PETG - Can't heat up Mk2 to 260  

Re: PETG - Can't heat up Mk2 to 260

So I tried stopping the fan for the hotend manually to see if it would heat up and the temp suddenly jumpted from 250 to 315. Is it possible that my thermistor isn't set correctly? I had to replace it recently, perhaps I did it wrong?

Re: PETG - Can't heat up Mk2 to 260

So I tried stopping the fan for the hotend manually to see if it would heat up and the temp suddenly jumpted from 250 to 315. Is it possible that my thermistor isn't set correctly? I had to replace it recently, perhaps I did it wrong?

Hard to tell, but seems like a reasonable assumption.
re-do the thermistor installation and try again.

Also, never ever stop the extruder fan (not the part fan) it will lead to all sorts of deasasters.

Re: PETG - Can't heat up Mk2 to 260

💡 the purpose of the hotend fan is to cool down the cooler-body of the hotend.
that's the round aluminium part with the cooling fins. it is fixed inside the extruder body and it is absolutely nescessary that this "cool-end" needs to be below the vicat temperature of the filament with what the extruder body has been printed.
usually it is abs, so the vicat temperature will be around 94°C.
if the cooler exceeds this temperature, it will "melt down" the extruder body, so that it looses it's form, fit & function.

❗ so never ever stop the cooling fan manually !!! not even to test if you can get higher temperatures at your nozzle !!! ❗

💡 between cooler and hotend block there is a small, hollow screw. it's called the heatbreak. at one side it is fixed inside the cooler (where the temperature should be <<100°C) and the hotend block at the other side, which could be heated up to a maximum of 305°C (at least that's the limit by the prusa mk2 firmware, marlin restricts temperature to 275° C). inside the hotend block the heatbreak should have a firm "non-leaking" contact with the backend of the nozzle.

there should be nothing else between cold- and hotend ! especially no molten filament from failed prints or a leaking hotend !

inside the hotend block is a small hole, where a little thermistor is mounted. this thermistor will report the temperature to the rambo board (it's simply a very temperature sensitive resistor). as long as it has a good thermal contact to the hotend block and the temperature it reports is not highly fluctuating, there is no reason to doubt it's function.

so if your hotend can't get higher than 260°C, it's most likely that you are loosing power somewhere. check the connectors of the heater cartridge at the rambo board. every little contact resistance will let you loose power at the hotend... and furthermore: a bad contact might melt down the connector at the RAMBOMini !

if everything is ok there, just check the power supply connector at the rambo. if you got a voltmeter, check the voltage.

and again: check that there is no molten filament between the cooler and the hotend !

❓ what you can do to increase the temperature at the nozzle:
because the power the heater cartridge will transfer into heat is related to the square of the voltage, you can squeeze more power out of the heater if you crank up the voltage a little bit. usually there is a small potentiometer inside the psu (near the array with the 12V leads) to control it's output voltage, which you can use to increase the voltage up to 13.8V. if you do so, you'll gain 32% of power.
but beware, this will stress the connectors, cables and the mosfet transistors as well (while it should be no problem for the transistors).
don't forget to recalibrate the hotend afterwards (look for the PID tuning inside the new firmware thread).

:geek: another point to mention: the heater cartridge inside your hotend will age and loose it's ability to provide the power. the higher you heat it up, the faster it will degrade. so sooner or later you'll need to replace the heater anyway.

Re: PETG - Can't heat up Mk2 to 260

Figured it out....found this article: http://help.prusa3d.com/mk2-electronics/thermal-runaway-and-temperature-drops

I'm using the v6.1 hotend so I had to solder the connection to the new thermistor. Now it works great!