Can anyone tell me what might be happening with my silicon heater?

I fear that this is the end of my flexible silicon heater, but I'm curious to see if anyone has experienced this or might have some insight. The heater is a 12" x 12", 12V flexible silicon heater that I purchased from qu-bd. I'm using ramps 1.4 and Marlin with the heatbed thermistor set to number 5. It's powered, through a solid state, relay by a 480W Meanwell power supply.

I first noticed an issue about a week ago. The bed would always heat to 110^oC in under 10 minutes. Last week, however, it heated for nearly a half hour without breaking 80^oC. I have since acquired a non-contact thermometer, and have noticed that the heating is uneven, at best. When set to 110^oC, the part of the heater nearest the entrance of the wiring will heat to 150^oC or 160^oC, but the edges of the bed hover around 78-90^oC. When set to 60^oC, the "inlet" area will heat to 90^oC and the edges around 45-50^oC.

Where the entire bed is heating, at least to some degree, I have to believe that all of the traces are intact. Could the locally high temperatures be indicative of an internal short? The heater is bonded to a borosilicate glass plate using high-temperature RTV. Even if it did have some kind of warranty, I'm sure that it was void as soon as I glued it down. Is there anything that I can do short of peeling it off and buying another one? Is there any way to re-seal the silicon if I open it up to take a look?

Any thoughts would be greatly appreciated!

While I have not used Silicone heaters in 3D printers I use to work in sublimation printing where I used them to print on coffee mugs, they were the only type of heater that could wrap fully around the mugs.

I was told by a company that made the heaters that designing them to give even heat is part science and part voodoo and very hard to get just right. Also you are not suppose to use them open air (without proper heat sync) to prevent them from overheating, it only takes a few minutes to burn one up. For 3D printing I would think you would want a good aluminum base on the bottom and the heater sandwiched between that and the glass. It sounds like the element may be deteriorating.

The heaters I saw could not be opened, the element was fused between to sheets of silicone so it would be like trying to get to a center piece of wood out of the middle of plywood. I would ask the seller about the issue (maybe not mentioning the RTV you used) and see what they say.

Hmm... that makes me wonder if a replacement would be any better. I measured the resistance across the heater and it was 1.5Ohms. That seems a little low, but I'm not sure what it's supposed to be. I have sent an email to qu-bd (quintessentialuniv......com or whatever they are now), but I'm not holding my breath.

My heater is bonded to the glass build plate, and attached to an aluminum plate with a 3/8 layer of cork in between. I don't think that operating it in "open air" is my problem.

Anyone know of a better solution to heat a 12" x 12" bed? I print a lot of ABS so it is a necessity.

They make 12 x 12 in the normal PCB heated beds. Just search on Google for one in your country.

Thank you tmorris9! I had only ever seen the 12" x 8" variants. Is there any reason to think that the 12x12 pcb would require more wattage than the 12x12 silicon heater that I already have?

Not that I am aware of. If it did it would mean it would heat up faster, if your silicone one heats up in a 3-5 minutes then it's probably going to be really close to the same wattage.