extruder temperature stability

I am having a problem with my extruder recovering from the fans starting up. The fans start on layer 3. There is no issue with temp on layer 1 and 2.
As soon as the fans start, the temp drops about 10° and stays there for about 60 sec. - long enough to cause a fault and stop printing. I set it back to only 50% and that seemed to work, sort of.

I then reran my PID calibrations for extruder and bed. Now even at 50% it will trip out. My fans are not pointing at the nozzle. If I turn fans off as it is retreating, it will recover. The I turn fans back on at 35% then advance and it again drops but recovers faster and everything is solid for the hole print. I mean, with the fans on the temp curve is flat. I can increase to 70% and it still is good. It is the first recovery that it too much for it.

Why? What to do about it?
Marlin 2.0, Repetier Host

thanks

Edited 2 time(s). Last edit at 01/18/2020 06:53PM by ruggb.

Have you tried not pointing the fan at the nozzle/heater block?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hey Doc, thanks for the reply. What I found out when I read questions I want to answer is that I must read the whole thing. I highlighted the answer.

It may not be pointing there, but clearly the fan is disturbing the air around the heater block or it wouldn't have such a big effect. Move the nozzle or design a new one, or add a thin piece of plastic to better direct the air so it doesn't hit the heater block.
How much power does the heater use?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Fit a silicone sock over the heater block if you don't have one already, then re-tune.

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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].

What is puzzling me is the fact that if I bring the fan speed up slowly, at 50-70% the temp curve is flat for the rest of the print. It is the initial shock that it doesn't handle. Like it does not react fast enough to a cooling.
It is obvious the fan is causing the problem. The shrouds are formed to direct the air under, in front of and behind the nozzle/block.

When I tune the PID should I have the fans running?

I looked at those socks long ago and totally forgot about them. That is probably the solution. Thanks.

Edited 1 time(s). Last edit at 01/19/2020 01:07PM by ruggb.

Do you need these fans, sounds like your talking part cooling.

Quote
ruggb
What is puzzling me is the fact that if I bring the fan speed up slowly, at 50-70% the temp curve is flat for the rest of the print. It is the initial shock that it doesn't handle.

You can have sensitive PID parameters that react quickly to changes in load such as increasing extrusion speed or turning the fan on. But if you use those PID parameters during initial heating, you will get a large overshoot, which is undesirable. So in most 3D printer firmwares, the PID parameters are a compromise.

However, in RepRapFirmware the tuning process fits the heater behaviour to a FOPDT model, and calculates two sets of PID parameters from that. The slow-and-gentle set is used during initial heating, and the fast-and-sensitive set is used when the temperature is within 5C of target. This provides better temperature maintenance while avoiding a large overshoot during initial heating.

No other firmware that I know of uses this approach. It's still not perfect, so I plan to add feed-forward terms too.

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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].

Quote
MechaBits
Do you need these fans, sounds like your talking part cooling.

Yes, they are the part cooling fans.
I guess the best short term solution is socks.
I like the Repetier firmware solution, but that involves another learning curve.

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dc42

Quote
ruggb
What is puzzling me is the fact that if I bring the fan speed up slowly, at 50-70% the temp curve is flat for the rest of the print. It is the initial shock that it doesn't handle.

You can have sensitive PID parameters that react quickly to changes in load such as increasing extrusion speed or turning the fan on. But if you use those PID parameters during initial heating, you will get a large overshoot, which is undesirable. So in most 3D printer firmwares, the PID parameters are a compromise.

However, in RepRapFirmware the tuning process fits the heater behaviour to a FOPDT model, and calculates two sets of PID parameters from that. The slow-and-gentle set is used during initial heating, and the fast-and-sensitive set is used when the temperature is within 5C of target. This provides better temperature maintenance while avoiding a large overshoot during initial heating.

No other firmware that I know of uses this approach. It's still not perfect, so I plan to add feed-forward terms too.

Interesting, thanks. I may look into that. It will be another learning curve as I am using Marlin now.
I am still waiting for Repetier to fix a script offset issue. My #1 script name appears as the tooltip on the #2 script button. and so on...2 on 3, 3 on 4, 4 on 5

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ruggb

Quote
MechaBits
Do you need these fans, sounds like your talking part cooling.

Yes, they are the part cooling fans.
I guess the best short term solution is socks.
I like the Repetier firmware solution, but that involves another learning curve.

To fully isolate the hotend, just leaving the nozzle free of course, is not a short term solution, it is the way to do.

You are not the first one having this kind of issue with fan used to cool parts.

If you had posted picture of your set up, it would have saved a lot of guesswork.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I cut a silicon trivet and made a little wind break, just incase, I doubt it would help in your case, you possibly dont need part cooling, when i used mine it was on 10% any less it would stop, but lately once bed adhesion got the ellnet hold i dont need part cooling for PLA, but it does help to have more than one part on the bed allowing enough time for each layer to cool.