4.2v power supply for 5v pixels?

Bradistherad1

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I found a bunch of 40a and 60a power supplies for free but they are 4.2v. I played around with the voltage adjustment and they can go up to 4.8v, would I be able to use these power supplies for my pixels?
 

Mark_M

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They'll just light up 5v pixels.
Although I guess you will have a a lot more power injection (ACL 101 manual states what power injection is).

My video from 2019 tested a 12v pixel with the lowest voltage it could go.
12v pixels are basically 5v pixels with a voltage converter inside. Lowest stable operation I got was exactly 4.8v, after that it wouldn't work.

I guess a 5v only pixel might be able to light up at 4.6v.
 

AussiePhil

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I found a bunch of 40a and 60a power supplies for free but they are 4.2v. I played around with the voltage adjustment and they can go up to 4.8v, would I be able to use these power supplies for my pixels?
Some real world experience and practical measures tell us that if you wind them up to 4.8v then in general you will be fine if your powered 5v pixels.
I literally just measured a 100 count string of 5v pixels.
Input voltage to String -> 5.03v
Voltage at end of the sting no lights -> 4.78v
Voltage at end one colour -> 2.9V @100% brightness for 100 bulbs
Voltage at end white -> 2.6V @100% for 100 ... last 20 odd lights tinged red

Blue leds typically have a Vf of 2.6v@20ma so it's not surprising blue drops away first but it is still on just not as bright

If you start with 4.8V rather than 5v you may have to inject maybe 10 pixels earlier or run at 70% or less global brightness.

TLDR: they will work fine, hook up a string and test.
 
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AussiePhil

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They'll just light up 5v pixels.
Although I guess you will have a a lot more power injection (ACL 101 manual states what power injection is).

My video from 2019 tested a 12v pixel with the lowest voltage it could go.
12v pixels are basically 5v pixels with a voltage converter inside. Lowest stable operation I got was exactly 4.8v, after that it wouldn't work.
sort of surprised you got down to 4.8 as that is under the voltage for proper regulation of a 78L05, spec sheets says line regulation from 5.3v to 20v so anything under 5.3 wasn't regulated
 

Dreamin

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Just have the PSU close to the prop and it will be fine, power inject every 100 pixels to keep the power up. Run your lights at 30% and it will have plenty of headroom.

5V gets bagged a lot (same with strip) but has some benefits, yes you have to wire more, but in most of my props that's just attaching the beginning power to the end. Not a major drama. The benefit is more lights per Power supply, and less power supplies to run my show. :)
 

bpratt

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5V gets bagged a lot (same with strip) but has some benefits, yes you have to wire more, but in most of my props that's just attaching the beginning power to the end. Not a major drama. The benefit is more lights per Power supply, and less power supplies to run my show. :)

My show was 12v only, but this year with HD props, I'm using 5v pixels in them because I can put the psu right next to it, as well as less psu's too.
:)

I use Ray Wu connectors for 12v and xconnect for my 5v stuff, so shouldn't accidentally hook up the wrong things.
 

Bradistherad1

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Just have the PSU close to the prop and it will be fine, power inject every 100 pixels to keep the power up.
That's good to hear, I will probably power inject every 50 pixels. I'm going to make extensions with ethernet cable meaning 0.75mm2 cable from the power supply to the prop (max distance 5 metres) would that cause problems?
 

TerryK

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As was mentioned in another post, set them as high as possible. If by chance any can reach higher, stop at 5.1 Volt. 5 Volt pixels can handle the extra 0.1 Volt and it will give a bit of added 'cushion' against voltage drop. The lower supply voltage may require either shorter or larger gauge size wire depending upon your design's physical structure.

Also as previously mentioned, the number of pixels between the points of power injection will need to be decreased. A bit of testing should give you an idea of how many.
 

AussiePhil

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As was mentioned in another post, set them as high as possible. If by chance any can reach higher, stop at 5.1 Volt. 5 Volt pixels can handle the extra 0.1 Volt and it will give a bit of added 'cushion' against voltage drop. The lower supply voltage may require either shorter or larger gauge size wire depending upon your design's physical structure.

Also as previously mentioned, the number of pixels between the points of power injection will need to be decreased. A bit of testing should give you an idea of how many.
Hi Terry, I'm curious were the 5.1v limit comes from. The common WS2811 IC actually calls for a Vdd of 6v to 7v with Vin +-0.5v from Vdd. 10% hot on the voltage is well within limits ie 5.5v.
In Brads case though he did say he could only get to 4.8v and real world this should also be fine, just a little less distance for power injection.
Cheers
Phil
 

TerryK

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The original post was not precise as to what would be connected to the supplies, so I opted for a conservative response. Most switching 5 Volt supplies new from the manufacturer with no load will regulate in the 5.1 to 5.2 Volt range give or take a bit. That is where the 'target voltage' of my post originated. And may I politely add, not a limit.

While correct that a WS2811 Vdd Absolute Maximum rating is 6.0 to 7.0 Volt, induced noise and transient spikes on the V+ cabling can easily raise the 5 Volt above a point where 5 Volt electronics get 'uncomfortable'. Too, if one was powering WS2811 pixels somewhere in a 6 to 7 volt range, then power to the controller may become an issue. An rPi powered via the GPIO pins appears to be speced at 4.75 to 5.25 Volts. WS2801s are 3.3 to 5.5 Volt and WS2812Bs are 3.5 to 5.3 Volt.
 

Bradistherad1

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So I have done some experimenting:

Luckily, these power supplies don't have much voltage sag under load, under no load I measured 4.82v, and under around 30a of load, I measured 4.75v. For testing I used an Arduino Nano, running FastLED outputting full brightness white, and on its own 5v power supply. The pixels I am using are the super cheap ones, similar to Ray Wu's "Promotion" pixels.

With a 50 pixel string, the last few pixels are noticeably orange, but when injecting power at the end of the string, there is no visible difference between the middle pixels and the end/beginning pixels. Just for fun, I tried with 100 pixels, the last 30 or so pixels were extremely orange, and the last 5 pixels were flickering red.

Most of my props are only 50 pixels, and it won't be an issue to inject power for the props with more than 50. I have ordered some cat5e solid core cable to make some extensions, but since I am in lockdown, it could take a while to arrive. I will update with voltage drop tests once I get the cable.
 

AussiePhil

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So I have done some experimenting:

Luckily, these power supplies don't have much voltage sag under load, under no load I measured 4.82v, and under around 30a of load, I measured 4.75v. For testing I used an Arduino Nano, running FastLED outputting full brightness white, and on its own 5v power supply. The pixels I am using are the super cheap ones, similar to Ray Wu's "Promotion" pixels.

With a 50 pixel string, the last few pixels are noticeably orange, but when injecting power at the end of the string, there is no visible difference between the middle pixels and the end/beginning pixels. Just for fun, I tried with 100 pixels, the last 30 or so pixels were extremely orange, and the last 5 pixels were flickering red.

Most of my props are only 50 pixels, and it won't be an issue to inject power for the props with more than 50. I have ordered some cat5e solid core cable to make some extensions, but since I am in lockdown, it could take a while to arrive. I will update with voltage drop tests once I get the cable.
Always good to prove the theory with tests, glad you will be able to use them
Cheers
Phil
 

i13

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Stranded cable is generally a better option than solid core cable in this hobby. Solid cores are a single wire core; they're prone to breaking unless they're permanently mounted on something. Cat5e cable is also quite thin so there may be a noticeable amount of voltage drop or heat within it. You might need to double up the cores if you're using it for power. Never double the data core.
 
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