powering more then 7.5A of pixels

jeffcrouse

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Dec 4, 2019
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I just ordered my first PixLite 16 Long Range MkII (and some Isolated receivers), but one thing that confuses me is the 7.5A fuse vs 1020 max LEDs per output. If we use the 60mA full-white value, that suggests that you can only power 125 pixels from the onboard power. First, I understand 60mA is an absolute max and it's unlikely that I'll get that high, but unfortunately I need to plan for the worst.

Second, I understand that I can reapply power directly to the strips to re-up the power, but this is where my electronics knowledge gets a little funny.
1. It's okay to apply several power sources (I'll probably be using Meanwell 5V60A) to the same strip?
2. That won't blow the fuse on the receiver?

Sorry for the basic question, but thanks in advance!
 

OzAz

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Hi Jeff, it's commonly called "Power Injection" do a search in the forums or wiki.
You can either not power the strings at all from the board, or power the first string but make sure following strings don't have a +ve return path back to the board.
 

scamper

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If you read the 101 manual there is a good write up on power injection in there.
But basically power is kind of like pressure, think of it like water pressure, if you run 1 sprinkler from a hose it will blast water. But the more sprinklers you add, the less distance the sprinkler will blast water and if you add too many it would just dribble out of all of them, To get around this you need to turn the pressure up, but you can only get so much pressure, and this is why there is a fuse, because if you try to run too much, in electronics, it will Try to run them and could damage the other electronics. So for instance like the sprinklers, if you could run more water supplies, then you can have more sprinklers and each supply will add to make up the difference, thinking of this, will also show you that you should power inject at even spacing to make sure the pressure is even across all pixels.
While thinking of it this way, the next question people have is, do I need to cut the power where I inject, basically if using the same supply, no. Like the sprinkler, if you put a sprinkler in the middle of 2 water sources, the water source is the same pressure and the sprinkler can only push out so much water, so the water just balances and in this case, there will be roughly the same amount of water supplied to the sprinkler from each source.

Hopefully you are not now more confused than you started o_O
 

jeffcrouse

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@OzAz -- Thank you! That's exactly what I needed to know to research it myself.

@scamper -- re: "do I need to cut the power where I inject?" ... " if using the same supply, no"

I am very curious about this - especially the "same supply" bit. Since each output can drive 1020 pixels @60mA, that's 61.2A per output, which is just tiny bit higher than the 5v60A that I am planning on using. Likely I will just try to never turn them all on at full white. But in theory, what if I did have to use multiple power supplies on a single strip? I've heard people say to connect their grounds, but I don't know if I'm interpreting that right.
 

BobMLT

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@scamper - that is the best analogy for power injection I have heard. I have been thinking of it in this way but was a little confused but this makes sense. In this analogy, is the volume of water Amps? and the litres per minute equivalent to Watts?
 

scamper

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@OzAz -- Thank you! That's exactly what I needed to know to research it myself.

@scamper -- re: "do I need to cut the power where I inject?" ... " if using the same supply, no"

I am very curious about this - especially the "same supply" bit. Since each output can drive 1020 pixels @60mA, that's 61.2A per output, which is just tiny bit higher than the 5v60A that I am planning on using. Likely I will just try to never turn them all on at full white. But in theory, what if I did have to use multiple power supplies on a single strip? I've heard people say to connect their grounds, but I don't know if I'm interpreting that right.
You do need to connect the grounds as that is basically a reference. 5v is only 5v with reference to the ground. So if you have 2 supplies and the grounds are not tied together, one could be floating higher than the other, which would mean the 5v may then not be 5v in reference to that particular ground.
The reason I say the same supply is because some supplies are different in the way they work and you could have problems.
In saying that, because I use all the same type of supply, I don't have a problem with connecting more than one, but I am not saying to do it as you could have problems then blame me :oops:
Also if you just turn your brightness down at the controller, you will hardly notice any difference in brightness, but will reduce the power consumption considerable. I tend to run all my pixels at around 40%
 

jeffcrouse

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Thanks again, @scamper. Your explanation is better than the Power Injection wiki page.

I'm still a little worried about blowing the 7.5A fuse because it seems like I will be creating a circuit with more than 7.5A of draw... I'm fairly sure I'm misunderstanding something.

EDIT: I found a Power Injection wiki page on DIYXmas that is a bit more detailed. It says

Using Power Injection at the end of a String nominally reduces the current thru the wire to the beginning of the string in half, since the Power Injection Wires carry roughly half of the current for the string.
And continues on about other power injection tips. Overall the takeaway for me seems to be that, if I inject power every 50 pixels, the draw at any of those points will be only be those 50 pixels. Therefore, the 7.5A fuse on the board will be safe.
 
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scamper

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Thanks again, @scamper. Your explanation is better than the Power Injection wiki page.

I'm still a little worried about blowing the 7.5A fuse because it seems like I will be creating a circuit with more than 7.5A of draw... I'm fairly sure I'm misunderstanding something.

EDIT: I found a Power Injection wiki page on DIYXmas that is a bit more detailed. It says



And continues on about other power injection tips. Overall the takeaway for me seems to be that, if I inject power every 50 pixels, the draw at any of those points will be only be those 50 pixels. Therefore, the 7.5A fuse on the board will be safe.
The draw will be whatever it requires in that direction at that particular time.
What I mean is for example you have 50 pixels with power injection at each end.
But because you are running a show, the pixels are all drawing different amounts of power. For an example lets say the first 10 pixels are all white, then the rest are red then the first 10 will draw around 60ma each and the rest 20ma each (very rough and rugged guide only) so the first 25 pixels would be drawing 900ma and the next 25 500ma.
The power supply at the start is NOT going to supply only the first 25 pixels, it will supply in this case will only be supplying around 15 to 20 (cannot be bothered with math) and the power supply at the end will supply the rest.
The power supplies are going to share the load.
This is the reason the 7.5a fuse will be OK. but also, why it could blow. It will be OK if everything is working fine, but if you lost your power at the injection point, then it will attempt to supply what is needed and therefor could blow.
This is also why people like to disconnect the power from running through.
I prefer a balanced load so leave the power to run through. But I also only run injection and don't actually run power from the control boards.
 
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