# How to calculate voltage drop capacitor value?

I have 3 volt 15 leds . Ac input voltage 230 volt 50 hz. Then what will be the voltage drop capacitor value?

Transformerless Power Supply Design.pdf (561.9 KB)

TLDR: current is more important than target voltage when the voltage is low.

You need to provide a link to the specifications of the leds you are using and show how you will connect them (ie series or parallel)

This is how led connected

You need to find out how much current is used by LEDs, let say it is 10 mA, so you need resistor 22k or 1.5k (led resistance) + 20.5k in series resistor or capacitor with reactance 20.5k, you can cakculate it here.
https://www.electronics2000.co.uk/calc/reactance-calculator.php
150nF.

So what was/ is the capacitor value already in the fitting and why do you think you need to replace it?

It is not working

Here we go again.
Since this circuit has distinct similarities to the ones you've been helped with in dozens of posts before, have you thought of trying the things suggested to you there?
Let me remind you, it was about a transformer called Bob or something: What is the name of this transformer

This is different.

So what was/ is the capacitor value already in the fitting?

Ceramic capacitor 473 J 400 VOLT and electrolyte capacitor 63 volt 100 uf. It gives very dim light.

Some of the things you could do are the same though.

One being giving complete information right away. First it didn't work, now it turns out to actually give dim light. Turns out there are also 2 caps in there now, so perhaps some more photos showing the entire circuit would be useful.

This is obviously not the most elegant method to to power led's, and high voltages exist which can be lethal.
Rather invest in a AC to DC converter(these are very cheap) and use the relevant resistor to control the current through the LED's.
In many countries the frequency of the AC supply is not a constant.

Emigrate!

I used 155J 250 volt pf capacitor and 10uf 250 volt electrolyte capacitor issue resolved . See attached photo

In an AC circuit? Turn it off, and think again.

New issue created: fire hazard. Congratulations.

And your grid voltage is 230V? So your electrolytic capacitor, apart from being reverse connected half the time, is actually underspec-ed by a huge margin. Double fire hazard. Cool.

If you think that you can use the reactance of a capacitor to drop voltage for the LEDs, that is wrong. Capacitive reactance, while measured in Ohms, does not dissipate power because it does NOT limit current like a resistor does. I fear that you will fry the LEDs.

What?
Of course you can use capacitive reactance to drop voltage for LEDs. Why do you think it is not possible?

Can you tell me what uf volt electrolyte capacitor can I use? 10 uf 100 volt, 100uf 100 volt?

No volt as koraks points out. You do not use electrolytics on AC (with certain exceptions).