Thermal fuse on bed issues

[sonic quail]

I built a 4.1 500 and built an enclosure for it out of Polyisocyanurate panels should be somewhere in the range of R-6 to R6.4 in terms of heat retention. Was printing fine all day after I let the printer cool to ambient temp and then did another heat soak for my new print. However when I didn't let it cool and then started another print I'm tripping the thermal fuse on the bed heater now. I had been printing ABS at 100 on the bed and now it makes an audible click at about 96C on the bed and shuts the bed heater off completely. The only difference is I didn't let it cool and I had added a few more clips for holding the panels on as they had finally finished printing. I'm assuming it is getting to hot for the thermal fuse as I hadn't had those issues before the enclosure and even when I let the printer cool off completely. However I thought those thermal fuses were rated up to 150C my toolhead boards at MAX are reading 88C and a low of 85ish and this photo was taken only after a 30 minute heat soak. Any ideas? I have already checked all my wiring and made sure they were secure connections and they were.

[coral zephyr]

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[tardy nest]

The bed heaters rat rig used to ship had a thermal fuse that cut off at 157c if I remember correctly. But they were a thermal fuse that blew and did not make a click noise or more importantly start working again. They had to be replaced. Not sure if something has changed or not with newer ones.

[sonic quail]

It does make the clicking noise still but thank you for the confirmation 😁

Little more info. After a print finished last night while running the bed at 90C and letting it cool all the way down, I woke up this morning and tried heating the printer to 90C again and it wouldnt get past 80C before the thermal fuse clicked and shut the bed off. I restartes klipper and it would then go back to 90C but not 100C

[tardy nest]

hmm.... do you have a volt meter that you can check to see if voltage is coming out of the SSR when you have it doing this? If it is still a normal thermal fuse that rat rig is using they are a one and done type thing and do not click. This is a stock photo but they look like this and are installed under the flap in the middle of the bed heater.

[sonic quail]

Hmmm so the SSR has a red flashing light on it when right before it clicks off and when it is heating down so maybe thats the clicking I was hearing. The bed seems to have one like this if my memory is serving me right. All of my wiring to and from the bed and board to my SSR seems to be snug and I dont see any places for a short (limited knowledge but still) could my SSR be getting to hot? I havent touched it after it clicks when I had everything un plugged I dont remember it feeling warm after having the LED flash at me.

[tardy nest]

if your bed has one of those, they reset from my understanding. Is it a stock rat rig bed heater?

[sonic quail]

It is

[tardy nest]

strange. Never seen a resetable thermal fuse on one of their heaters. Maybe its something they are now doing as early beds had bad reliability on thermal fuses

[sonic quail]

Im leaning towards it is the SSR and I had made a mistake earlier in my thinking. I'm still not sure, Im thinking of buying another one similar to it to test and see if it does it. I just don't see how it would work some of the time and then not at other times, that doesnt make and sense to me.

[tardy nest]

Do you have a volt meter? If so just test the output of the SSR while it should be heating but the temp is dropping.

[sonic quail]

Ill do that when I have it back together. I had an interesting development. I couldnt get it to 100 so I let it heat as much as it would (about 90c at the time) then when it shut of I restarted the firmware and retried heating it to 100c because it was closer to 100c and it did fine and held it for the length of an entire print

[tardy nest]

Sounds like a flaky ssr. Do some testing when it’s back together with a volt meter

[sonic quail]

what exactly should I be looking for? If Im checking it for volt output when it stops heating I would expect it to be reading a low voltage right? Im just kind of confused hahah

[tardy nest]

yes thats what I would be looking for. I do not know exactly what the output of the SSR is going to look like voltage wise as it cycles so quickly. If its just dead it would be zero volts I suspect. If its keeping it hot but not getting any higher, thats where I am not totally sure what it would look like.

[sonic quail]

Ok so I tested it. 24v the entire time coming from the board to the ssr even when the bed decides to shut off. Im hearing a click still which I still believe it to be the self reseting thermal fuse.

Also when the bed heater shut off there was no continuity on the bed heater side

Which makes sense as it was no longer heating

[tardy nest]

What about the output of the ssr when it stops heating. It sounds like the thermal fuse but as I said earlier I have not seen the resettable ones on a rat rig bed. Maybe that’s what they are shipping now a days. Can you get a picture of the thermal fuse?

[sonic quail]

Thank you for your contact!

If the underside of the heater pad is marked “150” then you should have the version with the thermostat. This version is self-resetting and rated to handle temperatures up to 150ºC, as indicated.

this is from an email I had with ratrig support, I can't really get a picture of it. It is covered by a section of the pad bottom that I would need to cut out.

[tardy nest]

That’s good that they are now using a self resetting one. Bad that it seems to be tripping at the wrong temperature. Do you have an infrared thermometer by chance?

Want to double check it’s not the thermistor that is reporting the wrong temp and the bed is tripping correctly

[sonic quail]

I dont unfortunately, I had one years ago but cant find it xD that is something I need to pick up because I have a sneaking suspicion that the bed isnt actually at the temp it is saying it is. Im now having warping issues with ABS even at temps that previously were not warping (Not as high as 100 as Id like but 90c was still warping)

and I didnt get a reading of the bed out when it shut off, I just checked continuity.