Answered Problem with Power Injection

[Max Kabilafkas]

I'm having some troubles with the power injection for my mini trees.

I have 8 mini trees which are broken into two lots of four. Each mini tree plus star uses 200 5v pixels (4 x 50 node strings). The wire diagram below shows how I have them wired up (I have only showed one group of four trees for clarity.

I have power injection at the junction between each string of pixels, with the very first string of Mini Tree 1 being the only one powered by the controller. In order to save cable length I built some homemade power busses to split the power injection wires up at each mini tree.

The power supply performing the power injection has a 300W capacity. According to this calculator - https://www.da-share.com/calculators/led-strip-string-current/ - the 750 pixels that are connected to that power supply should draw 208W of power at 100% brightness. I have the pixels set to 30% brightness which should be 63W, well below the 300W capacity of the power supply




Homemade Power Bus 1 looks like this -



And Homemade Power Bus 2, 3 and 4 look like this -



All wiring used throughout the whole circuit is 18AWG.

I can see that there is a power injection issue as (aside from the very first string of lights which is power via the controller), when I get the lights to shine a white colour, they get progressively redder the further away from the controller the strings are.

I'm guessing that the issue is something to do with my power busses, but I am not sure why. I thought that the way I have wired it all up basically means that all the wires are all melded together, effectively making all the power injection points operate in parallel.

Alternatively maybe as the length of power cable needed to reach each mini tree gets longer, the resistance increases, resulting in less current able to reach the trees?

Any help would be much appreciated

Thanks

Max

 

[uncledan]

In the diagram you are missing one important thing. There is no V- connected for the power injection. Power injection is V+ and V-. Its amazing you havent melted some wire on V- of those pixel strings

 

[Max Kabilafkas]

Oops, that's a mistake with my diagram. Each power injection point has a V+ and V- connection.

Diagram is fixed now

 

[uncledan]

Alternatively maybe as the length of power cable needed to reach each mini tree gets longer, the resistance increases, resulting in less current able to reach the trees?

I think you figured out your problem with this statement. 18AWG is pretty small stuff for power injection, especially with 5v. I have similar setup with power injection on my mini tree forest and have had issues with 12v and much larger power injection wire (minimum of 14AWG). Also good to fuse if possible. Some people choose not too fuse power injection but its a good idea. I have no clue how long these cable lengths are but it looks like a likely issue with 18AWG and 5v. You can always check the voltage while testing

 

[KiwiPhil]

Red is a sign of voltage drop across the length of cable from the power supply to the last pixel - instead of daisy chaining your power bus they should all connect directly back to the PSU - this will lower the resistance somewhat. The length of the cable from PSU to the last pixel will be the main determining thing after you have wireled them all back.

measure the voltage at each bus point and I imagine you have .5-1v drop by the last bus bar

 

[Max Kabilafkas]

Ok, sounds like I'll try repositioning the power supply. At the moment the distance between the power supply and Mini Tree 1 is long - around 20m or so. The distance between the Mini Trees however is relatively short, only 2m or so.

I might try placing the power supply in between Mini Tree 2 and Mini Tree 3 first and see if that works, before I go out and buy more wire and redo all my cabling!

 

[uncledan]

Reposition the power supply closer to the prop or get some MUCH bigger wire than 18AWG for the 20m run. Most of my mini trees are powered like this, but I have a 15-20m power feed from the PSU to power distro boards that's #8 or larger with 14AWG fused power injection to the trees. With 5V repositioning the power supply as close to the props as possible is the best solution I would think. As @KiwiPhil mentioned it would be best to not daisy chain the feed from the psu. Have a dedicated feed to each buss bar with wire much larger than 18AWG. Right now you are trying to power inject 800 pixels with 18AWG wire with 20m+ of cable. Not going to work well

 

[AussiePhil]

20M, 5v, 18awg and any current above 1A is a no go just won't work. And running the PI in series won't work.

Unless you have access to 12 awg or better then you need to be running all the PI in parallel from the PSU located near your props and even then you need to be calculating voltage drop v wire gauge.

Move the Power suppy for PI out near the props, PI every point with parallel cables from the supply.

Feel free to message me and arrange a zoom/teams chat to discuss if that might help.

5v power runs just need care and calculations to avoid voltage drops, there are no real short cuts

Cheers
Phil

 

[Max Kabilafkas]

Moved the power supply in between trees 2 and 3 and plugged the power busses directly into the power supply and it works properly now.

Thanks for the help everyone