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LED Strip - Power supply

Posted 2yr ago
by DeathBloom | Junior | 772 exp
Posted 2yr ago
by DeathBloom | Junior | 772 exp
Dear friends,

I beg for your knowledge of electricity in order to sort out the following problem.

What I have:
- 1m strip of WS2813 - 60 LEDs total
- FEZ Panda2 to send the signal to basically light all the LEDs
- The 1000 µF, 6.3V capacitor is added between + and - of the power supply outputs as it's stated here:
https://learn.adafruit.com/adafruit-neopixel-uberguide?view=all#improper-use-can-damage-your-neopixels-before-diving-in-be-aware-of-the-following

So, when I use a 4.5V 0.5A 6W wall adapter from my old Panasonic CD player I am able to make the whole strip lit with no problems.
However, my final project needs about 600 LEDs and I've decided to buy a much larger power supply. Here's basically it:
https://goo.gl/dqBiiQ

As you see it's 5V 40A 200W. Since I don't have 600 LEDs right now I've decided to test it with the same LED strip as above. As a result only 2 or 3 LEDs lit with some random colors. When I switch the power supply back to the smallest one - everything is fine again.

Do you know the reason for this mystery?
Reply #1 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
Reply #1 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
@DeathBloom, Did you try switchin the power on and then connecting the neo pixels?
From AdaFruit:
Some — even reputable, well-regarded brands — can produce a large voltage spike when initially switched on, instantly destroying your NeoPix

Also, if you're running the neo pixels at 5V, are you using a logic level shifter to convert the µC voltage to 5V levels? If you were using 4.5V before without a level shifter, then you were doing it wrong in the first place. If you can, try getting a voltage regulator to convert the 5V down to ~3.3V (don't forget the heat sink on that regulator).
Reply #2 — Posted 2yr ago
by Brett | Superhuman | 125,590 exp
Reply #2 — Posted 2yr ago
by Brett | Superhuman | 125,590 exp
So my first instinct is to talk about signal integrity and my second is to talk about voltage level shifters for signals. Honestly though, if you're asking these kinds of questions when you are about to scale up, you have many things to worry about. Power is certainly going to be your #1 concern (as you need a heap of power to light all WS2813's at full intensity white, if your demand requires it), but there are other aspects like speed you can send the data to the chain(s) will also be pushing things. If you aren't comfortable with the power change to 5v power supply, you'll have other power challenges you won't be able to deal with as you scale up
Reply #3 — Posted 2yr ago
by VersaModule | Senior | 4,994 exp
Reply #3 — Posted 2yr ago
by VersaModule | Senior | 4,994 exp
Something else to be aware of. Most of these strips have a plug on either end, This misleads people into thinking they can just keep slapping one led strip onto the end of the next, and make one super long strip.
Many people miss this point that you cannot keep adding strips, because the power and ground traces on the strip cannot handle that kind of current. If using say 3, 15 meter strips back to back, the 3'rd strip will have dimmed leds compared to the first 2.

Just something else to know.
1 like
Reply #4 — Posted 2yr ago
by Dave McLaughlin | Legend | 58,471 exp
Reply #4 — Posted 2yr ago
by Dave McLaughlin | Legend | 58,471 exp
Another thing to consider is that often larger current output supplies often require a minimum load to maintain good regulation on the output. I could not find anything in the website about this but something to consider.

Have you checked the actual voltage of the supply when you use it on the smaller LED strip? It may be higher than 5V.
Reply #5 — Posted 2yr ago
by DeathBloom | Junior | 772 exp
Reply #5 — Posted 2yr ago
by DeathBloom | Junior | 772 exp
Hi! Thanks all for the replies! Here're my comments:

Mr. John Smith says:

@DeathBloom, Did you try switchin the power on and then connecting the neo pixels?

No, the schema was assembled and I've just switched on the power. I will try this out, thanks for the hint. However, none of NeoPixels were destroyed as I've then checked all of them again with the initial smaller capacity power supply.

Mr. John Smith says:
Also, if you're running the neo pixels at 5V, are you using a logic level shifter to convert the µC voltage to 5V levels? If you were using 4.5V before without a level shifter, then you were doing it wrong in the first place. If you can, try getting a voltage regulator to convert the 5V down to ~3.3V (don't forget the heat sink on that regulator
According to the datasheet it can run 3.5-5.3V. So it looks like both power supplies are good.
https://www.element14.com/community/servlet/JiveServlet/downloadBody/82167-102-1-346252/WS2813%20LED%20Datasheet.pdf
I believe there's something in WS2813 that takes care of this.
Brett says:
If you aren't comfortable with the power change to 5v power supply, you'll have other power challenges you won't be able to deal with as you scale up
I think I am ok with it, just the thing that I can't understand why my larger power supply doesn't work as expected. I will get a multi-meter soon and check out the real voltage and current strength.
VersaModule says:

Something else to be aware of. Most of these strips have a plug on either end, This misleads people into thinking they can just keep slapping one led strip onto the end of the next, and make one super long strip.
This is true. For my project I will need around 4 meters of the strip. I've calculated and came up with the plan that I need to run it in parallel every 2 meters, so basically only 2 power connections. The data signal though will run serially.
Dave McLaughlin says:

Another thing to consider is that often larger current output supplies often require a minimum load to maintain good regulation on the output. I could not find anything in the website about this but something to consider.

