LED power management

Question

I am creating a led grid with 176 cells. Details:

• The size of each cell is 30cm x 30cm.
• Each cell contains two WS2812 LEDs that work under 5 volts.
• The power supply unit has to be placed 10~20 meters away from the led grid.
• To minimize the current value and voltage drop, I decided to use a 350W, 24V power supply unit.

Power management proposal:

• Each led @ full brightness consumes about 0.5W, one row has 16 cells, each row consumes about 0.5w x 2leds/cell x 16 cells = 16W
• At the location of the PSU, split the power into 12 channels: 11 channels to 11 rows and 1 channel to MCU. Each channel is protected by a 2A PTC resettable fuse.
• Each row consumes 16W which is going to be about 16w/24v = 0.66A. Considering the power consumption through the wire. I assume each row uses 24V/1A~0A (Sometimes one row can be all off and another row is on full brightness)
• Each channel feeds the power to one row.
• 24V channels are stepped down to 5V by a buck converter. This is to ensure every LED has the same brightness without voltage drop.

Questions:

• How can I ensure that each signal shares the same ground reference? How should I connect the grounds properly?
• How can I improve the design?

Answer 1

a) NO buck converter is 100% efficient, 85% is more realistic. 0.66A/85% = 0.77A

c)Worst case scenario: Assume star ground connections with star point on the side of the grid.

Assuming 5m per row and 0.5mm2 wire we get 171 mOhms per row. Current will be dropping with every cell, thus voltage drop will be well below 100mV. If we take into account fact that each WS2812 is acting as amplifier you can ignore ground wire voltage drop.

d) Run one thick(2.5-4mm2) cable from PSU to the grid, then spit it into 11 rows.