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To Inject of NOT Inject?

Started by akakfreeman, October 09, 2019, 08:18:57 PM

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0 Members and 1 Guest are viewing this topic.

akakfreeman

I'm a rookie!
Controller: F16v3
Falcon Player on Raspberry Pi 3 B+
12 volt lights
 - Roofline has about 600 pixels (30LED/M strips in aluminum channel that will stay on the house year round)
 - Star, 6 layer with 270 pixels (Bullet pixels)
 - Arch with about 300 pixels (60LED/M strips)

I'm trying to decide whether to avoid any power injection by running more channels, or go to the effort of adding power injection to conserve channels. I'm assuming that on the roofline I would need to inject power 2 or 3 extra times (I plan to user power from the F16v3 for the first string). The star will likely need 1 power injection point, and the arch will likely need extra power at the end. If I do power injection I'm assuming I can use just 3 channels out of the 16. Without power injection I would likely use 4 channels for the roofline, 2 for the star and 2 for the arch for a total of 8.

I suspect down the road I would want more channels as I add more props and would either need to add power injection or buy more controllers. I assume there is no right/wrong way to do it, but was hoping the group could advise me of the pros and cons. I tend to think as a beginner the non power injection method may be best, but down the road it may require a lot of effort to add power injection and I assume I would have to edit my sequences a bit (reassign channels). Maybe it's better to just do the power injection now and be done with it.

Looking forward to all your advice!

Poporacer

Welcome to this hobby! First, there is some terminology that you need to know so that we understand each other. The part of the controller that you connect the pixels to are called ports. Strings are not how you purchase the pixels but the total pixels connected to each port of the controller. Channels are the addresses for the pixels and each pixel needs 3 channels. One thing to consider is that most people don't run the pixels at 100% and that can increase the number of pixels you can run before injection, but don't limit yourself on a brightness, leave room to increase if you need to. Power injection isn't that difficult and you are right, there is more than one way to do it right! If you set things up correctly in xLights, changing your model/port assignments is actually pretty simple.
If to err is human, I am more human than most people.

pixelpuppy

Also note that power injection does not have to occur in the middle of a string.  You can inject power at the end of a string and often that is much easier.   For example a long roofline may be tricky to get power to the middle but easy to connect power at both end.  IF the power is coming from the same power supply then its really easy but if its coming from two different power supplies then you'll need to make sure to cut the V+ line in the middle of the string.
-Mark

JonB256

Quote from: pixelpuppy on October 10, 2019, 04:58:51 AM... but if its coming from two different power supplies then you'll need to make sure to cut the V+ line in the middle of the string.

alternate opinion - in this specific case, I would not (have not) bother(ed) to cut the V+ line. If the number of pixels and length of wire is long enough to need Power Inject at both ends, the electrical load from circuitry and wire is sufficient to keep the two power supplies from competing for voltage control (oscillating). Even with all pixels dark. If you are sufficiently detail oriented, set one of their output voltages slightly lower than the other.

In any case, you must connect the V- point of the multiple contributing power supplies to stabilize the pixel Data line. Otherwise, you'll get flicker and misbehavior of pixels.
Long time Falcon, FPP and xLights user

pixelpuppy

#4
Quote from: JonB256 on October 10, 2019, 05:22:05 AMalternate opinion - in this specific case, I would not (have not) bother(ed) to cut the V+ line. If the number of pixels and length of wire is long enough to need Power Inject at both ends, the electrical load from circuitry and wire is sufficient to keep the two power supplies from competing for voltage control (oscillating). Even with all pixels dark. If you are sufficiently detail oriented, set one of their output voltages slightly lower than the other.

I hear ya and understand exactly what you're talking about.  ;)  I actually do that in some specific cases where it will work.  8)  However, it does require a thorough understanding of the principles of electricity and proper measuring of voltage at various points to validate if this specific case applies in each situation. 

Simply setting one of the two power supplies slightly lower does not ensure this will work safely.  That only biases the failure to the lower voltage power supply.  What really matters is that the voltage measured at the point of injection is less than the voltage of the injecting power supply.  This needs to be tested at both ends with each power supply separately and prior to connecting both at the same time.  Its not enough to just see the end is <12v and then connect  a 12v supply to the end.  You also need to verify the start of the string has less voltage than the primary supply when the injecting supply is connected to the end and the primary supply is disconnected from the start. 

You need to remember that voltage drop with the lights off is very little compared with the lights on.  You may find that with the lights off, the voltage at the end is much higher than you thought and could overdrive your injecting supply - or worse, the injecting supply could overdrive your controller's power supply when the lights are off.

Because of the extra specific details that are needed to do this safely, I do not recommend it casually in an open forum because you can definitely burn up the power supplies if you don't validate the specific cases where this will work.  Yes, it can be done in specific cases and I indeed do it myself in several cases.  But I also know where and how to check/verify the voltage drop before connecting two different power supplies to the same string.  If anybody doesn't fully understand the specific cases and details where this is ok to do then they'll be safer to just cut the V+ in the middle and not have to fully understand the specific details :)
-Mark

akakfreeman

Thanks for the comments!

I like the idea of injecting the power where needed at the end of a string. I think that will work nicely for each the roofline, star and arch. I think I'll do the power injection and reserve the controller ports for future growth.

For the roofline I plan to insert pixel strips inside an aluminum channel. But rather than putting the power wires inside the aluminum channel, if I inject power at the ends I think I can just come out of the soffits near the RED dots on the photo below (I plan to have controller, power supply and Raspberry Pi in the attic). The GREEN dots are where the wire from the controller will start. Will that work well (connect + and ground at the ends)?

Image link: https://drive.google.com/file/d/1jJwkRj2ivM1-hyGA6vBhD135dXcQZJnS/view?usp=sharing


akakfreeman

I guess the arch will need it's own power supply, so maybe I'll just run data to it from the controller and power from the second power supply? Is that correct? Then I can add more arches later.

w8one

Quote from: akakfreeman on October 10, 2019, 07:38:59 PMI guess the arch will need it's own power supply, so maybe I'll just run data to it from the controller and power from the second power supply? Is that correct? Then I can add more arches later.
Close, the ground (V-, 0 volts) has to go with the data and connect to the next power supplies ground.
Quando omni flunkus moritati

akakfreeman

Ok. How does this diagram look?

Red = V+
Violet = V-
Green = Data

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