I'd like to implement a redundant thermistor. Good idea or bad idea?

[d1rron]

So last night I was heating up my hot end (Prometheus V2) for a print. I looked at my computer for a couple of minutes, turned around, and saw plastic (PLA) oozing out of my hot end like water. I immediately cut power and pointed the little table fan I have next to my printer at the hot end and turned it on since the hot end fan was off after I cut power to the printer. After inspecting, I saw that one of my thermistor wires had broken and the heater ran away. My reported temp was something like 12°C. This kind of freaked me out, since sometimes I let my printer do it's thing overnight.

So I was thinking, would it feasible to attach a second thermistor and program the Arduino to cut power to the hot end if it reaches a certain temp? Or perhaps use the same thermistor and program the Arduino to cut power to the hot end if the thermistor reports below a certain temperature value? At room temp my thermistor reports about 25°C. So I thought that perhaps I could make it cut hot end power if the temperature reported is below, say, 18°C?

I eventually want to build an enclosure and include a fire suppression system, simply because I know that also covers other possible causes of a fire. But I know the thermistors have delicate wires, and if there were to be a fire, it seems like it'd be the most probable culprit. I've played around with programming Arduinos here and there, but I don't want to just take a stab at it and end up having my printer walk off into the night or become sentient or something. Lol So how difficult would this be to implement in either configuration? If it's not too difficult, it might even be a decent safety feature to implement -- a fail-safe in case of thermistor failure.

I've already ordered a new thermistor and heater cartridge for the hot end. The heater still works, but I don't know if it was damaged in any way and it looks a little haggard. I also ordered a second hot end so I could more easily swap between nozzle sizes.

Anyway, thoughts? Lol

[Xenocrates]

Repetier's latest versions have both support for a second thermistor, and a watchdog that will look for errors like pumping power in and getting no heating. Seemecnc doesn't have that version preconfigured for the max for whatever reason, but you can either configure it yourself once you download it, or use the online configuration tool.

I wish you the best of luck with it, and It's good to know that you caught that.

[d1rron]

Good to know, Thanks! I wonder if there are any plans for SeeMeCNC to officially update to a newer version of Repetier.

[d1rron]

So I found a minimum temp setting for the hot end thermistor that was set to 10 degrees, which is just below what my printer reports with a disconnected thermistor. I changed the value to 16 degree so that if the thermistor wire breaks again it'll catch it. I am thinking about configuring 0.92.x but I'm not sure yet. I understand why SeeMeCNC stuck with 0.91 for now, apparently it's still the latest stable build.

[joe]

I am thinking about configuring 0.92.x but I'm not sure yet. I understand why SeeMeCNC stuck with 0.91 for now, apparently it's still the latest stable build.

I am using 92.9 with great success.

[d1rron]

Are there any noticeable improvements to your prints, or what are the benefits? I was configuring 0.92.9 in the configuration tool, but got a little overwhelmed with not being sure about certain values. Then again, many said Eeprom would override them anyway.

[joe]

Are there any noticeable improvements to your prints, or what are the benefits?

I could see no difference in the prints. Benefits? I just did it cause I could.