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Brian Anderson

LED Lights loose half of their glow

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@Max-Paul did you ever have the chance to get/check-out those sets that "went dim"?

As you can guess, this is really not a good time of year to be messing with something like this. But I received a blue and green string from a fellow member Friday. This weekend has been my time to start setting up my display. I am still working on my display and will be for several more days. Then I have a song to finish seq for. And then there is the week to tweak the seqs. And that member is cool with me getting back after Christmas. My plan is to start working on it in earnest the week after Thanksgiving.

The problem is that this is a single string of 100 LEDs. So, as another has said, the electronics in the plug and socket makes what they call a voltage doubler. Thats how they can have 100 Green or blue LEDs in a single string. From my past experience and that of yours is that about 46 is the max in a full bridge system. But in order to have all, well almost all of the string. I might cut out one LED so we have 3 strings of 33 LEDs. Thus I can use one set of resistors for all 3 strings. Just my current will be triple at about 45mA. But this will cause the wattage of the resistor to be 3 times higher. But will this fit in the available space. All are questions that need to be looked at. I really hate the idea of going down to two sub strings of 46 or a total of 92, loosing 8 total LEDs. but then too, we will not need any resistors (so I hope) for the higher voltage LEDs (white, green, blue and so on).

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@ Max-Paul - Yep, I know what you mean...this always is a busy time of year (I started putting up lights in Oct & I'm not doing anything big...just work on it alittle bit at a time)

-----

Not sure if I'd split the set in 2 sections & remove a few bulbs, or do 3 sections LOL that'd be a tough decision (I'd probably lean towards 2 sections just because it'd be easier) ... with 3 sections, i'd probably do 2 resistors per section just because they'd stay cooler.

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Getting close to start working on those two strings in earnest. Getting the porch (enclosed) cleaned up from projects and get the wood burning stove going. I have gotten a set of incans striped down for the long runs. Got the one set broken down and have an idea how I want to put in diodes. Just need to sit down and do a few voltage test and then wire up so we have 3 mini sets of 33 LEDs in a single string. Think I will half the value of resistance into 2 resistors to keep the wattage down. Do this three times for each mini set.

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Getting close to start working on those two strings in earnest. Getting the porch (enclosed) cleaned up from projects and get the wood burning stove going. I have gotten a set of incans striped down for the long runs. Got the one set broken down and have an idea how I want to put in diodes. Just need to sit down and do a few voltage test and then wire up so we have 3 mini sets of 33 LEDs in a single string. Think I will half the value of resistance into 2 resistors to keep the wattage down. Do this three times for each mini set.

If you can after you get the stings like you want them hook them up to a controller and hammer on them awhile to see if they survive. : )

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I have 6 strings of Blue 100ct LEDs do the "fade" or even "dark" thing this year. They worked all last year, but failing this year and I'm almost out of spares. They have the identical little power modules as pictured, one in each end. I'm fairly certain that the problem is the underrated capacitor (200volt) because the diodes are still fine, and they were well sealed so it wasn't environmental. If I didn't have to virtually destroy things to get it open, I'd just replace the capacitor with a 300volt rated version with the same capacitance value. The different resistors and the capacitor are actually well chosen values, allowing a 100ct string to be powered from both end. The capacitor boosts the voltage to near Peak of the Peak to Peak AC waveform. The resistors bleed off the voltage at the proper rate to still get good fades but keep the voltage high.

Last year I bought some super cheap strings (known to be half wave) but they had the same style power blob. As delivered, they DID NOT FLICKER because the capacitor didn't discharge fast enough between cycles. They looked like Full Wave during a "shake test" but they really were Half Wave. I opened the modules and added a resistor across the capacitor. After some experimenting, I found the best combo for Capacitor and resistors. They are still running this year. They have 300volt rated capacitors, though. 200volt will not last. There is virtually no difference in cost or size, so it is a totally avoidable failure.

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I assume most folks know that you can't fade LED strings with caps in the circuitry, without risking early failure...

Caps are prone to failure, much more so than diodes/resistors (unless the latter 2 are under valued), so if you have caps, and there are string failures - that should be your first area of investigation.

Greg

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Hi, Could you tell me please the company's name that Paul has? Thanks.

You got bad lights from a vendor that replaced them with good ones, and you got to keep the bad ones? Sounds like someone I would like to buy from.

This sounds like the same exact symptoms my LEDs showed during last years display. I got them from Paul's/CDI's exchange program.

I (and others) got junk for lights in 08. Paul did the right thing and they were replaced in 09, but some of them were replaced with junk, and he would not replace these new lights. These lights were used about a week before I noticed there was a problem. I was told thru email that "my lights may not meet your standards" when I contacted him about exchanging the bad lights. I was also told "I am thru with the exchange".

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Well it's a month after Christmas. Has anyone had any luck with fixing these lights? I want to order more lights but I need to know if these can be fixed first.

THanks

Brian

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Well it's a month after Christmas. Has anyone had any luck with fixing these lights? I want to order more lights but I need to know if these can be fixed first.

