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Thread: Are there higher voltage pixels?

  1. #11
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    Default Re: Are there higher voltage pixels?

    Just when I think I understand voltage and pixels, I read this thread. <Sigh> Now I'm back to the 5v vs. 12v debate right before the pre-sales start.

  2. #12
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    Default Re: Are there higher voltage pixels?

    Quote Originally Posted by L1011 View Post
    Just when I think I understand voltage and pixels, I read this thread. <Sigh> Now I'm back to the 5v vs. 12v debate right before the pre-sales start.
    The only real debate here is money vs. build time. 12V are more expensive and require more power supplies for the same prop, but they are easier to build with less power injection. 5V will save you money but require more injection points. Both avenues can be 'cheated' a bit by reducing max brightness. Everything else is just us engineers making noise about good design practices.

    So the only question to consider is do you want to save a little bit of money but do more work wiring or vise-versa.
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  3. #13
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    Default Re: Are there higher voltage pixels?

    Quote Originally Posted by plasmadrive View Post
    So true but I think you meant higher current not "higher wattage"... no? He said the 12v was 1/2 as bright as the 5v.. which would be backward from power. Not sure why he said it that way...

    I got my power specs off of Ray's pages... for what those are worth sometimes.. :-)
    Anyway, unless I have tested them myself or have better data sources, I try to keep my comments a bit generic ("assume", "I doubt", "not sure".... things like that) because I don't want to start posting something as fact that I can't back up.. I was unable to find a luminosity spec so can't really compare brightness... hence the vagueness on my part.
    FLux ix a function of forward current.


    It's close to linear so if we reduce forward current of the LED we reduce flux the same percentage. But like you said the pixel consumer more power at 12V, 0.54 Watts compared to 0.3 watts. So a 12V pixel consumes nearly twice the power for a 75% brightness of a 5V pixel.

    If HolidayCoro's specs are to be believed.
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  4. #14
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    Default Re: Are there higher voltage pixels?

    The interesting thing I've noticed with pixels, 5v or 12v is that voltage drop over a length wire impacts the amount of current the pixels use. As an example I had a long 5v run 16 GA wire to my mini trees and the voltage dropped below 4v. The pixels worked fine. Were they a little dimmer, probably. But measuring the current used was lower and at night I would have been hard pressed to tell the difference. I was running them at 80 %

  5. #15
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    Default Re: Are there higher voltage pixels?

    Because of voltage drop, should I insist on 18GA wire for 5V pixels? (Sorry for the noob question)

  6. #16
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    Default Re: Are there higher voltage pixels?

    I've always been suspect of the statement that 12v isn't as bright as 5v. I understand that the whole node draws more power (watts) in 12v than 5v, but isn't the led itself driven exactly the same? I haven't really dissected one to verify, but I would think that there's some component in the 12v node that drops the voltage from 12v to 5v. It would be that component that uses the extra power and also accounts for the extra cost. But I don't see how this relates to the power and brightness or the led itself.
    Also that not all pixels are 1 led per pixel. There's several pixels wth multiple leds per pixel and in those cases the extra bolts are spread across the grouping of leds so the current (and brightness) remains the same and the voltage is divided evenly across the series chain. So instead of disapating that extra energy as heat, it's using the voltage to produce useful light.


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  7. #17
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    Default Re: Are there higher voltage pixels?

    The salient points of the whole 5v vs. 12V discussion are thus:

    1. The WS2811 chip (and others like it) driving these pixels provides a constant-current supply to drive the LED’s, but it does not do any sort of buck conversion, which means the electrical characteristics are defined by current in = current out, NOT power in = power out. In other words, the same amount of current is required to drive the LEDs regardless of the voltage being supplied.

    2. To drive a string of 100 pixels full white (20ma per channel x 3 channels = 60ma) at 5V requires a power supply that can deliver 60ma x 5V x 100 = 30 watts.

    3. To drive a string of 100 pixels full white (20ma per channel x 3 channels = 60ma) at 12V requires a power supply that can deliver 60ma x 12V x 100 = 72 watts.

    4. In the 5V case, each pixel is consuming .3 watts, and in the 12V case each pixel is consuming .72 watts. They are producing the exact same amount of light, so the entire .42 watts of extra power that the 12V pixel consumes is wasted as extra heat generated at the pixel node.

    5. To compensate for the dramatic increase in power necessary to drive the pixels at 12V, some manufacturers will lower the per-channel drive current to 15ma or even 10ma. Setting the drive current to 10ma for our 12V string example (full white- 10ma per channel x 3 channels = 30ma) means that we only need a power supply to deliver 30ma x 12V x 100 = 36 watts. The idea here is is that cutting the drive current in half results in a very minimal decrease in perceived brightness, due to the logarithmic nature of our eye sensitivity.

    6. A 12V-driven pixel is not inherently brighter or dimmer than a 5V-driven pixel, it is only if the manufacturer chooses to lower the drive current of the 12V pixel that it might appear to be slightly dimmer. The only way to know beforehand is to see the manufacturer build specs.

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  9. #18
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    Default Re: Are there higher voltage pixels?

    rhildinger, THANK YOU for the excellent explanation! I really appreciate it!

  10. #19
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    Default Re: Are there higher voltage pixels?

    Quote Originally Posted by plasmadrive View Post
    So true but I think you meant higher current not "higher wattage"... no? He said the 12v was 1/2 as bright as the 5v.. which would be backward from power. Not sure why he said it that way...
    I was repeating/questioning madsci1016's statement on the half as bright.

  11. #20
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    Default Re: Are there higher voltage pixels?

    Quote Originally Posted by rhildinger View Post
    The salient points of the whole 5v vs. 12V discussion are thus:

    1. The WS2811 chip (and others like it) driving these pixels provides a constant-current supply to drive the LED’s, but it does not do any sort of buck conversion, which means the electrical characteristics are defined by current in = current out, NOT power in = power out. In other words, the same amount of current is required to drive the LEDs regardless of the voltage being supplied.

    2. To drive a string of 100 pixels full white (20ma per channel x 3 channels = 60ma) at 5V requires a power supply that can deliver 60ma x 5V x 100 = 30 watts.

    3. To drive a string of 100 pixels full white (20ma per channel x 3 channels = 60ma) at 12V requires a power supply that can deliver 60ma x 12V x 100 = 72 watts.

    4. In the 5V case, each pixel is consuming .3 watts, and in the 12V case each pixel is consuming .72 watts. They are producing the exact same amount of light, so the entire .42 watts of extra power that the 12V pixel consumes is wasted as extra heat generated at the pixel node.

    5. To compensate for the dramatic increase in power necessary to drive the pixels at 12V, some manufacturers will lower the per-channel drive current to 15ma or even 10ma. Setting the drive current to 10ma for our 12V string example (full white- 10ma per channel x 3 channels = 30ma) means that we only need a power supply to deliver 30ma x 12V x 100 = 36 watts. The idea here is is that cutting the drive current in half results in a very minimal decrease in perceived brightness, due to the logarithmic nature of our eye sensitivity.

    6. A 12V-driven pixel is not inherently brighter or dimmer than a 5V-driven pixel, it is only if the manufacturer chooses to lower the drive current of the 12V pixel that it might appear to be slightly dimmer. The only way to know beforehand is to see the manufacturer build specs.
    This is very true. Ray specs the 12v at 66ma per pixel. I was unaware that HC drops his to 45ma. I therefore assume Rays are equal brightness for 12v and 5v. Again, was not aware of HC's scheme... that is why I use vague terms given so many variables.

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