Great half vs full wave explanation - L.E.D.s Read Only. No more posting. - PlanetChristmas! Forums. Read Only. We've moved to http://talk.planetchristmas.com - The Forums of PlanetChristmas have moved to http://talk.PlanetChristmas.com
Here is a link to a great explanation between half and full wave leds. I looked over the stuff they had for sale, pricey in my opinion, better deals on here, but they do explain in great detail about leds. They also have a neat mini and c7 vs led calculator you can use.
Here is a email I sent to a supplier - perhaps somebody else can enlighten me :
I have a question that I have wanted an answer to for sometime . . .
I find it interesting that much fanfare is made of “Full Wave technology” as if it’s something new, when it has been used since the beginning of electronics, but back to the subject at hand.
How can a manufacturer supply a LED string from a full wave bridge and still be able to plug another set of lights on the end without running the AC leads all the way to the end? Or do they actually do this? What I am saying is there is NO way you can common up the output from the full wave bridge to the AC supply to the next set of lights. To do this properly would take 4 wires all the way to the end – the 110v AC for the piggy back plug and the “DC” supply to the furthest led and its return via the individual leds. Any less would short out the four connections as shown on your web image below . . .
Also are any current limiting resistors inserted in series with the leds?
You see, in our country all our outside lights work at low voltage – usually 24v but sometimes 35v. Our mains of 230 is just too dangerous outside, and our most common source of 110v is only available when the telephone is ringing – LOL
Most of the led strings available in this country are rubbish AND overpriced – just normal strings “re-powered” with little thought given to the 3 rules for using leds. I however use 1000’s of LED’s in our display, but they are all hand soldered and feed correctly, and whether I have used half wave or full wave there is NO difference in the light output as I have smoothed the output from my rectifier(s). Notice that I refer to LED strings when they are a string of LED’s as LED’s are the individual “bulbs” that are used in the LED string. Here is a link to one example of our use of LED’s.
I made mention of the “3 rules” for using leds – here they are:
1) Feed them with DC - this can be rectified AC, preferably with a bit of smoothing to reduce flicker but DONT rely on the LEDs to do the rectification (LED STRING MAKERS _ LISTEN UP!!!!!)
2) Always (at least) use a resistor to reduce current flow and drop at least 20% of the available voltage across this resistor. It is okay to feed leds in series (as long as this rule is not broken) but each string must have its own dropping resistor.
3) Keep the max current flow at max expected voltage within the makers max current - usually 20ma. There is not much difference in brightness between a led passing 15ma and one passing 20ma - except that power consumed by led goes from 0.048w to 0.064w! That is heat. And heat is electronics enemy!
If you fail to follow these 3 rules, you will end up with a lot shorter lifetime for your leds. You CAN abuse leds by using them to block AC, passing 30ma thru them, etc like lots of led string makers do, but you will shorten the life - leds will go dark, stop working, etc. You see, if you abuse a normal lamp in a similar way they would blow within 10 seconds . . . . the leds long life in relation to a normal lamp allows it to take abuse for say 10 hours . . .
I find it interesting that I have a led string here imported from the US, and initial investigations have revealed NO rectifier OR limit resistor!?????. And these have come from a reputable manufacturer of Christmas light controllers. I however have no doubt in my mind as to why so many people seem to complain about the longevity or rather the lack of it in regards to LED strings as I read the forums at Planet Christmas ., which incidentally I will also be posting this letter less your name. As you can probably guess I am in the electronics industry, but I am unfamiliar with the exact items that are sold in the US, and hence the reason I look forward to your answers.
____________________ John Muldrock
Hawera - Taranaki''Why would anyone not want to be here'' - Tom Cruise during the TARANAKI filming of the 'last Samurai Movie'
NEW ZEALAND http://www.kamahilights.com
Here is a image of a TEST set of NZ style light string with SOME sections modified to LED - standard 5mm - I think you call that size T13/4. Our typical light sets have multiple sets of 10x 2.4v lamps is series across 24v - these ones have 15x 2.4v lamps across 36v which are ideal for conversion into lots of 7 and 8 leds. These are being fed with 26 volts HALF wave BUT smoothed supply giving me around 33 volts - the load is so light the 24 volts go high!
