Power injection - negative wire

JordoLights

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Hello all, I have been browsing and reading threads and found out that in order to avoid the controller fuse to blow when power injecting, you could cut the positive wire so that power doesn't "flow back" to the controller which could overload the fuse and blow it. So the idea is to start a fresh line of positive - this would come from a fused distro board. My question is, do I keep the negative wire running from the controller all the way to the last pixel in the one output? Or do I also cut the negative wire where I cut the positive wire?

Note: Only using 1 power supply for controller and lights.

Another question, my power supply has 3x V+ and V- outputs. My power distro board has 2 inputs. Is it okay to piggy back these inputs onto 1x output (V+ and V-) from the power supply?

Thanks in advance.
 

Notenoughlights

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You need to keep the Negative wire connected throughout otherwise you will end up with strange effects on your lights, flickering, lights not working, etc.

The 3 V+ and V- terminals on your power supply are all linked together, they are spread out as 3 for each for connection convenience.
 

Grozzy

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You don't need to cut the positive wire if you are only using one power supply.

As an example if you have a string of 300 pixels and you cut the wire and inject at pixel 151 you will have voltage drop at pixel 150 and 300 that could cause issues depending on wire gauge and pixel voltage 5v vs 12v. However if you don't cut the wire and inject at 150 and 300 the voltage drop is reduced as you are feeding both back and forward.

Yes there are situations where you may want to power pixels independently and that is if your overall load is really high and you want to fuse it in sections but for most situations not needed.

And yes it is possible that if one fuse blows the rest will cascade as the amps increase on each injection but as long as you calculate your overall load then you should be right.

I only inject to counter for the voltage drop caused by distance rather than for balancing the current draw. I just don't overload my ports.
 
Last edited:

Martin Mueller

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As for V-, V- is the reference against which the data signal is derived. The general guideline is "Where goes data, so goes V-" That means from the controller to the first pixel then minimum connection is Data and V-. At a power injection point the minimum connectivity between any two pixels is Data and V-. FYI: Tying V- together is NOT what is being suggested here. Tying V- together at the PSUs does not meet the "Where goes data so goes V-" statement.

When V- and Data diverge you will get "Interesting Random Lighting" effects that have no relationship to your desired effects.
 

Christmas30

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You don't need to cut the positive wire if you are only using one power supply.

As an example if you have a string of 300 pixels and you cut the wire and inject at pixel 151 you will have voltage drop at pixel 150 and 300 that could cause issues depending on wire gauge and pixel voltage 5v vs 12v. However if you don't cut the wire and inject at 150 and 300 the voltage drop is reduced as you are feeding both back and forward.

Yes there are situations where you may want to power pixels independently and that is if your overall load is really high and you want to fuse it in sections but for most situations not needed.

And yes it is possible that if one fuse blows the rest will cascade as the amps increase on each injection but as long as you calculate your overall load then you should be right.

I only inject to counter for the voltage drop caused by distance rather than for balancing the current draw. I just don't overload my ports.
I'd concur with above about not. Overloading the ports I'd rather use all 3 avaible ports through a b and c expansion smart recievers mode than try running all through one port and not spreading through different units
 

JordoLights

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You don't need to cut the positive wire if you are only using one power supply.

As an example if you have a string of 300 pixels and you cut the wire and inject at pixel 151 you will have voltage drop at pixel 150 and 300 that could cause issues depending on wire gauge and pixel voltage 5v vs 12v. However if you don't cut the wire and inject at 150 and 300 the voltage drop is reduced as you are feeding both back and forward.

Yes there are situations where you may want to power pixels independently and that is if your overall load is really high and you want to fuse it in sections but for most situations not needed.

And yes it is possible that if one fuse blows the rest will cascade as the amps increase on each injection but as long as you calculate your overall load then you should be right.

I only inject to counter for the voltage drop caused by distance rather than for balancing the current draw. I just don't overload my ports.
My concern is if I don't cut the positive wire and keep power injecting along the line, the 7.5A controller fuse might blow as the total current will be too much for it (assuming I power everything at 100% full white).


I've attached my wiring diagram that shows my proposed cuts and power injection points. Would love to hear everyone's input as to how I can improve and or any tips/suggestions.


Another question I have in regards to the Null pixel between Spinner R and Star 1. Will that work if I just connect the negative and data wires to it? Or do I have to connect positive as well? If the latter is true, then do I end the Spinner R positive wire after the null pixel?

Thank you everyone, I'm learning a lot from this forum. You are all very knowledgeable and helpful.


1631321789951.png
 

BAZMick

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The null pixels need power in order to work and pass on the data.
No real need to cut power of you're using the same PSU, all the components will only draw the current they need to function.
After each component there is a voltage drop so power injection is used to raise the voltage again back up above the pixels minimum voltage threshold
 
Last edited:

Grozzy

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Depending on the location of your distribution board the Power8 has a built in F-Amp (Null Pixel) but it is transparent so you don't need to program it in XLights. However 5 metres shouldn't be a problem with no boost. I have plenty of props that are 5 to 10 metres away from either a controller or a prop with no issues. If you are going to use a null pixel power it from whichever side is closest.

Your calculations are fine except that there is more give in real world and the current draw isn't as high as what the specs say.
If I get a chance I'll put an amp meter to some strings and post back some results.

I know people design everything for 100% brightness I have never run over 25% and everything is cabled/programmed that way. Haven't popped a fuse in 3 years.

