Heater Fault Temperature Exceeded

I've build a mini Kossel with duet wifi and 7in panel due. Firmware is the latest Panel Due 7.0-1.15c, DuetWiFiServer-1.03-ch, DuetWebControl-1.14-b4, and DuetWiFi Firmware-1.17.

Unit has a 24V Heated Bed, 30W 24V Heater on hot end (E3Dv6), and Thermistors on both. Both have been tuned

;********HOT END #1 Thermistor
M305 P1 T100000 B4388 R4700 H0 L0

;********BED Thermistor
M305 P0 T100000 B3950 R4700 H0 L0

M307 H1 A348.3 C141.9 D4.9 B0 S1.0
M307 H0 A317.9 C555.4 D10.9 B0 S0.5

In the first screen shot (time 1:58) there are two small downward ticks in the ramp up that appeared when I ran the autocalibration from the drop down menu. The major dip is when the hot end started printing. Second file (2:04) shows an unsteady hot end temperature (248 +/- 3 C). The last screen shot shows the print failure as the temperature falls out below 15C. I changed the default to 15C trying to give the hot end time to recover.

-I had a lot of trouble getting the hot end to calibrate, having heating faults continually. Due to an incorrect B value.
-I continued to have heater faults at random times. I've temporarily wrapped the hot end thermistor and heater connectors (at the hot end) with aluminum foil thinking I had cross interference and things improved to the point where I successfully printed for two hours with what appeared rock steady temperatures (245 +/- 0.5 C) and I thought the issue was identified.
-But now today I'm back to thermal faults while heating up to temperature and drop out issues as in the screen shots.

I've only got a few hours on the machine, maybe 3 hrs total print time.

I've also got a 40W cartridge and PT100 on order for the hot end, but believe my problem lies elsewhere, I just don't know what to check next.

Any assistance will be appreciated.

Otherwise, auto calibration seems to be working well and print quality (when it prints) is very good for this stage of the build.



Thanks, Ed

Sharp changes in thermistor temperature readings usually indicate wiring issues, typically a bad connection to the thermistor or a short between a thermistor wire and the heater block. Such shorts happen easily when using the old style E3D thermistors, but should be much less common using the new heater blocks with cartridge-style thermistors.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

dc42

It is the new style cartridge, but will recheck all hot end connections again with a tear down and close inspection. Thanks, I'm looking for the most likely places to start.

Ed

Quote
edavis1211
dc42

It is the new style cartridge, but will recheck all hot end connections again with a tear down and close inspection. Thanks, I'm looking for the most likely places to start.

Ed

You could check with a multimeter that you are getting infinite resistance between the thermistor wires and the cartridge body. Cartridge heaters sometimes develop shorts between the element and the body, so I'm wondering whether this can happen to cartridge thermistors too. They may use the same type of mineral insulation.

And check your cartridge heater this way too.

Edited 1 time(s). Last edit at 01/04/2017 05:30PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Just disassembled the hot end and didn't see any obvious bare, broken, or shorted wires so I reassembled a bare bones hot end, just the E3D, fan, heater and thermistor. I commanded it to 245 TE and 90 TB and as it got up in temp, stable trace all the way, I flicked the thermistor lead, and "YEP" got the temperature drop I'd been seeing. Without touching the leads the hot end and bed reached full temperature with a smooth curve. Will check the resistance when things cool off and let you know what I find.

Thanks,

Ed

Heater checks out fine at 18.3 ohm with no shorts.

Thermistor doesn't show any shorts either but the resistance which seems to be 75K ohm, however if its leads are disturbed the readings go all over with a range of at least 200K to well under 75K ohms.

I'll let you know how it works once I receive the new parts and reassemble but I consider this issue solved.

Thanks, You've been of great assistance.

Ed

Sounds like a bad connection inside the thermistor then, assuming your connections to its leads are ok.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

dc42

Just a final follow up. After our discussions I decided to replace thermistor and not upgrade to the PT100 at this time to keep the configuration consistent. Well the new thermistor works great! Tuned it at:

M303 H1 P0.5 S260

reached max temp of 234.7 in 531 sec with the following:

Gain 447.6
Time Constant 193.4
Dear Time 5.8
PWM max 1.0

Looks to be holding temp (235C) within +/- 0.2C with a very smooth and steady temp curve.

Now to reassemble. Thanks for your assistance and pinpoint diagnostics.

Ed