This unit is clearly made down to a price, but it still manages to be a good logical design.
In a sense it almost looks a bit old fashioned, but if it works then it makes sense to keep using the same circuitry. It's very similar circuitry to the cheap eBay boxy looking dusk sensors, but with proper cable connection facility as opposed to the slightly shady individual cores on the Chinese ones.
These units are also designed for easy maintenance. If the circuitry fails or the relay welds shut with a high current load or fault, then you can just twist the old unit off and twist another on. There are also bypass versions that bridge the live and load connections for testing, and there are more specialist versions with smart circuitry that measures the length of the night and then switches off at a surprisingly accurate mid-darkness time based on the previous night's duration.
I've installed this to test it and also to test some LED festoon for storm and time resilience. It was easy to mount, but did require four core cable (don't use earth as a circuit conductor, even if sleeved).
Products like this make you realise that the humble 555 timer chip is not going away soon despite being one of the earliest integrated circuits. Even the name "photocell" is a hint to the heritage of these units.
There's an error on my schematic. The MOV transient suppressor is across live and neutral and not across the contacts. I guess it's probably to protect the circuitry, especially the dropper cap.
One thing that might have been an interesting addition is an NTC inrush limiting component to take the switching stress off the contacts. I'm not sure if the extra heat it generated would be an issue though. Now that I've just typed that I've realised that the 470 ohm resistor will be acting as a heater. I've just calculated that it will have about 24V across it and dissipate about 1W at 50mA. That's possibly to keep the unit slightly warm for reducing condensation and stop snow from sitting on the sensor. That's clever. It also explains the 2W standby power. Just over a watt for the heater and about 0.75W for the zener. (15V * 50mA).
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
http://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.
In a sense it almost looks a bit old fashioned, but if it works then it makes sense to keep using the same circuitry. It's very similar circuitry to the cheap eBay boxy looking dusk sensors, but with proper cable connection facility as opposed to the slightly shady individual cores on the Chinese ones.
These units are also designed for easy maintenance. If the circuitry fails or the relay welds shut with a high current load or fault, then you can just twist the old unit off and twist another on. There are also bypass versions that bridge the live and load connections for testing, and there are more specialist versions with smart circuitry that measures the length of the night and then switches off at a surprisingly accurate mid-darkness time based on the previous night's duration.
I've installed this to test it and also to test some LED festoon for storm and time resilience. It was easy to mount, but did require four core cable (don't use earth as a circuit conductor, even if sleeved).
Products like this make you realise that the humble 555 timer chip is not going away soon despite being one of the earliest integrated circuits. Even the name "photocell" is a hint to the heritage of these units.
There's an error on my schematic. The MOV transient suppressor is across live and neutral and not across the contacts. I guess it's probably to protect the circuitry, especially the dropper cap.
One thing that might have been an interesting addition is an NTC inrush limiting component to take the switching stress off the contacts. I'm not sure if the extra heat it generated would be an issue though. Now that I've just typed that I've realised that the 470 ohm resistor will be acting as a heater. I've just calculated that it will have about 24V across it and dissipate about 1W at 50mA. That's possibly to keep the unit slightly warm for reducing condensation and stop snow from sitting on the sensor. That's clever. It also explains the 2W standby power. Just over a watt for the heater and about 0.75W for the zener. (15V * 50mA).
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
http://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.
My outside lights sray on my sensor gone bad..if i tap withstick they go off..can i replace just the top bit you twist off
Are these the same photocells found on top of street lights?
Clive, happy new year. you deserve to invest in a big bear of a soldering iron that can unsolder such joints. Excellent fellow YouTuber d-lab electronics calls it “the schnauzasaurus”
Would not a sensor that increased resistance with more light, a current limiting resistor and a zener diode with suitable trigger voltage be adequate to turn the relay on and off with the sun setting and rising? It would seem to be a cheaper and simpler design than using the 555, would it not?
So this is branded CED – I've had bad experiences withn this brand. Would be interesting to see how this device compares with the Zodian version – which it appears to be a copy of.
Clive, we have every faith in your ability to sort out your glands.
Pretty Cool
I had a power-cut recently and the said mentioned sensor is no longer working.
Do you think that I only need to replace the sensor head? Rather than a whole unit?
Many thx 🙏🏻
I have one of these running in my garden running a 4w led, 70w MH and 70w son. Interesting to see how they work.
When my kids were young I had a plugin night light on the landing that only came on when the house lights were switched off. I remember laying in bed playing through my mind what would happen if you had two of them – each facing one another.
Is that a NEMA L13-30 connector? If so, this would be a great way to automatically blow a circuit breaker at dusk.
The voltage dividing part that goes to the input of the timer would explain why you would sometimes see street lighting flashing on and off before eventually stopping on, the capacitive dropper failing could also cause the relay to cycle aswell.
That's a way better built unit than the "Newlec" branded (fake copy, I think) sensor that I bought for one of our yard lights some years ago.
Why do the lights come on for a few seconds when power is applied? – Simple, it's to provide a function test for the load to be switched, and avoids the indecisive method of covering the sensor to turn it on. The old LDR variety had the same delay, and for the same reason.
If it doesn't say so in the information leaflet, the light sensor should be positioned to face North, or at very least, away from the mounting surface. It should not face South, nor directly toward the Sun.
I'm surprised they're allowed to have such a high standby power dissipation of 12VA and 2W, yet still comply with the regulations. The power consumption could be drastically reduced by using a CMOS 555/comparator/74HC1G14 and a TRIAC, preferably a sensitive gate one, so it doesn't need a large trigger current.