Pixels per Power Supply

[deblen]

Hi,

I am trying to find out how one works out to calculate pixels per power supply, by using percentage's

Is there any formula one can use.

Example, have a 350 watt power supply, if i run at 80% how many pixels,, if I choose to run at 50% how many pixels.

I f I have a 500 watt power supply same again, how many at 80%, 50% or 40%.

12 volt pixels.

The reason is to find out how many pixels I can use for High Dentsity props.

Trying to cut down on power supplies..

Thanks In Advance

Len

 

[djgra79]

I used David's calculator online: https://www.da-share.com/calculators/led-strip-string-current/

An example of how I do this is below for one of my 12v PSUs
Below is 12v 2811 strip (3x leds per pixel)


Below is 5v nodes:

 

[i13]

The wattage of a pixel is its current draw multiplied by the voltage. WS2811 pixels (I'm assuming that's what you're using because they're the most common) can't exceed 0.0555 amperes at 100% brightness white. Multiplying this by 12 volts gives a wattage of 0.666 watts per pixel. If you want to run them at 80% brightness, multiply their wattage by 0.8 to get 0.5328 watts per pixel. To calculate the maximum number of pixels that you can have on a power supply, divide the power supply's wattage by the wattage per pixel. For a 350 watt power supply and pixels at 80% brightness, this is 350/0.5328 = 656 pixels. Repeating this calculation:

• 350 watt power supply, pixels at 80% brightness: 656 pixels
• 350 watt power supply, pixels at 50% brightness: 1051 pixels
• 500 watt power supply, pixels at 80% brightness: 938 pixels
• 500 watt power supply, pixels at 50% brightness: 1501 pixels
• 500 watt power supply, pixels at 40% brightness: 1876 pixels

There are other factors that may affect these numbers:

• The pixels might draw less than 0.0555 amps. If they draw less then you can have more pixels per power supply.
• There is some risk in lowering the brightness to reduce the total load. This is because you're relying on the data signal to do it. If the data signal goes corrupt or you misconfigure it, there is no guarantee that the pixels won't exceed the set brightness. I'd recommend fusing, being prepared to replace fuses and leaving some headroom if you do this.
• Voltage drop may lower the current draw (and therefore the wattage) of the pixels. There will always be some amount of voltage drop, even if it isn't enough to noticeably affect the colours.
• If these are Mean Well power supplies, check the datasheet and don't assume that it is 350 or 500 watts based on the model number. For example, the LRS-350-5 power supply is 300 watts and the LRS-350-12 is 348 watts.

Another point that I want to raise: If you want to have high density props without many power supplies, I'd suggest trying 5V pixels. The only advantage of 12V pixels is that voltage drop is less of a problem; it doesn't need power injection as frequently. In my opinion, there isn't much to gain from this advantage when you have a high density display items with power supplies nearby. Voltage drop happens over distance and in long runs of cable. High density props have a large number of pixels in a small area, making power injection practical. If I repeat the above calculations with 5V pixels, I get:

• 5V, 350 watt power supply, pixels at 80% brightness: 1576 pixels
• 5V, 350 watt power supply, pixels at 50% brightness: 2522 pixels
• 5V, 500 watt power supply, pixels at 80% brightness: 2252 pixels
• 5V, 500 watt power supply, pixels at 50% brightness: 3603 pixels
• 5V, 500 watt power supply, pixels at 40% brightness: 4504 pixels

 

[AAH]

For high density props there really is no better option than 5V pixels. Cheaper, more efficient and less than half the number of power supplies required.

 

[deblen]

Hi All,

Thanks for the feed back, especially I13, a great amount of excellent detail.

Now I have a better understanding .

Than ks Len

 

[AussiePhil]

One thing not yet mentioned is that you really should consider max current from the supply to be 80% of it's rated value, yes you can push it harder but your not really leaving any headroom.
so it's easier to deal in amps rather than power.
Lets say we push it to 90% so a generic 5v supply would be around 45A of current available from it's 50A rating yep those 350w supplies at 5v top out at 50A/250w and the LRS350 tops at 60A/300w
Allowing 10% headroom further pulls this down to 54A

At 100% White
100 cnt of 5v pixels will draw 4.6A in the real world tests and would need 5.5A based on the older 55mA per pixel rule

This table is based on the actual measurements of a brand new string of Ray Wu 5v pixels with 18awg wiring

	100%	90%	80%	70%	60%	50%	40%	30%	20%	10%
Single Colour	1.76	1.58	1.4	1.24	1.06	0.88	0.72	0.54	0.38	0.2
Dual Colour	3.32	3	2.68	2.32	2	1.66	1.32	0.96	0.64	0.29
White	4.64	4.23	3.8	3.35	2.88	2.39	1.9	1.38	0.88	0.37

It is up to you how you calculate you maximum number of pixels but remember that the % brightness is under software control and it is always possible a display may get 100% setting by accident.... this can cause supplies to shutdown when driven overload.

 

[deblen]

Hi Phil,

Thanks for the info.

If I did increase the number of pixels to correspond with the brightness percentage done by the software, and I fused the positive with a fuse that would blow if there was a spike.

Example run a 350 watt power supply, pixels at 50% brightness: 1051 pixels, use a low amp fuse .

I am talking 12 volts

Thanks Len