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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, Ill 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

chelmuth
02-20-2011, 01:06 AM
Voltage Drops on the LED's seem off..

http://led.linear1.org/led.wiz

That site also gives some standard forward voltages for LED's.. and does the math for you. :)

griffixdc
02-20-2011, 01:12 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, Ill 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

well what is it you want to do ? i agree with chelmuth your voltages seem off, and the wizard page he links is the one i was going to give you :)

budude
02-20-2011, 01:16 AM
Well - - a couple comments. The Vf on the LEDs sound a bit lower than normal. Red/Orange are typically around 2.0v (give or take a tenth or two) and Blue/Green are around 3.1v or so. Try using a small resistor (470) as I think you are limiting the current too much using a 1K resistor. For example, even if the Vf was 2.0v, you would be dropping 7v so with 1K, you would only have 7mA running to the LEDs.

As for the resistors, you generally pick something around twice the power dissipated - so with .74W (assuming the numbers stay there...) you would want a 1.5 or 2W resistor to keep them cool. Will a 1W work, yes - but it will be very warm and may melt off any insulation you put on it. I'm guessing you aren't making tons of these so go with the bigger resistors to be safe.

Brian Anderson
02-20-2011, 01:35 AM
I moved this from another thread no one was answering. I'll try the 470 if I can find on laying around. Other wise I can try it with the 2v. I am trying to fix sone led 100 m5 strings. Sorry if this wan't clear in the post. I figure I have to at least brake them down to 50 count strings.
Brian

griffixdc
02-20-2011, 01:38 AM
I moved this from another thread no one was answering. I'll try the 470 if I can find on laying around. Other wise I can try it with the 2v. I am trying to fix sone led 100 m5 strings. Sorry if this wan't clear in the post. I figure I have to at least brake them down to 50 count strings.
Brian

most lights are higher than 2 volts and no more than 3.7 volts in our light strings....use that wizard if you are going to break it down to 50 LED strings...what ever you do look for the 2 wire seperation points not the 3 or 4 wire points

budude
02-20-2011, 01:45 AM
I am doing something along these lines as well. I have about 120 strings of 35-count half-wave LEDs I got dirt cheap but will be converting them to full-wave, 70-count for a new mega-tree - - haven't even started on these yet at all. Pretty bad when you feel you're behind in February...

griffixdc
02-20-2011, 02:00 AM
I am doing something along these lines as well. I have about 120 strings of 35-count half-wave LEDs I got dirt cheap but will be converting them to full-wave, 70-count for a new mega-tree - - haven't even started on these yet at all. Pretty bad when you feel you're behind in February...

yeah i need to start mine as well ...have to change my multi color led strings to single color and change the resistor values and then i have about 40 boxes of half waves i want to convert into full waves.....i dont know about you but i can tell when they are half wave and full wave...my eyes are sensitive to flickering same with some florescent lights what may look smooth to some people seem like they are flickering to me drives me nuts talk about migrains

Brian Anderson
02-20-2011, 02:12 AM
I check the values again with a 780 and a 480 and it is still the same. Red it constant at 1.3v. I am fine with ordering 2 watt resistors as I would rather be safe then sorry. I have a really dumb question; is 1.85k ohm = to 185 ohm? I'm sure this is an easy problem and I am just over looking it on the Internet but I'm tired and could use a link or the answer. I'm not sure I could even fine a 1.85k or what the next closest value would be. I'd like to go to radio shack and try this tomorrow before I order all the parts. I have the Diodes. Maybe I should just but a assortment of resistors.
Brian
oh oh oh by the way there is no 2 wire section in these lights. So many quality issues. If you want to see what is in the plugs of these lights you can go here for some pictures.

http://forums.planetchristmas.com/index.php?/topic/43117-led-lights-loose-half-of-their-glow/

griffixdc
02-20-2011, 02:19 AM
I check the values again with a 780 and a 480 and it is still the same. Red it constant at 1.3v. I am fine with ordering 2 watt resistors as I would rather be safe then sorry. I have a really dumb question; is 1.85k ohm = to 185 ohm? I'm sure this is an easy problem and I am just over looking it on the Internet but I'm tired and could use a link or the answer. I'm not sure I could even fine a 1.85k or what the next closest value would be. I'd like to go to radio shack and try this tomorrow before I order all the parts. I have the Diodes. Maybe I should just but a assortment of resistors.
Brian
oh oh oh by the way there is no 2 wire section in these lights. So many quality issues. If you want to see what is in the plugs of these lights you can go here for some pictures.

