Pixel Ports and Fuses

[BrianZ]

Had a question about the Falcon’s 5a fused ports and dist. board with 5a fuses...if I were to connect a pixel string to a 5a port and daisy chain the strings and power inject at the end from another 5a dist board fused port, does that entire string have a total of 10a it could withstand?

 

[Nojoy]

The strings won't pull an exact 50/50 from each end. Depending on so many factors it could end up 70/30. Would calc the total Amp draw and not exceed the max fused Amp rating from one end to be safe.
Imagine one fuse fails, the other is now carrying the total load leading to its failure or worse the lights burning out

 

[BrianZ]

The strings won't pull an exact 50/50 from each end. Depending on so many factors it could end up 70/30. Would calc the total Amp draw and not exceed the max fused Amp rating from one end to be safe.
Imagine one fuse fails, the other is now carrying the total load leading to its failure or worse the lights burning out

Great point. Thanks.

 

[David_AVD]

You should never power anything from more than one fused source.

 

[BrianZ]

You should never power anything from more than one fused source.

Kind of understand. If I run 100 pixels from port 1, I shouldn’t power inject from another fuse block?

 

[David_AVD]

Scenario 1:
You're feeding power to a string at the beginning and end.
Both power feeds should go back to the same source / fuse.

Scenario 2:
You're feeding power to a long string at the beginning and at one or more places along the string.
Each power inject point should be fed from a separate cable and fuse.
The V+ line of the string should be cut just before each PI point, so each one is only feeding one smaller section.

 

[BrianZ]

Scenario 1:
You're feeding power to a string at the beginning and end.
Both power feeds should go back to the same source / fuse.

Scenario 2:
You're feeding power to a long string at the beginning and at one or more places along the string.
Each power inject point should be fed from a separate cable and fuse.
The V+ line of the string should be cut just before each PI point, so each one is only feeding one smaller section.

Oh I see. Scenario two is what I’m familiar with, but I thought that I could run a string from a port and daisy chain another string totaling 100 pixels and I could power inject at the end, I didn’t know I had to cut the V+. And this is assuming I’m using the same power supply? Or is it if I’m using two? I thought if I used one PSU and power injected, I didn’t have to cut.

 

[David_AVD]

If you cut the V+, each section is powered from a different fuse. That could be on the same PSU or a different PSU.

Put another way, as soon as you add a fuse to a PI line (a good idea usually) then you need to cut the V+ line in the string.

 

[BrianZ]

If you cut the V+, each section is powered from a different fuse. That could be on the same PSU or a different PSU.

Put another way, as soon as you add a fuse to a PI line (a good idea usually) then you need to cut the V+ line in the string.

Ok, understood. I’ll go back and re-read and watch some more videos because I missed that. Glad I asked.

 

[i13]

I'd suggest doing scenario 2 slightly differently by cutting the positive half way between each injection point instead of immediately before each injection point. The power will travel in both directions from the injection point so you can either use fewer injection points or have shorter distances and therefore less voltage drop from the injection point to its furthest pixel. By the time your pixels add up to 5 amps, there might (or might not) be voltage drop causing incorrect colours.

 

[BrianZ]

I'd suggest doing scenario 2 slightly differently by cutting the positive half way between each injection point instead of immediately before each injection point. The power will travel in both directions from the injection point so you can either use fewer injection points or have shorter distances and therefore less voltage drop from the injection point to its furthest pixel. By the time your pixels add up to 5 amps, there might (or might not) be voltage drop causing incorrect colours.

Ok, thanks. I’ll take all of this into account. So, If inject at the end of the string from a 15a fuse block, cut the V+ In between, does that mean I could then increase the amp draw for those strings instead of being limited to 5a? But I wouldn’t go crazy because the wires are usually 18awg.

 

[TerryK]

Ok, thanks. I’ll take all of this into account. So, If inject at the end of the string from a 15a fuse block, cut the V+ In between, does that mean I could then increase the amp draw for those strings instead of being limited to 5a? But I wouldn’t go crazy because the wires are usually 18awg.

A bit difficult to answer without knowing more about the physical layout of your display. Yes and no. Yes you can inject at the end of a string from a 15 Amp fuse block but you need to add amperage protection (sub-fusing) to insure the string does not burn. So yes while the amperage for the entire string will or can be increased, no because anywhere within the string amperage needs limited to approximately 5 Amp or less. A question is, where is the 15 Amp fuse? Rather obvious I think that a 15 Amp fuse immediately prior to an injection point is not beneficial.
An example may help. I have a 350 pixel prop about 40 feet from the controller and supply. The electronics are in a garage. The prop has a single power injection cable fused at 15 Amp near the supply. The controller to the prop is a smaller 22 AWG 2 conductor V- and data (no V+). I sometimes like to wake the neighborhood so I designed it for 80% White which calculates to about 16 Amp. To equalize the string voltage drop I inject at the beginning, middle (about pixel 150), and the end. If something happens the string could consume all 15 amp in a localized area and burn the string. To prevent that I sub-fuse, that is each injection point has it own 5 Amp weatherproof fuse. I could have ran 3 power injection cables but that is more cable management; not sure but I think a single larger AWG was a bit more economical as well.

 

[i13]

TerryK makes a good point.

That won't work. Ignoring the problems and assuming that you're fusing the positives, if you wanted to do a 15 amp injection point at the end of the string when the beginning is powered through a 5 amp fuse, you'd need to cut the positive closer to the beginning to divide up the current accordingly.

There are three main problems here:

• TerryK explained one problem which is that a 15 amp fuse might be too large to blow when there's a problem.
• Ignoring the first part of the string, you're powering 15 amps' worth of pixels (approximately 300 pixels) at one end. This will definitely result in voltage drop and incorrect colours. This will happen regardless of the power supply's capacity.
• 15 amps is more current than the 18 AWG (and typically thinner) wire between the pixels can safely handle.

In other words, if you have a run of pixels that's long enough to draw 15 amps, you need more injection points.

 

[TRAVISTY]

Fuses are for cable protection. Nothing more

 

[David_AVD]

Fuses are for cable protection. Nothing more

In the case of PI cables in your display, yes. Fuses are used for other reasons as well.