Please Explain This

[Charles Belcher]

You read everywhere that the general rule of power injection is that for every 50-60 pixels, you probably need to inject power in a 5v system.


If that is the case, then how do you correctly power up a 4m strip with a 60 pixel/m count? Like this one:


http://www.aliexpress.com/store/product/4m-DC5V-WS2812B-led-pixel-srip-IP68-60pcs-WS2812B-M-with-60pixels-white-PCB-in-silicon/701799_935645023.html


What am I missing here?


Charles

 

[AAH]

Strip is a bit different to pixel nodes. Strip is pretty much designed so that it doesn't need any power injection over its 4m or 5m length. I haven't used any of the high pixel per metre stuff but the 30 led/metre stuff certainly works without injection.
Pixel nodes have a lot more potential for variation in wiring. There is at least 2 different gauges of wire used and the spacing between nodes can be varied from the "standard" 100mm. In a lot of cases you could get more than 50 nodes without needing power injection but best practice is to assume that you will need injection after 50 nodes.

 

[Charles Belcher]

Strip is a bit different to pixel nodes. Strip is pretty much designed so that it doesn't need any power injection over its 4m or 5m length. I haven't used any of the high pixel per metre stuff but the 30 led/metre stuff certainly works without injection.
Pixel nodes have a lot more potential for variation in wiring. There is at least 2 different gauges of wire used and the spacing between nodes can be varied from the "standard" 100mm. In a lot of cases you could get more than 50 nodes without needing power injection but best practice is to assume that you will need injection after 50 nodes.

Alan,


Thanks for the quick reply. I am wanting to use these 2812B led strips, not strings, not nodes for my mega tree. There are no extra resistors nor components of any sort on the strip; just the led with embedded chip, cut point, another led with embedded chip, cut point and so on.


How is this "made to use" accomplished? Am I safe to hang one of these 5V, 60pixel/m strips on my controller without worrying about power injection?


BTW, one of my goals is to have a high density pixel count for animation without having to power inject. With that said, I am limiting the height of my tree to whatever makes this possible.


Charles

 

[AAH]

The 2812 has everything embedded inside the led and there's nothing else to see. I would be ensuring that you are powering the strip with nice heavy cable as close to the strip as possible. By my maths each 4m strip will draw about 7.2A when on fully white. That will take decent cable to ensure there is negligible voltage drop and you will gobble lots of 5V power supplies unless you're having only a few strips on your tree.

 

[Charles Belcher]

The 2812 has everything embedded inside the led and there's nothing else to see. I would be ensuring that you are powering the strip with nice heavy cable as close to the strip as possible. By my maths each 4m strip will draw about 7.2A when on fully white. That will take decent cable to ensure there is negligible voltage drop and you will gobble lots of 5V power supplies unless you're having only a few strips on your tree.

Well, the amp draw makes connecting power to a controller a bit of a problem (4A per output max on many controllers) and makes pulling power from an external power supply more of a reality, but it still doesn't answer my original question.


Do you know how this 60 pixel/M in a 4M length can maintain color and signal integrity to the last pixel?


Charles

 

[fmt1962]

I use a lot of 5V pixel strips and you will notice that 30 pixel/m is sold in 5m lengths and 60 pixel / m in 4 m lengths. You will find that they are sold that way as that is close to the maximum length for the number of pixels, copper track etc for the materials used.

I find that power at one end of the strip is fine, but I do inject at both ends, you will see a brightness jump significantly if you inject at both ends.

So for strip I have injection every 4 or 5 meters and get excellent results. I tried going longer, but very poor results.

As 5V has a lot of current, yes, as AAH noted, you need heavy cable and you can tolerate only a VERY small voltage loss, it is a real challenge. I have given up trying to feed 5V over any distance, now I use 24v power supplies and a 24/5V buck converter at each string. This gets outstanding results.

http://www.aliexpress.com/item/waterproof-DC-DC-buck-convertor-DC12V-dc24v-input-DC5V-10A-50W-output-alu-case/32225806451.html

For megatrees you can direct feed as you can get all the injection points close together.

 

[fasteddy]

What do you plan to do with this strip as that should determine if this is the right strip for the task.

 

[Charles Belcher]

What do you plan to do with this strip as that should determine if this is the right strip for the task.

I am going to build a 24 strip Mega Tree with these strips. One strip per controller channel if needed. Extra power supplies for injection if needed; but if I don't have to inject, all the better. I would like to use the full 4m strip intact, if possible so the height of the tree will be fixed to that dimension.