http://forums.planetchristmas.com/index.php?/topic/43117-led-lights-loose-half-of-their-glow/
wouldn't put my life on it but i would say 1.85k ohm is 1850 ohms

budude
02-20-2011, 02:21 AM
is 1.85k ohm = to 185 ohm? I'm sure this is an easy problem and I am just over looking it on the Internet but I'm tired and could use a link or the answer. I'm not sure I could even fine a 1.85k or what the next closest value would be. I'd like to go to radio shack and try this tomorrow before I order all the parts. I have the Diodes. Maybe I should just but a assortment of resistors.
Brian

No - 1.85K is 1850 (K = 1,000, M = 1,000,000). For "standard" values there are charts for this like this: http://www.elexp.com/t_eia.htm. Basically, the run-of-the mill stuff you might find in RadioShack would be in the 3rd/4th columns. When get to the 1st and 2nd columns, they are typically more (much) expensive. You might look for flame-resistant/proof versions but that's not completely necessary.

Brian Anderson
02-20-2011, 03:05 AM
Let me ask you guys....
Is there a way to find the value of the mA of an LED? I think next time I'm going to at least ask for any paperwork that could come with the LED's
I have a clamp on Digital Multi Meter and I would like to get a different one around $50. Is the something I should look for that would tell me the mA of components?
Brian

griffixdc
02-20-2011, 03:52 AM
Let me ask you guys....
Is there a way to find the value of the mA of an LED? I think next time I'm going to at least ask for any paperwork that could come with the LED's
I have a clamp on Digital Multi Meter and I would like to get a different one around $50. Is the something I should look for that would tell me the mA of components?
Brian
well finding its watt output...or hooking up a sensitive ammeter to one LED lit...kinda starts you over again....most 5mm leds are the same in reference to color not too much difference...the ones that are different by spec are: SMD's and flux SMD's and luxeon LEDs; some even require a driver to help their massive output ..like the 15 watt LED

Brian Anderson
02-20-2011, 03:55 AM
Well look what I found: http://forums.planetchristmas.com/index.php?/topic/44272-2008-cdi-replacement-led-question/page__st__20

I'm going to try this tomorrow. I'll let everyone know if it workers out.
Brian

Brian Anderson
02-20-2011, 10:23 PM
I found this it's from 2008 when everyone was having problems:

http://forums.planetchristmas.com/index.php?/topic/44272-2008-cdi-replacement-led-question/page__st__20

Which leads you to here:

http://www.ahwatukeeholidays.com/led/LED_Repair.xls

And I am using this:

http://www.palombolights.com/documents/LED%20Modifications.doc

Is there a reason why I couldn't use Mouser part number 821-1N4005
over the 821-1N4007. I thin the difference is 4005 is 600v and 4007 is 1000v. Which do you think would be better.

I am going to go with:
Red 2v @17 mA
Green 2.9v @ 18mA
Blue 3.1v @ 18ma
Orange 2v @ 17ma

So I figure i need the following Resistors
Red 3.94k ohm gong to use 2.2k ohm 2w and a 1.8k ohm 2w
Green 1.22k ohm going to use 1.5k ohm 2w
Blue .67 ohm going to use 680 ohm 1/2w (I will order 2w when I place the order but right now I only have 1/2 watt)
Orange 3.72 going to use 3.9k ohm 2w

So does this sound right?
thank for your help

Brian

griffixdc
02-20-2011, 11:07 PM
the numbers sound better than your first numbers :)...you wouldnt need a more than 600v for 2 reasons your not going that high in voltage and the wire you are using isnt rated above that :)

Brian Anderson
02-23-2011, 04:27 PM
Hello All,
Thank you all for your helpful replies. I messed around with a set of Green LED's and found out my math was wrong. I posted "Green 1.22k ohm going to use 1.5k ohm 2w" well that actually took my resistor value to 3k. The lights did light up but they were very dim. What I should have done was to put 611 ohm resistor on each side to equal the 1.22k ohm I needed. So I think I am almost done and now can fix the entire 60 broken strings. Once I'm done I'll try to put all the information I'm gathered into a how-to post so those with bad LEDs can fix their own. Thanks everyone again for you post, solutions, and suggestions!

I do have one more question though. If I need two different resistors to make up lets just say 1.22k ohm can I use one 1k ohm one one side and 220 ohm on the other? I guess I'm asking does the value of the resistor have to be the same on each side? Not sure what I am asking? Look at the schematic that was in this post, please.

Brian