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Rules for power injecting


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Actually both. Too mny pixels and you will pull too much power. Too long of a distance and too much voltage drop.

Edited by Mr. P
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Make sure you blow the dust off your Kill-A-Watt meter.  I had gotten used to the negligible power requirements of single-color LEDs and figured I might never need to use the Kill-A-Watt ever again.  I've gotta admit that I was either shocked or amazed (probably both) the first time(s) I saw how much power both dumb and smart pixels require.

Voltage drop is a much greater issue with 5v pixels as compared to 12v.  IMO, not having to worry very much about injecting power makes any added cost of 12v well worth it.  12v pixels also seem to be more forgiving than 5v when you screw things up.

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Voltage drop and power injection is a pain.  I jumped all in last year going from close to 100k incans to all dumb rgb and pixels.  It was a big jump but was worth it.  I'm all 12 volt but with a big yard and large display the power injection and psu's add up.  18ga wire and 12v on the pixels help but its still a lot...  I would recommend turning the intensity down to help with voltage drop and power consumption.  Like George said 12v is much easier but is less efficient.  Electric bill still went way up.  Was still pushing close to 100 amps at 120v with everything 100% intensity on all white with all RGB last year

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" is it based on # of pixels or distance? "  it is neither.  the number of pixels is used as a yard stick (meter stick if there is one outside the US).

Power injection is a result of voltage drop due to resistance.    Each pixel creates resistance, each inch (cm) of wire creates resistance, each connector creates resistance.  All these add up resulting in insufficient voltage to properly power the pixels and chip in the pixels.  You can reduce resistance by larger gauge wire, shorter power to pixel distance, less pixels or by adding additional power along the line (power injection). Know how much power your pixels are going to use and the limit of your power supply.

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I would suggest on power runs to increase your wire size from your 12v power supply to the first pixel on your prop or locate multiple power supplies close to your props.

Also, use an on-line voltage drop calculator and do the math.

Test lights wired as you are planning to wire in yard/house prior to assembling in your display.

 

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One general rule I learned early on is that a strip or string of lights (either smart or dumb) should not have to carry any more current than required for itself. Since most strings of individual nodes are sold in strings of 50 nodes, and strips are typically 5M long, I will make that assumption for the rest of this. What that means is that if you will have more than a 5M strip or 50 nodes, you should plan on power injection. Plan your PI based on this rule. Remember that PI can come from either end of a strip or string. So for example, if I was going to have 50 Meters of smart strips tied end to end, and assuming I was going to supply power along with data from the controller (a normal configuration) at the beginning of strip #1, I would need to make sure that the power source from the controller was only powering the first strip. I could then supply power to the junction of strips 2 & 3, and again at the junction of strips 4 & 5, and the junction of strips 6 & 7, and again at the junction of strips 8 & 9 and lastly at either end of strip 10. Many variations of this is possible.

In my yard for my year round landscape lighting, I have two strips that are a total of just under 10M each. They are fed from both ends. I also have two strips (with lots of wire splices between segments) of about 6M each. I observed that the colors were off at the ends, so those have power injection about 2M from the ends. That location was based on where I had conduit which made it convenient. Lastly I have three dumb strips that are 5 or 6 meters long. All three of these are a ring so both ends of each strip are within a few inches of each other. Although not really needed (except maybe the one 6M strip), I am feeding power to both ends since it was so easy.

Sent from my Droid Turbo via Tapatalk, so blame any typos or spelling errors on Android

Edited by k6ccc
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10 hours ago, jerrymac said:

" is it based on # of pixels or distance? "  it is neither.  the number of pixels is used as a yard stick (meter stick if there is one outside the US).

Power injection is a result of voltage drop due to resistance.    Each pixel creates resistance, each inch (cm) of wire creates resistance, each connector creates resistance.  All these add up resulting in insufficient voltage to properly power the pixels and chip in the pixels.  You can reduce resistance by larger gauge wire, shorter power to pixel distance, less pixels or by adding additional power along the line (power injection). Know how much power your pixels are going to use and the limit of your power supply.

Oh man.. I am sorry Jerrymac but I can't resist...

The requirement for power injection is a result of voltage drop due to resistance.... 

Pixels do not create resistance.  They do draw current and the resulting voltage drop is due to either or both of the wire and/or printed circuit board trace resistance. 

Each "connector" does create a resistance, but should be negligible unless it is a poor connector or in bad shape.  Wire size is important as well as protection for the wire.  Fuses are your friends...

For the newbies: 

Talking about Dumb pixels, the lower voltage will drop the brightness of the RGB LEDs and usually not equally for R,G and B.  That is why you see a color temperature shift (when combining colors) as the voltage drops alone the pixel string or strip.

Talking about Smart pixels, some of the processor chips have constant current drivers which try to maintain a constant current to each LED regardless of the voltage that is available.  However, they can't supply what isn't there, so if the voltage drops

below the regulation threshold of the driver, it will just turn on as hard as possible.  Because the LEDs are not equally efficient, the combined color of the combination of the RGB (when combining colors) will shift when there is no more headroom to regulate with.  In the case of my strips they shift to the yellow side from white as voltage drops along the strips. 

Some drivers are not constant current and are just PWM with resistors for current limiting.  Those fall somewhere between the above two but favor the Dumb strip curve...

I hope you should get the idea.  Power injection is important if you plan on using longer strips or strings.  Personally I like DC-DC converters and using 24vdc supplies, but it is up to the preference of those using the pixels. 

 

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Plasmadrive is of course correct.  I was attempting to simplify.  Point is based on a number of issues you may or may not have to overcome voltage drop for success.  The more of these issues you encounter the more likely you will need to apply additional voltage to overcome them.  Most basic measure is 50 pixels or single 5 meter ribbon without injection. (this is a simplification but seems to work generally well). 

 

 

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Somebody posted a link to a 4 pin extension cable that was about a foot or two and had wires tapped off the center for power injection. Can someone point me to those? I can't for the life of me find them now. 

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 Be aware there are a few different style connectors (and they are NOT interchangeable). Although most are the same size, the centering devices are very differerent.  Some have a flat spot on the inner plug, some have a molded pin (and some of them are different sized).

Just be sure the type you have is the SAME as the type you are purchasing.

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