Strangest problem yet, Power loss when hotend is over 80C

Hey,

This is the strangest problem I've encountered on my 3D printer. A hypercube btw.

I've modded my PSU with a relay so I can turn the PSU on and off using ramps. I did this months ago for 2 printers. No issue whatsoever, I don't think this is related to the relay.
For this reason I need a constant 5V supply through USB so I can use the LCD to turn on the printer. I use a USB phone charger to provide this 5V to USB.

Here's where the problem starts:
When I turn on the hotend's heater and as it goes over 80-100C my LCD starts getting fainter and fainter till eventually I lose 5V power and I hear the relay click and the PSU turns off.
Could be the regulator?

Here's the strange part:
After the PSU turns off I need to turn off the power strip and turn it on again to gain the 5V to be able to turn on my printer. PSU and phone charger are both connected to this power strip.
After I turn it on, even when there's no load and the heater is off, The lcd goes fainter and fainter after a few seconds until I hear the relay click and lose power again. And this happens over and over again when my heater is over 80C. Once it's in 70-75C-ish I can turn the printer on and it'll stay on.
Keep in mind, this happens even when the heater, motors etc... are off.

Here's a couple of things I tried:
I checked the phone charger's voltage, constant 5V.
Tried a different phone charger.
Used a different USB cable.
Disconnected all the stepper drivers and motors and my ramps fan extender.
Disconnected my LCD right after I turned the printer on.
Checked all the wiring of course.

I might have forgotten a few other things I've tried.

Any help would be appreciate it,
Thanks!

Try a new heater cartridge. These cartridges sometimes develop a short between the element and the casing, which may only happen at high temperatures. That could cause a large ground current to flow if there is a path from the hot end metalwork to ground e.g. via a thermistor wire that is shorting against the metalwork, and that might be responsible for the problem.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Interesting...
So to confirm this, I turned on the heaters and let it heated up the hotend and after the problem started happening again, I turned off the printer.
Then removed the thermistor and heater cartridge cables from the ramps and turned on my printer. And it happened again, without the heater and thermistor connected.

This should mean that the problem isn't them, right?

I think you're right that you've excluded heater and thermistor electrical problems.

Where are the hot end and PCB(s) in relation to each other? Could it be that the heat from the hotend actually heats the PCB and voltage regulators and so on?

Another thought is that maybe something else starts to happen at 80C e.g. maybe the hot-end fan tries to turn on, but it is shorted somewhere? Or maybe something else (the PSU?) is also gradually heating up and gets to a critical point when the hot end gets to 80C?

Quote
frankvdh
I think you're right that you've excluded heater and thermistor electrical problems.

Where are the hot end and PCB(s) in relation to each other? Could it be that the heat from the hotend actually heats the PCB and voltage regulators and so on?

Another thought is that maybe something else starts to happen at 80C e.g. maybe the hot-end fan tries to turn on, but it is shorted somewhere? Or maybe something else (the PSU?) is also gradually heating up and gets to a critical point when the hot end gets to 80C?

I doubt the heat from hotend would get to the PCB in less than 1 min over 1.5m cable. I also have an 8mm fan on Ramps.
I just tried this again with hotend fan disconnected, even removed my fan extender completely. No changes and problem persists.

I believe I've solved the problem.
I took ramps apart to take a look at the pcb, everything seemed fine. But then I noticed the mosfet. It had a broken leg that I had soldered again a few weeks ago and totally forgotten about it. It looked ok, but I decided to change the mosfet anyway.
I replaced it with a IRF540N. I have a 220V SSR driven bed btw.

Then I plugged everything back in and turned on the heater and the problem seems to have been fixed! Noice!
Maybe it was the mosfet or perhaps this reassembly fixed some wiring issue.

Thanks everyone for you help