I am interested in this tightly packed strip because I want to do xLights animation across the trees. Characters singing, sprites, gifs, etc


Charles

 

[fasteddy]

Most will say using this strip for a tree is an overkill. Is it worth the extra hassle to use this strip for the end result because all you are doing is increasing the resolution on the strip itself but then the resolution between strips will not increase. So what do you see as the advanatges to using this strip versus the extra cost and design hassles that comes with using this strip.

This strip is great for creating a matrix because you can then make the length and width resolution match much better
If using this strip in a tree where the ratio between the number of LEDs/pixels on a strip versus the number of strips and the gap between the strips is greatly different.

So is it worth the extra cost and effort needed to use this because you will be adding a lot more cost using this.

 

[AussiePhil]

Hi Charles,

think there is some maths mistakes but ultimately you or someone needs a physical length and actually test it. Theory and practice often don't align.

60 leds per meter assume 20mA per colour per led
60 x 60mA = 3200 mA = 3.2A per meter
4 x 3.2A = 14.4 A per 4M length, you have about 1v of allowed voltage drop across the entire length at best.

Now if they are set for 10mA per colour that will halve to 7.2A per length.

no matter what you are not powering these from the controller and as Daryl was said the best solution would be local convertors or 10AWG cable from the huge power supply.

working at 5V is a whole new ball game even from the 12v world.

 

[Charles Belcher]

Eddie/Phil,


I understand that the vertical pixel spacing will be different from the horizontal pixel spacing and that may kill the deal.


What will not kill the deal is the fact that it will take a lot of channels (I am using xLights).
What will not kill the deal is the fact that no controller channel is going to have enough power for it (I will use T's or however, to get power from external supplies).
What will not kill the deal is heavy wiring requirements (I come from the concert production world, so heavy in Christmas is still lightweight by show production standards where overkill is the norm and we start with 4/0 size wire to get into our ETC dimmer racks)
_____________________


Let's backtrack a bit: My initial question was how can they offer a 4m 60pixel/m 5 v strip when the conventional wisdom is that one must power injection every 50-60 pixels. Regardless of what I end up doing, I would like someone's opinion on this.


Next: Here is the history of my research.
1) I projection map the entire front of my house
2) I wanted two mega trees to share character animation with the projection
3) I have had better luck with strips than strings or strands or modules and looking for as close to trouble free as possible. (I will have spare strips mounted on the pixel strips that Boscoyo sells ready to go)
4) I originally liked the TM1809 because of the individual led control and was almost ready to pull the trigger on those
5) When I came across the 2812 now modified to 2812B and like the construction
__________
Added thought: I am using P10 panels across my eve for other animations this year with the BBB/octoscroller setup

So, with all of that---do you have any guiding words? ???


Charles

 

[fasteddy]

Let's backtrack a bit: My initial question was how can they offer a 4m 60pixel/m 5 v strip when the conventional wisdom is that one must power injection every 50-60 pixels. Regardless of what I end up doing, I would like someone's opinion on this.

Its all got to do with Ohms law and the part that resistance plays.

Voltage = current x resistance
Current = voltage / resistance
Resistance = voltage / current


The strip uses a flexible PCB and has the lights much closer thus having a lower resistance level over the length for the number of LEDs used compared to a string of lights.

With Strings you have to take the cable resistance into account and the longer the spacing between the lights the higher the resistance. The guage of the cable used in the string also determines how many pixels can be used.

So for example the general rule may say that you can get only 50 to 60 pixels before injection is true for a 5vdc string with a bulb spacing of approx 10cm with a 1 metre lead in cable and using 22 guage string, but that same rule would not apply if you had a string at 5vdc with bulb spacing at 30cm, because the cable resistance would cause too much voltage drop over the distance.

 

[Charles Belcher]

Eddy,


Got it--makes sense. Any other thoughts on what would best serve this project?


(24 strips in a 180 degree configuration for a mega tree.) The spacing at the bottom would probably be on the order of 4"-6"


Charles

 

[fasteddy]

Eddy,


Got it--makes sense. Any other thoughts on what would best serve this project?


(24 strips in a 180 degree configuration for a mega tree.) The spacing at the bottom would probably be on the order of 4"-6"


Charles

Personally i would use the 30 led/m and make the tree 5 metres tall (bigger is better here). I think that would be better money spent, but thats just my opinion which doesnt really mean much

 

[Charles Belcher]

Eddy,


Got it--makes sense. Any other thoughts on what would best serve this project?


(24 strips in a 180 degree configuration for a mega tree.) The spacing at the bottom would probably be on the order of 4"-6"


Charles

Personally i would use the 30 led/m and make the tree 5 metres tall (bigger is better here). I think that would be better money spent, but thats just my opinion which doesnt really mean much

You have "been there; done that" many more times than I have in this Christmas Holiday World we live in.


╰(◉ᾥ◉)╯


Charles