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PHJ426
01-13-2008, 12:04 AM
What is the difference with the Full and Half wave LED's

I can make an assumption about the replacement lamps for current incadescent strings are half wave and will blink more, am I correct?

And the populated new strings with the LED's installed that are Full Wave have a rectifier in them to invert the negative portion of the sine wave for the power?

So Am I right in thinking like this?

Also why can a Full Wave LED be dimmed and a Half Wave cannot?

Thanks

Macrosill
01-13-2008, 08:01 AM
You are correct in your understanding of the FW vs HW leds. The difference on stationary bulbs is negligible imho. When the leds start to move or blow in the wind is when you can really see a difference. I have not heard that HW leds can not be dimmed. As a matter of fact I have dimmed both.

pixeldigger
01-13-2008, 12:15 PM
You are correct in your understanding of the FW vs HW leds. The difference on stationary bulbs is negligible imho. When the leds start to move or blow in the wind is when you can really see a difference. I have not heard that HW leds can not be dimmed. As a matter of fact I have dimmed both.

I use thousands of ForeverBright brand 1/2 wave LEDs. Up close, when they are wiggling, I can see a "shimmer" in the yard I can tell no difference.
They dim just as good as any other bulbs I have.

mrpackethead
01-14-2008, 05:50 AM
[quote=Macrosill]You are correct in your understanding of the FW vs HW leds. The difference on stationary bulbs is negligible imho. When the leds start to move or blow in the wind is when you can really see a difference. I have not heard that HW leds can not be dimmed. As a matter of fact I have dimmed both.

HW LED Strings are effectiively being driven by a PWM type current.. its on for 50% of the time, and off for 50% of the time. No surprizes there. The frequency of the 'modulation' is the line frequency of the mains.. Ie 50 or 60Hertz.

At that frequency most people will detect *some* flickering.. some won't see it at all, and some will see lots.. Its very dependant on the individual. Most people can't detect flickering at frequencys over 80Hz. I have heard that there is a technique involving peripheral vision where it is possible to see flickering at 200Hz, though have not experienced my self. On my LED dimming system, i am modulating the leds using 100Hz ( very close to ), and it proves satisfactory.

There is no technical reason why you can't dim Half wave or full wave retifiyed systems.. both will work..

However, LEDS don't have the same characterics as filaments.. A bulb has some thermal ineteria in it, so keeps glowing for some time after the current stops.. ( light output is a function of the temperture of the filament ), so for a moment in time after you switch it off, it keeps glowing.. This effect tends to 'even' out the the dimming and you get a resonably constant light output even at 50Hz.. With LEDS however, they turn on and off very quickly.. ( a high slew rate ).. and they dont' even out the output.. Your brain does the evening out in the way in which it perceives it.

Dimming led strings works, and you'll get way with the low cost, low output leds that are found on $5.99 stings.. If that works for you GREAT!! go for it..

If you want to start using high power LEDS ( ones that draw > 100mA ) then you really need to start treating them with a little more respect, or they will suffer significant drop off in output and a change in colour..

PHJ426
01-14-2008, 07:02 AM
How about running the higher power LEDs with a regulated DC power supply?

I know that adds equipment to the display but shouldnt that increase the life and output of the strings?

If you were to design a controller/dimmer/relay package from scratch this might be a different approach to utilize with DC instead of AC.

My thoughts for supply voltage are something low around 24VDC nothing too high or you can have a nice DC welder on your hands and DC is harder to break away from than AC so what are the thoughts on this.........

mrpackethead
01-14-2008, 01:56 PM
How about running the higher power LEDs with a regulated DC power supply?

Yes, and that is in fact what is often done. Its not a voltage regulated supply though, its a current regulated supply. It is critical to ensure that you do not exceed the rated current of the LEDs or you will 'cook' them in rapid fashion..

In the simplest case, current regulation is achieved by having a resistor in series with the led(s). This is simple, but often in-efficent, as there is often considerable energy to loose in the resistor ( heat ).. Note: On all teh LED strings i've seen so far that are halfwave/fullwae rectified, this is what they use as well, so this technique is not restricted just to DC.

A more complex design, might use a Switch mode Power supply, with a current sense feedback loop. This in fact is what my RGBW ( Red-Greeen-Blue-White ) highpower driver board employs.

It will run on pretty much anythign between 7 and 70V DC.. You can follow it in the DMX forum in the thread My 2008 Project.

Sloanhaus
12-17-2008, 05:09 AM
What is the difference with the Full and Half wave LED's

I can make an assumption about the replacement lamps for current incadescent strings are half wave and will blink more, am I correct?

And the populated new strings with the LED's installed that are Full Wave have a rectifier in them to invert the negative portion of the sine wave for the power?

So Am I right in thinking like this?

Also why can a Full Wave LED be dimmed and a Half Wave cannot?

Thanks

I am almost positive you can dim the half wave

ErnieHorning
12-17-2008, 08:13 AM
All led’s are dimmable, but not all led’s will dim equally as well with all dimmers that were meant for incandescent lights. Some LED strings have a power supply and wont won’t work as you would expect.

