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BrightChristmas

Converting Half-wave To Full-wave For $0.50

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This keeps coming up, so I'm going to consolidate the info into one post for people. If you decide to do this modification, you'll need to be able to use a soldering iron and apply heatshrink tubing.

Most big box retailers sell half-wave LED sets for considerably less than online stores -- even with pre-sale prices. Prices on the order of ten cents a bulb are easy to come by. These sets are, otherwise, often of pretty good quality and dim well. The problem is that the flicker can be considerably annoying to many (myself included).

Last year, I set out to convert my display over to LED. This was a late decision and based on some online experiences, I didn't have any choice but to buy from the retailers. I bought a sample set of warm white, red, green, and blue LED "mini's" from walmart and gave them a test. I liked everything about them but the flicker.

I built a simple half-wave to full-wave converter out of a bridge rectifier and the cut-off ends of an old set of minis and plugged the LED string into this pigtail. One half of the string lit up and the other half was out. The side that was cured of the flicker problem since it was now flashing 120 times a second instead of 60 times a second -- most people stop perceiving flicker between 60 and 70 Hertz.

It seems that to balance the load, the two circuits of the string were wired to energize on the alternating AC polarity to balance the load. So, all I had to do was get them wired with the same polarity. This was as simple as cutting the string at the half-way point between the two circuits, flipping the wires, and resoldering and heat shrinking.

I've gotten this step down to about 3 minutes per string. So, I can convert about 20 strings an hour or about 1000 lights an hour -- more than enough to justify the time with the cost savings.

Here's how it's done. Rather than include pictures, I'll just spell it out. I might take and post pictures later.

First, the pigtail to convert the AC to full-wave rectified AC.

You'll need a bridge rectifier. I use these: http://www.allelectronics.com/make-a-store/item/FWB-46/4-AMP-600-VOLT-BRIDGE-RECTIFIER/1.html

They are $0.35 each if you buy 100 ($0.25 if you buy 300).

You'll need a number of male and female plugs. Start salvaging every plug end you can from old strings. If you know people getting rid of lights, ask them to cut off the ends for you. If you are building longer super strings, combine them by cutting off the plugs between strings and soldering them so you have plugs for your converter. I like using the mini string plugs because they already have a 3 amp fuse inside that matches well with the 4 amp rectifier.

Some 3/4" heatshrink tubing -- I like clear for reasons you'll soon see.

Some low-temp hot glue and hot glue gun.

The rectifier has four pins. Two are AC input and two are DC outputs. Cut them to about 1/4" long and solder the male and female plug ends to the AC and DC pins respectively. The orientation on the AC side doesn't matter. The orientation on the DC side doesn't matter, but follow the wire from the (+) terminal to the plug and label that spade side with a (+). Make sure the wires are not shorted. Put a good line of hot glue on the front and back of the soldered leads to make them waterproof. Now put about a 1.5" piece of the 3/4" heatshrink over the assembly and heat it up good. The hot glue will start to reflow and you'll have a well-sealed and secure converter. Having the clear heatshrink will let you see it reflowing so you'll know when the process is complete and the heatshrink can't shrink anymore.

I estimate you have spent $0.35 for the rectifier, about $0.15 for the piece of heatshrink, and the hot glue and plug ends are marginal or free. This is the primary cost of the conversion ($0.50) and you only need one pigtail per channel of lights that are being controlled. So, if you have one string of 50 or 20 strings of 60, you can amortize this cost across them.

The next step is to orient yourself -- and the light strings. When you are done with this conversion, the light strings will only work when plugged in one direction. This is why we labeled the (+) coming out of the bridge rectifier pigtail. Now, plug in your first set of LEDs and note the direction that causes the first section of lights (those closest to the male plug) to light. Now that you know which way to plug in the string, Label the male plug on the LED string with a (+) as well so you'll know which way to plug it in from now on.

