Welcome to the SeeMeCNC Community

So I have built and rebuilt the hotend multiple times and still run into the same issue. I have a fresh copy of the firmware, Repetier Host and run this on several different computers. I can run the temp up to lets say 190c and everything is fine. Maybe bump it to 192 and off it goes....no issues. If I try to set the temp at lets say 195 it might reach 193.xx and just bounce around a half a degree but it will never reach 195 on the LCD. The problem is the software is still pumping 100% power to the hotend. It gets hotter, but the LCD never reads close to 195 or whatever I set the hotend to. I have gone through three or more thermistors and this keeps happening. My wiring appears fine. To be safe at first run I did the PID tuning at 190 and set the values. The graph is rock solid with no variation. With the hotend off and everything idle the temp is also steady..no bouncing at all. I don't get it. BTW this machine has never printed a thing bacause of this issue. I'm stumped.

To me this might suggest you have chosen the wrong thermistor type in Configuration.h, *if* you are sure that it is getting hotter. If you have the SeeMeCNC thermistor, they use a generic table in Repetier, type 97.

Thanks Edward. I'll give that a try although i'm sure I have a 100k one and chose 1 in the config. I had considered changing that to 97 on a hunch but wanted to post here first.

Are you using the RepetierMAX version (the "customized" version done by SeeMeCNC)? If so, it should have been set to 97 as it came. I not 100% sure if type 1 is compatible with the thermistor they ship.

In my case, still using the stock thermistor in the bed but on Marlin firmware, I have selected type 5, described as "// 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan) (4.7k pullup)" in the *Marlin* Configuration.h. It works perfectly, checked with a thermocouple. I don't recall where I found that brand/make, but it works great.

THIS IS DIFFERENT FOR REPETIER. I only mention it because Marlin's type 1 is also an EPCOS 100k, which did not work for me when I tried it. Try 97 and report back

Looks like now I'm stuck at 177c with the same 100% power behavior. I tried 98 and 99 with the same results. Should I run the calibration after each change? I am using the firmware from the seemecnc site...
https://github.com/seemecnc/RepetierMAX ... master.zip

Do you have a multi-meter? If so, measure the resistance of the thermistor at room temp. It should be around 100kOhm.

If that turns out to be true, then I can only think that you have some issue with your thermistor wiring or installation into the hot-end.

Also measure the resistance of the resistors, should be in the 3Ohm range.
It's unclear from your description if you set the temperature to say 230 does it get in the general vicinity or is it stuck at 190.
If it's the former, it's probably a PID issue, increase P slightly and decrease D slightly, if it's the latter, there is probably something wrong with the heater wiring, I've seen at least one case where the resistors were wired in series instead of parallel which results in pretty much 190 maximum temperature.
If you have a heater cartridge, then it could be a bad one, it's not unusual for manufacturers to ship 24V heaters instead of 12V ones, externally they are identical, you need to measure the resistance to verify.

So I did a little experimenting and decided to choose a 200k thermistor in the firmware. The hotend now makes it to about 214c before stopping. I did this before reading the last posts here. To answer the questions.... The resistance of the thermistor but a room temp. it is 0. It does increase as the temp increases, but it's pretty hard to find a way to heat the hotend while trying to mesure the resistance while the thermistor is disconnected from the board. I do know there are two types of thermistors....those that at room temp will show resistance and those that increase resistance as they are heated. I pulled out another aftermarket thermistor I purchased, which is the same type I have on the hotend, and it also measures 0 at room temp. The other question was the resistors. I actually replaced the OEM end with one that has a heat cart. As for the temp question... I set the temp to 230 and hit a wall at either 190 or so until i started messing with the thermistor table settings. I checked for continuity in the thermistor wiring and all seems fine.

To give you a little history I had melted 2 OEM hotends before I gave up and went third party. It took me getting this third hotend before I realized what was happening....the whole temp reading sticks while the board pumps 100% power to the hotend. So this means it is unlikely thst it is a bad thermistor since I have gone through 3+. The wiring seems fine and the firmware is updated (this happened on earlier firmware as well). I have also run Repetier on two different computers with the same results. I have done the PID tuning on every new head/thermistor build but i stay at 190c at first run just to be safe. Rock solid at 190. Everything just goes to hell from there.

