temperature sensor setting for Ultimaker Original heated bed upgrade?

[dbotos 5]

I fed the Arduino 2560 with different voltages. I bumped BED_MAXTEMP up to 1500 in the firmware so it wouldn't complain. Also added another row to the bottom of the sensor 20 temperature table (1200 °C / 1017). Here are the results:

0 V: Error: MINTEMP triggered, system stopped! (had ground and sensor voltage pins shorted)

1.65 V: 195 °C / 389 (should be more like 130 °C / 337 based on closest row)

3.30 V: 760.7 °C / 781 (should be more like 600 ° / 681 based on closest row)

4.95 V: 1200 °C / 1023 (looks like it maxed out; probably not a reliable data point)

So, at ambient, it reads ~50°C higher than it should, at a voltage equivalent to ~130°C it's reading ~65°C higher, and at a voltage equivalent to ~600°C it's reading ~161°C higher. Apparently not an offset problem...

[dbotos 5]

I set the Uno up as a spy (reading the TEMP 3 cable voltage, but not interrupting it). I made a little sketch that read the digital value and also did the math to convert back to analog (repeating once every second). At ambient, the Uno said 1.18 V / 242 (which is close to 20 °C in the table).

[dbotos 5]

I ordered a new 2560. We'll see if that helps. I've been messing with this for too long not to try that for as cheap as it is.

[gr5 2,173]

Did you ever check the analog reference? It's the AREF pin. The top left pin here:

[gr5 2,173]

The AREF pin is used by the ADC on the arduino and is the reference for value 1023. I'm thinking instead of being at 5V for some reason it is closer to 4.5V.

[dbotos 5]

gr5 - I think you just hit the nail on the head.  I pulled the 2560 out of the Ultimaker this morning during breakfast (not as bad as I thought - didn't have to unplug all the cables from the main board) and fed it various multiples of battery voltage at lunch just now.  It thought 1.68 V was 1.93 V and 3.38 V was 3.87 V.  I saw your post and checked the AREF pin with a multimeter: 4.35 V.  So instead of 1023/5, it's multiplying by 1023/4.35 to get the digital values (which inflates them by about 15%).  If you look back at my results at the bottom of page 2 of this thread, it makes perfect sense:

337 (should-be digital value) x 1.15 ≈ 388 (got 389)

681 (should-be digital value) x 1.15 ≈ 783 (got 781)

I looked at the Arduino page about analog reference ( https://www.arduino.cc/en/Reference/AnalogReference ) and it looks like it's supposed to default to 5 V on the 2560.  I tried adding a line to my sketch to explicity tell it to do that, but it stayed at 4.35 V.  There's also an option to use an external reference (not sure if the combo of main board circuitry and firmware is employing this or not).  So, my hot end temperature readings are probably off too, but perhaps not by the same magnitude since it's a different type of sensor and the ratio of analog voltage difference to temperature difference is different.

Edited June 21, 2016 by Guest

[gr5 2,173]

The head uses a thermocouple and then it goes through a circuit board that translates the nozzle temp to a voltage from 0 to 5V where 0v=0C and 5V=500C. With an error of 15% a temp reading of 210C would actually be 180C. That's significant. You can print PLA at 180-240C but I wouldn't go outside that. So until you fix this try printing more like 240C (210C actual).

[dbotos 5]

Hopefully the whole machine will work better when I get the new 2560 installed with correct analog reference voltage. Stay tuned...

I checked that Uno I had and its AREF was a smidge over 5 V.

[dbotos 5]

Good news: the new 2560's AREF measured 5.05 V and once I got it installed, it reported ambient temperature of the hot end and bed correctly (low 20s °C).

Bad news: when I went to print, the bed temperature went up to 88 °C and did not come down during printing, despite being set for 70 °C. :angry:

[gr5 2,173]

Probably a loose wire at the connection to the bed. Slightly loose such that the resistance is 10(?) ohms higher than reality. Jiggle those wires - see if one comes out. Check the resistance in reality when it's reading 88C (but cut power and remove cable at bottom of printer first).

[dbotos 5]

I believe it's measuring fine. I've confirmed proper sensor resistance at ambient where the cable plugs into the little board. If it had excess resistance due to a poor connection that would show up at all temperatures. I can check it at hot to get another data point.

