Issue with extruder temp stability when bed is heated

So I'm having an issue with my Creality Ender 3. I've upgraded the extruder heater cartridge with a 50W 24V cartridge. My goal is to print ABS on a glass bed. I've tested the bed and it can hold 100 degrees C very stable (+/- 1 degree). I've also PID autotuned the extruder (ran 15x, saved to EEPROM) and it can hit 230 degrees C stable (+/- 1 degree). However, when I attempt to print something, the bed heats up and hits 100, then the extruder begins heating. However, it can't stabilize. It overshoots 230 by ~10+ degrees, then drops below 230 by ~10+ degrees, and keeps bouncing back and forth +/- 10 degrees around 230. Any thoughts as to what's causing this? I've tested the voltage going to the heaters from the PCB with a voltmeter and it confirms that the bed gets a steady 24V and the extruder gets 24v when warming up, and then fluctuates around 0 - 14V (up & down, on and off) when it tries to stabilize around 230 but isn't able to. I know the extruder and bed can hold their temps when tuned separately, but the extruder can't stabilize when the bed is heated. I've tried PID autotuning while the bed is heated, but the bed heater shuts off when running an extruder autotune. My power supply is a Meanwell 500w 24v PSU. Any help would be greatly appreciated.

Are you running the bed heater in PID or bang-bang mode? If it's bang-bang mode, is the power input voltage at the controller stable while the bed heater cycles on and off?

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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].

I've tried both on the bed and it maintains a stable temp. Yes, the power voltage is stable at 24v.

Did you at some point change firmware versions? Try resetting the eeprom to default. Make sure you record any settings you currently have stored in it. It fixed some weird behavior with mine. I've upgraded marlin v1.0 to v1.1.9 and when I turned on pid for heated bed it just did't heat up when running a print job. Manually it worked great.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

So I've been on 1.1.9 for quite some time now. I reset my EEPROM but that didn't help. I've also tried switching power outlets, thinking maybe it was a power issue, but it wasn't as the printer still has issues stabilizing the extruder temp there as well. I'm still at a loss as to why the extruder has issues stabilizing when the bed is heated up, but has no issues when autotuning each individually. One thing I've noticed is that when I try to autotune the extruder, I get very different values when trying to autotune multiple times. The P (of PID) can range from as low as 9 to as high as 187. Could this be a faulty temperature gauge in the extruder? It seems to detect just fine what the temperature is, so maybe it's working.

It is possible, with being such a cheap printer, that they have cheaped out on the quality of the wiring. Did you check to see the gauge of wire? Can it handle the new power requirements?

Most wires are 26awg while the heater is 16awg. I may unscrew/disconnect all connections and redo them to make sure there's no bad connections. However, considering it does heat and does detect temps, makes me think that maybe it's a firmware issue.