According to the schematics for RAMPS 1.4, the resistors for the Mosfet LEDs are supposed to be 1.8 K ohm (1K8)
If the voltage drop over the diode is about 2 volt, then the rest of the voltage is handled by the resistor.
At 12V this will leave 10V for the resistor. 10V / 1K8 ohm = 5.5mA
At 24V the resistor has about 22V to deal with. 22V / 1K8 ohm = 12mA
A LED will typically work just fine, all the way up to 20mA, so even though you use 24V, then the LED is not beyond its specified limits.
The resistors, however, they might get quite hot.
0805 sizes are typically rated for 1/8th watt (0.125W = 125mW), but recommended for only 1/10th watt (0,1W = 100mW)
0603 sizes are typically rated for 1/10th watt (0.1W = 100mW), but recommended for only about 60% of that (0,063W = 63mW)
At 12V the resistor deals with 10V x 5.5mA = 55mW - so that is okay.
At 24V the resistor deals with 22 x 12mA = 264mW - this is way over the recommended limit
If there is enough copper connected to the resistors, it will act as a heat sink, and will keep the temperatures lower.
But otherwise the heat from the resistors, will likely cause the LEDs to heat up, and the LEDs will no longer be able to sustain 20mA through them.
As the worst case (24V operation) will still only subject the LEDs to 12mA, everything may be okay. For a very long time. LEDs typically have a 20,000 to 50,000 hours lifespan. But longer if they are not subjected to the full 20mA.
I will typically use 3K3 resistors when I have a LED + resistor, that is subjected to 24V
With a 3K3 resistor (with 22V over the resistor) is 22V / 3K3 Ohm = 6mA
6mA x 22V = 146mW - still very high, but with enough copper around the resistor, it will survive just fine.
I hope these numbers are helpful for you, to determine if you want to worry further about the LEDs
Edited 2 time(s). Last edit at 03/06/2022 11:04AM by MrAlvin.