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My hot end temperature reading is way off as it keeps melting the PTFE liner. Room temperature reads fine but at operating temperature it must be off as it melted the liner even when I set the temperature to 235 C and it spiked at 242 C during the initial overshoot (PID adjustments were disabled after I enabled the EEPROM which is why it spiked so much). I believe the stable operating temperature of PTFE is supposed to be 260 C and it should be able to spike above that a bit before it actually melts so just how off is temperature it's reading?

The hot bed and hot end thermistors are the same right? I shouldn't matter if I accidentally switch them during setup? I've ordered a new thermistor as adjusting the table values seems like too much work but what are the chances I run into the same problem again?


An unrelated side question, but I've ordered an Onyx heatbed and according to this site it's 1.1 Ohms to be run at 12V but isn't that too high for the Rambo? I thought it was fused at 10 amps?

halopend wrote:My hot end temperature reading is way off as it keeps melting the PTFE liner. Room temperature reads fine but at operating temperature it must be off as it melted the liner even when I set the temperature to 235 C and it spiked at 242 C during the initial overshoot (PID adjustments were disabled after I enabled the EEPROM which is why it spiked so much). I believe the stable operating temperature of PTFE is supposed to be 260 C and it should be able to spike above that a bit before it actually melts so just how off is temperature it's reading?

The hot bed and hot end thermistors are the same right? I shouldn't matter if I accidentally switch them during setup? I've ordered a new thermistor as adjusting the table values seems like too much work but what are the chances I run into the same problem again?


An unrelated side question, but I've ordered an Onyx heatbed and according to this site it's 1.1 Ohms to be run at 12V but isn't that too high for the Rambo? I thought it was fused at 10 amps?

I doubt the thermistor is bad, it's more likely it's not in good contact with the Hotend.
It's always a good idea to use a thermocouple on a multimeter to verify what your thermistor is reading and to approach the higher temperatures incrementally the first time.

My heated bed thermistor reads 25degrees low at 100C, but that's not because the thermistor is bad, or the software is wrong, it's because of the placement of the thermistor and it's contact with the heated bed.

You actually don't need accurate temperature readings, just repeatable readings and knowledge of what temperature to set for the plastic you happen to be printing.

I'd agree the exact bed temperature isn't important and I can see why it be off given how far the thermistor is off to the side, but the hot end one was stuck in a tiny hole right by the heat source. When I installed it I put my focus on insulating it rather than making good contact cause the leads are soo close its almost impossible not to short them to the body if seated all the way in the hole.

I just broke a lead off my old thermistor so I'll definitely be using the new one anyway, but I guess if I Insulate the leads right where they come out of the thermistor using PTFE tape I could try using aluminum foil to give it a nice snug fit.

As for the hot bed question I just looked it up and the fuse is actually rated for 14 amps so that solves that problem! I don't know where I got 10 amps from.

halopend wrote:I'd agree the exact bed temperature isn't important and I can see why it be off given how far the thermistor is off to the side, but the hot end one was stuck in a tiny hole right by the heat source. When I installed it I put my focus on insulating it rather than making good contact cause the leads are soo close its almost impossible not to short them to the body if seated all the way in the hole.

I just broke a lead off my old thermistor so I'll definitely be using the new one anyway, but I guess if I Insulate the leads right where they come out of the thermistor using PTFE tape I could try using aluminum foil to give it a nice snug fit.

As for the hot bed question I just looked it up and the fuse is actually rated for 14 amps so that solves that problem! I don't know where I got 10 amps from.

The easy way to insulate the legs is to either use some really small silicone tube, if you have some high temperature wire, you can use a piece of insulation off that, or to split the legs and create a sandwich of Kapton tape. It needs to be in the hole as far as you can get it, and it needs to have something holding it in.

I lost my very first Hotend because the thermister wasn't quite secured enough, it gradually worked its way loose over a long print, as it did so the temperature read constant, but the actual Hotend temperature was rising until the peak melted.

I forgot I had kapton tape on order. That'll make easy enough work of the thermistor, I'll just have to be patient enough to wait for it to arrive. To make sure I don't melt another liner or detroy the peek I'll just run a test without either attached running the temp up till it melts any PTFE I touch to the end or reaches 250 C. Not as safe as just measuring the the temperature through another device, but it is the most reliable! I'll just do it in a ventilated area and stop breathing.