Need help with LED capacitive dropper math

[iamdarkyoshi]

I have some 230V leds from an Ebay listing, the seller's listing said 120v. The seller was a US supplier. Anyway, They use a capacitive dropper circuit. The mains comes in, through two paralleled 330nf capacitors with a 1megaohm resistor in parallel with the caps, then into a bridge rectifier. The output of the diode bridge goes into two series strings of 54 LEDs, and each string has a 100ohm resistor in series with it. What value of capacitor should I use to make them work on 120v, driving each LED at 15-20mA? I suck at complex math.

[W-L]

I have some 230V leds from an Ebay listing, the seller's listing said 120v. The seller was a US supplier. Anyway, They use a capacitive dropper circuit. The mains comes in, through two paralleled 330nf capacitors with a 1megaohm resistor in parallel with the caps, then into a bridge rectifier. The output of the diode bridge goes into two series strings of 54 LEDs, and each string has a 100ohm resistor in series with it. What value of capacitor should I use to make them work on 120v, driving each LED at 15-20mA? I suck at complex math.

 

I believe this the the formula for it I'm not very well versed in this stuff and the technicalities so I would double check:

http://www.edn.com/design/power-management/4418393/AC-power-your-circuit-without-a-transformer

[RedSphyxis]

I have some 230V leds from an Ebay listing, the seller's listing said 120v. The seller was a US supplier. Anyway, They use a capacitive dropper circuit. The mains comes in, through two paralleled 330nf capacitors with a 1megaohm resistor in parallel with the caps, then into a bridge rectifier. The output of the diode bridge goes into two series strings of 54 LEDs, and each string has a 100ohm resistor in series with it. What value of capacitor should I use to make them work on 120v, driving each LED at 15-20mA? I suck at complex math.

seee? I literally just woke up and checked ltt.

 

here you are again. btw I'm supposed to know all these stuff considering the electives I took in HighSchool we're all electronics sadly I can't remember shit now.

[W-L]

I'm not sure how your are wired up but this shows both 240v and 120v for converting old school bulb lights to led using a very very simple circuit with some resistors and a bridge rectifier. 

@3:00

-https://www.youtube.com/watch?v=zopCnL3LS-s-

[iamdarkyoshi]

I'm not sure how your are wired up but this shows both 240v and 120v for converting old school bulb lights to led using a very very simple circuit with some resistors and a bridge rectifier. 

@3:00

-https://www.youtube.com/watch?v=zopCnL3LS-s-

OOH More bigclive! here is the schematic of the bulbs I have: 

Clive and I are actually discussing it right now.

[Stefan1024]

I have some 230V leds from an Ebay listing, the seller's listing said 120v. The seller was a US supplier. Anyway, They use a capacitive dropper circuit. The mains comes in, through two paralleled 330nf capacitors with a 1megaohm resistor in parallel with the caps, then into a bridge rectifier. The output of the diode bridge goes into two series strings of 54 LEDs, and each string has a 100ohm resistor in series with it. What value of capacitor should I use to make them work on 120v, driving each LED at 15-20mA? I suck at complex math.

 

"Resistance" of the capasitors (Xc): 1/(2*pi*f*c) = 1/(2*pi*50*660nF) = 4.82kOhm

100 Ohms in series: total resistance = sqrt(Xc^2+R^2) = 4.82kOhm

Assumption: 2.8 volts per LED -> one string = 151.2 volts

Average current at 220 volt: (220-151.2)/4.8kOhm = 14.26mA -> seams reasonable.

 

You can runn the LED without the capasitors at 120 volts but they won't be as brigth as on 220 volts. The voltage is to low for 54 LEDs in series.