As an example I have running on one port
5 x 85 node spinners (425 pixels) and
4 x 96 node pixel poles (380 pixels) on another.

Now I'm not saying I'm the poster boy for proper Christmas lighting but just sharing what works for me.

As I said in my previous post it is voltage drop particularly with 5v that will give you added grief if you don't inject at the end of the first singing bulb.
If you are going to cut the wire inject into the end from your first pixel.

There is an additional term called power balancing. It basically means you take power +/- from the start of the string and inject it back at the end of the string. As your power goes from one pixel to the next there is voltage drop due to the resistance of the wire, solder joints and tracks on the pixel. By taking the higher 5v from the start you bypass the resistance and it brings the end of the string back up to 5 volts.

Back to my Spinners I have done that on each one and I have no separate power injection anywhere.
They are also 18AWG wire pixels where as my pixel poles are 22AWG wire and I have had to inject because the wire is crap and thin.
 
Last edited:

bpratt

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No real need to cut power of you're using the same PSU, all the components will only draw the current they need to function.
After each component there is a voltage drop so power injection is used to raise the voltage again back up above the pixels minimum voltage threshold

What about for fusing purposes ?

I've cut v+ to isolate the separately fused segment, i.e. first 100 pixels out of the controller via the controller fuse, the next few hundred pixels on the same psu, but different fused segment.
 

AussiePhil

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My concern is if I don't cut the positive wire and keep power injecting along the line, the 7.5A controller fuse might blow as the total current will be too much for it (assuming I power everything at 100% full white).
DON'T cut the positive wire for for goodness sake, you loose half the benefits of power injection by not back feeding towards the controller.

a 7.5A fuse will NEVER blow unless you have a short in the first section that results in current draw from the controller of 10A or more.

the absolute worst thing that could happen is you get a short between the the two power points that results in both fuses blowing but the likelyhood when doing properly spaced power inject is zero, really it is.

TLDR: don't cut the red wire :)

Edit: and at least design and plan for 100% brightness even if you don't run at 100%
 

AussiePhil

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What about for fusing purposes ?

I've cut v+ to isolate the separately fused segment, i.e. first 100 pixels out of the controller via the controller fuse, the next few hundred pixels on the same psu, but different fused segment.
it really doesn't matter.... voltage drops will limit current generally well before fuses blowing.
Cheers
 

BAZMick

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What about for fusing purposes ?

I've cut v+ to isolate the separately fused segment, i.e. first 100 pixels out of the controller via the controller fuse, the next few hundred pixels on the same psu, but different fused segment.
Fusing is mostly done to protect the cable, if there's too much current draw the cable heats up and creates a fire risk.
 

JordoLights

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Depending on the location of your distribution board the Power8 has a built in F-Amp (Null Pixel) but it is transparent so you don't need to program it in XLights. However 5 metres shouldn't be a problem with no boost. I have plenty of props that are 5 to 10 metres away from either a controller or a prop with no issues. If you are going to use a null pixel power it from whichever side is closest.

Your calculations are fine except that there is more give in real world and the current draw isn't as high as what the specs say.
If I get a chance I'll put an amp meter to some strings and post back some results.

I know people design everything for 100% brightness I have never run over 25% and everything is cabled/programmed that way. Haven't popped a fuse in 3 years.

As an example I have running on one port
5 x 85 node spinners (425 pixels) and
4 x 96 node pixel poles (380 pixels) on another.

Now I'm not saying I'm the poster boy for proper Christmas lighting but just sharing what works for me.

As I said in my previous post it is voltage drop particularly with 5v that will give you added grief if you don't inject at the end of the first singing bulb.
If you are going to cut the wire inject into the end from your first pixel.

There is an additional term called power balancing. It basically means you take power +/- from the start of the string and inject it back at the end of the string. As your power goes from one pixel to the next there is voltage drop due to the resistance of the wire, solder joints and tracks on the pixel. By taking the higher 5v from the start you bypass the resistance and it brings the end of the string back up to 5 volts.

Back to my Spinners I have done that on each one and I have no separate power injection anywhere.
They are also 18AWG wire pixels where as my pixel poles are 22AWG wire and I have had to inject because the wire is crap and thin.
Good to know about the built-in null pixel on the Power8. I will try and utilise that if necessary. I'm also interested to see if 25% will be more than enough for my display. Interesting point about power balancing, I think I've stumbled across some videos on that topic. I will revisit and might do the same for my props.

DON'T cut the positive wire for for goodness sake, you loose half the benefits of power injection by not back feeding towards the controller.

a 7.5A fuse will NEVER blow unless you have a short in the first section that results in current draw from the controller of 10A or more.

the absolute worst thing that could happen is you get a short between the the two power points that results in both fuses blowing but the likelyhood when doing properly spaced power inject is zero, really it is.

TLDR: don't cut the red wire :)

Edit: and at least design and plan for 100% brightness even if you don't run at 100%
I amended my wiring now to connect the positive wire from the controller to the last pixel. Then injecting power in spots to ensure every 50 pixels has access to a power injection point. If I do this, there will be a total of 447 pixels on one output, and if I want to design it at 100%, that would mean around 25A before voltage drops, etc. However, I don't think I will run it at 100%, most likely 25% which is around 6.25A.

Is this setup better that what I had before?

Thanks again everyone.

1631369768705.png
 
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