sun goes down the fans stop. My problem is keeping the greenhouse warm without spending a fortune on electricity. Here in Austria it can get bloody cold in winter. Last week I just put up some 8cm insulation panels painted matt black on one which seems to help keep the temperature up a few degrees. The weathers still surprisingly warm here at the moment.
Cheers
Andrew
 

hairy

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I have a pair of approx 5" fans that come with solar panels that were about £10 each off flaebay in my greenhouse. The panels face kind of west wedged between the skin and the frame so come on most afternoons when the sun is on them. Both facing the same direction a reasonable circulation is achieved :) They go faster when the sun is stronger in the summer, auto controlled! One season so far.
 

HamsterJam

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It might be overkill but it should be possible to program an Arduino to do exactly what you want.
If you use an Arduino Nano clone it will be about £3. Add a power supply, light sensor and relay unit and the parts will likely cost about £10-£15
These will need to be mounted in a weatherproof box.

Edit: Better still, this unit does what you want. Just need to add 12v power supply.

 
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