Service life of heater cartridges and thermistors



  • Yesterday I had issues reaching 260C hotend temperature with the cooling fan running on the 'main' nozzle of my Chimera+E3D hotend. The other one, which is only used when doing dual material prints, has no issues.
    Re-ran the PID-tuning, and the most-used nozzle is indeed more sluggish than the other. The difference used to be small. Re-assembling the hotend with fresh aluminium paste did not make a difference.

    Which raised the question: what is the service life that can be expected from standard 30W E3D heater cartridges and thermistors at those temperatures?



  • Tens of thousands of hours.



  • They are mechanical, they should be VERY long lived on average. You could have one that is failing... but look for degradation in the wiring connections first. Crimps, screws, etc.



  • Crimps and screws are OK. If I had that much power loss at the heater connector it would burn out anyway, but loosening and retightening the screws was one of the first things I did. Maybe there is something wrong in the (factory) wire towards the cartridge; I did not measure it's resistance.

    Thermistor seems fine; idle temperatures are OK and the temperature reported when the inactive heater block picks up some heat from it's active neighbor seems to match too.

    I guess that just ordering a new cartridge is the easiest thing to do. I would like to have a bit more heater power to accelerate tool changes anyway.



  • FYI .... don't order a 50W heater, they are too powerful. I use 40W heaters and even those have to be turned down by adjusting the PWM value on the heater output in order to keep temperature overshoot in check.



  • I think 40W is enough, and those are quite cheap as well compared to 'brand name' 50W cartridges such as the Slice Engineering ones.

    Limiting the PWM kind of defeats having a more powerful heater. Should PID tuning not take care of overshoot?

    When my printer was running LinuxCNC and single nozzle I used my own design hotend. That one used two 40W cartridges on either side of the nozzle in a copper block:

    alt text

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    That thing was absolutely rock solid once the PID was tuned. Never had issues with overshooting temperature more than 1-2 degrees and it was totally not impressed by external disturbances such as the cooling fan.
    But I never tried using this with Duet.



  • As you say, PID tuning should take care of it.



  • @DaBit said in Service life of heater cartridges and thermistors:

    I think 40W is enough, and those are quite cheap as well compared to 'brand name' 50W cartridges such as the Slice Engineering ones.

    Limiting the PWM kind of defeats having a more powerful heater. Should PID tuning not take care of overshoot?

    There are cheap 50W cartridges readily available but yes, 40W is plenty. I agree that turning down the PWM should not be necessary but I guess I never got my PID parameters tuned perfectly because I did have issues which I was able to mitigate by reducing the PWM setting.
    I also had copper hot ends at one time, figuring they would be superior to aluminum. Turned out that aluminum was more responsive when going from active to standby on a dual extruder setup and was heating up faster (both of those probably because of the lower mass of the aluminum) and there was less overshoot as well.


  • administrators

    @DaBit said in Service life of heater cartridges and thermistors:

    Limiting the PWM kind of defeats having a more powerful heater. Should PID tuning not take care of overshoot?

    It's a matter of safety. If something goes wrong and the heater gets stuck on at full power, 50W is certainly enough to melt an aluminium heater block on a V6, and 40W may be enough if there is a silicone sock over the heater block.



  • With 40W I doubt that; heat leakage through the Chimera+ heat break is fairly substantial and it is only 33% more power than stock.
    With 50W I simply don't know.

    I wish manufacturers like E3D spent a bit more effort to make incorporating safety devices such as thermal fuses easier. It is not that hard for them to incorporate a thermal fuse in the heater block. For me it is equally easy to mill a heaterblock that incorporates such a device, but then I lose compatibility with the ecosystem; a silicone sock would not fit anymore if I did so, for example. And their ecosystem is about the only reason why I went E3D.

    And we have been discussing it multiple times; a bit more help from the firmware driving a power kill switch would not hurt either.


  • Moderator

    @DaBit said in Service life of heater cartridges and thermistors:

    thermal fuse in the heater block.

    The problem there is the service life of the thermal fuse itself. The standby temp needs to be low enough for it to survive. It's also more difficult to find thermal fuses with such high trigger temps.

    I think it's far more practical to add the fuse to the heatsink area since a thermal runaway would still be able to trigger it at a much lower temp, and the normal working temps would be low enough to ensure longevity.

    http://www.be-electronics.com/v/vspfiles/datasheet/nte/thermalCutoff.pdf



  • @Phaedrux said in Service life of heater cartridges and thermistors:

    I think it's far more practical to add the fuse to the heatsink area

    This would also catch a failed fan, sooner.



  • @DaBit said in Service life of heater cartridges and thermistors:

    With 40W I doubt that; heat leakage through the Chimera+ heat break is fairly substantial and it is only 33% more power than stock.

    40w can melt a block without a sock, i’ve seen it myself.

    This is why the default heater is 30w.

    I wish manufacturers like E3D spent a bit more effort to make incorporating safety devices such as thermal fuses easier. It is not that hard for them to incorporate a thermal fuse in the heater block.

    Could you supply me with a 300C thermal fuse?

    And we have been discussing it multiple times; a bit more help from the firmware driving a power kill switch would not hurt either.

    Already exists.