They have been turned on and off every couple of days for a couple of months - at Easter I noticed one set of the standard lights was out. They were left on and the next night ALL the standard lights were out! No problems with the LED's (as I expected) as they are NOT being abused, and should give their 100,000 hours of operation!
Most of the leds are white but there is one blue. In the standard lights there is one blue lamp also! About 8 lamps down from the apex . . .
____________________ John Muldrock
Hawera - Taranaki''Why would anyone not want to be here'' - Tom Cruise during the TARANAKI filming of the 'last Samurai Movie'
NEW ZEALAND http://www.kamahilights.com
John, on of the half-wave strings I took apart when one half died, did indeed have a wire going from one end to the other that connected to nothing. I didn't check to see if it was Hot or Common. Wiring on strings is not standard. Some have rectifier "blobs" at only one end, some have one at each end. I'm just not willing to dissect working strings.
I did run into one long LED string of C6 bulbs that was polarity sensitive at the end. If I plugged in the next string one way, only half of the string would light. Reverse it and it would light the whole string. I suspect a bad rectifier somewhere, but I'm not taking it apart to find out.
And personally, I have nothing against half-wave. They will theoretically last twice as long since the LEDs only conduct half of the time. And unless your body and/or your head are moving, most people including me don't notice the flicker.
Last edited on Wednesday April 9th, 2008 01:16 am by JonB256
Well, I have had a reply to my letter, and you will all be surprised at the content so you better read it!
Good Morning John (or is it good evening there),
I will look into some of your questions and see if I can get them answered. I am not a electrician nor a engineer so my info is pretty basic. But here is what I understand about the full-wave product. First you are correct there is nothing new about full-wave rectifiers, the use in the LED light string is new! We brought the first container in the country in 2002 (half-wave) and they had not so much as had a patent before that time (I believe it was patented in 2001). The full wave was offered to me last year and we were the only one to import it for distribution use. So to say that the Full-Wave “Technology’ is new (the use in the light string) would be correct.
Your next question I will need to get some help on but these sets do not fault nor have any problem with end to end connections. The wiring guide is that we have two lines going into the rectifier then three lines going out to the end rectifier, which then two lines come out. So you do have the two ends at the beginning coming in to work the positive and negative side of the rectifier. Three wires then come out (which are the positive and negative sides of the rectifier and one neutral, not four as you have stated here). It then ends with a rectifier so as you say the end can be connected to another set or any other electrical appliance. (not recommended to string anything but LED sets end to end) I would ‘think’ they use resistors, you have too to convert the power. I will cc this to my husband who is a commercial electrician and I will run your questions by him and get back to you with a professional answer to your questions.
I have not sold any lights in New Zealand but I have talked with people on different power sources than US 120v and they have had to use a converter of some sort! (could that be the reason for the no change between half and full-wave?). Here the biggest difference between the two technologies is not that they are so much brighter (although they are brighter) it’s the wonderful No flickering that attracts buyers to the full-wave. Some people see the flicker so much that they will not use the LED’s.
As to the set of lights you have purchased from the US, I would have to agree you probably do not have a set that is fully rectified. Only myself and one other (very small) distributor are importing these full-wave light sets into the US for 2008. We buy from (----removed-----)which is the leader of LED lighting distribution in the US since 2003. Prior to that time we imported directly from the inventor of the product line which is Forever Bright, our trade name.
You can use my name and company name I do not have a problem with that. It’s Rene’e Lake, President of Forever LED, LLC. I would like to send you out a set of the full-wave LED light string for you to experiment with (at no cost to you). Please return your shipping information so that I may do that. You have peaked my curiosity as to how they work on your power system. As to posting any of my comments, I would only ask that you follow up with the information that you will be receiving from the electrician.
Thank you for your time, Rene’e
End of letter
____________________ John Muldrock
Hawera - Taranaki''Why would anyone not want to be here'' - Tom Cruise during the TARANAKI filming of the 'last Samurai Movie'
NEW ZEALAND http://www.kamahilights.com
JonB256 wrote: A) John, on of the half-wave strings I took apart when one half died, did indeed have a wire going from one end to the other that connected to nothing. B) I did run into one long LED string of C6 bulbs that was polarity sensitive at the end. If I plugged in the next string one way, only half of the string would light. Reverse it and it would light the whole string. I suspect a bad rectifier somewhere, but I'm not taking it apart to find out.C) And personally, I have nothing against half-wave. They will theoretically last twice as long since the LEDs only conduct half of the time. And unless your body and/or your head are moving, most people including me don't notice the flicker.
