Fire safety command?

Hey printer commanders,

Some days ago I read here in the forum about someone printer going up in flames. I´m also not completely trusting of my machine yet but I had an idea to better that.

Its probably not new, but is there a command one could put in the firmware which would shut down the printer if the hot end is on full power for longer than 2-3 minutes?

Of course this doesnt help if your board fries but, what I experienced already two times is the thermistor malfunctioning or falling out of the hot end and the machine that powering up the resistor to full 255 duty cycle and almost melting my PTFE heatshield.

Cheers

Edited 1 time(s). Last edit at 02/02/2014 01:58AM by sungod3k.

A very good idea. And should not be too difficult to do

There is already a separate post on that:

[forums.reprap.org]

It is for a scenario when full power is on for a certain time but the hot end temp is also dropping.
Repetier is thinking about it.

Edited 1 time(s). Last edit at 02/02/2014 03:42AM by dave3d.

Ah interesting thats exactly the topic. Lets see what comes out of this.

If the thermistor falls out, that is something you can prevent. In the case of preparing a hotend and then not securing the thermistor well, I can imagine the same kind of person would not go the length to study the printer enough to even discover that there is such a thing as a fire safety command

Just put a piece of kapton around a cleaned heater block and make sure you watch the printer very closely on the first few prints to make sure that the tape doesn't unstick from heat working on the tapes glue. I've had the tape loosen up a few times, but I fixed it and now the tape is on quite well and there is no risk of a thermistor falling out.

Ohmarinus: my thermistor was secured with kapton tape around the hot end. The wires were also secured to the peek bit of the hot end with a cable tie. It did not fall out. It was pulled out. A ball of plastic and a detached print got tangled up with the thermistor wiring as the whole lot went round and round. It then pulled the thermister out with a lot of force.

What about comparing how closely actual hotend response matches theoretical based on PID values stored in firmware?

Quote
dave3d
Ohmarinus: my thermistor was secured with kapton tape around the hot end. The wires were also secured to the peek bit of the hot end with a cable tie. It did not fall out. It was pulled out. A ball of plastic and a detached print got tangled up with the thermistor wiring as the whole lot went round and round. It then pulled the thermister out with a lot of force.

Well, I don't mean to insult you, but it should still be secured in a way that it simply can not happen. I don't think I can remove the thermistor with even a pair of pliers. I would have to cut through a very secure package of heat insulation, hotend cooling shield and a few layers of very carefully placed kapton. If the wires are correctly managed, it should not be possible for any print detaching to rip out the thermistor.

Maybe it would be more valuable to create a good and clear guide on hotend-preparation and handling instead of trying to design all kinds of safety measures to battle the effects of incorrectly prepared hotends?

I think a lot of problems can be prevented and when I just started out fresh, I also made a lot of mistakes with the hotend packaging, however, I had always managed to correctly and safely wire the system. But a lot has improved since then. And the mistakes I've made were mostly because I had no examples of how it should be done, but eventually I found out the best way for my Budahschnozzle and J-head to be insulated and wired, and a lot of people can learn from looking at how others have done the wiring.

Just to be sure, I'm not claiming you did anything wrong, ofcourse there is always the chance of a 'freak accident' happening, and nothing is perfect, not even me. My printer may just explode tomorrow and I have to admit that besides the hotend, a lot of my cable management is terribly poor still so I'm working on a way to connect all motors to the Ramps without having all the cables run in plain view. I think minimizing cable clutter already makes it much easier to manage a machine and to solve potential problems in wiring/electronics.

Ohmarinus: you are right. I would not disagree wiith anything you have said. Electrical wiring is an important safety factor. Problem is when you do you own build some parts of the build are not quite as you want them. I have recently built an Ord bot and I have tried to pay attention to the wiring. Some of it is run in metal springs but I have still got my Ramps board hanging off the back.