Power injection - (edit by mod) Not recommended by ACL

Giles1

Giles
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I was always under the impression that I should never combine the positive wires of different DC Power supplies. So, I have always broken the positive wire, when adding the power injection, to prevent the power from another Power Supply from mixing together, as well as preventing the power consumption from exceeding 5 Amps.

However, I just watched a YouTube Video (Power Injection Flaws Exposed -
View: https://www.youtube.com/watch?v=6Qv4fkoEZ3s
), where they said that they usually inject power into their Pixels from another power supply. According to this guy, the advantages of this method, is the power all stays at the same level, even after injecting additional power, from a second Power Supply. While the disadvantage with this is that if your controller’s Power Supply fails, then the second Power Supply would then back-feed to the Controller giving it power, but the lower voltage may then cause issues.

To prevent back powering the Controller, He was advising that a Diode could be fitted at certain points (e.g., at the controller’s port plug). According to him, this would prevent back-feeding the Controller, while still keeping the power levels uniform.

What’s everyone’s feeling on this?
He mentioned nothing about fusing, or how to prevent any fuse levels from combining from multiple Power Supplies. I would also be concerned about just commoning up all the positive wires, would then negate the safety that the Fuses give.

I really don’t know what to make of this one (Good or Bad).
 

Skymaster

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This was discussed at length in the chat a few days ago.
No, just no.
Diodes are not the answer. It will cause more problems than it solves.
 

Skymaster

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If you're concerned about the PSU on the controller dying and the back feed not giving enough voltage to the controller, then you should run just the controller off it's own independent low-wattage power supply, and not connect it to pixel power. Then if a PSU dies, a segment of lights would be out, but not your whole show.
 

i13

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Backfeeding into the controller is not the reason why we cut the positive wire. It is because the power supplies don't cooperate with each other when their positives are connected together. Another reason is so that we can choose how to divide up the current between multiple power supplies and fuses.

I don't power pixels through the controller but I did once accidentally connect the positive between two neighbouring injection points on different power supplies. It made the pixels flicker until I disconnected it.
 

ezellner

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I have done this accidentally and the results are not good. In my case, it just resulted in numerous blown fuses and some head scratching to figure out what I did. Without the fuses, I'm sure there would have been more damage.
 

TerryK

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BAD

That video has enough errors in it that i'm considering removing this thread
Regards
Phil
I suggest leaving it. Rather, casting opinions aside, politely and professionally point out what the weak and wrong points in the video are. Help ACL members who are learning or weak in the technical aspects of our hobby to learn not only what to do but also what NOT to do.

If anything, I would change the thread title to point out that the thread contains a Power Injection scheme which is not recommended.
 

AussiePhil

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Terry is absolutely correct for the reminder to discuss why the video is bad.
Apologies my first reply was to get the "it's Bad" out there

Up to 2:20 all the issues discussed are quite valid however the setup is hardly real world. Running power into the end of a 50 pixel string from a second supply would never be needed. In addition in what scenario would each of the SMPS's be individually powered.
The concerns about back feeding and fusing is real and valid
At 2:17 he speaks about using external power from the internal supply and then calling it being the same issue.
It is one very good reason to cut the positive that is actively championed.

2:53 he speaks about starting with a real life demo, it is closer to an artificial scenario to support the outcome.

at 4:08 the diagram is quite typical

at 4:40 he shows the wire being cut which is more common these days

at 5:15 the brightness comment is true but dependent on where the cut is.

at 5:50 he talks about the diode but seems to be ignoring the immediate 0.7v drop
at 6:50 the diode where the cut would be would result in a brightness difference

at 7:44 the outcome is valid but really who wants their pixels left on.

at 8:50 the diode with 0.7v drop at say 5A would result in 3.5w of power, doesn't sound like much but it would warm up

the idea is sort of valid but increases voltage drop anytime a diode is placed into series

By far the better way to deal with this would be to ensure ALL power supplies used with the controller go off at the same time with AC being lost.

TLDR: BAD based on the type od diode used, the issues raised are quite valid and the solution would be valid if he used "ideal diodes" rather than 0.7v drop common power diodes.
An "ideal diode" has mV's of drop across it and would make sense

More info on ideal diodes here https://www.elprocus.com/ideal-diod...de operates like a,works like a closed switch.
 
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