I've read about it yesterday somewhere. Nice catch. Do you think a resistor will be a good / enough load? Any ideas on Ohms?

Dave McLaughlin says:

Have you checked the actual voltage of the supply when you use it on the smaller LED strip? It may be higher than 5V.

Yeah, this one I am about to check soon... The typical case when you are a programmer and not electrician: you usually believe on whatever is written in specs and don't check with multi-meters as you don't have one Cheesy
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Reply #6 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
Reply #6 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
@DeathBloom -
According to the datasheet it can run 3.5-5.3V. So it looks like both power supplies are good.
https://www.element14.com/community/servlet/JiveServlet/downloadBody/82167-102-1-346252/WS2813%20LED%20Datasheet.pdf
I believe there's something in WS2813 that takes care of this.

No, I'm talking about logic levels. For a voltage to be considered logic level high, it has to be at least two thirds (2/3) of the supply voltage (aka VCC). If you're running at 4.5 volts then logic level high starts at 3 volts. If you're running at 5 volts then it's 3.3 volts. Now since your µC is running at 3.3 volts, then it's 2.2 volts. Now since there will definitely be a voltage drop between the pin of the µC and the first LED, if you're running at 5 volts, then that first chip is most likely never going to identify the µC's less than 3.3v logic output as logic level high.

This can explain why it works at 4.5 volts and not at 5 volts.
Reply #7 — Posted 2yr ago (modified)
by DeathBloom | Junior | 772 exp
Reply #7 — Posted 2yr ago (modified)
by DeathBloom | Junior | 772 exp
Mr. John Smith says:

No, I'm talking about logic levels.

Ah... you are totally right... and it's also written on Adafruit:

NeoPixels powered by 5v require a 5V data signal. If using a 3.3V microcontroller you must use a logic level shifter such as a 74AHCT125 or 74HCT245. (If you are powering your NeoPixels with 3.7v like from a LiPoly, a 3.3v data signal is OK)

I've did some calculations using the WS2813 datasheet where:
Vih = 0.7 * Vdd = 0.7 * 5.3 = 3.71
Vil = 0.3 * Vdd = 0.3 * 5.3 = 1.59

and it looks like with 3.3V logic I am missing the HIGH segment, though LOW is ok. I suppose there's no 5.5v MOSI pin in Fez Panda2 so I will really need a logic level shifter.

And ongoing question: If I have that shifter in place do I need to place a resistor in between the data output of my controller and data input of the LED strip as it's said here:
Place a 300 to 500 Ohm resistor between the Arduino data output pin and the input to the first NeoPixel. The resistor should be at the end of the wire closest to the NeoPixel(s), not the microcontroller.
Is it to protect the NeoPixel from a voltage spike of a controller? If I have a shifter I suppose that resistor still should be place between the shifter and LED strip, correct?

I was also checking the output voltage of power supply and it is ok - 5.2 V. I've accidentally touched the data input of the LED strip and it all turned white - so it proves the Power Supply is ok.
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Reply #8 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
Reply #8 — Posted 2yr ago
by Mr. John Smith | Legend | 42,263 exp
@DeathBloom - If the power supply is driving at 5.2V then logic level high is 3.46 Volts! I think the resistor is mainly to ensure that there isn't too much current draw from the µC (which has its own set of problems). Since you're doing the logic level one way, you might just need a NPN transistor to drive the LEDs (but only if you can't get a logic level shiftier).

Connect Base to µC with 500Ω resistor in series.
Connect 1KΩ between the base and GND.
Connect the Collector to VCC via a 1KΩ resistor.
Connect the Emitter to the LED, and the Emitter to GND via a 1KΩ resistor.

Your resistor values will vary based on supply voltage.
Reply #9 — Posted 2yr ago (modified)
by DeathBloom | Junior | 772 exp
Reply #9 — Posted 2yr ago (modified)
by DeathBloom | Junior | 772 exp
@Mr. John Smith,

thanks for the reply!

Do you think this schema is what I need?

http://dspview.com/download/file.php?id=385&sid=c2db657f14de96a2c8ffc0cc5159fe37


but only if you can't get a logic level shiftier

I probably can, however, I am unable to find any schema with it in action. I am really lost in all of its pin-outs and data-sheet doesn't make it easier to understand. Do you have any examples maybe?
Or is it only about connecting:
- Digital output of a controller to A1
- input of the LED strip to B1
- 3.3V from the controller to VL
- 5V from the controller to VH

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