# How to reduce +/- 5 degree temp swings of hotend (after PID tuning)

I have a Monoprice Maker Ultimate 3D printer (a rebranded Wanhao Duplicator 6) and out of the box the hotend temps when set to 200 would vary between 190 and 210. I used repetier-host to run PID tuning and stored the last set of values it gave when it finished, however I'm still seeing around 5 degree temp swings.

Here's a screenshot of the temp during a Benchy print from Octoprint:

I tried PID tuning again, which gave different values, but basically the same results. Is there anything I can do to improve this? The Maker Select Plus I had only seemed to vary +/- 1 degree so I'm assuming this is more than expected. (I don't actually know what the implications are, so I don't know whether it is/will affect my print quality).

Is there another way of tuning (I don't fancy manually tweaking numbers and testing for hours), or if I do more than 8 cycles (the default on the Wiki page linked above) would that improve the accuracy?

• Did the PID tuning improve the saw tooth pattern? It really looks as if the board is using bang-bang heating. – 0scar Dec 16 '18 at 22:51
• @0scar No, it didn't. And I'm also wondering if it's using bang-bang now, however I cannot find any way to verify it (it's stock firmware). I found M307 maybe should do it, however I only get back an "OK" response, so maybe it's not implemented. I factory reset again, and the temp is now fairly consistent. I'm wondering if my attempt to set PID values is messing up whatever it is using, making it worse. Gonna leave it un-tuned for a while and see how it goes. – Danny Tuppeny Dec 17 '18 at 18:18

If you are sure that PID is enabled (and not using bang-bang heating, as this gives a very similar heating profile) and did not fix the fluctuations, the best guess for this phenomenon is that the printer board has incorrect capacitors installed on the printer board. This is not very uncommon and can be found on the internet. You should at least show the graph to the vendor and ask for support.

If incorrect or faulty capacitors are the cause it requires desoldering, and resoldering new ones. If this is out of your comfort zone, it is better to steer your communication with the vendor to replacing the board.

• I'm also wondering if it's using bang-bang now, however I cannot find any way to verify it (it's stock firmware). I found M307 maybe should do it, however I only get back an "OK" response, so maybe it's not implemented. I factory reset again, and the temp is now fairly consistent. I'm wondering if my attempt to set PID values is messing up whatever it is using, making it worse. Gonna leave it un-tuned for a while and see how it goes. – Danny Tuppeny Dec 17 '18 at 18:18
• I don't know for sure, but I'm going to assume it's not using PID, but setting the PID values may be messing with whatever it is using. After I factory reset, the temperature is a bit spiky at first, but then really settles down to a very constant temp. – Danny Tuppeny Dec 17 '18 at 19:16

# Software

You might want to look at your firmware. When running a PID tune, the firmware decides on a smoothing.

in Marlin, configuration.h contains a line that determines how much the machine shall try to work out the curves. For my ender 3 it reads:

#define PID_K1 0.95      // Smoothing factor within the PID


Playing with the value carefully might result in better calibration.

# Hardware

A different trick to widen the waves might come from adjusting the physical properties of the printer:

• Make sure that no draft from the cool end fans runs over the heater block. If it does, a shroud or a little tinfoil can help to dampen the changes.
• e3D uses a silicon sock to isolate their heater blocks and prevent air drafting over them.
• I'm just using stock firmware and trying to avoid getting into flashing my own right now (it's my first printer, so I want to try and stick as close to the manufacturer made it to being with) :( – Danny Tuppeny Dec 16 '18 at 20:39
• @DannyTuppeny well, you might try to widen them a little... – Trish Dec 16 '18 at 20:47
• Thanks - I can reproduce this behaviour with the part fan turn off, so I don't think it's because of a draft (the room is warm and all doors/windows closed too). I did look, but couldn't find a silicon sock the right size for the Monoprice Ultimate that was easily available, but maybe I'll order some "slow" shipped ones since it seems useful to have :-) – Danny Tuppeny Dec 16 '18 at 21:01
• @DannyTuppeny You might experiment with a piece of tinfoil wrapped around to test if this helps a little, just to confirm if it helps or not. – Trish Dec 16 '18 at 21:22