Polygonhell: If the heat cart were bad I don't think that would explain why the hotend is actually increasing in temp, but the readout sticks at a certain temp...in this case 192-194c and just bounces around -+.5 degrees. The hotend starts spitting ABS and smoking...which pretty much tells me the cart is cooking away, but Repetier or firmware is misconfigured. I'm new to all this so I'm not really sure where to go from here.

ps: any chance it could be a baud issue with the board? I'm at 250000

Selecting a 200K thermistor when you have a 100K one will just show the wrong temperature.
The thermistor should read about 100KOhms at room temperature, the fact you are reading 0 on two of them implies to me that you are either not reading the meter properly, or you don't have a thermistor.
Measure the resistance of the heater cartridge disconnected from the board, it should be a little over 3 ohms.
Get a thermocouple and measure the actual temperature you are getting at the Hotend, it would surprise me I'd you were getting a constant reading in the right ballpark and increasing temperature, you need to verify the actual Hotend temperature.
If the baud rate were wrong you would get nothing at all from the RAMBO board.

OK...had to take a break from the printing thing, but I did get around to re-measuring the thermistor. It is coming in at 50k not 100. I guess I will start breaking down the head again and see if it is wiring or the thermistor itself. I have one spare left that does indeed measure around 100k. If I didn't want to replace it but instead change the tables to match the 50k difference would that be possible or even advisable? I would rather not take this thing apart for the millionth time.

Before you even apply heat, see if the thermistor will read room temperature on a cold hot end correctly. If that's wrong, then it's probably reporting wrong when hot too.

I hope you have multimeter with a temperature probe to confirm the actual temperature.

So I went ahead and replace the thermistor yet again. It was a known good (100k). It reads fine at room temp...within a degree of the bed temp. I run the calibration test and the temp is still stuck at about 190-192, but checking the head with my multimeter it is coming in at 250+. This is the newest firmware and I selected the proper tables. I tried 97 with the same results. I should mention that my Rambo board was one of the many that came without a bootloader. Instead of sending it back I just picked up a programmer and flashed it myself then loaded the firmware. I can't see how that would have anything to do with it though. I guess my next fix would be replacing the wires from the thermistor to the board and see if there is possibly a short there. I would think if there was it wouldn't read properly at room temp. I'm pretty much running out of options here. If it isn't the wires the only other thing I can come up with is something not configured properly in the firmware.

calabus wrote:So I went ahead and replace the thermistor yet again. It was a known good (100k). It reads fine at room temp...within a degree of the bed temp. I run the calibration test and the temp is still stuck at about 190-192, but checking the head with my multimeter it is coming in at 250+. This is the newest firmware and I selected the proper tables. I tried 97 with the same results. I should mention that my Rambo board was one of the many that came without a bootloader. Instead of sending it back I just picked up a programmer and flashed it myself then loaded the firmware. I can't see how that would have anything to do with it though. I guess my next fix would be replacing the wires from the thermistor to the board and see if there is possibly a short there. I would think if there was it wouldn't read properly at room temp. I'm pretty much running out of options here. If it isn't the wires the only other thing I can come up with is something not configured properly in the firmware.

There is a max temp setting in your configuration.h
I doubt that it is your problem but it is worth checking.

Have you tested you thermistor by putting it in a cup of boiling water? (use a microwave to heat the water, about 1 min or so). You should see a reading of 100°C, if not, you have a thermistor problem or you have the wrong thermistor set in firmware.

This has been an ongoing problem since day one. I have been through three print heads (first two were stock and melted due to the improper temp readings). I am using an aftermarket head now which I can't recall the name right now. It uses a heat cartridge and is all aluminum *edit...it's an E3D hotend. Essentially I can't burn it up. Although I could fry the thermistor. So I have been through many thermistors and I think I can rule that out as the problem. The max temp setting in the firmware is default, but I will check it again and I know the thermistor is 100k and has been selected correctly in the firmware as well.

