Sliced thermistor wire on heatbed
I went to use my printer after my longest print yet (16 hours). I started preheating for PLA and I noticed the heatbed temp wasn't going up after a few minutes (usually only takes a minute or two to get to 50° C). I touched the glass plate and it was definitely hot. As I was inspecting the printer I found the white wire running from the heatbed to the rambo board is sliced clean through.
It looks like it came out of the wire wrap at some point (possibly when I took the heatbed off yesterday while I was doing some repairs) and has been rubbing against the steel frame ever since. Before I start stripping and soldering, I have a couple questions:
1. Is this actually the thermistor wire?
2. I believe the thermistor is the sensor that tells the rambo the temp of the plate, right?
3. If the thermistor is broken would the heatbed ever know when to stop heating? How high would it get before the glass breaks?
4. Is stripping/soldering/heat shrinking an okay way to fix this? I'd rather not have to wait for a new heatbed to ship before I can print again.
Thanks!
Re: Sliced thermistor wire on heatbed
Hi Joe
1. Yes
2. Yes
3. There should be a safety cutout on the thermistor; when not connected it should read way too high and refuse to heat up.
4. Yes. You don't need a new heatbed; thermistors are readily available, but if you do get a replacement, get the correct one (there are many types... best buy a replacement from Prusa.)
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Sliced thermistor wire on heatbed
Peter,
Thanks for the quick reply.
The thermistor itself isn't bad, just the wire, right? Would it be a big problem to splice it back together for now as a stopgap until a replacement arrives?
Re: Sliced thermistor wire on heatbed
Joe - it's just the wire and not the thermistor. Solder and heat-shrink will be a permanent repair.
One more thing, I have re-router the heater/thermistor wires so that they exit more centrally from the back of the chassis. This helps to avoid rubbing issues.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Sliced thermistor wire on heatbed
All spliced and working again! I have one final question... I'm assuming the thermistor gives the temperature of the glass instead of the bed. When I'm starting with a cold plate, do need to give it a couple minutes after it says its done heating to let the glass come to temp or is it pretty much right on with the bed?
Re: Sliced thermistor wire on heatbed
Great. Brilliant. Well done!
Yeah, the thermistor senses the temperature where it is located. Glass has quite a high thermal resistance. It does take a few minutes for the glass to get heated evenly across its surface.
I have moved the thermistor to the hole in the heater, so it is touching the glass, but these heaters are pretty inaccurate with both hot and cool spots.
I normally have the heater over temp for a few minutes before print - when printing at 50 degrees, I have pre-heated at 60.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Sliced thermistor wire on heatbed
Great. Brilliant. Well done!
Yeah, the thermistor senses the temperature where it is located. Glass has quite a high thermal resistance. It does take a few minutes for the glass to get heated evenly across its surface.
I have moved the thermistor to the hole in the heater, so it is touching the glass, but these heaters are pretty inaccurate with both hot and cool spots.
I normally have the heater over temp for a few minutes before print - when printing at 50 degrees, I have pre-heated at 60.
Peter
So it's not only me who does this. I too have noticed that the bed isn't even ready for calibration directly after it reaches 50C, so I usually preheat and leave it for 5 minutes after it has reached the goal temp before I calibrate.
/Sascha
Re: Sliced thermistor wire on heatbed
Hi..i am a new user here. As per my knowledge there should be a safety cutout on the thermistor; when not connected it should read way too high and refuse to heat up. Also you don't need a new heatbed; thermistors are readily available, but if you do get a replacement, get the correct one.