Avoiding/bypassing thermal runaway protections

A Former User

As DocTrucker asked; what is the power rating and size of the bed? If you're using an extruder output you're probaly limited in power and if the size isn't also quite limited you'll have a hard time getting to 70C.

What temperature does it get to before timing out?

dc42

@adhanabal said in Avoiding/bypassing thermal runaway protections:

@dc42 i set the limit as 70'C

Perhaps your bed heater can't reach 70C? Did the temperature graph flatten off before it got to that temperature?

adhanabal

@bearer i use the heater to heatup aluminium pipe, Outer dia, 40mm thickness 5mm
Heater capacity: 12V 40watts

adhanabal

@dc42 im replacing the sensor, having doubt about it, so once replace i will try again.

DocTrucker

That heater sounds under powered. What is the length of pipe? Is anything in the pipe?

A Former User

@adhanabal said in Avoiding/bypassing thermal runaway protections:

@bearer i use the heater to heatup aluminium pipe, Outer dia, 40mm thickness 5mm
Heater capacity: 12V 40watts

thats half the story; length of the pipe, medium inside and flow of medium would be relevant even if air and not moving.

the easiest is probably to post a picture of the temperature graph shown in duet web control, the shape of the graph would be correct even if the value is wrong. If you consider 40w is only enouh to bring Ø2-3mm plastic to melting temperature at very slow flow rates Ø40mm might be pushing it even if the target is just 70C.

DocTrucker

The recommendation is around 0.4W per 100mm2. 40W would there for be enough for a 100*100mm bed, or 80mm of your pipe - with nothing in it.

https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater

adhanabal

@DocTrucker pipe is 100 mm long i want to heat it only max of 50'C

adhanabal

@bearer okay guys i tried the same thing with 24v system it works well,
Only 12v system has the problem
I have 24v heaters too

A Former User

@adhanabal said in Avoiding/bypassing thermal runaway protections:

i want to heat it only max of 50'C

why are you tuning it to 70C if your target is 50? let it completely cool to room temp and do it again for 50?