Can you post your Pins.h and Configuration.h files from Repetier. There is something not right here. If you've tried multiple thermistors and the max firmware temp is at default there is something else going on. I think we should start from square 1 and go through your configuration. I'm on my way out to my son's soccer game but perhaps you can post the pins.h and configuration.h and I and check them from the sidelines and get back to you this evening.

cheers,
Michael

Sent a PM..and thanks for looking into this.

Calabus, I've gone through your files and they are in perfect order. That leads me to believe something else is going on. The one thing I can't validate is the PID settings so that is suspect. Could you try a test and use the simple on/off heat control for the hot end. See what that does. Was your hot end at rom temperature when you ran the PID calibration (just curious)?

I recommend doing this:

1) try the on/off heat control and see what that gets you

2) try the boiling water test - you don't have to remove the hot end from the machine if you are careful. Just carefully (by hand) lower it into a cup of boiling water. Do not have the hot end on, you just want to get a temperature measurement. If it is not 100° or really close then that indicates a thermistor or wiring problem.

Let me know how the above go and we'll take it from there.

regards,
Michael

Welp the water test showed a huge variance in temp. The head reading was about 72 but my probe was reading 90-95 (the cup went from the microwave to the garage so I didn't expect 100). I will pull the thermistor and test it outside the head or I may just replace the wires and test again. The wiring will be easier to test than having to put the thermistor back.

Great, now we are zeroing in on the issue. Might it be something resistive shorting the thermistor leads? How do you have the thermistor mounted?

So after the water test I decided to replace the wiring. I have a splice near the thermistor (4-5 inches). I cut out the splice and decided the measure the resistance from the cut to the thermistor. It was right at 100k...good. I yanked the old line to the board and replace it with not only new line but a new connector. Now the odd part. The resistance from the board end (disconnected from the board) comes in at about 50k. So a 50k drop in resistance from somewhere. The new splices are not touching at all. The wire is new as well as the connector.

calabus wrote:So after the water test I decided to replace the wiring. I have a splice near the thermistor (4-5 inches). I cut out the splice and decided the measure the resistance from the cut to the thermistor. It was right at 100k...good. I yanked the old line to the board and replace it with not only new line but a new connector. Now the odd part. The resistance from the board end (disconnected from the board) comes in at about 50k. So a 50k drop in resistance from somewhere. The new splices are not touching at all. The wire is new as well as the connector.

Start near the thermistor and measure where the first connector is and see what the resistance is. If you are measuring 100K near the thermistor, you should be measuring 100k at the card.
When you measure at the card do you remove the connector from the card or do you measure with the connector plugged into the card? I would disconnect the connector from the card and measure it. (turn off power before pulling any
connector). If after pulling the connector from the card and you measure 100K then everything should be fine.

Did all that...100k at the thermistor but 50k and the unplugged end near the board. New wires and connector. The wires and single x2 and not, I guess you can say bonded. They are separate all the from area at the thermistor splice to the board. The wires are in no way touching. Strangest thing I have ever seen...just odd. I am going to rip it all out again from the thermistor splice all the back to the board. Heading to the store to get new smaller gauge wire as what i am using is a little heavier than I would like. I was using much smaller gauge originally, but it was all I had to test with yesterday.

calabus wrote:Did all that...100k at the thermistor but 50k and the unplugged end near the board. New wires and connector. The wires and single x2 and not, I guess you can say bonded. They are separate all the from area at the thermistor splice to the board. The wires are in no way touching. Strangest thing I have ever seen...just odd. I am going to rip it all out again from the thermistor splice all the back to the board. Heading to the store to get new smaller gauge wire as what i am using is a little heavier than I would like. I was using much smaller gauge originally, but it was all I had to test with yesterday.

Strange indeed, I could understand the resistance going up if the wires were too small or too long but the resistance is going down which as you say is just odd. Best of luck tracking down the problem.

OK....some more measuring and frustration I have come to the conclusion that my technique sucks. since I only have two hands and no needle probes for my meter I simply hold one wire and probe in one hand and the other wire and probe in the other. This seems to lead to a 20 ohm variance in my readings. Hey... i'm not an electronics guy...who knew So the hands off approach gives me a thermistor reading of 120k at room temp which is 20c. So having said that....am I way off on the readings? Is this thermistor bad? Can i adjust for the variance?