Thermal Runaway Shutdown Control  

Re: Thermal Runaway Shutdown Control

Complete speculation from reading about the topic, so would love clairification on this specific printer as well.

They say those inexpensive "Chinese" printers have the sensors set up to ramp up the current if the thermistor detects a "low temperature" which is the same signal if the sensor gets unplugged, causing thermal runaway?

How specifically does the Prusa system handle failures of the system, and issues that could go wrong, and cause a chain reaction failure elsewhere?

Are there any other systems that could cause a similiar fault and snowball into a problem?

Both the heated bed and the extruded probably work in similiar ways? The heat bed probably having a better scenario because of the large surface area if there where a fault like this in the system?

And just for curiosity sake, other than cost, how did many of the "Chinese clones" end up with a system that had inherent failure points if they are cloned from better systems that take higher safety into account?

Are there any threads detailing systems like this for the MK2/MK2S to better understand how these are set up to handle failures?

Re: Thermal Runaway Shutdown Control

This feature has worked well for me on my MK2. I've had several failures over the past 8 months with the temp sensor on the hotend (never on the bed). These usually have been from a failed print that ran for hours when I'm not home and then break the wire trying the remove the plastic from the hot end. The temp sensor wire is very thin and easily can break. My last one lasted a while, but still failed not immediately after a failed print. Its cheap and easy to replace. I'm currently using the default e3D black clip. Its bulky, but with how many times I've had to replace it, it makes the changing of it easy.

What happens when it fails:

The temp is no longer consistant. The prints will start to have black marks in it (hard to tell if you're using black plastic). The prints are printing at a higher temperature because the temp sensor is reading lower never higher (at least its never been higher for me, and I don't see how a failed wire would read higher).
eventually the rambo board will notice it cannot keep up with the temperature demands. Increasing power to the hot end and the temp goes down. It then throws the error Thermal Runaway to prevent the heating element from getting too hot. And the print stops. You may still end up with a jam if you turn off the printer entirely since the fan for the heat break will turn off in a complete failure (temp of 15 degrees C). Leaving the printer on leaves the fan running. So you may want to leave it running until the hot end cools down to room temp to prevent a jam.

Re: Thermal Runaway Shutdown Control

This feature has worked well for me on my MK2. I've had several failures over the past 8 months with the temp sensor on the hotend (never on the bed). These usually have been from a failed print that ran for hours when I'm not home and then break the wire trying the remove the plastic from the hot end. The temp sensor wire is very thin and easily can break. My last one lasted a while, but still failed not immediately after a failed print. Its cheap and easy to replace. I'm currently using the default e3D black clip. Its bulky, but with how many times I've had to replace it, it makes the changing of it easy.

What happens when it fails:

The temp is no longer consistant. The prints will start to have black marks in it (hard to tell if you're using black plastic). The prints are printing at a higher temperature because the temp sensor is reading lower never higher (at least its never been higher for me, and I don't see how a failed wire would read higher).
eventually the rambo board will notice it cannot keep up with the temperature demands. Increasing power to the hot end and the temp goes down. It then throws the error Thermal Runaway to prevent the heating element from getting too hot. And the print stops. You may still end up with a jam if you turn off the printer entirely since the fan for the heat break will turn off in a complete failure (temp of 15 degrees C). Leaving the printer on leaves the fan running. So you may want to leave it running until the hot end cools down to room temp to prevent a jam.

I read that commonly.

Why are the electronics not specifically sheathed as they come off the heat block to protect from block huggers?

It always seems like there should be a high temperature sheeth that encapsulates the heaterblock and electronics from what seem like a fairly common malfunction and issue when things go horribly wrong. And from what I have read, it seems beneficial to insulate the block as well from a energy standpoint as well as protecting the components.

It seems like if there were a sheeth encapsulating this area, even in the worst of conditions, the block could be heated and the sheeth used to pull away all the offending plastic leaving the sensors and heati g element completely unphased.

It would be cool is they could build object sensing into the system, and compare a initial nozzle geometry to current and detect a failure trying to destroy the system by buildup.

Re: Thermal Runaway Shutdown Control

This feature has worked well for me on my MK2. I've had several failures over the past 8 months with the temp sensor on the hotend (never on the bed). These usually have been from a failed print that ran for hours when I'm not home and then break the wire trying the remove the plastic from the hot end. The temp sensor wire is very thin and easily can break. My last one lasted a while, but still failed not immediately after a failed print. Its cheap and easy to replace. I'm currently using the default e3D black clip. Its bulky, but with how many times I've had to replace it, it makes the changing of it easy.

What happens when it fails:

The temp is no longer consistant. The prints will start to have black marks in it (hard to tell if you're using black plastic). The prints are printing at a higher temperature because the temp sensor is reading lower never higher (at least its never been higher for me, and I don't see how a failed wire would read higher).
eventually the rambo board will notice it cannot keep up with the temperature demands. Increasing power to the hot end and the temp goes down. It then throws the error Thermal Runaway to prevent the heating element from getting too hot. And the print stops. You may still end up with a jam if you turn off the printer entirely since the fan for the heat break will turn off in a complete failure (temp of 15 degrees C). Leaving the printer on leaves the fan running. So you may want to leave it running until the hot end cools down to room temp to prevent a jam.

Okay that feature seems to be reasonable to keep the hot end thermal run away from happening. On my digital dashboard design I had made the temp sender tables set up for a display notification (EEE or ---) when a temp and pressure sensors were disconnected or the wires were shorted together. Seems as though the Einsy-Rambo board firmware could use a similar process in addition to just waiting for the Rambo bd. to reach its maximum over temp condition. I wonder if the heat bed is handled in a similar manner.

This type design information would be great to review.

I do see a additional Rambo bd. thermistor input that might be available to use in addition with possible firmware update.

This Prusa community is great by the way.

Thanks for the feedback!

Re: Thermal Runaway Shutdown Control

Printer will recognise loose or disconnected thermistors and shut down. Try it for yourself 🙂

Re: Thermal Runaway Shutdown Control

Printer will recognise loose or disconnected thermistors and shut down. Try it for yourself 🙂

Thanks for the information Josef.

I feel better knowing your design has been thought through with good safe guards put in place.

Rob

Re: Thermal Runaway Shutdown Control

We can even recognise stuck mosfet in on position, then the printer spins up both fans which prevents serious damage and starts beeping like crazy. Since MK3 we also added watchdog which resets the printer if the FW is stuck for 3 seconds.
On top of that we have good insurance if something happens, we luckily never had to use it 😉

BTW. French insurance company wanted money from us as someones Anet A8 burned someones house. "But there is Prusa written on it!"

Happy printing!

Re: Thermal Runaway Shutdown Control

On Tom's Dolly there is also "Prusa" written on it:-) I bet it burns better than the original tho:-)