Input voltage limits

Which chip? The NB679 or the RK3399?

24V. Limit is 20V. HMMMM.

It was said multiple times here, that users even unsure, that 20V is alright for RockPi and here you are. Using 24V.

Like, why? Tell me, why?

With EN connected to VCC via a 10/5.1 Ohm divider, and EN max voltage being 4.5V, my calculation says that VCC max is not 9V but 4.5/5.1*(5.1+10) = 13.32V

I am just saying this because i wanted to power the rockpi4 from a PC power supply 12V line, so that i can more safely power 2.5" HDD attached to the rockpi4 USB3 ports. Should be a sae setup, also the radxa diagram has labelled VCC with 12V.

Alas, no help for when you want to run it with > 20V.

the nb679, C1 removed. R3, R4 Adapted to 24V
Since I want to use it as a PLC, it must be 24V fixed.
9v, 12V are not an advantage as PLC operation.

Correct. AFAICT 12V operation is totally fine.

C1 removed, not replaced? Doesn’t seem like a good idea to me. You need C1. Read page 15 ff. of the NB679 datasheet.

Is R1 fuckered or does it still work?

What voltage divider did you use? Between 1.4V to 1.8V on the EN pin will enable USM mode. Not sure if that would interefere with something (it shouldn’t, but …).

I need a pi that is 24V fixed, since the hardware then only works with 24v.
“B&R X64” bus system.
The Pi is unfortunately in the press.
Sorry my english is a bit bad

Understand the purpose of that capacitor, its there to handle the high but discontinuous current demands of the converter. A good quality power supply and low impedance wires, and that capacitor isn’t all that important. Its much more important for power supplies that are marginal, or wires that are relatively high impedance.