“Why when I DIM my LED strips using high quality LED controller are not damaged”?
Proper dimming is not by varying the voltage but through a PWM LED controller that still supplies 24 Volts to the LED strips and controls the brightness by varying the frequency and not the voltage.
Installing LED Strip Lighting - Voltage Drop considerations!
DC Voltage drop calculation example for 20 meters distance from the PSU using 4.0 mm copper cable - Load: 300W / 24 Volts
DC Voltage Drop = (2 X L X R X I) / S
L= 20m (distance from the LED Driver/PSU)
R= 0.0175 (generally used for copper stranded cable)
I= 12.5Amps (as an example for 300W/24V)
S= 4mm diameter cable (Using a 4mm dia. cable)
Voltage Drop= (2 X 20 X 0.0175 X 12.5) / 4 = 2.19 Volts
If we supply 24 Volts from the PSU the Led Strips will operate at 21.81 Volts since 2.19 Volts will be the voltage drop due to wiring (24V - 2.19V)
Results for the same load using 1mm copper wire:
Voltage drop = 8.75 Volts!
In this case LED Strips will operate at 15.25 Volts!
Except that the brightness will reduce about 60%, the LED strips will be unstable and decay of the LED chips will increase dramatically. As a result within a few months or less the LED strips will get damaged!