If the string has more than one circuit, those lights did not light in this orientation. Examine the string and you'll notice that it goes from three wires to two wires and back to three wires. The section that has only two wires is between two circuits of lights -- one that lights and one that doesn't. You'll want to cut the string at this point (unplug the string first!!!).

Slip two pieces of 1/8" heatshrink on each wire, swap the wires, resolder them, and seal the connections with the heatshrink. I find that if I put the heat shrink on the wire that goes past the socket (one goes to the adjoining light and the other continues past it) on each side of the cut and then align them such that each connection only has one wire with the heatshrink, that it works. That's my system anyways so I don't have to figure out the orientation each time. And it also gives room to slide the heatshrink away from the solder joint while I solder and heat up the wire.

Once reassembled, plug the set back in and now this second circuit should be lit. If there are more than two circuits, you'll need to repeat this process down the string.

Once done with the string, you'll want to label the female end with a (+) as well so you know how to daisy-chain strings. You'll have to complete two strings first so you can have one string to keep as a daisy-chained reference. Then plug this string into the first and mark the (+) on the first string's end plug.

Since 1/8" heatshrink is fairly inexpensive, I'm not worried about the cost. But you can add 4 cents if you want a complete figure :)

That's it really. Everything else -- icicle lights and net lights -- are a variation of this process.

You'll be able to use the strings without the pigtails as well -- they will just now only light on one half of the AC waveform instead of balancing it.

Now the disclaimers.

Since you haven't changed anything else on the string, you are lighting the lights up twice as often than before. This mean that the string is consuming twice as much power as before. And, the current-limiting resistors are dissipating twice as much power as before. And the LED's themselves are not changing the amount of peak current they consumed before, but are consuming it twice as often so their heat dissipation is also twice as much.

What does this mean?

Well, the most obvious issue is the resistor's heat dissipation. If they got noticably warm before the conversion, they will be really warm now. But they were designed to run 100% of the time. And the resistors fail from heat, not from current. So, if you can keep them within their operating range, they'll be fine. With an animated show, this is usually not a problem since most channels are not at 100% brightness 100% of the time. So the resistor has periods to heat up and cool down. With the big resistors blobs, they can go for many minutes at 100% before getting appreciably warm. And most resistors will work up to 200 degrees Celsius before they start entering the range of failure. The plastic will probably melt before the resistor fails. In my testing, I never saw signs that the resistors were getting close to exceeding their maximum operating temperatures.

If you have a string that needs to run 100% of the time, but is on a dimmer, then run it at 50% brightness. Since you are doubling the amount of time it is on, it will be back to the same as the unmodified string at 100% brightness, but without the flicker and extra heat dissipation.

As for the LED's running twice as much, we should expect some shortening of longevity. However, since LED's are rated for 25,000 or more hours (that's three straight years), even if they lasted 2,500 hours, most of us wouldn't notice. I had 21,000 lights converted and running this way last year in my show and didn't see but maybe a half-dozen lights fail and they could have failed for any number of reasons other than the power output.

But I don't think the lifespan would be this drastically reduced. Again, we haven't changed the peak current through the LED -- which is usually what causes the light to fail prematurely -- just the "on" period and heat dissipation -- fairly minimal for LED's and these LED's are operating in temperatures usually well below their absolute maximums in our displays.

An actual benefit, is that the string is never operating in reverse bias conditions -- look it up if you are not familiar with the term. So, any breakdown of the LED from the reverse biasing (when they are "off") is prevented. So, you could potentially end up with better longevity as a result.

And lastly, don't forget to double your power budget numbers -- if power is a concern. Those "90% less power" strings are now "80% less power" :)

Last year, I modified 21,000 walmart LED's. This year, I've modified 9,600 Ace LED's and have another 9,600 to go. So far, they have taken the modification wonderfully. All of them dim perfectly on LOR PC controllers without the need for snubbers. I have some elements that run 600 lights per rectifier.

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Would love to see a video of you doing this... I'm more of a visual person, but definitely appreciate all the information you have shared. It will definitely come in handy!

