My Numbers are out of wack.

A

algerdes

Supporting Member
Please help me get my head straight on this. My math keeps going all over the place when I try to figure it out. (Been up most of the night.)

32 strings of 12vdc pixels (Mega Tree). Each string is 130 pixels long.
Kulp K32A-B for the controller with each of the outputs driving a string.

The K32A-B has 8 outputs on each of the power inputs (4 total).

I have two HP750watt (12 vdc) power supplies. The breakout board has 4 outputs (power), each fused with 25 Amp fuses.

Can these power supplies drive the tree?
 
Roughly speaking...

Each power supply can source/sink 50A (750W/12V*.080 = 50). Each power supply can provide power for 833 pixels @ 100% while (50A/(.060A/pixel)). Two such power supplies can therefore drive 1666 pixels. You have 32*130 = 4160 pixels.

Another way to look at it is each string dissipates 93.6W (130 * 12V * .060A) at full brightness. 32 such string would dissipate 3000W, about 2-1/2 times what your two power supplies can supply in total (1200W = 750 * 2 * .80).

This is just looking at total numbers, ignoring how you would split the current up among the 32 strings.
 
32 ports x 132 pixels = 4224 pixels.
12v x 0.06a = 0.72w per pixel
4224 * 0.72 = 3041W
Your two supplies have 2 * 750 * 0.8 = 1200w capacity so at full brightness, the answer is no they cannot support your pixel tree.
You will need five supplies for your tree.
 
`I have similar trees and calculated the same as above, but I run one tree at 25% and the other 30% and I have never worried with 4 30 amp supplies for each.
At 100%, yeah, you would need more supplies.
 
Measure your strings before buying more power supplies. I run Paul Zhang lights from Amazon and they use less than half of your calculations. I run at 40% which uses about 1 amp per 100 leds, with power balancing I run a PPD wreath of 600 pixels on one output with no problems. With no power balancing or power injection I run up to 300-350 pixels on a K16 output.
 
Just thought I would leave you all with this "lesson learned".

As stated, the K32A-B has 4 power inputs with 8 outputs assigned to each one of them. If all 8 of the outputs were to pull a "full load", that would be 40 Amps being fed for the section.
We decided to run two 750 watt HP power supplies, with each one feeding two of the inputs. We also decided to run the entire tree at 20% load. Math says it will work, nicely.

I set the controller, manually, and ran tests. Sure enough, it worked.

Then we setup xLights to take over the job of setting up the controller. So far, so good.
After running through a couple of our sequences, we hit one where the big tree did a momentary "all white". Very short, but it was there.
I promptly blew all 4 of the 25 Amp fuses on the two 750s that were feeding the tree. "What the heck?" We had been running the tree for some time, in test. (Red-Green-Blue-Repeat)

Turns out that xLights had the "Default Port Brightness" set to 100%. When I updated the controller with other changes (using FPP Connect), the controller was reset to that 100% from the 20% that I manually set earlier. 4,150 pixels at full white at 100%! 1,037 per power input. 2,075 per power supply. Hmmmm.....

The idea to have power supplies equal to, or bigger than the need of the controller at 100% is a good thing, but not realistic for us. The idea of setting the power level in the controller lower is much more our speed.

Just know who/what is controlling your system. I know I will from now on!!!
 
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