Temperature on hotend is always below target

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richardphat
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Temperature on hotend is always below target

Post by richardphat » Thu Jul 10, 2014 4:37 pm

Hey,

this issue happened recently and hasn't been up until now. I have printed about 20-25 hours so far. Usually the temperature is oscillating and off by 1-2 degree max. Now, the temperature detected by the sensor never get past the target and is way off by.... let's Say the targeted temp is 228, but the actual temperature is oscillating around 210-213 C.

All I can say is I've been applying permatex high red temperature sillicone gasket. Between the hotend and the thermistor. Could that be the issue?

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Re: Temperature on hotend is always below target

Post by Polygonhell » Thu Jul 10, 2014 10:02 pm

It's more likely a bad PID setting.

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Re: Temperature on hotend is always below target

Post by richardphat » Fri Jul 11, 2014 1:27 pm

It's to believe it's something related to the PID value.

No matter how high Kp or low it is, it should have a peak value. In this case, there was no peak, and the signal starts oscillating already. It's like the signal chosen, is different from the signal injected in the controller.

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Re: Temperature on hotend is always below target

Post by Polygonhell » Fri Jul 11, 2014 3:44 pm

Assuming it will actually reach a specific temperature (i.e. if you set the target higher it reaches the previously unreached lower temp), then about the only thing is can be is the PID tuning

If your I is too high (might be low), you can end up in a state where it will be perpetually below the requested value.
I find Repetier's PID autotune to be useless for higher powered heaters, like the dual resistors on the SeeMeCNC and the 40W cartridges people seem to like, I always end up having to manually adjust after the fact to get stable temperatures.

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Re: Temperature on hotend is always below target

Post by jmpreuss » Fri Jul 11, 2014 8:44 pm

Polygonhell wrote:I always end up having to manually adjust after the fact to get stable temperatures.


How do you manually figure out the pid settings? I just got the ed3 v6 and the auto pid setting gives me a hot end that overshoot the set temperature by 10C on warm up.
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Re: Temperature on hotend is always below target

Post by Polygonhell » Fri Jul 11, 2014 9:25 pm

I posted a link to tuning PID for quad copters somewhere on the boards, it's fundamentally the same, but basically, take the autotune values as a starting point! then I usually just play with I to get it in the right range, and remaining oscillation, can usually be dealt with by teaks to D.

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Re: Temperature on hotend is always below target

Post by richardphat » Mon Jul 14, 2014 7:27 pm

I'll give a check in the next few days, the only way to get the machine print so far is to increase the temperature target and then lower the temperature back. The machine then understand that it "has" reached the target temperature when the real temperature match the one fixed at.

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Re: Temperature on hotend is always below target

Post by 1ggy » Tue Jul 15, 2014 10:40 am

Bump up your Ki and see what happens. Alternatively, try switching to dead-time control for your hot end and see what happens.

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Re: Temperature on hotend is always below target

Post by Hans » Sun Jul 27, 2014 8:23 pm

I've been struggling with the same issue as well. My theory is that the the plastic being extruded is acting like an additional heat sink, and the PID auto-tune was of course done without the extruder running. The problem just gets worse when trying to print again soon after running, I have to let the hot end cool off quite a while or it will never reach target temp to start a print.

-Hans

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Re: Temperature on hotend is always below target

Post by gestalt73 » Mon Jul 28, 2014 1:00 am

So far here's the only online resource that made sense to me for manually tuning and tweaking PID values:

From http://reprap.org/wiki/PID_Tuning

Code: Select all

For manual adjustments:
if it overshoots a lot and oscillates, either the integral gain needs to be increased or all gains should be reduced
Too much overshoot? Increase D, decrease P.
Response too damped? Increase P.
Ramps up quickly to a value below target temperature (0-160 fast) and then slows down as it approaches target (160-170 slow, 170-180 really slow, etc) temperature? Try increasing the I constant.


You can adjust these values live by issuing an M301, and watching repetier or pronterface (displays temps in a graph, which is nice)

I'll either run a G0 E300 F100 and tune the values while I'm extruding in air, or start printing a model and adjust them during the print.

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Re: Temperature on hotend is always below target

Post by richardphat » Mon Aug 25, 2014 8:21 pm

Hey,

I was involved with other works and when I tried to check again this week. The heating resistor seems to broken. Temperature is now barely heating properly. And as gestalt mentionned, the auto tuning really blow. I end up having 10 to 1000x times bigger/smaller values in all kp, ki and kd.


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Re: Temperature on hotend is always below target

Post by richardphat » Mon Aug 25, 2014 10:42 pm

Yup, I have already planned to buy one in one of the local store in montreal.

By the way to remove the sillicone, did you guys use some solvent or use some knife and carver tools to remove the RTV?

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Re: Temperature on hotend is always below target

Post by PhoenixNZ » Wed Aug 27, 2014 3:08 am

I had to rip out some resistors recently. I just scrapped out the crud using a knife and drill bit

Some other users have experienced a similar problem with hot end not reaching temperature and the solution for them was to insulate the hot end barrel just below the PEEK section on the stock hotend.

It's interesting that others in this thread are suggesting manual tweaking of the integration settings for the PID controller. Might have to try that myself as I am suffering similar issues.

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Re: Temperature on hotend is always below target

Post by PhoenixNZ » Sun Aug 31, 2014 8:59 pm

Just quickly replying here to say: Hot end not reaching temperature solved by removing the hot end, wrapping the barrel below the PEEK section in Kapton tape until it was thick enough to remove the gap between barrel and PEEK fan shroud, and re-running PID autotune

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Re: Temperature on hotend is always below target

Post by geneb » Mon Sep 01, 2014 11:28 am

FYI, that's way more Kapton than you needed. :)

g.
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Re: Temperature on hotend is always below target

Post by richardphat » Mon Sep 01, 2014 1:57 pm

I just upgraded for a 40W heating cartridge. It works much better, temperature may be off by 5-6C. Now, I'll need to cover any heating parts that is in contact with air.

Might used clay over kapton, might be overkill though :lol:

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Re: Temperature on hotend is always below target

Post by PhoenixNZ » Mon Sep 01, 2014 7:29 pm

geneb wrote:FYI, that's way more Kapton than you needed. :)

g.



eh, it wasn't a big gap - only about 4 or 5 layers worth - and it solved the issue so I can't complain :P
I had put 2 layers on before the fan shroud went on but must have wrapped it too tight and it unstuck itself when the barrel expanded when heating up for the first time

Not going to have issues with it getting too hot am I? The kapton is only on the metal part

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Re: Temperature on hotend is always below target

Post by geneb » Tue Sep 02, 2014 9:33 am

Nah. I typically apply a single wrap of Kapton around the barrel at the PEEK/Aluminum interface, and that's more to keep them from unscrewing from the constant heating/cooling cycles.

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Re: Temperature on hotend is always below target

Post by teoman » Thu Sep 04, 2014 8:48 am

If you are still using the stock hot end and heating resistors, have a look at the resistors. I am having similar issues as I used to be able to reach 240 degrees without problems now it is stuck at 235 and does not go any higher.

What i did notice was that I was able to see one of the resistors glowing red hod through a small gap in the RTV. I am sure that i packed the RTV well but maybe expanding air or such has blown a little hole in it. If the resistor is in air it will not conduct heat to the hotend easily...

I will try to inject some rtv in to the hole when i get a chance.
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