Brian Anderson

02-20-2011, 12:59 AM

No one answered so I am posting this here. I'd like to order my parts with another order so I don't have to pay shipping. Doe my math work out?

I use a 9V battery connected to a 1k ohm resistor and my Voltage Meeter and found the voltage drop for the LEDs.

Blue 1.8v

Green 1.7v

Orange 1.4v

Red 1.3v

I think it would be safe to assume 20mA as the maximum continuous current rating? I've read a lot of people use 30mA but isn't is safe to use the lower value?

So now if:

1. Peek Voltage - Peek voltage out of the full wave rectifier from 120VAC RMS equals 170V minus the voltage dropped by the diodes. This would result in about 167V.

a. Rounded voltages, 120VAC *1.414 = 170V.

2. LED Voltage and Current

a. Voltage varies by manufacturer and color for LEDs. The most common current is near 20mA. You

b. In my examples below, I’ll be using: Red = 1.3V, 20mA or 0.02A

3. Resistor Calculation (Example using a shortened string of 100 Red LEDs.)

a. Calculate voltage drop of LEDs

i. 1.3V x 100 = 130V

b. Calculate peek voltage minus voltage dropped by the LEDs

i. 167V – 130V = 37v

c. Calculate Resistor(s) needed to drop remaining voltage

i. Ohms - 37V / 0.02A = 1.85 KOhm (Use next higher standard value, for example, not sure what this is KOhm)

Watts - 37V * 0.02A = .74 Watt (should I use a 1 watt or a 2 watt resistor.

4. Rectification – You will need 4 diodes per string to make the full wave rectifiers.

a. I use 600V/1A diodes. Mouser part number 821-1N4005

So does my math work out?

If you are afraid to comment in the open forum then please pm me. I need to order a bunch of other parts and I don't want to pay shipping twice. Thanks guys!

Brian

I use a 9V battery connected to a 1k ohm resistor and my Voltage Meeter and found the voltage drop for the LEDs.

Blue 1.8v

Green 1.7v

Orange 1.4v

Red 1.3v

I think it would be safe to assume 20mA as the maximum continuous current rating? I've read a lot of people use 30mA but isn't is safe to use the lower value?

So now if:

1. Peek Voltage - Peek voltage out of the full wave rectifier from 120VAC RMS equals 170V minus the voltage dropped by the diodes. This would result in about 167V.

a. Rounded voltages, 120VAC *1.414 = 170V.

2. LED Voltage and Current

a. Voltage varies by manufacturer and color for LEDs. The most common current is near 20mA. You

b. In my examples below, I’ll be using: Red = 1.3V, 20mA or 0.02A

3. Resistor Calculation (Example using a shortened string of 100 Red LEDs.)

a. Calculate voltage drop of LEDs

i. 1.3V x 100 = 130V

b. Calculate peek voltage minus voltage dropped by the LEDs

i. 167V – 130V = 37v

c. Calculate Resistor(s) needed to drop remaining voltage

i. Ohms - 37V / 0.02A = 1.85 KOhm (Use next higher standard value, for example, not sure what this is KOhm)

Watts - 37V * 0.02A = .74 Watt (should I use a 1 watt or a 2 watt resistor.

4. Rectification – You will need 4 diodes per string to make the full wave rectifiers.

a. I use 600V/1A diodes. Mouser part number 821-1N4005

So does my math work out?

If you are afraid to comment in the open forum then please pm me. I need to order a bunch of other parts and I don't want to pay shipping twice. Thanks guys!

Brian