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szyhxc
User Rank
Iron
Re: Half-wave vs Full-wave
szyhxc   4/30/2013 6:23:15 PM
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Don't talk to me about heat in Michigan around Christmas.  I'll take all I can get.

3drob
User Rank
Platinum
Re: One warning
3drob   4/30/2013 6:12:27 PM
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One quick note about refresh rates.  Commercial movies do run at 24 frames per second, but their duty cycle is very high, so the "flicker" is less noticable.  However, the larger the screen (peripheral vision "sees" flicker better) and brighter the movie is, the more noticable it becomes.  Flicker doesn't bother me much (although I do notice it), but I find IMAX movies frustrating because I really WANT to enjoy them, but the flicker is just too much.

LED Christmas suffer a double whammy because not only do they have a 60 Hz flash rate, but the duty cycle is awful;  for two reasons.  The first is, as noted in the post, the BEST duty cycle to expect is 50%.  The second is:  you don't come anywhere near 50% because the LED's don't turn on until the very peak of the cycle.  You may be lucky if you get 10-20% duty cycle.

I likc the idea of a high frequency, current regulated, square wave inverter.  Perhaps in time for the next holiday?

szyhxc
User Rank
Iron
Re: Question
szyhxc   4/30/2013 6:11:48 PM
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I don't know but I would bet that the FWBR is already included in commercial light bulb replacments.  It would be needed to get the desired high light level and helps explain the high cost.

szyhxc
User Rank
Iron
Re: Product improvement
szyhxc   4/30/2013 6:08:48 PM
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It was because all my good strings are put away until next Christmas and this one was still out waiting for repair.  Thanks for noticing.

szyhxc
User Rank
Iron
Re: Product improvement
szyhxc   4/30/2013 6:05:13 PM
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I have encountered strings of outdoor LED lights made by Phillips that are wired in such a way that the first two LEDs at each end form the bridge rectifier.  I rewored these to elimiate this feature which had thess four LEDs still flickering and dimmer than the rest.

78RPM
User Rank
Gold
Re: Safety
78RPM   4/30/2013 6:01:22 PM
NO RATINGS
Marty48, I agree that this should be housed in a waterproof box. I also recommend strain relief on the wires.  One good pull on the device as presented could put bare wires on your ladder or wet bushes.  And as someone mentioned, it should have a warning label that it is for LEDs only.

alzie
User Rank
Silver
Led string bridge rectifier wont work in all cases
alzie   4/30/2013 3:31:28 PM
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I have some 50 led strings that are actually split into 2 strings of 25,

each operated on alternate half waves.

A single polarity voltage will only light half of the string.

What we need to cover this is a pwr supply that would still produce AC

at a high enough freq that the flicker is not sensed, a few 100 Hz.

Another project for the pile!

 

KenL
User Rank
Gold
Re: Cheap vs commercial LEDs / 25Hz power
KenL   4/30/2013 1:12:48 PM
NO RATINGS
I believe it's because the tail-lights are lit with 100% duty cycle for the higher brightness stop-light mode.  In tail-light mode, they run on a low duty cycle pulse to reduce the brightness.  It's at a low enough frequency that the strobe effect can be seen.  But probably higher than 120Hz.

I recall reading that when the first Tesla hydro plants were built at Niagra Falls, they produced 25Hz.  When the river bank eroded, the power plant on the US side fell into the river.  The new plant was built for 60Hz.

Last I heard, the Canadian side was still running at 25Hz, but it's used only to supply power to electric arc furnaces for aluminum refining.

  

 

D. Sherman
User Rank
Silver
Re: One warning
D. Sherman   4/30/2013 12:47:11 PM
NO RATINGS
Good historical points. There was also 16-2/3 Hz power at one time. The low frequencies were generally used for streetcars. I dont know if this was because they wanted slow-speed induction motors for direct drive, or they just wanted to use thicker iron. Our current 60 Hz grid is largely a relic of poor quality transformer iron in the early days. There was serious discussion in the 1950s of raising the grid frequency to 400 Hz, since modern iron could handle that with no great loss, and it would of course make all the transformers and motors MUCH smaller and cheaper, but replacing the installed equipment would be prohibitively expensive. It's interesting that we're gradually returning to that with the proliferation of VFD motor drives and universal switching power suppllies. It may be that at some point in the future we really will either convert the grid to a higher frequency or to DC, with solid-state converters at the point of service to handle legacy equipment.

Buster_Cherry
User Rank
Iron
Re: Cheap vs commercial LEDs
Buster_Cherry   4/30/2013 12:19:53 PM
NO RATINGS
@KenL, Why would automotive led's flicker?

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