How to power UV LEDS!!

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
Ok guys long story short, I have an antique wall sconce, that I am rewiring, it has a standard 120vac bulb socket on top, and it has a beautiful uranium milk glass decorative glass piece that hangs underneath. I want it to look as original as possible, except, I want to drop UV LEDS, down inside the milk glass piece so it glows green from the inside. For those that don’t know, uranium glass glows bright green when hit with UV light. How can I power these LED bulbs, I have either individual 5mm led, or I have UV smd strips? Obviously the leds run on dc, the lamp is AC, and the fixture is REALLY SMALL. I don’t have any room for even a small ac/dc converter. I even cut down an apple USB power block, and really had no room to mount the circuit board. Is there a way, in such confined space, that I can somehow power these LEDS off AC POWER, or what’s the smallest amount of components, I could use to complete this task? I cannot find any LED modules or anything that can accept AC directly. It would need to convert 120VAC to a 5-6VDC? I just have no idea, how to do it. I will post pics to give an idea of what I’m talking about, thanks in advance
 

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Dodgydave

Joined Jun 22, 2012
10,310
You can use a transformer-less supply in side the glass housing, or you can run 5V into the lamp and keep the dc psu external separately.
 

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
Yeah, I wanted a concealed look, I didn’t want to have a dc converter anywhere down the line, where you could see it. BUT what do you mean by a transformer-less supply?
 

Dodgydave

Joined Jun 22, 2012
10,310
You can use a capacitor and series resistor to lower the voltage drop and put the leds in anti parallel like in the drawing, the capacitor is 450V rated and the resistors are 1/2W. The capacitor is about 12K at 60Hz and 14K at 50Hz , if the leds are too bright you can use a 180nF capacitor , or if they are too dim use a 270nF..

PLEASE NOTE THAT THE CIRCUIT IS LIVE !!

IMG_20220112_093424_7.jpg
 
Last edited:

Ya’akov

Joined Jan 27, 2019
5,663
SAFETY NOTE:

Transformerless power supplies (also called capacitive droppers) PROVIDE NO ISOLATION FROM THE MAINS and so great care must be taken to ensure they are safe both in building and operating them. It is possible to receive a serious electrical shock. The circuit MUST BE ELECTRICALLY ISOLATED FROM THE FIXTURE and insulated at every point.

This is a serious thing, please don't take it lightly.
 

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
Thanks for the reply’s guys, after so research, I came across an almost copy of what you drew Dodgydave. But tearing through electric boards I have, cannot find any capacitors around 400v, plus i would have to order more zenor diodes. I dunno guys, I’m stumped as to best way to go on this one?? Want it done compact, but don’t wanna burn the house down
 

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Thread Starter

Noobtech1

Joined Jan 11, 2022
8
You don't need any zeners or diodes, the circuit i drew will work , i use it all the time..and it doesn't get warm.
I’m really sorry Dodgydave, I’m not good with reading electrical schematics, can you draw it out, like the pic I included, and just write next to it the parts list. I’m good with electrical, just not reading schematics, I would really appreciate it if you can take the time to do that for me, again thank you
 

BobTPH

Joined Jun 5, 2013
4,907
If you cannot even read a schematic as simple as that one, you have no business trying to build this. Capacitors will explode if connected to mains the wrong way, and, as others have said, this circuit is very dangerous. Bite the bullet and use a wall wart.

Bob
 

Ya’akov

Joined Jan 27, 2019
5,663

sagor

Joined Mar 10, 2019
695
Also to add to dodgydave's drawing, note that there are 2 LEDs wired in opposite directions. Each one lights up on one side of each AC cycle, so they alternate with AC frequency. In effect, the two LEDs in that diagram are the "diodes".
 

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
If you cannot even read a schematic as simple as that one, you have no business trying to build this. Capacitors will explode if connected to mains the wrong way, and, as others have said, this circuit is very dangerous. Bite the bullet and use a wall wart.

Thanks, I may not know every aspect but I can read schematics, I just wanted clarification, however I still need 120v for the actual lightbulb, and I’m not going to have this sconce have two plugs at the bottom, so wall wart will not work, I need it converted up in the lamp itself
 

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
View attachment 257552
Is this better, ?
Capacitor 220 nano Farads, 250V or 450V
Resistor 470 Kilo-ohms 1/4W
Resistor 1.5Kilo-ohms, 1/4 W
thanks for this, this makes sense now, and definitely is much simpler than the pic I posted. This doesn’t seem so bad, and I can build it stretched out horizontally on a long solder board to make it fit behind the sconce , maybe even in a small concealed box! Thanks
 

Thread Starter

Noobtech1

Joined Jan 11, 2022
8
Maybe this: https://www.amazon.com/Converter-Universal-Isolated-Switching-Version/dp/B07SGQ6XXR/
They specify the dimensions at 1"x.5"x.5"

The safety warnings still apply but just because you are dealing with mains voltages. This is a "safer" circuit but you MUST insulate the high side of it very carefully. Heat shrink tubing like this: https://www.amazon.com/XHF-1-1-Inch-30mm-Waterproof/dp/B07FPBKVXC/ would be a very good option.
thanks yakoov, these seem much larger in the pic, I’ll have to see if I have that room behind sconce when I get home.
 

DickCappels

Joined Aug 21, 2008
8,710
How many UV LEDs do you want to power? If it is very many you might find an isolated power supply is the ideal solution. 220 nf is ok for a few LEDs but if you need many LEDs then it is a more complex requirement.

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1642096594406.png
 

DickCappels

Joined Aug 21, 2008
8,710
That's easy to do with a transformerless power supply or a cell phone charger. Personally, I would go with the cell phone charger because somebody has also worried over most of the safety concerns.
 

Ya’akov

Joined Jan 27, 2019
5,663
That's easy to do with a transformerless power supply or a cell phone charger. Personally, I would go with the cell phone charger because somebody has also worried over most of the safety concerns.
@DickCappels the TS has a space constraint but few posts up I linked a tiny SMPS that is only an inch by half by half that looks pretty well suited.
 
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