Another post by me!
In regards to A) - that is what I would expect - the end plug needs to be feed with pure AC. The power comes in (say the cold) and goes right to the end, and here feeds the far end of the leds AND one side of the end plug. The other (hot wire) comes in and "Y's" to a diode and goes right to the end for the end plug. The diode then feeds the 1st led anode, its cathode goes to the 2nd led anode and so on until it reaches the end.
B) - The only way I can see that this can happen is if half wave AC is being supplied to the end plug, and I suspect this is the case.
c) I could on on and on about this, but in a nutshell half or full wave doesn't matter - its wether they are feed with smooth DC or not, and half wave OR full wave does NOT provide smooth DC - it is full of ripple! Take this example - a diode is like a non return valve - will allow flow in one direction, but not the other. When the current reduces thru it it has to block any flow. Okay, if you take a water non return valve and pass a flow thru it then stop it the flap has to close. Clank! Now do it 50or 60 times a second! Power diodes are build to do this but Light Emitting DIODES are not. They will not give the 100,000 hours when treated this way.
The other thing I don't see is any mention of limiting resistors or "ballast"s. Here is a test I did for a mate who is converting some of our 24v AC lights to LED's - you end up with around 33v when it is has "full wave technolgy" applied and is SMOOTHED. Simple logic would tell you you could supply 10x 3.2v from this supply.
First I test with 8 lamps (my recommendation)
White – Green - Blue
LED current should be kept to around 20 ma and you will see a 370 ohm resistor is in series with the 8 lamps. We can increase the voltage 10% and get a 25% in current - can live with that! Now for the LED string makers way - lets try 10:
Sorry - I tried to put the table in here but it got messed up - attached as a image
Whoo - we increase the volts by 2 volts and get DOUBLE the current - how long do you think these leds would last? And they have a 75 ohm resistor in series with them!
Imagine what it would be like with NO limit resistor - well, thats what the set of LED lights I have from the US is like! I will be taking this set and the ForeverLED lights when they arrive to work and putting on the variac for some tests . . . and shall report back!
BTW I have modified several toys/animated Santa's/Villages, etc, and those manufactures don't seem to get it either - I measured 85ma (400+%) thru one led - you could smell it cooking - they don't care once its out the door! Or is it they are ignorance to what a led is? It is NOT a light bulb - I repeat it is NOT a light bulb. It is a DIODE that happens to emit light, and in doing so has a voltage drop across the junction and the ONLY way to increase that voltage across said junction is to exponentially increase the current
Last edited on Wednesday April 9th, 2008 05:03 am by kamahilights
____________________ John Muldrock
Hawera - Taranaki''Why would anyone not want to be here'' - Tom Cruise during the TARANAKI filming of the 'last Samurai Movie'
NEW ZEALAND http://www.kamahilights.com
I don't think that most people here in the US regard flicker as a big problem for outdoor displays. The higher power-line frequency here makes it less of a problem, and most people (I think) don't find flicker a problem when they are some distance away from the lights. Where it becomes a problem is when you are close up to the lights and you (or the lights) are moving. Then it becomes quite noticeable, at least with the few LED strings (all half-wave) that I own.
As far as current limiting goes, I think that they are relying on the highly non-linear nature of the LEDs. For most of the AC power cycle the voltage is below the threshold of the LEDs, so the current is very low (on the order of micro-amps or less). The LEDs are conducting for only a portion of the cycle (when the voltage is near its peak). The peak current at this point is well above the 20 mA that you were mentioning, but for a short duration and low duty cycle. You should be able to observe this if you have access to equipment (such as an oscilloscope) that shows current waveforms through the LEDs over the course of an AC cycle.
The 30 mA limit that you normally see in the data sheets is for continuous operation, and the manufacturors are relying on the LEDs working with much higher currents for non-continuous operation. I've seem lots of semiconductor datasheets that show other parts rated in this fashion, so it is fairly common. As an engineer I don't really like designing this way, and question whether the LEDs will actually attain the 100,000 hours of operation (or whatever the spec is) this way. I think that they are probably being disenguous when they say 100,000 hours...that is for the LEDs by themselves operated within the manufacturors specs, not in the usual circuit.
of AC and 
of DC from D-Light