I’m trying to use the metal extruder from the shop here to replace my stock ender 3 extruder and hot end. I wired it all up last night but I must need to change some settings in the firmware, because when I started up everything just started running away. The cooling fan appeared to be indefinitely accelerating to a point where it started to smell like burning. I swapped in the stock ender fan and all was well again. But when I tried to preheat the hot end, it also just ran away, getting crazy hot really fast. Like closing in on 300c within a minute or two. This despite it being set to 200. It also smelled like burning and started smoking. Has anyone on here tried to do what I’m describing? Have you encountered similar problems? How did you solve things?
Sounds like you plugged them in to each others ports.
I’d say almost certainly not. For one, all the wires are color coded in exactly the same scheme as the new components. I also didn’t unplug anything, but rather just snipped and added Dupont connectors. Also the runaway fan behavior stopped once I put back the stock fan. And lastly as it’s currently set up, the fan turns on when things power on but the hot end only turns on if i preheat it.
Initial thoughts are 12 or 24 voltage differences, which would mean significant hardware changes, or different thermister types which can be corrected with firmware configuration.
Thanks Tom. So for a little more detail, the runaway hotend is returning a runaway temperature to the control board. So, while the thing is getting crazy hot, my display also says it’s crazy hot. Does this sound like a mis-calibrated thermister? I would imagine if the software “knows” it’s overheating, it could reduce power to the hotend, but I’m clearly no expert here and very well could be off the mark.
Also, any clues as to what the thermister is on this extruder that’s sold here? I’m having trouble finding specs…
Though I suppose I could try swapping in the stock thermiser. Maybe that’s a place to start before diving into firmware?
To Toms point though, do you have a 12V power supply connected or a 24V power supply connected?
Different thermistors have different default resistance and different temperature curves, so the firmware needs to know which one you’re using in order to properly interpret the resistance it is seeing as the temperature. “Crazy hot” could still be interpreted as 5 or 10 degrees lower than target, so the firmware would tell the control board to keep pumping in the current.
I would think the manufacturer of the hot end would publish a spec sheet listing the thermistor so it could be specified in firmware.
Running a 12 volt heater cartridge on a 24 volts power supply would also result in “crazy hot” really fast and could damage the cartridge in a dangerous (read “major fire hazard”) way.
Yeah, and cause a fan to smoke…
The temperature is closed loop, so if you had a small error in the thermistor table, then it would be possible to have it overshoot a bit, but I wouldn’t expect it to stay on once it passed the set point (that the firmware thought it had). It can “overshoot”, like if you asked for 200C, it might turn off the heat at 195C, and still have enough heat in the block that by the time the thermistor registered 195C, the actual block was over 200C, which would cause the temperature to still increase, up to something like 205C, but not 300C. I don’t see how the wrong thermistor could cause that much of a swing. If you had the wrong temperature table configured, then the actual hotend might be 200C while the firmware thinks it is 250C, but it would still be able to turn off the heater…
#define TEMP_SENSOR_0 11 // 11-MK8 5-Aero
I think 11 is the right one. This is from the preconfigured firmware Ryan has.
I know nothing about the ender 3, FWIW. Maybe someone with some specific experience on that controller could chime in?
This is all super helpful thanks for these ideas and suggestions. I’ll investigate this later tonight and report back.
Sorry I’m still learning all this. Just to clarify, what is the “cartridge”? Is that the actual heating element? How would I determine what the voltage is on it?
Yes. I’m assuming that your hot end uses a ceramic heater cartridge, which is a metal cylinder with the heater wires coming out one end which is clamped into the heater block. Cartridges for different wattages have different resistance and are expected to be used with different voltages. A quick google search found this:
e3D Heater Cartridges are documented to be around 4.8 Ω for 12 V & 30 W, 3.6 Ω for 12 V & 40 W, 19.2 Ω for 24 V 30 W and 14.4 Ω for 24 V 40 W.
Different manufacturers could have different specs. Higher wattage will get to desired temp faster, or get to higher overall temps, but then you have to be careful not to exceed the effective temp range of the thermistor, or switch to a thermocouple if you’re looking to do really hot filaments.
The one from Ryan’s shop should be 12V. Instead of looking at the heater, look at your power supply. Share a photo of the label, if you like. But it should be 12V.
Yeah, then you’d need a 24V heater for the mk8 extruder. I think they are sold as 1/4", but I don’t know for sure. That explains why your fan was cooking too.
If you went the other way, and got a 12V psu, then you’d need to at least modify the bed, if not replace it.
I’m assuming I’d need different stepper motors too and maybe a different control board as well? Sounds like the more complicated option to me.
So it’s the wrong cartridge but will I need a different heat block as well? Or will swapping in a 12 volt thermistor do the trick? I’ve got one on order that I think should be here next week. If the heat block is an issue do you think I could swap in that one part from the stock hotend? Or is there a reason I shouldn’t do that?
The thermistor is driven by 5V, stepped down from the source voltage, so that is fine with either suplly. The heater element (the electrical part that heats up) needs to match the source voltage, which is 24V. The heat block (the chunk of aluminum the heater goes into) doesn’t care what voltage the heater gets. It should be fine.
Steppers can handle both voltages. The controller has always used 24V, right? So it is fine.
I am assuming you had a working printer that was designed for 24V, and you are just trying to change the extruder to the mk8. In that case, the part and extruder fans need to be 24V and the heater does too. Otherwise, it should all be fine.
But just to be sure, maybe start from the top and explain what you are trying to do, what parts you have, and share lots of pictures. I’m sure we can help you get there.