PID autotune fails with a temp too high

3D Printing Asked by Keith Rawson on December 23, 2020

Working on upgrading my Ender 3 to a dual extruder setup using the Winsinn dual hot end and MKS Base V1.6 motherboard using Marlin FW 2.0.5 and am unable to get the PID autotune to work. When I start the autotune, the temperature spikes pretty quickly and quickly fails, either heating to 60 °C or 200 °C (M303 C5 E0 S60) for either hot end (E0 or E1). After looking through other online messages, I used 24 V heater cartridges rather than the 12 V ones that came with the hot end. Aditionally, I have the thermisistor settings to use config 6 (rather than 1) after reading through user recommendations on the hot end. After failing to get the hotend to heat properly, I have the following questions:

  1. Should I try reducing the current to the cartridge? Currently set to default of 255?

  2. Are there any other PID changes I should make to allow the autotune to figure out the right parameters to use?

  3. Are there any other tests recommended to figure out why the hot end heats without being stopped by Marlin?

Here is a chart showing the temperatures of the hotends and bed while running autotune on T0 and T1. Weird gap in second attempt was verifying that the right sensor was plugged into the right mainboard pin (no power going to hot end at this time).

PID autotune temperature

Thermistor settings:

#define TEMP_SENSOR_0 6
#define TEMP_SENSOR_1 6

One Answer

As the heating curve is very steep, it could be that the wrong cartridges are inserted, or you have been supplied the incorrect cartridges. (Not long ago I've had a similar experience with a 12 V cartridge in between my 24 V spares...)

To find out for which voltage the cartridge has to be used you can measure the resistance with a multitester/multimeter. You can calculate the resistance roughly by using the formulas: $$ U = I times R$$ $$ P = {U}times{I} $$ Combing these formulas gives: $$ R = frac{U^2}{P}$$

(P is power in Watt [W], I is current [A], U is voltage [V] and R is the resistance in Ohm [Ω])

Your multimeter readings should be close to the calculated values. About 4 Ohms for a 12 V/40 W cartridge and about 14 Ohms for a 24 V/40 W cartridge.

Since the Ender 3 is running on 24 V, you need the higher resistance cartridges.

If you are using a 4 Ω (12 V/40 W) cartridge on 24 V, the power would become:

$$ P = frac{U^2}{R}= frac{24^2}{4}=144 {W} $$

This amount of power will quickly raise the temperature of the nozzle! It then becomes very difficult for the PID control schedule to harness that power (e.g. overshoot control).

From the question is read that:

I used 24 V heater cartridges rather than the 12 V ones that came with the hot end

If the cartridges are truly 24 V this rapid heat-up is not expected, it could be that you accidentally received incorrect cartridges, you should measure the resistance to be sure.

Answered by 0scar on December 23, 2020

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