Thermistor is secured to the heater wires and heatsink to make sure it never falls out. This is done by heat shrinking a heat shrink tube around the heater and thermistor wires so there’s a “cushion” for the zip tie that then secures it to the aluminum heatsink so that when you tug on the connections to disconnect, you don’t rip the wires of the thermistor accidentally. It also makes sure the thermistor never falls out especially with the help of the red silicone tubing that makes sure it stays inside the nozzle and keeps any sudden wind/draft from creating fluctuating temperatures.
Putting the thermistor inside the nozzle enables better, more precise readings.
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The heatshrink is in the fan zone, so that should keep it cooler. Still, might be a good idea to use the high-temp PTFE heatshrink there, for some added safety margin.
Or we could use fiberglass sleeving. This is really a minuscule feature that can always have a solution found if heat shrink or whatever doesn’t work. Focus on the hotend!
I don’t know that it would melt if you have that fan running. They should run cool on the peek so you should be ok. Might want to try wire mesh or just a zip tie.
You really shouldn’t use a heater that powerful. The PID algorithms don’t stabilize as well with heaters that heat up significantly faster than they cool down. The algorithm assumes roughly equal rates of heating and cooling. Also, with the separation you have between that heater and the thermistor, your hot zone will probably get significantly hotter during heat-up than the thermistor reads, at least briefly. Powerful heaters need closer coupling of the sensor to the heater.
@Whosa_whatsis We’re testing different ohms at the moment. I don’t think we’ll be going with a heater that heats up that fast. As you mentioned, it will jump past the set temperature, which we’ve already tested and seen, so we’re just testing different ohms now to see which one works best.
@Mr_covert That’s not exactly true. The PID algorithm, and the autotune function in particular, are not well-suited to heaters that don’t heat and cool at roughly the same rate. In the past, I’ve had to configure a heater to never go over 50% duty cycle while the temperature is within 30 degrees of the setpoint, otherwise the autotune would just fail.
Also, of course, a heater that doesn’t self-limit at safe temperature creates a danger of melting down the hot end (and potentially burning down your house) if the firmware happens to hang during its on-cycle).
