240VAC 50Hz 160LED Chandelier - How to turn it on?

[Fluence]

I will make this awesome LED chandelier: STEP-3

But i want to install this type of white LED on it:
Current: 23mA
Voltage: 3.2v
Quantity of LED on the chandelier: 160

I will use 5 LED "arrays" (or warever you say in english) and the 5 LED need 16V.

So my "problem" is exactly that, how can i make a Transformer that transforms 240VAC 50Hz in 15.3VAC (to be safe)?
I've saw many opinions, and this is what i've understood until now:

The LED at 15.3VAC will flicker. To mitigate the flicker i need to use a 0.22uF 400V capacitor. Hopefully the flicker will not be noticeable, but i'm not sure on this one, if someone knows what can be done to reduce flicker it would be awesome;
I'm connecting the LED in a way, that only AC current can power them up, that means that i just can't use DC current;
Someone said, that there could be "spikes" in the current, and to prevent the LED burning, it should be installed a 1K 1W Metal Oxide resistor, i agree, but i don't think the resistor value fits my need for more power.
And if i turn on and off fast the LED chandelier, i can end up burning all the LED! D: (i think the capacitor mitigates this problem too? i'm not sure)

Resuming, i need to know how to build a 240VAC 50Hz transformer to output 15.3VAC 100Hz? (maybe 100Hz mitigates the flicker completly?).
I have a schematic here, but i want to make sure that the chandelier will work at least one year without burning.
**broken link removed**

Maybe i just need to reduce the resistor a little to have 23mA instead of 20mA?

 

[ericgibbs]

hi,
White LED's have nominal forward voltage drop of about 3.5V.
So with a 15.3Vac transformer the most LED's you can connect in series is 4, leaving approx 0.37V to drop across a series resistor at 20mA, this means a18R series resistor
The problem is that the Vfwd of 3.5V can vary by at least 0.2V, so to be sure that the LED's light, you could only use 3 LED's in series with higher value resistor.

I would suggest you consider a 25V or 30V transformer connected into a bridge rectifier capable of driving all the series chains of LED's.

Do you follow OK.?

 

[Fluence]

So to be safe: 3.3Vfwd x 5 = 16.5V

I need to build a 16.5VAC transformer.

The bridge rectifier will turn my AC current to DC right? I can't use DC current i really need AC to power up the LED.

 

[crutschow]

LEDs work fine on DC, even better than on AC.

 

[Hero999]

Don't forget the peak voltage is about 1.4 times the RMS voltage.

Well you could use the same circuit you posted above but with two strings of 80 back-to-back, a 100R resistor and a 1µF capacitor but I assuming you're looking for other ideas.

A 12V transformer should be able to power four LEDs in series, don't forget the peak voltage is 12√2 which is 17V. Four LEDs in series will have a forward voltage drop of between 12.8V and 14V, then there'll be 1,4V to 2V of loss for the bridge rectifier.

You could use a 12V 1A transformer, a bridge rectifier, a 2200µF capacitor, with 40 strings of four in series, each with a 150R resistor.

If you think 12V is cutting it fine, a 15V transformer will a certainly be able to power a string of five LEDs with no problem.

 

[Fluence]

I know the LED work fine on DC and AC current, but the problem is that the Primary AC current (240VAC) has spikes, and it can burn up my LED! D:

Here's the reason because i can't use DC, and i really need AC:
**broken link removed**

As you see, if i use DC it will just light up one "row" of LED, while the other will be off. But if i use AC (the currents flows two-ways or something lol), all the LED turn on.
And i really need to maintain that design, because it's for a LED chandelier like this one:
**broken link removed**

Someone has any idea how to do this transformer the "right" way?

 

[Fluence]

I understand what you'r saying Hero999, but i really need to power 5 LED with this design, so i can't use one resistor for each string.
I can only send current through this 4 "pillars":
**broken link removed**

 

[Hero999]

All right, I see what you mean.

The trouble is with AC, you're always going to get flicker, unless you use a high frequency.

A 15VA transformer and a 270R resistor will power two strings of five LEDs back-to-back, as you've drawn them.

 

[Fluence]

I will use three strings not two, what do you think it's the more suitable resistor? Maybe 220Ohm?

In general, the transformer have to power up 160 LED, i dunno what 15VA is, but you think it's enough to power the 160 LED at the same time?

To use a "high frequency" what do you mean? I want to do something about the flicker, i willing to use that, but i dunno what's it. D:

And the AC "spikes" do you think i'll not have any trouble with that if i only use a resistor?

 

[Hero999]

You can't use three strings, you need to have even numbers.

Each string of two should have its own series resistor.

EDIT:
I think we're confused about the definition of a string of LEDs.

Repeat the LEDs and resistor attached to the transformer in the schematic below, 16 times.

 

[Fluence]

Hmm there's no other way to not use 1 resistor for each string?

Did you see the chandelier photo? It would look bad to use it D:

About the flickering? Can you tell me how to take care of that in the schematic you've make?

 

[Hero999]

You could use one resistor for two but it's not recommended because LEDs don't always current share very well, keeping the current low is the answer.

By the way I was wrong earlier, for 10 LEDs, you need 120R.

For 20 LEDs, try reducing the resistor to 56R. This will limit the current to about 40mA RMS which is an RMS current of 10mA though each LED.

 

[Fluence]

And the flickering do you know any solution?

 

[Hero999]

There is no solution to that.

The flickering will happen on AC because the current stops flowing every half cycle causing the LEDs to turn off.

If you need to eliminate the flicker switch to DC - there's no other way.

 

[Fluence]

I've saw someone telling that 240VAC 50Hz make the LED flicker, because they turn off and on 50 times (50Hz), so, if i by some means, can make 100Hz instead of 50Hz, the flickering would be less perceptible.

Do you think it's possible to do this? For now it's just a theory.

 

[Hero999]

That's true but as the LEDs are flashing alternately the light filling the room won't flicker much but you'll notice flickering when you look at the LEDs.

100Hz flicker is unfiltered rectified DC which isn't an option as you don't want to use DC.

 

[Fluence]

Mehh, i have to live with it.

Anyway, now for the last one:

I need to build a transformer that transforms 240VAC in 16.5VAC, do you know how can i obtain the 16.5VAC?

 

[Hero999]

You don't build it, you buy it and get a 15V transformer because you won't be able to get 16.5V.

 

[Fluence]

Even if i buy the 15v transformer i can't change any component inside of it to output 16.5V instead?

It's not possible because there's no components that can do it?

 

[Hero999]

What do you think?

I've told you before, use 56R and a 15V transformer.