Upgraded to Mk2.5S, thermal runaway every time the fan turns on  

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

Sure you can slow down the fan. Or I would recomend the silicon hotend sock. It solves the problem.

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

+1 for silicon sock. I use these and it limits the temperature drop to no more than 2 C at ABS temps and it recovers within a couple of seconds.

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

I am having the same problem using the stock print fan. I was able to solve the problem by lowering the fan speed below 80%. The temperature still drops by 10 degrees or so when the fan comes on, but it is able to recover after a minute or two.

Definitely going to try the silicone sock to see if that helps too.

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

Put blue socks on an do an PID-calibration for extruder and bed.

Thomas

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

I'm having the same issue since upgrading to mk2.5s this week. Very annoying to require lowering the fan speeds to get it to work right. If a silicon sock is needed, it should have been included in the upgrade kit. Does anyone know of a solution besides using a sock??

Edit: also, i ran the PID and temp calibration but didn't fix anything.

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

PID calibration is good to make after you put the sock on. There are several threads on the forum because of this, it is also related to MK3S. So far the sock is only thing that works. I am just suprised, that there are not much often questions on this. From my point of view this has to limit everybody. So why just only a couple of people is complaining about?. All the new users of the printers, and that has to be tousands of them, should have this issue. Most of them newbies. I would expect much more complains and proper actions from Prusa. Like having the sock as a default accessories and coming with the printer.
The printer is realy aborting the print because of this. Sure not everytime. The big drop down causing temp runaway error is happening only on the bottom layers (the air is coming not just directly from the fan but also get bounced from the heated bed) and therefor it influents especialy PLA prints, where fan starts with second layer (at default Slic3r profiles)

Milos

Re: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

Yes, it's same on my MK2.5. With the current fan/extruder design you have only this three options (from best to worst):

1. Sock -> stable temp, good cooling
2. Lower fan speed -> stable temp, worse cooling
3. Aggressive PID values (PID calibration with 50% fan speed) -> slightly bouncing temp -> good cooling

RE: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

I'm having the same problem. Old gcode that turns the fan on after the first few layers causes thermal runaway as soon as the fan kicks on. Resliced with no cooling fan and the problem goes away. This looks like a pretty big oversight, honestly. I don't quite have the chops to redesign the fan duct to aim lower but I assume someone out there is looking at it.

RE: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

We're discussing it here: https://github.com/prusa3d/Prusa-Firmware/issues/1746

RE: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

I didn't have any luck until I hit 50% fan speed.

This is really a horrible design issue that every MK25.S owner will run into right after they just spend all day wrenching on their printer. So of course they're going to think they screwed something up.

I spent 5 hours futzing around with things until I finally hit on the right google search where I found the solution. That is really crappy. They've had two years to fix this design, why isn't it fixed yet?

RE: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

This happens to me when the heater cartridge is starting to fail. Replacing the heater has solved it for me 2 times, with many hours of prints before the heater starts acting up.  The first symptom was always Thermal Runaway upon parts cooling fan activation.  A sock appears to work for awhile but it worsens over time.

The heater resistance goes high, reducing the heat output.  This can be checked at the MiniRambo with an ohmmeter. 

RE: Upgraded to Mk2.5S, thermal runaway every time the fan turns on

The silicone sock around the print head worked fine for me, so I just went with that. I have a spool of ASA so I downloaded a fixed nozzle from the Prusa model web site, and it printed fine. I never installed it though because the silicone sock worked so well.

However, I am in the middle of a full Bear upgrade and I did change out the heater for a 40W one (stock is 30W) from printedsolid.com. I also changed out the hot end for a nickel plated copper one, changed out the nozzle for nickel plated copy, and changed out the heat break to a titanium one. So, we'll see how all these upgrades turn out in the end.

I do think it's really ridiculous they haven't fixed this design, as it's been over a couple of years now.