Hotend not heating fully duet 0.6

Have a custom built corexy that was running perfectly with a smoothie board until i made a bonehead mistake and fried it. So i decided for my next board i would try out the duet, liked some of the features it offers, espcially the web controll. I got a 0.6 version from t3p3 and DC42 firmware (most recent). Took a while to get set up as it is more involved than the smoothie was. But i am stuck right now with my hotend not heating completely. Have messed with the PID settings etc to no avail. Switched thermistors and heater and no change. It comes within 5-30 deg depending on how high the temp is set. Example, at 190 it gets to 185, at 235 it gets to 215-220 and at 250 it gets to 220-225. Checked voltage of the board and heater, both are getting 12 volts.

Had a hard time getting the thermistors to read correctly at first. Played with the M305 command quite a bit, using the H and L values to get close. Ended up raising the thermistor B value to get a more accurate reading. Still a little off, but closer. Going to get an IR thermometer tonight to see if i can dial it in closer.

At this point i am completely stuck. Not sure if i have a bad board or if im just putting the wrong parameters in. Any help is appreciated.

It sounds to me that your heater power is lower than the default PID parameters assume. Please revert to the default PID parameters and attach a screen shot of the temperature graph from the web interface when you try to heat the nozzle to 250C from cold. When the temperature has stabilised, run M573 a few times to find the average PWM.

A quick fix may be to reset to the default PID parameters and then increase the S parameter from its default of 1.0 to e.g. 1.5.

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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].

Attached is the screenshot with my M301 and M305 (should be default) settings. Along with the results of the M573

That screenshot and those figures show the following:

- Severe undershoot, indicating that the heater power is too low for the PID parameters in use

- The temperature settles at 223C with the heater running at full power (average PWM = 1.0)

So either your heater is way under-powered, or 12V is not reaching the heater (perhaps due to the PSI not putting out 12V, or a bad connection), or you have calibrated the thermistor such that the temperature under-reads by a very large amount. I suggest you start by measuring the resistance of the heater (which will allow us to work out its power),, and measuring the voltage across the heater terminals when M573 P1 indicates the average PWM is 1.0.

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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].

Heater resistance is 4.3 ohms and the power at the terminals 12.14 V and 11.46 V at the hotend itself. Verified the temperature setting on the thermistor with a digital thermometer and an IR thermometer and i am within a few degrees.

By coincidence i just ran the hotend without my cooling fan on it in order to measure the voltage and it had no problems getting up to 250 and leveling off. I have a 40mm fan running full bore on it (did before also with no issues).

Edit - just got the closest to 250 that i have gotten (241). Took about 10 minutes and is heat soak obviously with how slow it was moving and was bouncing up and back a couple tenths.

Edit again - reduced power to my fan to about 50% (was running it off the 12V coming to the board since i have a part cooler) It got to 248 and is hovering there, never got to 250. I can run the fan off a 5V location on the board since it is stable at 248 w/ this fan power setting. How do i get those last few degrees? Print wont start unless it hits that target right?

Edited 2 time(s). Last edit at 03/24/2016 07:41AM by josh.pierce.

Thanks for providing detailed measurements, which makes things easy to work out.

- Your heater power is 30W, which is low but should still be sufficient for a hot end with a good heat break, such a genuine E3Dv6.

- You are losing 0.7V in the cable to the hot end. If you had no losses in the cable, your heater power would increase by more than 10%, which should give you about another 20C.

- My guess is that your cooling fan is cooling not only the heatsink, but also the heater block and nozzle. Can you post a photo of your hot end and fan ducting?

What's happening is that the heater block or nozzle is being cooled faster than the heater can heat it. I recall that you had to adjust the B value because the temperature measured at the nozzle was lower than reported by the thermistor. That suggests to me that the nozzle is quite a lot cooler than the heater block. So either the fan is cooling the nozzle excessively, or the heat break is doing a very poor job, by conducting a lot of heat from the nozzle to the heatsink. If it's cheap Chinese hot end, then the heat break is probably not very good, and you might want to either replace the hot end or install a 40W heater instead of the 30W one.

If you are using a LED/CCTV PSU with a voltage adjustment, you could turn up the voltage a little, provided that the extra bed heater current will not overload either the bed heater circuit or the PSU.

It's not possible that changing from a Smoothieboard to a Duet has caused this problem. The heating time on the Duet is longer than it should because the PID is tuned for a higher-powered heater, but you can easily fix that by increasing the S parameter to about 2. Alternatively, leave S as 1.0, double all of P I D and T, increase W to 255, and reduce B to 20. But these won't affect the maximum temperature you can achieve. One of these days I'll post a PID tuning guide for RepRapFirmware and/or implement auto tuning.

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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].

Thank you for your help. It was as you say, i am getting some fan blowing on my hotend and have a cheap e3d clone (real one is next on my list) mine has a really short heat break. I was running the fan off the 12v power coming into the board and have switched over to a 5v power to slow the fan down and all is working well now. It is reaching temp and holding. So far i am very impressed with the duet over my smoothie. Not sure if i was over driving the steppers on my smoothie, but it is running the same speeds as i was before, quieter and less heat in the steppers.

Thanks!