THanks

Brian

You can find my how-to here. http://doityourselfchristmas.com/forums/showthread.php?9995-LED-String-Modifications

Direct link to document here. http://www.palombolights.com/documents/LED%20Modifications.doc

Hope this helps.

Tony

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Thanks for the information. My problem is I don't know how to calculate the values for the formals. But it's good to know there is a solution out there. If I could just get some help to do the math.

Brian

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Thanks for the information. My problem is I don't know how to calculate the values for the formals. But it's good to know there is a solution out there. If I could just get some help to do the math.

Brian

After reading through the document, which of the calulations are an issue?

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OK, let’s see....

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.

Ok so I have 115v at my house but everyone tells me it 120v so which is it? Where did the *1.414 come from?

b. 170V - 2.8V = 167V

2. LED Voltage and Current

a. Voltage varies by manufacturer and color for LEDs. The most common current is near 20mA. You must look up the specifications for your LED string.

I don’t have anything form the Manufacturer to let me know this. Is there a way I can use my Multi Meter to figure this out?[b]

b. In my examples below, I’ll be using: Red = 2.0V, 17mA or 0.017A

I would be using:

Blue ?

Red ?

Green ?

Orange ?

How would I know the v or the mA?

3. Resistor Calculation (Example using a shortened string of 26 Red LEDs.)

a. Calculate voltage drop of LEDs

i. 2.0V x 26 = 52V

Ok I know how to get this once I have the information above.

b. Calculate peek voltage minus voltage dropped by the LEDs

i. 167V – 52V = 115V

Ok I understand this but again I need the other information.

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

i. Ohms - 115V / 0.017A = 6.764KOhm (Use next higher standard value, for example, 8.2KOhm)

I understand the math but don’t know how to guess the next higher standard value to come up with an 8.2K Ohm Resistorii. Watts - 115V * 0.017A = 1.955Watt (Use a minimum of 2 watt resistor)

Ok I got this.

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

Now why did you I mean they use a 600V/1A diode?

Thank you so much for looking at all of this. It means a lot to know there are people out there willing to help out.

Brian

Edited by Brian Anderson

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1 – The power in your house is 120v RMS but peak to peak it is 170v. 120v is what you get when you average all the peaks and valleys in AC power. Yes, you still have 120v but it is 170 PPV. http://en.wikipedia.org/wiki/Root_mean_square

2 – Can’t help you there – the answer is “it depends” though there are some common voltages for the different colors. The table at the bottom of this should help: http://www.kpsec.freeuk.com/components/led.htm

3 – Standard resistor values: http://www.elexp.com/t_eia.htm

4 – The 600V/1A indicates the safe working limit of the diode. So, being 600 volts – you are good there and being that it’s a single string of lights for one color, 1 amp is sufficient current.

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So maybe it just easier to ask the question, what do you think the V is on a led from the 2009 replacement led strings? They were 100 M5 strings. After reading a few items on the internet I think it is safe to assume 2v for each led?

Brian

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Brian,

Ask roberson3 real nice and he might share what I did for him and his blue string. To be truthful I can not remember what values I used. I can tell you that I ended up having to buy and dissect a 100 ct mini string for the wire. In short I ended up putting a half of a full wave in the male plug and the other half of the full wave rectifier in the socket end. Then splitting up the 100 ct LEDs in two 33 counts and one 34 count circuits. With a resistor at the head end of each sub-string.

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So tonite 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.

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?

Edited by Brian Anderson

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Hi Brian,

Sorry I dont frequent this site much anymore. I am surprised that your red led have a 1.3 forward voltage. Mine were closer to 2 or 2.2 volts each. But Otherwise you math looks good. I think that in your case a 1 watt resistor should be enough. But at the same time as long as space is not issue you cant go wrong with a 2 watt resistor.

One thing I have learned is that sometimes even my math does not match up with the real world. Esp. when working with non-filtered D.C. circuits. If you use a filter (aka cap.) then the string does not play nicely with LOR controllers. But D.C. calculations dont play well with non-filtered D.C. so I have found that doing some calculations and best guess from there till I have a chance to measure with a meter. Note: I keep the current readings to 15mA. I think that this is a RMS value and so the peak current is more like 20mA.

All I know is that I now have two seasons with my converted 18" spiral trees.

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1 – The power in your house is 120v RMS but peak to peak it is 170v. 120v is what you get when you average all the peaks and valleys in AC power. Yes, you still have 120v but it is 170 PPV. http://en.wikipedia.org/wiki/Root_mean_square

2 – Can’t help you there – the answer is “it depends” though there are some common voltages for the different colors. The table at the bottom of this should help: http://www.kpsec.freeuk.com/components/led.htm

3 – Standard resistor values: http://www.elexp.com/t_eia.htm

4 – The 600V/1A indicates the safe working limit of the diode. So, being 600 volts – you are good there and being that it’s a single string of lights for one color, 1 amp is sufficient current.

Oey Vey, boy is this a list of incorrect info. So, lets take it item by item.

#1 RMS is the DC equivalent of the D.C. energy of a Peak A.C. signal. Peak is 1/2 of Peak to peak. Or Peak is one half of a sine wave. Where as peak to peak is a complete sine wave.

Ok, just the one item, but a list of errors in that one point.

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