Bed thermal fuse blown, what should I look for?

[RocketTurtle]

Printer Model

V2.4

Extruder Type

Clockwork 2

Cooling Type

Stealthburner

So I started warming up for a print today and found that the bed wasn't heating, I discovered that the thermal fuse was blown. I can't find anything to suggest there was a runaway condition, do these things just fail sometimes, or do I need to be concerned that there is a thermal runaway issue? What should I check before firing it up to print again? Thanks!

 

[jtdowney]

The thing I'd be most concerned about is the SSR failing closed (so it runs constantly). You can replace the fuse and watch it carefully after powering it on to see what is happening. Just be quick with the power button. If the SSR did fail, an estop wouldn't help.

 

[LoadMaster7]

So I started warming up for a print today and found that the bed wasn't heating, I discovered that the thermal fuse was blown. I can't find anything to suggest there was a runaway condition, do these things just fail sometimes, or do I need to be concerned that there is a thermal runaway issue? What should I check before firing it up to print again? Thanks!

Past SSR I have worked with, fail closed, not open. Meaning whatever is connected on the switch side stays on. In your case, the bed heater. This can be bad and the reason for a thermal fuse. So, what you need to do is replace the fuse and monitor that the bed temp is being regulated with on off cycles. If you don't see it cycle after temp is reach, your SSR most likely has failed and needs to be replaced.

 

[msaeger]

Past SSR I have worked with, fail closed, not open. Meaning whatever is connected on the switch side stays on. In your case, the bed heater. This can be bad and the reason for a thermal fuse. So, what you need to do is replace the fuse and monitor that the bed temp is being regulated with on off cycles. If you don't see it cycle after temp is reach, your SSR most likely has failed and needs to be replaced.

This is what scares me about the line voltage bed heater. Anyone just use a 24v one powered by the octopus board. I know it would take longer but people are already limiting the bed heater output to prevent warping. I only have experience with 12v and 24v directly powered off the board and marlin always seemed to give a error pretty easily if there was a potential issue.

I was reading 120decibells message about the system he is making to help with this and that makes me think there should be a thermal fuse on the hotend too.

 

[LoadMaster7]

msaeger, do you have your printer fixed?

To your comment about 12 - 24 volt directly to the controller, I have prints with this type of system, like my Creality Ender 3 Max's. However, I personally prefer the SSR control with the signal from the control board and 110 volt a/c heaters. I have two Tevo Little Monsters that each have a 310mm bedplate running 110 volt using an SSR. Both machines are used many times a week, both have been running since 2019. I have had zero issues with the heatbed heater system. In my humble opinion, a good thermal fuse gives the system more than enough protection. Thermal fuses have been around for a long time with very good track records. Anyone with a coffee maker will find they have a thermal fuse to keep the maker from ever getting to a meltdown state.

As far as the SSR, when replacing, replace with one rated higher than the calculated load by at least a 1/3 more to 1/2 more. Also make sure it is designed for DC signal (input) and switching AC (output) and in the voltage range you are using.

 

[msaeger]

msaeger, do you have your printer fixed?

???? I didn't have one that was having issues when I posted this but I do now.

 

[LoadMaster7]

???? I didn't have one that was having issues when I posted this but I do now.

Bummer. Sorry to hear this. Yeah, my mistake, I thought for some reason you were the original poster. Hope you get yours sorted out.

 

[lotech]

What temperature thermal fuse is recommended?

 

[NoGuru]

What temperature thermal fuse is recommended?

130c and 15 amp is what you should look for.

 

[lotech]

I'm finding several 125C and 135C fuses.
But not any 130C,..
are you messing with me? ha.

 

[NoGuru]

Thermal Fuses 15A

Temperature fuses to be used in bed heaters for safety. will cut the power if temperature gets over the threshold notes: picture says 150c but actual thermal fuse is 130c

www.fabreeko.com

But they are sold out.

So pick one that will closest match your material of preference. I sometimes print very high temp so I would choose the 135 but I think most would be okay with 125c,