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First off Thanks for taking the time to share the info.

My Question:

You said up to 600 lights per rectifier? The rectified first string of lets say 60 lights, and then you just daisy chain the rest ( 9 more strings of 60)?

Do you modify the following strings? Cut at the two wire point and flip with no rectifier?

Thanks..

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First off Thanks for taking the time to share the info.

My Question:

You said up to 600 lights per rectifier? The rectified first string of lets say 60 lights, and then you just daisy chain the rest ( 9 more strings of 60)?

Do you modify the following strings? Cut at the two wire point and flip with no rectifier?

Thanks..

Yup. Once the rectifier pigtail is in place, then anything connected to it will get the rectified AC waveform.

So:

AC outlet -> rectifier pigtail -> string 1 -> string 2 -> string 3 -> ... -> string n, where n is only limited by the current pulled per set and the current rating of the bridge rectifier.

You could put the rectifier on the first string, but personally I like keeping the pigtails and strings separate.

And each string will need the wire swap regardless if the string has the rectifier or not. Although it's always a good idea to test the string first. I've had a small percentage of strings where the manufacturer got one circuit backwards -- so they were already on the same orientation and didn't need the mod. I have modified a string, plugged it in, and realized I had to switch it back to the way it was :P Or, in the case of some of the 100-count strings that have four circuits, circuits 1 and 3 are usually together and 2 and 4 are together, but I've had 1, 2, and 3 together and 4 was different for example.

I'll try to get some pictures of the setup online for people to see.

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You are increasing current through the string by doing this (weather the LEDs can handle it or depends on how its made - did they leave any allowance or are the LEDs already driven to maximum specs at half-wave)

If you run the set as steady-on you do risk turning it into DLEDs (thats Dead Light Emitting Diodes...LOL). If its being flashed (so just on for short periods) it may just well be fine (particularly if its outside in the cold) Heat is ofcouse the #1 issue (not so much for the resistors, but for the LEDs).

Personally I recommend that if you do this (esp for indoor use and/or contentious on) Add a resistor to the string... Find out what the resistance is for the resistor(s) in a section and: Ideally add another of the same rating, but at least add one thats half of the existing. (resistors are cheap LOL)

So lets say existing resistor(s) in one section are 2K total.

Ideally add another 2K (will give some overhead, but might _very slightly_ dim the set, not noticeably tho)

At minimum add another 1K (LEDs may still be overdriven, they'll be no loss of brightness, but at least it'll be better protected)

If you measure most half-wave lights with an average multimeter, you'll probably see 10ma per section - remove a 'bulb' from all sections except one (so they go off) while testing. You want to see around the same current when running full-wave.

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Jay, don't get RMS current readings from the meter confused with peak current.

Since we're not changing the maximum voltage applied across the string -- in fact, we're dropping it about a volt with the bridge :) -- we're not changing the maximum current. However, the current profile from one half of the AC sinewave is happening twice in the same period that it was previously only occuring once. Summing the area under the curve and dividing by the period, the meter will show the RMS current as having doubled. And, consequently, the power has doubled.

Because the LED's are being exposed to no additional current, but are exposed to additional heat dissipation, there will be some shorter life as they are being operated at an elevated temperature internally but not as bad as LED's that were overdriven by 2x the peak current. But we're talking about 20mA LED's and not 1-watters. So, their junction temperature is going to be fairly minimal anyways.

Now adding the resistors will allow you to bring the power back down. And I agree, if being used indoors where the ambient temperature is higher than most animated outdoor displays, and the lights are being left on for more than about 5 minutes at a time, you're light string can get darn toasty on those resistors and you should probably cut the power back. If it is outdoors in the cold and running sporadically, then the resistors will probably not get any warmer than their original design for ambient environment running 24/7.

