<p>Turns out I'm using a 12V hot end and should be using 24V. I looked up the resistance to be sure; so no amount of tuning the PID would fix that.</p>

CC BY-SA 4.0
2019-05-30T18:23:50.623Z
A 12V hotend with 24V supplied to it? That just means it's producing about 4x the power it should be. Not recommended, but I'm doing exactly that with my Fleabay machine. It's been a while since I messed with that machine's firmware, but you should be able to set the PWM of your hotend to a much lower value (start at 1/4th of what it should be for 12V) and then retry the PID tuning. See if that gets you anywhere. If you meant that you're running 12V through a 24V hotend though, you might just be S.O.L.
Nach0z
CC BY-SA 4.0
2019-12-18T16:40:26.637Z
Just so. Rather than adjust my PID any further, I swapped out the 24V parts for 12V parts. My Prusa clone is now functional and I have made quite a few prints with it, all to my current satisfaction.

My thanks to the many helpful people here.
Peltier Cooler
CC BY-SA 4.0
2019-05-30T17:55:13.520Z
2019-05-30T17:55:13.520Z
Peltier Cooler
<p>I got some Prusa i3 clones with Melzi boards with Marlin, or nearly so. One of them performed very well (considering that the board would reboot whenever power was applied to the build plate. But I digress) until finally the hot end failed, possibly due to me running it for two days with little respite. The replacement, a typical MK8 clone, installed almost painlessly but failed to start due to over-temperature conditions (we're talking as much as 45&nbsp;&deg;C over set temperature).  I tried the known solutions, continually reducing my P value (got down to 7 before I gave up) and attempting autotune. I also tried autotuning to both higher (230&nbsp;&deg;C) and lower (150&nbsp;&deg;C) temperatures.</p>

<p>None of these seemed to produce an autotune successfully, and the same error message <code>temp to[sic] high</code> appeared in all cases. Can anyone suggest something besides a new hot end (I have one on order, but what if I have the same problem with another new one)?</p>

CC BY-SA 4.0
2019-05-23T14:51:08.173Z
Maybe you can find some hints in [this thread](http://forum.seemecnc.com/viewtopic.php?t=7682)?
0scar
CC BY-SA 4.0
2019-05-23T19:55:25.977Z
Nope. It pretty much tells me to do what I did (and wrote about above). I may have left out a few hours of details, though.  I am going with the idea that my replacment is a 12V hot end, and the requirement is 24V hot end.  I bagged one and will try it this evening...and tomorrow will update.

Watch this space.
Peltier Cooler
CC BY-SA 4.0
2019-05-24T06:45:28.080Z
You can manually tune the PID.
Jeroen3
CC BY-SA 4.0
2019-05-25T03:02:18.110Z
Yes I know. Turns out I'm using a 12V hot end and should be using 24V.  I looked up the resistance to be sure; so no amount of tuning the PID would fix _that_
Peltier Cooler
CC BY-SA 4.0
2019-05-28T11:30:04.590Z
You can always just limit the maximum PWM rate to supply to your 12V heater, via `#define BANG_MAX 64`
`64` would have a 12V cartridge run in a 24V system as it if was a 12V system.
Make absolutely sure to enable thermal runaway protections, since a 12V cartridge on 24V can get *very* hot.
towe
CC BY-SA 4.0
2019-05-30T02:12:10.433Z
I like this idea, but I do not know how to change #defines (do I take it that I need to find the source code, modify the #defines, recompile and upload the code to the board?), as I only use either the front panel or gcodes to change PID values. #define BANG_MAX 64 64 sounds like it would open that sucker up all the way, though. Besides not understanding my #defines, did I misunderstand what BANG_MAX does?
Peltier Cooler
<prusa-i3><hotend><pid>
PID autotune fails under all conditions so far. Any ideas I haven't tried?
Peltier Cooler
# PID autotune fails under all conditions so far. Any ideas I haven't tried?

(Asked by: username_0 on 2019-05-21)

I got some Prusa i3 clones with Melzi boards with Marlin, or nearly so. One of them performed very well (considering that the board would reboot whenever power was applied to the build plate. But I digress) until finally the hot end failed, possibly due to me running it for two days with little respite. The replacement, a typical MK8 clone, installed almost painlessly but failed to start due to over-temperature conditions (we're talking as much as 45 °C over set temperature). I tried the known solutions, continually reducing my P value (got down to 7 before I gave up) and attempting autotune. I also tried autotuning to both higher (230 °C) and lower (150 °C) temperatures.

None of these seemed to produce an autotune successfully, and the same error message `temp to[sic] high` appeared in all cases. Can anyone suggest something besides a new hot end (I have one on order, but what if I have the same problem with another new one)?

**Tags:** prusa-i3, hotend, pid

> **Comments:**
> **username_1**: Maybe you can find some hints in [this thread](http://forum.seemecnc.com/viewtopic.php?t=7682)?  
> **username_0**: Nope. It pretty much tells me to do what I did (and wrote about above). I may have left out a few hours of details, though.  I am going with the idea that my replacment is a 12V hot end, and the requirement is 24V hot end.  I bagged one and will try it this evening...and tomorrow will update.  Watch this space.  
> **username_2**: You can manually tune the PID.  
> **username_0**: Yes I know. Turns out I'm using a 12V hot end and should be using 24V.  I looked up the resistance to be sure; so no amount of tuning the PID would fix _that_  
> **username_3**: You can always just limit the maximum PWM rate to supply to your 12V heater, via `#define BANG_MAX 64` `64` would have a 12V cartridge run in a 24V system as it if was a 12V system. Make absolutely sure to enable thermal runaway protections, since a 12V cartridge on 24V can get *very* hot.  
> **username_0**: I like this idea, but I do not know how to change #defines (do I take it that I need to find the source code, modify the #defines, recompile and upload the code to the board?), as I only use either the front panel or gcodes to change PID values. #define BANG_MAX 64 64 sounds like it would open that sucker up all the way, though. Besides not understanding my #defines, did I misunderstand what BANG_MAX does?  

---

## 1 answers

### Answer by username_0 on 2019-05-30. Score: 0 | Accepted answer

Turns out I'm using a 12V hot end and should be using 24V. I looked up the resistance to be sure; so no amount of tuning the PID would fix that.

> **Comments:**
> **username_4**: A 12V hotend with 24V supplied to it? That just means it's producing about 4x the power it should be. Not recommended, but I'm doing exactly that with my Fleabay machine. It's been a while since I messed with that machine's firmware, but you should be able to set the PWM of your hotend to a much lower value (start at 1/4th of what it should be for 12V) and then retry the PID tuning. See if that gets you anywhere. If you meant that you're running 12V through a 24V hotend though, you might just be S.O.L.  
> **username_0**: Just so. Rather than adjust my PID any further, I swapped out the 24V parts for 12V parts. My Prusa clone is now functional and I have made quite a few prints with it, all to my current satisfaction.  My thanks to the many helpful people here.  

---

