As Barbie said, "Math class is tough!"

[bobschm]

I have 2811 rgb 5v nodes and I'll run only 100 pixels off each 5v 10A buck convertor. But how do I determine how many of these drops I can run from a 24v 15A power supply? 

Do I convert everything to watts and calculate that? 

[EmmienLightFan]

4 hours ago, bobschm said:

I have 2811 rgb 5v nodes and I'll run only 100 pixels off each 5v 10A buck convertor. But how do I determine how many of these drops I can run from a 24v 15A power supply? 

Do I convert everything to watts and calculate that? 

Convert all to VA or watts.

[k6ccc]

I have 2811 rgb 5v nodes and I'll run only 100 pixels off each 5v 10A buck convertor. But how do I determine how many of these drops I can run from a 24v 15A power supply? 

Do I convert everything to watts and calculate that? 

It depends on the converter. In the worst case, the converter simply drops the voltage as heat to convert 24 volts to 5 volts. In that case, amps is everything - 10 amps at 5 volts will require 10 amps at 24 volts (with 190 watts of heat generated at full load). That would be normal for most linear converters - not common any more.

In the best case, the converter will have the same wattage in as out. In other words, 10 amps at 5 volts (50 watts), would require just over 2 amps at 24 volts (50 watts). You will never get a converter that meets that beat case (100% efficiency). For many switching regulators, they will be far closer to the best case, but you need to check the specs of the converter. In many cases, the specs will give an idle current plus an efficiency. For example it might spec 90% plus 5 watts. In that example, if there was 27 watts of 5 volt load (5.4 amps), the converter would input 35 watts (5 watts of idle load, plus 30 watts for the 90% conversion) - or just under 1.5 amps at 24 volts (with 8 watts of heat produced). BTW, the numbers I just gave would be pretty bad, but I picked the numbers to make the math easy.

Sent from my Droid Turbo via Tapatalk, so blame any typos or spelling errors on Android

[bobschm]

Ok. If I convert everything to watts, I end up with 15A able to run 1200 pixels. Since I'll only be running 1088 pixels on this matrix prop, I should be safe. I suspect the convertors are pretty efficient, since I tested one with 100 pixels on full white for several hours and there was no heat change at all.