# Checking my calculations

#### MikeyK

##### New elf
Hi,
I'm not sure if this is the right place to post this;
I'm only a beginner in this, and starting small compared to some of the pixel counts I've been seeing.
From my calculations I think I need a third PSU, and will probably get one anyway to do some power injection.
This is my setup;
E682 controller, with two 350W Ray Wu PSU's
On outputs 1-1 to 1-4 I have 4 X 100 square pixel strings (Ray Wu's site says 0.6w each)
On output 2-1 one 5 meter length of 60leds per meter strip. (Ray Wu's site says 72w per 5 meter strip)
On outputs 3-1 to 3-4 I have 4 X 100 bullet pixel strings (Ray Wu's site says 0.8w each)
On outputs 4-1 to 4-2 I have 2 X 100 technicolour pixel strings (Ray Wu's site says 0.6w each)
And output 4-3 1 X 50 technicolour pixel strings.

So;
650 pixels X 0.6W = 390W
plus
400 pixels X 0.8W = 320W
plus
5 Meter pixel strip 72W
= 782W
P(W) / V(V) = I(A)
782W/12V=65.16A
Is this correct?
So am I right in needing a 3rd PSU? And can I use the 3rd PSU to just power inject for the 4 X 100 bullet strings as they will be running along a fence line the far end being a long way from the controller.

This is my setup so far, I still need to add fuses, run cabling correctly ect. I have a spare 3rd CG1500 that I might put the 3rd PSU in for power injection.

#### AAH

##### I love blinky lights :)
Community project designer
Most of your calculations look right and based on them it looks like you're using 12V pixels. For nodes 5V would have saved you heaps of wattage at the expense of having to add a bit of extra/heavier cable. Same light for more than double the power for 12V vs 5V.
Great to see the use of bootlace ferrules
It will be necessary to ventilate the boxes as there will be a fair bit of heat to get rid of in such small boxes.
The power injection power supply will be needed. All you need to do is get gnd and data out to the pixels and tap in gnd and 12V out close to those pixels.

#### MikeyK

##### New elf
Thanks for your reply. I still need to tidy up the cabling.
I've been looking at some vents with a cowl on the outside to keep the weather out.
For extending the pigtails to the locations where I want to put the pixels, would something like this do? "3 CORE .75mm 24/0.20 BLACK FLEX" or should I use something thicker? like "3 CORE 1mm 32/0.20 BLACK FLEX 100m ROLL"

Cheers

#### AAH

##### I love blinky lights :)
Community project designer
Without knowing how far you're running it's hard to say what cable is suitable. There's never any harm in using heavier cable then necessary.
In the new ACL101 there's some info on calculating cable voltage drop and what's suitable.

#### Kitman

##### Full time elf
Just also be aware that if you are running power through your E682 in order to power the pixels you only have a 5amp fuse on each output. Running 100 pixels off the one connection should be OK unless you ran the 100 pixels on full white which comes out to exactly 5amps so you may blow the fuse on the E682.

I do run multiple E682's for my display and limit each output to 100 pixels or less, then when programming I ensure I avoid running at full white.