Heated Bed Temperature is the heater, not the bed

[jweaver]

I have just fitted my heated bed and heated it up for the first time.

I was pleased that the temperature increased pretty quickly and got to 50 degrees within a matter of minutes.. But when I felt the bed, it was luke warm at best, but underneath the heater was too hot to touch

I left it for 10 mins and the bed got pretty hot, but clearly the thermistor is affected by the temperature of the heater, rather than the bed.. And to be honest, this isn't really a surprise based on the design, as the thermistor is just sandwiched between the bed and heater, so its got to work like this.

Has anyone come up with a way to make it more accurate?

Jon

[pellhall]

I moved my thermistor to the edge of the heater, (on my Metal Plus there's a little milled out section) and stuck it there with a little heat transfer compound.
On the big bed be prepared for depressingly slow heat rates though. On my older upgrade, with the provided 350W PSU and shims and insulation blanket it could take 20 minutes to get to an actual 70C and flattens out after that. Some folks use a heat gun to speed things up. I place a piece of rigid foil-faced insulation on top of the bed while it heats up to cut heat loss.

[MileHigh3DII]

I use a 250x250 piece of the silver bubble wrap insulation from the hardware store as a blanket over the top of my bed while heating. I think it makes it heat faster and more evenly. I also used that insultion to make a bed backer on the underside of the heated bed on my PB+2.1 to keep heat loss down. On my PB+ Dual, I usd the high temp silver tape that I have around from working with my filament extruder to tape up the underside of the bed. Not as insualtive, but less emissive than wood.

I figured with all the wood around, these materials would be OK, and they have been for 100s of hours on each. Watch the top blanket with the hot extruder tip- I haven;t run into issues, but I usually pull it off before heating the nozzles. G29 zeroing with the foil on sucks with an auto sensor or with out...