# PID autotune fails with a temp too high

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).

Thermistor settings:

#define TEMP_SENSOR_0 6
#define TEMP_SENSOR_1 6

• Have you looked into this question?
– 0scar
May 18 '20 at 7:19
• Are you sure the temperature readings are correct? If I read the graph the hotend is heating up 200 °C in about 30 seconds. This seems unreasonably fast (just based on the heat capacity of a standard E3D heater block this would require at least 64 W). You write that you used a 24 V heater in place of a 12 V one. Doing this should drastically decrease the heater power. Did you make a mistake when writing the post, and actually used a 12 V heater in place of a 24 V one? If so, that might explain a lot. In this case, you should immediately revert to the appropriate heater cartridges for safety. May 18 '20 at 9:25
• Good catch, the heating up is so fast that the #define PID_FUNCTIONAL_RANGE 10 is too little for the amount of heat pumped into the heater block causing a large overshoot causing the PID tuning to stop. Maybe you can measure the resistance of all 4 heater cartridges?
– 0scar
May 18 '20 at 12:36
• @Tom: OP has an aftermarket hotend that came with 12 V cartridge, but power supply is 24 V so the replacement should be correct. May 18 '20 at 14:14
• I tested the resistance on the factory hot end for the Ender3 and saw 14 Ohms of resistance (same reading as you said I should expect for 24 then checked the 12v ones supplied with the hot end and the measured 4 Ohms, unfortunately the cartridges I have measure 4 Ohms just like the 12v cartridges do. I left a review on the product in Amazon, and have a better rated set on the way (should arrive Sunday). I updated the post to reflect the product that was in my order. May 22 '20 at 17:50

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.