Min Bed Temp error

After a couple of years use, my Anet A6 printer has started giving MIN BED TEMP errors, sometimes immediately the print tries to start, but also, more seriously, in the middle of a print, as today after printing for about 2 hours. I initially thought that this was because the connector to the bed heater and thermistor was moving slightly as the bed moved, but I have installed a clamp and chain to hold it securely, so I think it must be something else. I have tested the bed thermistor with a multimeter, and it seems ok, reading just under 100K ohms when the bed is at room temperature and decreasing as the bed heats up. I am now wondering if the control board might be the problem, but don't know how that might be, or how to test it. Has anyone had similar problems or can suggest what i might do to fix it. The print I am currently trying to make takes about 13 hours and over a quarter of a reel of filament, so I don't think I have much chance of success at the moment.

I was seeing this quite a bit, but I think I fixed it. I kept re-tuning my PID settings using the M303 autotune feature - but specifying a realistic temperature may be important. For instance, if you tune the PID settings at the default 150C, you may get a different result than if you tune it at 230C. (I do this with "M303 S230", then I put the resulting kp, ki, kd values into my firmware and reload it).

Another thing I found is that, when tuning the PID, the heat of the bed mattered a lot. Try positioning the nozzle near the heated bed, heating up the bed to your normal temperature (I use 77C), then running the PID tuner for the nozzle.

The bottom line is, if the PID settings aren't set to values that are realistic for the middle of a print, then they could go haywire, resulting in large temperature fluctuations. These can include large enough temperature drops to result in a MIN TEMP error, and that has happened to me quite frequently up until recently, when I investigated the PID tuning.

EDIT: I realized you were talking about the bed temp, not the nozzle. So this may not apply to your situation.

Edited 1 time(s). Last edit at 04/27/2020 10:57AM by Wissing.

Thanks for your advice. However, I think my problem probably is caused by a hardware problem, either in the controller, thermistor or wiring. I probably need to replace some or all of these. I posted my query in the hope of getting some advice on testing which of these parts is causing the problem, so that I don't replace something that is working ok. Thanks again, anyway.

I have had a heater fail intermittently causing me to replace the heater to correct the MIN TEMP error.

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Computer Programmer / Electronics Technician

Thanks for that suggestion. I will check if that could be my problem.

What did you find for a solution?

I think it was a faulty power booster board for my heated bed, that I fitted to take the strain of a big current from my main board. Anyway, I replaced it and the heated bed seems to be working now. i also fitted an attachment to hold in place the connector on the heated bed, as it would occasionally pull loose. Although the attachment does prevent the connector pulling completely loose, it doesn't always prevent a bad contact there, so I still need to improve that.

I didn't realise that the power booster was faulty at first, because it appeared to work when there was no load on it, giving 12V at the output, but when it was trying to heat to bed the output voltage dropped to about 3 or 4V.

Yeah, I have a questionable issue with my hotbed also. It is 120V and I use an SSR and sometimes it does not seem to be operating and the temp drops. Other times it does not seem to be operating and the temp is stable. Other times everything looks fine.

Don't u love electronics?

Yes, but things are a lot better than they used to be. The first computer I worked on used valves/vacuum tubes and relays and needed a special air-conditioned room and a resident engineer on site, as the mean time between failures was less than a day. The stabilised power supply was about 8 feet high and 30 foot long and still could not cope with the drop in supply voltage around 7:30 am, when everyone woke up and switched on the lights etc. Actually, I never cease to be surprised by how well things work now, most of the time; and how small, courtesy integrated circuits, and cheap, courtesy our Chinese suppliers. Technology keeps getting better, even if war, pestilence and protests seem to be getting worse.

OK, so u are pushing 90, I just missed that gen. Mine had no vacuum tubes. However, there was a 4K memory module at the school that was full of 12AU7s and stood 6 ft tall by 6 ft wide by 3 ft deep.

Only 82, but sometimes feel like 90. Anyway, good luck to you. Bye.