AutoTuned hot-end, but very slow heat-up to endpoint

jason71

Hi!
Is it normal for the autotune to complete, but then for the system to take a long time to actually reach the set-point?

The screenshot shows the autotune completed (I repeated it to get the timings listed below). My config.g file has;

[[language]]
M307 H1 A471.1 C133.9 D20 B0

However, to reach my set-point of 220degC took a very long time compared to Marlin when I autotuned that.

The hot-end was started with the temperature matching the bed/ambient (so ~23degC)

To reach 200degC took 1min 50 seconds.
To reach the final set-point of 220degC took 4mins 40 seconds!

I never had problems with Marlin autotune on this printer.

I had to back the max PWM value down on the autotune.

Firmware Name: RepRapFirmware for Duet WiFi
Firmware Version: 1.15e (2016-10-02)
WiFi Server Version: 1.02
Web Interface Version: 1.12

jason71

Hmm, I think my question was lost in the mess above.

From "room temperature". How long should a typical hot end take to reach (approx) 220C?

I did run the tune (details above) and don't mind that taking a while (about 7 minutes).
My main concern is that it takes so long to stabilise on a normal heat.

I don't have much details on the hot-end other than it's a J-Head, with a proper heat cartridge (not a leaded power resistor)

DjDemonD

My e3d v6 genuine hot end on 12v (30w heater) takes about 2 minutes to reach 220.
I have another which runs via a 24v to 12v converter and is a bit slower maybe 3 minutes.

I don't find there is any long slowdown as it nears the set point maybe 5-10 seconds to stabilise once it gets within 5 degrees.

I have another printer which "hunts" around the set point when I ask for quite high temps like 255 deg C I assumed it was the thermistor being a little less accurate at these higher temperatures. Thats running marlin, I am not too fussy about the temperature being very precise, so I set the time to stabilise as 3 seconds.

jason71

Thanks, your numbers are roughly what I get on my other printer (currently running Rumba).
I totally get the bed will take a few minutes to reach 100C, but the hot-end should be much quicker.

I'm running on 15V, but don't have a clue about the power rating of the heating block. It was previously running off Ramps 1.4.

I expect this is a tuning issue, so may look at playing with the numbers when I get in from the office.

W3DRK

When you say it takes a long time to reach it's set-point, were you running the auto-tune a second time or did you actually command a temperature?

It's completely normal for the PID auto-tune routine to take a long time as it slowly heats the tool while attempting to fit a PID model, regardless of how many times you've run the auto-tune in the past.

But when simply enabling your heater to a specified temperature, unless you've set a PWM limit (useful to prevent overshoot with over-sized heating cartridges –ie anything greater than 30 watts), it should heat just as quickly as any other controller/firmware.

jason71

I've run and successfully auto-tuned. That took about 7 minutes.
I applied the values then told the printer to heat to 220degC.

It gets to 200degC fairly quickly, but the final stage is very, very slow.

dc42

If it heats quickly to 200C and then takes a long time to reach 220C then it sounds as though the auto tuning has over estimated the gain parameter. Let your hot end stabilise at 220C and then send M573 P1 to find the average PWM. Divide that figure into (220C - room temperature) and see how that figure compares with the 471 found by auto tuning.