Power injection help

[Broomy111]

Hey Guys

This will be my first year with pixels and I need to get some clarification with the power injection.  I am going to be building several pixel matrix's and since my bullet pixel strings have 3 conductor water proof connectors on both ends, Im planning on adding some splitters into the mix to supply power every two strings.  So all my wiring will be the 3 conductor ententions and 3 conductor splitters.  Here is my diagram.  Is this how to do it?
If so, do I need to ground the second power supply with the first one?  I have orderd some of the power distro boards and was planning on using those.

Any help would be appreciated.

Thanks

Kevin

[mararunr]

The grounds will be connected through the strands (keep all grounds connected in a continuous loop).  What's more important is to break the positives when switching PSUs.  Do not have the positive from one cross with the other.

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[pixelpuppy]

Do not have the positive from one cross with the other.

Yes that would be bad ...



sorry, I couldn't resist   

[Broomy111]

I love that ghostbusters line. Use it many times in the network engineering field.  HAHA

So electrical engineering is not natural hobby, so bare with me  :-)

In separating the PSU's, so using the all in one 3 conductor connection and extenstion's, there really no way to break out the power and keep the data separate other than to run the PSU's separate from the board?  Im sure Im just confusing this even more.  If anyone has any drawing diagrams of their set up and how they inject power without crossing the streams, please help.  :-)

Thanks so much!

[pixelpuppy]

Its OK to connect the positives of two strings that are fed from the SAME power supply.  Its only when the two strings are fed from two different power supplies that you need to make sure the positive line is not connected across both.

Several vendors sell "T" connectors that are made for power injection.  These carry the data and ground straight through, but break the positive line.  Your drawing above is fine, except you would use these Power-Injection "T" connectors instead of the "Y" connector that you drew.   Actually, I'm not sure that I've seen anybody selling a "Y" connector like you drew.  Usually they are P-I Tees.


Here is a very good resource for Power Injection info...
http://www.doityourselfchristmas.com/wiki/index.php?title=Power_Injection

[Broomy111]

I think I just called it the wrong letter.  Its the T's sold by holiday coro is what I was thinking.

Thanks

[Aesl1982]

Its OK to connect the positives of two strings that are fed from the SAME power supply.  Its only when the two strings are fed from two different power supplies that you need to make sure the positive line is not connected across both.

Several vendors sell "T" connectors that are made for power injection.  These carry the data and ground straight through, but break the positive line.  Your drawing above is fine, except you would use these Power-Injection "T" connectors instead of the "Y" connector that you drew.   Actually, I'm not sure that I've seen anybody selling a "Y" connector like you drew.  Usually they are P-I Tees.


Here is a very good resource for Power Injection info...
http://www.doityourselfchristmas.com/wiki/index.php?title=Power_Injection

so off the power supply you would solder a pig tail to the v+ in both spots and the ground in the one spot then plug it into the t?


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[tbone321]

I can honestly say that I don't have a clue as to what that diagram is representing either.  If anything, it makes things FAR more confusing than it really is but maybe I just don't understand what that diagram is saying.

[Broomy111]

This way I look at the diagram is the power does not pass through, on the T, to the next string.  Only the data is passing and the ground, and so the injection would bring the power to the next string, and not go backward to the other string.  Right?  I still am a little confused and may not try power injection this year, to try and keep it easy.  Just might have to add 1-2 controllers additional.


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[tbone321]

Ok, if this is representing the connections of the T connector, then it does make sense.  Now I see why the two ports are labeled "to string" and yes, the data line passes through untouched and the ground is tapped into but remains connected.  The positive is separated so that if you are using separate power supplies on the two sections, they are not connected on the positive side. 

[AussiePhil]

What's more important is to break the positives when switching PSUs. 
Do not have the positive from one cross with the other.

Why?

I agree with regards to connecting them together in the one box but it's completely irrelevant by the time you get out to a pixel string and can actually be of benefit.

The ONLY time you have to break the positive is if you have different voltage strings.

[markrvp]

What's more important is to break the positives when switching PSUs. 
Do not have the positive from one cross with the other.

Why?

I agree with regards to connecting them together in the one box but it's completely irrelevant by the time you get out to a pixel string and can actually be of benefit.

The ONLY time you have to break the positive is if you have different voltage strings.

Are you sure?  EVERYTHING I've read says you have to break the positive leads when using different power supplies.  It would be much more convenient if you didn't have to. 

[AussiePhil]

Are you sure?  EVERYTHING I've read says you have to break the positive leads when using different power supplies.  It would be much more convenient if you didn't have to.

Yes i'm absolutely sure with the following criteria

* You DON'T join the supply positives directly together at the supply.
* You DON'T join the supply positives directly together without some pixels between each connection.
* You MUST have the two or more power supplies at the same voltage or as close as you can get.

The SMPS units that are generally used have no current sharing capability, however all power supplies can share current via balancing resistors.......... guess what a string of pixels works perfectly as..........

[JonB256]

From way, way back in my electronics training -

Power supplies maintain a constant voltage by using "feedback."  They have an internal reference voltage that can be either fixed or adjustable. When the main output voltage drops below the internal reference voltage, the main circuitry adjusts to raise the voltage back to equal with the reference. If main voltage goes above the internal reference voltage, the main circuitry adjusts to bring it down to equal the reference.

Those adjustments take time. Not a long time, but it is measurable. The adjustment method is not exact, either, so it usually overshoots a little and has to readjust until it becomes a steady output. Now, imagine connecting two power supply outputs together. If one is even slightly higher than the other, they will both adjust trying to match. Now the other one is higher. They try to match again, and again and again. This puts them in a feedback loop, like when someone gets a microphone too close to a speaker and you hear than horrible high pitched squealing. Power supplies can actually damage themselves if not designed well.

But, if you have a "load" between the two power supply connections (some pixels, more than a few), that load will usually stop feedback.

[AussiePhil]

From way, way back in my electronics training -

Power supplies maintain a constant voltage by using "feedback."  They have an internal reference voltage that can be either fixed or adjustable. When the main output voltage drops below the internal reference voltage, the main circuitry adjusts to raise the voltage back to equal with the reference. If main voltage goes above the internal reference voltage, the main circuitry adjusts to bring it down to equal the reference.

Those adjustments take time. Not a long time, but it is measurable. The adjustment method is not exact, either, so it usually overshoots a little and has to readjust until it becomes a steady output. Now, imagine connecting two power supply outputs together. If one is even slightly higher than the other, they will both adjust trying to match. Now the other one is higher. They try to match again, and again and again. This puts them in a feedback loop, like when someone gets a microphone too close to a speaker and you hear than horrible high pitched squealing. Power supplies can actually damage themselves if not designed well.

But, if you have a "load" between the two power supply connections (some pixels, more than a few), that load will usually stop feedback.

Agreed, but that string of 50 pixels means that the voltage from one supply is effectively not seen by the other one due to voltage drop.

Guess what I'm saying is that for pure power injection at a T junction it's just not required to break the positive, just don't join the supplies together in the one box.