Because they use very little power, sometimes they don’t use the minimum current required for the controller. If it’s right on the edge, they may work sometimes and not at others.

When they don’t work properly, you can usually add a small load such as a single C7 bulb (nightlight) and then they will dim.

bmcgeeny
12-17-2008, 08:25 AM
Well I suppose the day will come but hopefully not in my lifetime. LED talk "if you have this kind and do this and put that unto them and do a high power low voltage or put an extra bulb or this brand works but that one doesn't" Wheeee. I'm confused. but guess what.
I CAN PLUG ANY STRING IN ANYWHERE and they dim, blink and don't flicker no matter how i look at them.
I hope LED's come around fast. That way all the people changeing over will give me their old lights.

Oh, and my elctric bill goes up about $40 for the month or so the lights are up. That's three strings of LED.

Did I mention I'm resistant to change?

TERBObob
12-17-2008, 11:33 AM
Did I mention I'm resistant to change?


LOL ... I see I'm no the only one being stubborn about this .
And FTR - seems I have heard JUST as many ( if not more ) problems with bad bulbs and bad sockets and bad connections as there is with the "oldies , but goodies" lights .

omzig
12-17-2008, 09:06 PM
I'm not a big fan of half-wave strings. I am one of those few people who can see them flicker if I'm within about 10 or 15 feet of them. The flicker is very evident for me and I find it kind of disturbing after being around them for a while.

We had a few HW strings that we used indoors last year that we eventually took down because they seemed to trigger my wife's migraines.

jpb
12-17-2008, 09:20 PM
When I was rebuilding a couple of incandesent strings to take LEDs I just wired a bridge rectifier into the power lead and then used a meter and adjusted the current with resistors until I got the current that I wanted through the LEDs.

By doing this I have changed the part of the AC that would have been reverse polarity to the LEDs to correct polarity and changed the frequency from 50Hz to 100 Hz.

It works fine for me.

Jon

tonypgst
12-17-2008, 09:30 PM
I rebuilt all of my LED strings from CDI this year. Replaced all the rectifiers. Easy enough to do and can apply to any LED string. Can convert half to full as needed.

ukewarrior
12-17-2008, 10:02 PM
Is conversion as simple as wiring in a bridge rectifier?
How are current levels set?

tonypgst
12-17-2008, 10:03 PM
Bridge rectifiers for the full wave conversions, resistors added in series with LEDs to limit current and drop voltage not used by LEDs.

bmcgeeny
12-17-2008, 10:21 PM
I rebuilt all of my LED strings from CDI this year. Replaced all the rectifiers. Easy enough to do and can apply to any LED string. Can convert half to full as needed.

I rebuilt a whole bunch of my mini lights this year too. Put new longer plugs on them and replaced a couple broken bulbs.

No bridge rectifiers needed. No testing of resistors to get the current right. I didn't worry about if I had them set for full wave or double or triple wave.

I just plugged them and they worked.

At $12.00 a box I would expect what I buy to work first time and for a long time.

Oh yeah, to be on the safe side I bought Menards North out of white, green, red, and about 1/2 the stock of blue. Wasn't much left. Fleet farm tommorrow.

stanward
12-27-2008, 09:47 PM
I rebuilt all of my LED strings from CDI this year. Replaced all the rectifiers. Easy enough to do and can apply to any LED string. Can convert half to full as needed.

How are the half-wave LED strings wired? Is there just a resistor in series with the LEDs near the plug?

How did you insert the bridge rectifier?

Stan

tonypgst
12-27-2008, 10:00 PM
My CDI LED strings were full wave, the 2008 strings just didn't take well to fading. Replaced their voltage doubling circuits with straight full wave rectifiers. I haven't yet needed to convert a half way string, but easy to do.

I didn't insert anything inline with the existing circuitry, but I cut off the rectifier blobs and soldered in my own diodes for the rectification and resistors in series with the LEDs to drop any unused voltage. I passed AC through from one end of the string to the other. Half of the FWR at each end of the string.

ukewarrior
12-27-2008, 10:20 PM
So, what's the calculation for the resistors?
What wattage to use?

I'm assuming there's some voltage drop across the resistors, correct?
Is it the drop of 4 or 2 resistors?

tonypgst
12-27-2008, 10:28 PM
Here is a link I use for my LED calculator. Use 167VDC as the battery voltage for FWR of 120VAC. As long as your resistors add up to the suggested resistance and wattage, you can have one, two or more in series with the LEDs. I divided by two and used one on each end of my strings.

http://wolfstone.halloweenhost.com/Lighting/litlec_LEDCalc.html

Elmo2resc
12-31-2008, 01:15 AM
I also have some 2008 CDI strings that were bought during and after the pre-sale. I am not able to return the ones after the presale. I have had a high rate of 2008 lights that have failed. I want to do what you did to the ones I can't send back. How did you determine the diodes to use? I have 100 and 50 bulb strings. Thanks for any help. Jerome