  • @Phaedrux said in [Service life of heater cartridges and thermistors]

    The problem there is the service life of the thermal fuse itself. The standby temp needs to be low enough for it to survive. It's also more difficult to find thermal fuses with such high trigger temps.

    Indeed, the regular manufacturers do not provide much above 240C. The Chinese do, but I suppose 300C stands for 300 Chinese degrees then.
    Fuse life at elevated temperatures is an issue indeed. Did not consider that.

    It is tempting to just use a piece/wire of zinc or lead as the fuse. Both seem to be capable of acting as a low current safety fuse.
    Pure lead melts at 330C, pure zinc at 420C. Both provide an oxide layer which prevents corrosion once the surface has corroded, although I am not certain if that process is also stable when exposed to long-term printing temperature.

    I think it's far more practical to add the fuse to the heatsink area since a thermal runaway would still be able to trigger it at a much lower temp, and the normal working temps would be low enough to ensure longevity.

    In my case the heatsink is liquid cooled. It won't become more than luke warm as long as the pump is running, even if the heater block is melting.

    @elmoret said in [Service life of heater cartridges and thermistors]

    40w can melt a block without a sock, i’ve seen it myself.

    30W barely reaches 300C when there is no airflow. I still find it hard to believe that 40W would do double that. Maybe I will just order a Chinese v6 block and heater, try it out, and see what happens.

    Could you supply me with a 300C thermal fuse?

    Depends. Do you trust Chinese degrees or not? See above 😊

    Already exists.

    With severe limitations. See also the experiments performed by @zapta here

    But I do understand that improving on what already exists is not as easy as it seems.



  • @elmoret said in Service life of heater cartridges and thermistors:

    40w can melt a block without a sock, i’ve seen it myself.

    I've seen pictures, always had an issue with them, math I did show that 40W cannot do it! But I've seen 2+ pictures of that happening.

    BTW WRT service life of the thermistor, I have original Semitec 204gt glass beads (needed a replacement for some bfb hotend some ~10-11 years ago and noone was selling per piece so I had to order 100pcs directly from Semitec, and they were darn expensive, iirc 5$ per piece) and I used them everywhere those years. I still have 4 in my original heated bed (going up to 150C) that still work 1/1 still have few in some old hotends me and Arcol made back in the day (0.2 and 0.25mm aluminium with nicro and khantal wire heaters) .. they are all still operating without a problem 10 years later. I have some PRC made unknown brand thermistors in bunch of machines both PTC and NTC that are up and running for 30+ years but they never operated in extreme conditions like the ones in heater blocks.

    So if you mechanically don't damage the leads or you don't push high current into them (by hooking them instead of heater) they will last longer then your printer.



  • @DaBit said in Service life of heater cartridges and thermistors:

    Indeed, the regular manufacturers do not provide much above 240C

    I tested some of the PRC made and some of the "brand name / expensive" ones from DigiKey... the "up to 140C" ones they behave according to specs. PRC ones too melt just like they suppose to at temps they suppose to melt. Above 240C I did not find anything on digikey as they sell 220/240C max. Mouser usually max at 140C...

    Anyhow the PRC 300C ones I tested behaved pretty good but unfortunately I only had 5 of them so I tested 3, incorporated 1 and left one spare.

    Just note that "240C" ones, for e.g. NTE (solid brand) they are 240 holding temp, so they can sit for a long time (not indefinetely) on 240C and they will melt at 290C. I'm not sure they are a safety solution for the hotends. I personally run mains powering the whole printer trough bed fuse and since I have huge heaters on beds I assume if the MCU fails it will fail with bed too and bed will trip the fuse before the hotend makes any serious damage 🙂



  • Still, something has changed... But fairly subtle; if I did not get a heater error with the have the cooling fan running to accelerate inactive nozzle cooldown I would not have noticed.

    I don't believe the thermistor is bad; both of them seem to react normal, also to 'cross-heating' between the heater blocks. But I will check the temperature with an external thermocouple once I receive my tiny one.

    I also ordered two 40W cartridges. I can use the extra power anyway.
    Chimera is not an ideal multimaterial solution, but for now I will live with it. The best results are obtained when the inactive nozzle is cooled really far down before continuing the print with the active nozzle. I intend to increase airflow over the heaterblocks during toolchange even more to accelerate cooldown of the inactive nozzle, but the active nozzle is also affected. I could put some effort in shielding the active nozzle from the airflow, but just a bit more power is far simpler.

    BTW: I tried simulating the Chimera heat transport in Fusion360, but the simulation results do not match reality. Even with no convection heat load on the block F360 says the heaterblock only gets up to 113C with 30W input. We all know that is not true.
    And adding a realistic convection load is not trivial either in F360, so I decided it was not going to give any useful results.



  • @DaBit, have you conjugated the resistance of the two heaters and the current through them when they start heating?



  • Not yet, I needed the printer to print.
    I will do that as soon as I have replacement cartridges so I only have to open it up once.



  • @dc42, since you are in contact with E3D, suggest to them to come with cartridges with built in thermal fuse?

    E3D are market leader and are in good position to bring innovations like this to the market.


  • administrators

    I've asked E3D. I'll let you know what response I get.



  • Resistance 'slow' heater cartridge, cold: 27.3 ohms
    Resistance 'normal' heater cartridge, cold: 20.6 ohms

    Voltage 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?



  • @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



  • 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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