I looked up some T-1 LED specs and most have a power dissipation limit of 100 to 120mW at 25'C. So, if you take a string of 60 lights, and the power consumption is under 6 watts, then you should be fine considering a lot of power is being lost in the resistor -- i.e. not all 6 watts is being lost in the diodes. My sets are averaging about 6 watts for the green, blue, and white, so I'm happy.

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I'm just wanting to add a note of caution - mainly for steady-on ... I did kill a set of LEDs once by running it full-wave (overnight in a warm room is all it took LOL)

I know a multimeter isn't going to show things quite right since its looking for true DC & its being given a DC-waveform (it'll show less than actual current). Half-wave shows around 10ma, full-wave shows 18-19ma (if those were true readings it'd be safe, but since they're less...)

I haven't yet modified any sets in this way, but I'm thinking of ebay'ing some resistors & trying a few sets this year. They'd be inside & very likely steady-on (I can pretty clearly see the half-wave flicker & while I can live with it perfectly fine, full-wave is better :) ). For my outside lights I don't really care if they're half-wave at this point (this is also the first year I'm gonna try a larger number of LEDs in the main display though)

I've 'converted' sets of normal mini's to LED in past years & made them for full-wave. This year I converted some multicolor sets to single color...but left them as half-wave, don't know why I didn't think to set them up for full-wave while modifying :( .

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Thanks BC for detailing your process and especially for the pictures. As soon as I saw the first one it totally crystallized how you are doing it. Just out of curiosity, what does the "W" stand for that you also marked on the plug? Is it Walmart, as in, I purchased these from Walmart?

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Thanks for posting this BrightChristmas. My decorating toolbox just got a little fuller.

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Thanks BC for detailing your process and especially for the pictures. As soon as I saw the first one it totally crystallized how you are doing it. Just out of curiosity, what does the "W" stand for that you also marked on the plug? Is it Walmart, as in, I purchased these from Walmart?

W = "White"

When I zip tie White, Red, Green, and Blue into super strings, labeling the plugs ends with W, R, G, and B makes it easy to hook them up.

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Is this safe to do? I just did all the soldering my radio shack didnt have a 4amp 600 volt so I used a 4amp 400 volt... I haven't hooked it up yet where I want it but did test it with a set of blue leds.. I mainly want to convert my roof to full wave because I'm having poor dimming effects (which I'm not sure if this will fix it or not) I have 3750 white leds on the roof, which aer all connected to one outlet, which maybe another problem with dimming? Any input? I really dont want to have to go on the roof and swap 38 sets of lights wires around to go full wave but if it will be benefical I won't mind...

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Well I got half of my answer I went out and hooked receitifer up and fired up the hardware utility, half the lights faded beautifully.. Guess I'll be on the roof Thursday when I'm off work swapping wires around. As long as the 400volt instead of 600volt isn't gonna mess anything up...

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For those of you doing this to the GE 100 ct strands.. you will have to splice it twice per strand.. the strands are separated in to 3 sections.

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400V will be fine. You could safely go as low as about 250V in the U.S where the maximum reverse voltage is 180V with typical 120VAC mains and adding some level of margin.

If you are having issues with dimming, then this conversion may or may not help, I expect. It could help in that you are putting a rectifier between the dimmer and the light string so you prevent having voltages being pushed back through to the dimmer. You are also "doubling" the load on the dimmer. Sounds like it is helping in your extreme case, so extra points for the conversion!

I found that all of the wal-mart 60-count strands from last year had two circuits. The Ace "mini" strands for this year, 100-count, have four circuits for green, blue, and white; and two circuits for red. The Ace 50-count strings have half as many circuits as the 100-count. Ace is using everstar this year to make their LED's (same as Wal-Mart). There is usually one resistor blob or dummy socket per circuit, so that's another sanity check.

