Temperature limits of bed heaters
2022 Nov 7
Embedded Files
Introduction
Introduction
This test simulates the condition below, and shows the highest temperature of the bed heaters can reach.
No thermal fuse for the bed heater is installed.
The bed control SSR is failed and the circuit is always closed.
The firmware temperature safety features are disabled or not triggered.
The 150°C repeatable thermal switch buried under the rubber skin of the bed heater is lifted.
Setup
Setup
Environment temperature
22°C
Bed heater
The bed heater was directly powered by a 110v wall socket with a 6A fuse in series only. A manual button switched it ON/OFF.
Three heaters were used in this test:
A SK-Go bed heater is placed on steel brackets to minimize touching the ground.
A SK-Cube bed heater is placed on steel brackets to minimize touching the ground.
A SK-Cube bed heater is sticked to a SK-Cube bed and placed in the enclosed chamber.
Go bed heater: 110V 400W, 300x300mm, 0.44 W/cm^2
Cube bed heater: 110V 350W, 200x200mm, 0.75 W/cm^2
Bed temperature values
The SK-Cube in the picture blow acted as a big temperature sensor only. RRF showed the bed temperature readings and the curve.
Thermal image
A mobile thermal camera Hikvision P10 showed the temperature of the heater wires and rubber skin.
Test 1: Go bed heater, elevated
Test 1: Go bed heater, elevated
As shown in the pictures, the highest thermistor reading was about 160°C, and the highest reading by the thermal camera was about 192°C and settled down.
Test 2: Cube bed heater, elevated
Test 2: Cube bed heater, elevated
As shown in the pictures, the highest thermistor reading was about 267°C, and the highest reading by the thermal camera was about 277°C.
The temperature oscillated due to the intervention by the repeatable 150°C thermal switch. If the thermal switch is embedded well, it will kick in earlier at lower temperature.
Test 3: Cube bed heater
Test 3: Cube bed heater
As shown in the pictures, the highest thermistor reading was about 250°C, and the highest reading by the thermal camera was about 263°C.
The temperature oscillated due to the intervention by the repeatable 150°C thermal switch. If the thermal switch is embedded well, it will kick in earlier at lower temperature.
Temperature ratings
Temperature ratings
3M 468MP tape (used in the heater pads)
Short term: 204°C / 400°F
Long term : 149°C / 300°F
Embedded, repeatable thermal switch: 150°C
Replaceable, one-shot thermal fuse in SecKit printer kits: 130°C
3M 300LSE adhesive (used in the PEI rubber magnet):
Short term: 149°C / 300°F
Long term : 93°C / 200°F
3M definitions
Short term means minutes, hours.
Long term means days, weeks.
Reference
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