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hi,
I think you are misunderstanding the current requirements of an LED, it will turn on at 1mA if a voltage greater than the Vfwd of the LED is applied.
A series resistor could be used to limit the current to 1mA, but the LED would be very dim, at 10mA it would be bright and at 20mA maximum brightness
I'm trying to figure out what resistor i should install, but i can't think in a solution to this: **broken link removed**
I must avoid install resistor in each string of LED, i must install the resistor in the transformer output, but i guess that's not functional... ahhh... how troublesome.
hi,
If you want to make it safe by using a mains transformer and you dont want the LED's to flicker then you must use a mains [230v] step down down transformer and a bridge rectifier with a smoothing capacitor. So thats a power supply.
Its bad practice to connect LED's in parallel and use only one resistor, it will give you LED damage problems.
So you will have to wire a ROW in series connected to the power supply as I have just described.
If you chose a 24Vac output transformer, you could drive up to 8 WHITE LED's in a 'string' with a single resistor.
You would have to repeat this for 20 strings of 8 LED's.
If the transformer and bridge rectifier has sufficient power you can drive all the 20 strings from the same power supply.
EDIT:
Like this, its 20mA per string, so 20 strings is approx 400mA, so 24V 12VA transformer and a 1amp bridge rectifier, the 4700uF cap must be rated at least 50Vworking.
I already found a way to use the resistors, i will use the DC current now.
I will supply 23mA to each LED, and i will create 40 strings (10 strings for each side of the chandelier).
It will use approx 1A of current, how many VA do you think the 24V power supply should have, a power supply with 1Amp should be able to power this up or you think i should get a more powerfull one?
The 1Amp rectifier and the 4700uF will still be enough or i need to change them too?
You should use a lower current, especially if you're paralleling them.
White LEDs tend to be more efficient at lower forward currents, in my experience 10mA is normally enough.
Running LEDs close to or near their absolute maximum ratings will shorten their life, especially if you've paralleled them because they won't current share very well, some LEDs will be driven at more than their maximum current rating.
For now i'll do as ericgibbs said, and i'll power the circuit giving 20mA to the LED, if i see they're too dim, i'll come here again to ask you what i need to do.
I only have three questions now:
What value are the resistors i need to use? Since i'll use 40 strings instead of 20.
What is the component "name" to make the rectifier?
How many VA the 24 transformer should have to power this up?
For now i have much soldering to do, but when it's finished i'll post here some pictures! :>
LEDs generally require the forward current they are rated for. Using a constant current source each individual LED will drop its forward voltage, which might differ up to 0.3V between LEDs.
Using a dome on top of the chandelier to hide the electronics won't spoil the overall picture and the constant current source(s) would take care of a long LED life. (approximately 300,000 hours of operation).
A constant current source requires DC, which is necessary for flicker free illumination anyway.
All it takes is a (preferably) toroidal transformer, a bridge rectifier, a smoothing capacitor and some adjustable voltage regulators (wired as constant current source).
That way the light will be flicker free with maximum LED life time.
Boncuk
P.S. I know transformers with an output voltage of 16.5V are hard to source, but no problem for me. I can get custom made toroidal transformers for any desired output voltage up to 500VA. Compared to European prices of custom made transformers the price is almost a laugh here. (Thailand). Shipping is also comparatively cheap. I got two toroidal transformers 220V/19.5V/250VA made for €45 each.
Maybe i'll buy the complete rectifier instead of the 4 diode one for the ultimate awesomeness :3
And i need to use the 4700uF capacitor too (it's on the schematic). When i buy the components i'll make a PCB schematic to be perfect. (or near that lol)
Ohoh, my chandelier will be awesome :>
Thank you for the help! I'll keep up updated about this.
You need to convert the AC to DC via a bridge, add a 100R resistor and put LEDs in series until the peak voltage is reached (345v for 240vAC). Place a 22u electro across the LEDs.
This is how I designed LED strips for freezer cabinets. I used 3 parallel strings. I also incorporated constant current so the strips would work from 220v to 245v.
White LEDs need just 17mA.
I will use your method colin55 when i'll build a different chandelier, that will have 2 paralel strings of LED in series.
That will be a 115 LED in series in each paralel string, it will be big lol.
About the white LED at 17mA, they would not give full bright at 17mA, at least my LED, i've tested, and if i install a 470Ohm resistor the LED look kinda dim, but if i install a 390Ohm resistor, the LED becomes ultra-bright. And if i'm not mistaken the LED and the resistor got warm, i mean, very warm, when i've used the 390Ohm resistor, but the LED kept on all the night and didn't burn.
I will use your method colin55 when i'll build a different chandelier, that will have 2 paralel strings of LED in series.
That will be a 115 LED in series in each paralel string, it will be big lol.
About the white LED at 17mA, they would not give full bright at 17mA, at least my LED, i've tested, and if i install a 470Ohm resistor the LED look kinda dim, but if i install a 390Ohm resistor, the LED becomes ultra-bright. And if i'm not mistaken the LED and the resistor got warm, i mean, very warm, when i've used the 390Ohm resistor, but the LED kept on all the night and didn't burn.
Meh..., well... i've soldered 1 string of LED and then i've begin to think about this whole thing, and i reach the conclusion that the points that the LED are soldered are too weak, if a weak "breeze" touches the chandelier i bet that some LED would just fall to the ground: **broken link removed**
I mean... look at that "joints" of course if i used many, many solder the LED would have more resistance to impact, but it would't look that awesome with that many perceptible solder.
Aaanyway, i've thought about the problem and i've decided to change the design: **broken link removed**
And yes, i got "another" problem with this design.
I'm "thinking" in wiring the LED in series. It's as colin55 said previously:
"You need to convert the AC to DC via a bridge, add a 100R resistor and put LEDs in series until the peak voltage is reached (345v for 240vAC). Place a 22u electro across the LEDs.
This is how I designed LED strips for freezer cabinets. I used 3 parallel strings. I also incorporated constant current so the strips would work from 220v to 245v.
White LEDs need just 17mA. "
But then i did some research about how "cool" is to power up the LED with 345V directly, and some people talked about excessive heating of the LED and if one LED goes down, all the other LED will down too.
I don't think i have any other viable option with that kind of design in mind, i even thought about using PWM to power up the LED, but i don't really know how to do that, and if it's viable in this situation.
Anyway my biggest problem it's the amperage, at least with my calculations:
100 LED @ 3.2v 22mA each
= 100 x 22mA = 22A!???
I'm doing wrong calculations or this design it's completly unpraticable?
Do you by any chance have a small obsession with LEDs?
Do not power the LEDs directly off the mains, they are not like lightbulbs and have very non linear characteristics and at least one will fail quickly and put your while string out, you are much better off (and safer off) using a transformer, as stated prieviously, to go down to 24v and rectifing / supressing with a cap. This will also massively reduce flicker which you will see if you run them from AC.
You could rectify the mains directly and use a cap to smooth, but you would end up with around 340v DC which will kill you instantly. Don't do it.
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