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I thought I'd mentioned this...but must've been on another site or thread LOL

No need to cut/splice wires between sections! : On the 2nd half of the set -- just pop the wires out of the first & last socket, untwist the string of sockets from the set, then turn it around so the last socket is now the first. Then simply re-twist the sockets back onto the set & reconnect wires. Now both halfs of set will be wired in-phase like the shoulda been to begin with (if its a set with 3 sections, do this to the middle one)

I've done this with plenty of sets :) not because I'm converting to full-wave, but because they work better with some flasher controls. (even though I can clearly see the half-wave flicker, at this point I don't feel like getting a bunch of resistors & splicing them into sets for conversion to full-wave)

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Quick question... First post here.

I am setting up a static light display featuring several strands of LEDs...

I am considering building a couple of these pig-tails (or as many as necessary).

I have a few different circuits that are currently wired in series:

60 CT LED -> 60 CT LED - > 60 CT LED -> 70 CT LED - 70 CT LED.....etc.

If I put the pigtail at the start of that 5 string circuit (320 LEDS), is that o.k.? How many strings can one support?

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Most 60 & 70 LED sets are rated at .04amps (4.8watts), so thats .2a total for 5 sets, as long as the diode-bridges you use are rated for at least .4a you'll be fine. If you used the 4a bridge linked in the 1st post you could easily run 2a (with a heatsink on it) .... that'd be something like 50 sets :)

oh and add resistors to those sets so u don't end up with D-LEDs (thats Dead LEDS) :o

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Welcome!

Yes. It depends on the size of the bridge rectifier. If you use the 4A rectifier, you can plug up to 4*120V = 480 watts of lights. For margin, should probably de-rate to about 300 watts. LED strings have 3A fuses in them -- that's why I selected 4A. So, you're more likely to blow the fuse before overloading the rectifier. And I believe the end-to-end limit is typically given as 210 watts.

So, if you assume a typical string of 60 LEDs is two circuits, each pulling 0.02A and you are doubling it with this mod, now each string is pulling 0.08A = 9.6 watts. You'll be able to plug in 22 or so strings to meet the end-to-end limit, about 31 to meet our conservative number, 31 to meet the fuse limit, and 50 to reach the rectifier limit.

In other words, it will be difficult to overload the rectifier. Especially if you use the 3A-fused "mini light" plugs for the ends.

And will the rectifiers get warm? Well, at 3 amps, they are putting out about 3 amps * 1.4 volts (2x diode drops) = 4.2 watts. Warm, but less heat than a C7. You'll probably want to watch to see if the hot glue is getting hot enough to re-melt since that would potentially let water get in there.

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Thank you both for the prompt reply! This sounds great. Seems like it's not going to be a problem. I'm trying to understand where to land the resistor. One resistor per set, or individual strand? Do I measure the resistance of the set or individual strands and match that? Many thanks in advance for the help!

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I overpaid for a rectifier today at Radio shack (2.69) for testing purposes. I had 2 strings to "play with" One 100ct multi dome leds and one set of Martha stewart red 60ct c3's. On the 100 ct. I saw a noticeable difference in the brightness. Very nice. I did not swap the two wires for the last 50 bulbs yet as this will be a post light show project for me before I put everything away.

The M.S. light set however did not want to cooperate. I plugged it in both ways and all I get is a very dim set of lights. There are no resistor blobs on this set, just large plugs on both ends. Also there are 4 wires on the set going into 3 at the center point. Can anything be done with this set that you know of?

Funny thing is the M.S. c3 60 ct. light sets which I got at 75% off last year, are the sets which give my show the most problems. They do not fade at all... Thanks,

Steve

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@InDashMP3:

With the resistor - one for each "section" of the set. Measure the resistance of only the existing resistor in one section (if there's more than one in a section, you simply add all together)

@SteveMaris Those M.S. sets have capacitors/diodes/resistors in the oversized plugs (this makes them flicker free so there's no need to convert full-wave)..its because of the capacitors they can't be dimmed/faded.

If you look along the set it will alternate between 3 & 4 wires...basically its designed so every 2 bulbs are in parallel & the set is 30 of those 'parallel/pairs' in series.

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