Power injection - negative wire

Martin Mueller

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FYI: The best place to cut the V+ (If your going to cut it) wire is about half way between two injection points. The thing to think about is:

"How many pixels between my injection point and the point at which I start a new power domain."​

That means any given injection point can send power it TWO directions. I happen to inject every 25 pixels. I DO run my pixels at 100% and I have a buck converter at each injection point to power the segment. Each buck converter supports about 25 pixels. In my case that is 12 to the left and 13 to the right. I almost NEVER run V+ from my controller unless I need a data buffer between the controller and the prop.
 

AussiePhil

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cool, so the only time you'd cut v+ is if you are using a second psu to power part of that long string.
I'd not even bother then... why you may ask
someone mentioned power balancing... not a term i've used but in reality the resistance of the wiring back to each power supply sets up really good current sharing via the resistance... each section will draw from each power supply and they won't hurt each other. so power balancing is just current sharing.
Current sharing via balancing resistors is exactly how N+1 power supplies in servers etc work..... all your doing is replacing the proper balancing electronics with some cable runs... electrically its the same thing.
 

Grozzy

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I'd not even bother then... why you may ask
someone mentioned power balancing... not a term i've used but in reality the resistance of the wiring back to each power supply sets up really good current sharing via the resistance... each section will draw from each power supply and they won't hurt each other. so power balancing is just current sharing.
Current sharing via balancing resistors is exactly how N+1 power supplies in servers etc work..... all your doing is replacing the proper balancing electronics with some cable runs... electrically its the same thing.
My comment about Power Balancing was not related to multiple power supplies.
Whether the term is correct (My personal belief is that it is just power injecting) but the broader community seem to have coined the term to differentiate between power injecting from a separate line/cable/source and reinjecting from the start of your prop into multiple points and the end of the same prop.

My window frames, spinners, stockings, snowflakes etc all have the +/- joined on the first and last pixel. Effectively creating a bus of higher gauge wire that each prop taps into.
It's not for everyone particularly people who just want to screw in pigtails and t connectors, as it involves soldering and a lot more work.
 

AussiePhil

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My comment about Power Balancing was not related to multiple power supplies.
Whether the term is correct (My personal belief is that it is just power injecting) but the broader community seem to have coined the term to differentiate between power injecting from a separate line/cable/source and reinjecting from the start of your prop into multiple points and the end of the same prop.

My window frames, spinners, stockings, snowflakes etc all have the +/- joined on the first and last pixel. Effectively creating a bus of higher gauge wire that each prop taps into.
It's not for everyone particularly people who just want to screw in pigtails and t connectors, as it involves soldering and a lot more work.
Like you regardless what you call it adding power at any point other than the start of the string run is a form of power injection.
different voltages (5v 12v) cannot be shared in the same total string unless you cut the power wires and then it is no longer injection but a fresh start.
Voltages from the same PSU will end up with slightly different voltage levels at the pixel depending on cable length and current draw. (keep this in mind)
Voltages from different PSU's should be within say 0.1v at the source but will still end up at different levels depending on cable lengths.

Current drawn will be shared based on the resistance of the cables going to the injection points. Good injection plans keep all the cable runs the same length.

The nearly never discussed issue is not the + voltage or current sharing but the potential for differing zero/ground levels presented at each point. This actually affects the zero reference level for data signal and can result on maybe rare occasions flickering and weird data issues.

Cheers
Phil
 

Martin Mueller

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Keep in mind that when the pixels are OFF, there is very little voltage drop on the wires and a difference in PSU output voltage will cause the PSU regulators to "Fight" each other to control the line voltage. This can burn out the regulators and this is one of the factors that drives the need to cut the V+ lines between power domains.

As for the V- and Data relationship. an easy statement to keep in mind is "Where goes a data wire, so goes a V- wire". Tying V- together at the PSUs does not hurt but does not really help. Dont waste your time and effort. When Data leaves one point (controller or pixel) and goes to another point (pixel, buffer, extender), the V- wire must go with it (as a wire pair). The exception to this is pixel extenders that convert pixel signals to another format and back again. Data and V- go to the extender and stop there.

FYI: A pixel buffer or NULL pixel is different than a pixel extender. Extenders tend to convert the media to something like RS485 differential signaling that can travel long distances and then back to a pixel data signal at the receiver.
 
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AussiePhil

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Keep in mind that when the pixels are OFF, there is very little voltage drop on the wires and a difference in PSU output voltage will cause the PSU regulators to "Fight" each other to control the line voltage. This can burn out the regulators and this is one of the factors that drives the need to cut the V+ lines between power domains.
Ideally you would have matched voltage supplies and even then you need the current sharing resistor and proper parallel supplies will have sense wires between them but back in the real world if the supplies are consistently within 0.1v or better and that's not hard to do/achieve and you are not connecting them together at the source then the cable resistance and string resistance provide more than enough to stop any fighting even with no lights turned on.
For at least two seasons one of my megatrees was powered by multiple 24>5 waterproof puck style convertors that ran 24/7 and were connected together via the power injection and strings.
If people connect these in parallel at the units then absolutely your right they will fight and burn out.

As for the V- and Data relationship. an easy statement to keep in mind is "Where goes a data wire, so goes a V- wire". Tying V- together at the PSUs does not hurt but does not really help. Dont waste your time and effort. When Data leaves one point (controller or pixel) and goes to another point (pixel, buffer, extender), the V- wire must go with it (as a wire pair). The exception to this is pixel extenders that convert pixel signals to another format and back again. Data and V- go to the extender and stop there.
Agreed it's not worth the effort in a normal show, just like cutting the + is not worth the effort but it is something to be aware of in the event you are experiencing flickering or poor behavior.
FYI: A pixel buffer or NULL pixel is different than a pixel extender. Extenders tend to convert the media to something like RS485 differential signaling that can travel long distances and then back to a pixel data signal at the receiver.
 
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