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Red LED specs


Duke
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Could anyone tell me what the "typical" specs might be for Red LED's?

Forward voltage:
Forward current:

I need to make a rectifier to drive a string of 50 in series.

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They are usually 2.0-2.2 V. Current is 20 mA. You could test one of your LEDs from a low voltage power supply and a few resistor values or a pot until you get 20mA and measure the LED voltage.

Wouldn't happen to be a failed CDI 50 red led string would it? I have a case of these but have not dimmed them. All work when plugged directly into the AC line.

I may try a series resistor to limit the surge current based on the idea a repeated surge when dimmed to about 50% is killing something. When dimmed to 50% the string would keep getting hit at the peak of the AC cycle.

Howard

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Duke wrote:

Could anyone tell me what the "typical" specs might be for Red LED's?

Forward voltage:
Forward current:

I need to make a rectifier to drive a string of 50 in series.
Normally the RED LED's have a 2.2V Forward Voltage. The current is still either 15 or 20 ma. Same as the other colors.

Look at your RED light string, see if there is a three wire to two wire change between the two center LED's if not the string is probably using 2.2 Volt LED's as the LED's are wired as one series string and not two series strings.

I have both G12 (2006 70 CNT HWR) and C6 (2008 50 CNT FWR) Reds wired as one series string.

The G12's are badly under powered as they only draw 7-8 ma of current. The manufacturer states these LED's are 1.6V but that is wrong, they are 2.2 Volt. I calculated how these should run and modified the string of lights and was right. The intensity came up to almost the same level as the other colors.

So if you are using a RED LED and not a white LED with a RED lens it will be 2.2 Volts.

So 50v * 2.2v = 110V

120V - 100V = 10 V

R = E / I

R = 10V / .02ma

R = 500 Ohms, nearest standard resistor value will be 470 or 560 ohms.

Wattage (P) = E * I

P = 10V * .02ma

P = .2 watts ( would use at least a 1/2 watt resistor)
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Howard, yes they are CDI Red M5 50's.



Dennis you're awesome dude!!!

I'll get the parts from RS tomorrow and try it out.

Yes, they are one string of 50 lights in series.

The same single wire passes through all the LED's.

I'll be nipping off the warts, wiring in the resistor at the end (last LED) and returning back to a rectifier at the begining of the string.

I'll post results here and over on Planet Christmas.

Thanks!

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Semi-Success!

I used a 4 amp 400 volt rectifier from RS and a 560 ohm, 1/2 watt resistor on the LED string and I now have the smoothest dimming LED's of the entire CDI lot!

The dimming range is now much wider as well with NO FLICKER anywhere in the range.

My concern is that the resistor gets hot to the touch and was wondering if a 1 watt would be a better choice?

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Dennis Cherry

Duke wrote:

Semi-Success!

I used a 4 amp 400 volt rectifier from RS and a 560 ohm, 1/2 watt resistor on the LED string and I now have the smoothest dimming LED's of the entire CDI lot!

The dimming range is now much wider as well with NO FLICKER anywhere in the range.

My concern is that the resistor gets hot to the touch and was wondering if a 1 watt would be a better choice?

Yes try a 1 watt resistor. If the resistor gets warm and you can still hold onto it then it is OK, but if the resistor is so hot that you cannot hold onto it or you see or smell smoke, or the resistor starts changing colors to brown, then it is under value or something else might be wrong.

Remember ir you have a animated display then the string will not be on all the time like a static display, the resistor should have time to cool down some.
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OK, I've had great success and have arrived at the final formula to FIX the fading issue on the CDI M5 RED 50 count strings. First off I modified the Fade Destructed strings in such a manner that there is no longer any female plug on the end so they can no longer be daisy chained in series which is fine for my application.

Here's the parts I used:
1. A full wave rectifier from RS part #274 1152 (100V DC @ 1.5 amps)
2. 2 1K Ohm 1/2 watt resistors.

The NEW rectifier was inserted where the old wart was on the male plug end.
The + on the rectifier goes to the single line that feeds the 1st LED on the the string.
The other 2 strings were soldered together and connected to the - side of the rectifier.
The male plug was reused and connected to the AC pins of the rectifier.
NOTE: place the heat shrink tubing on the wires BEFORE you solder anything. (DOH!)

On the female plug end of the string, I discarded the wart again.
The 2 resistors were connected here to te single wire from the LAST LED and the other 2 wires were again, soldered together and to the end of the 2 resistors in series.

These lights now fade VERY VERY SMOOTHLY with NO FLICKER AT ALL.

See the photos below:

Attached files 158331=9168-IMG_0164.jpg

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  • 3 weeks later...

Dennis Cherry wrote:

Duke wrote:
Could anyone tell me what the "typical" specs might be for Red LED's?

Forward voltage:
Forward current:

I need to make a rectifier to drive a string of 50 in series.
Normally the RED LED's have a 2.2V Forward Voltage. The current is still either 15 or 20 ma. Same as the other colors.

Look at your RED light string, see if there is a three wire to two wire change between the two center LED's if not the string is probably using 2.2 Volt LED's as the LED's are wired as one series string and not two series strings.

I have both G12 (2006 70 CNT HWR) and C6 (2008 50 CNT FWR) Reds wired as one series string.

The G12's are badly under powered as they only draw 7-8 ma of current. The manufacturer states these LED's are 1.6V but that is wrong, they are 2.2 Volt. I calculated how these should run and modified the string of lights and was right. The intensity came up to almost the same level as the other colors.

So if you are using a RED LED and not a white LED with a RED lens it will be 2.2 Volts.

So 50v * 2.2v = 110V

120V - 100V = 10 V

R = E / I

R = 10V / .02ma

R = 500 Ohms, nearest standard resistor value will be 470 or 560 ohms.

Wattage (P) = E * I

P = 10V * .02ma

P = .2 watts ( would use at least a 1/2 watt resistor)




Dennis, very nice fix. Not to pick but, there are a few things in your equations that should be explained to the casual observer with no electronics background.
I studied electronics years ago so iI fully understand the numbers.
It should say:
50 leds x 2.2V=110V
120V supply-110V drop across the led string=10V ( which will be dropped across the resistor).
Like I say.....very nice fixWay to go.
Richard
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