Service life of heater cartridges and thermistors
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I've asked E3D. I'll let you know what response I get.
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Resistance 'slow' heater cartridge, cold: 27.3 ohms
Resistance 'normal' heater cartridge, cold: 20.6 ohmsVoltage to the heaters is 23.6V, measured on the screws of the terminals. I did not measure the current; forgot to take the (DC-)current clamp with me from work.
That results in a calculated power to the heater of 20.4W for the slow one, and 27W for the quicker one.
The 40W heaters I ordered also differ 10% in cold resistance. But the results of a PID autotune are much closer together now for both heater blocks.
M307 H1 A675.5 C232.3 D2.8 S1.00 V23.7 B0 M307 H2 A650.8 C253.7 D3.6 S1.00 V23.8 B0 -
@DaBit said in Service life of heater cartridges and thermistors:
That results in a calculated power to the heater of 20.4W for the slow one, and 27W for the quicker one.
That's a significant difference.
Anybody knows if the resistance of a nozzle heater changes significantly when it get hot?
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@zapta said in Service life of heater cartridges and thermistors:
Anybody knows if the resistance of a nozzle heater changes significantly when it get hot?
Would depend on what it's made from, kanthal and that type of proper heater wire does change, but much less than say copper.
To quote Wikipedia
Ordinary Kanthal FeCrAl alloy has a melting point of 1,500 °C (2,730 °F). Special grades can be used as high as 1,425 °C (2,597 °F). Depending on specific composition the resistivity is about 1,4 μΩ. m and temperature coefficient is +49 ppm/K.
50ppm and generally quite low resistance to start with, the absolute change would be small but measurable methinks
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50ppm and >300C temperature difference with room temperature (the heating wire in the cartridge becomes a lot hotter than the heater block) is still a few percent.
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That is less than I expected, especially for Kanthal A1.
It might still be interesting to hook up the current clamp on a running Duet, see if the heater current drops.
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If you assume they'd used something like the Nichrome to save some cost as the temperature of Kanthal isn't needed, you'd see about 100mA drop on a 40w/24v heater.
(But the current clamp would probably show a lot more current reduction as it would likely average out the pwm'ed current as the PI loop starts regulating)
