I have 300x200mm PCB 12v 150w heatbed on a 3mm aluminum plate with 0.4mm PEI surface.
Before I would get it up to 119c (with a layer of foil on the surface to get up to temp then removed once there) and then start print because it would gradually drop down after start to around 104c and then slowly pick up to my desired 110c for printing ABS. The printer is in an enclosure so that is why I could maintain 110c. The heatbed is connected direct to the PSU through a DC-DC SSR. The heatbed also has a insulation mat under it to retain the heat.
The problem is now slowly drops and when it reached around 98c the print lifts from the PEI surface and hotend ends up crashing in the print and failing.
I have rewired the hotbed to the 24v configuration and connected it to a separate 24v PSU while running the rest of the electronics off of the original 12v PSU. The same thing still happens and the temperature still drops even on 24v setup.
So to sum up everything was working fine the last year but all of a sudden the heatbed is not maintaining and building up enough heat while printing. Switching from 12v to 24 did not improve the situation and I noticed it still took 30min to heat up to the 119c like it did before on the 12v setup.
Any thoughts ideas?