hunt Down comunication errors on Ramps 1.4"ish"

hey everyone,
I got some wired Issues like.. for 5month now and i dont find it.
setup: Arduino Mega / modified Ramps Marlin 1.8 // 2.0-dev
I can print.. 5-20miuts than i get com-errors and the serial comunication brakes.
I tried Octoprint(not Octopi) and Pronterface same problem so no host problem
I tried Marlin 1.8 1.8 with advanced OK and Marlin 2.0-dev so maybe no firmware Problem
I tried a diffrent Arduino board.
I tried 3diferrent USB cables, and finaly even wrapped Aluminium foil around them. no change
i do run only 112500 baudrate...

I dont have a clue on how to proceed.

** any hints ar wellcome but dont tell me to switch the powersuply of my pi ;-)

5amp polyfuse getting hot and randomly powering down the mega?
Bad ramps powersupply? (under rated for current or old with bad caps?)
using a glcd? (they suck to much current) try unplugging it

Edited 1 time(s). Last edit at 08/10/2018 09:43AM by Dust.

no polyfuses,
the powersuply is 20A and the Heated Bed is 230V but maybe the Relay is sucking to much on 5V and no display or SD
how would i find out the Powersuply has Bad caps? I have no oszi. but i could add a few supression caps ..

and Thanks for the serios answer^^

Edited 1 time(s). Last edit at 08/10/2018 09:51AM by kabelfrikkler.

The 5v rail is not very powerful

Is this a mechanical relay? how is it connected? to 12v mosfet output or 5v digital?

If it is 5v can you use something like an optical isolater and a separate coil power supply?

jep it is on vcc and as i run 30V it is only powerd via USB but the 5v Rail is (with the rely on) on 4.87V but i keep that in mind too the 5v rail is pretty weak your right
To be sure on the PSU (it is a Meanwell china (clone) ) I just got my two car batteries up and started a Print

@Dust ((do you know a good linear Voltage regulator by the way 2-3A? regulatin from ~+6to +11V))