It seems like a control problem since I told it 70 and it proceeds to go to what it thinks is 88 and stay there. I'm assuming it would have gotten even hotter if something in the circuitry was stuck "ON". I saw there was an option for PID control of the bed heater in the firmware - I wonder if that might do better if I enabled it. Anyone know good starting values for the PID constants?

[gr5 2,173]

Bed works fine in non-pid mode.  Stays within 1C of goal temp.  It's large and so the temp moves slowly so it's easy to control the temp and overshoot is not a problem.

Um - did it feel hot to the touch?  This is strange.  If you tilt your printer you can see the control board and there should be a LED for the nozzle and another for the nozzle heater.  I could be wrong about this - I don't use my UMO often.  On mine you can see when heat is on and off.

I think more likely it heated up to a certain temp, then sensor read 88 ohms suddenly, then the heat was just turned off and it seemed fine to you because it takes 10 or 30 minutes to cool down.

Edited June 28, 2016 by Guest

[dbotos 5]

Yup, the bed got hot.  Could feel and smell it.

I'll have to run it again and see what the "bed on" LED (D1) on the little board does when it gets above 70 °C:

I don't remember the temperature jumping up at all.  It just kept climbing and I was sitting there waiting for it to stop its overshoot.

Edited June 28, 2016 by Guest

[dbotos 5]

I found a post where someone had almost the same problem (nearly identical setpoint and too-hot steady state bed temp). Unfortunately, no replies to that post...

https://ultimaker.com/en/community/18127-heat-bed-too-hot

[dbotos 5]

1) D1 LED on the little board stayed on constantly. Displayed bed temperature ramped steadily up to 97 °C before I shut things off, despite a 70 °C setpoint. I verified bed temperature with my IR thermometer (measured both sides of the bed, emissivity setting of 0.95), so it looks like the PT100 sensor and its wiring is good.

2) When I had one side of the Ultimaker propped up slightly to observe the D1 LED, I noticed the smell I had smelled last time (silicon / circuit-board like) was coming from underneath the machine and was not something burning off the bed as I had initially assumed. I wonder if something in the circuitry got toasted now that the bed is actually kicking on.

3) When I go to print now, I get a serial timeout exception error. Apparently, problems like to come in threes... :(

[dbotos 5]

Here is the error log:

 

Recv: echo:  M204 P3000.00 R3000.00 T3000.00Recv: echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s),  Z=maximum Z jerk (mm/s),  E=maximum E jerk (mm/s)Recv: echo:  M205 S0.00 T0.00 B20000 X20.00 Z0.40 E5.00Recv: echo:Home offset (mm):Recv: echo:  M206 X0.00 Y0.00 Z0.00Recv: echo:PID settings:Recv: echo:  M301 P22.20 I1.08 D114.00 C100.00 L20Recv: echo:Filament settings: DisabledRecv: echo:  M200 D3.00Recv: echo:  M200 D0Send: M105Recv: ok T:25.4 /0.0 B:33.7 /0.0 B@:0 @:0    ADC B:33.7C->256  T0:25.4C->52Changing monitoring state from 'Connecting' to 'Operational'Send: M105 T0Recv: ok T:25.4 /0.0 B:34.4 /0.0 B@:0 @:0    ADC B:34.4C->257  T0:25.4C->52Changing monitoring state from 'Operational' to 'Printing'Send: N0M110*3Send: N1M92 E100.000000*67Send: N2M190 S70.000000*83Recv: okSend: N2M190 S70.000000*83Recv: okSend: N3M109 S210.000000*102Send: N4G21*62Serial timeout while writing to serial port, trying again.Serial timeout while writing to serial port, trying again.Unexpected error while writing serial port: SerialTimeoutException: 'Write timeout' @ machineCom.py:_sendCommand:565Unexpected error while writing serial port: SerialTimeoutException: 'Write timeout' @ machineCom.py:_sendCommand:565Changing monitoring state from 'Printing' to 'Error: SerialTimeoutException: 'Write time...'Connection closed, closing down monitor

 

[dbotos 5]

Found the source of the smell. Toasted Q2 MOSFET on the heater board (v1.1):

I contacted the vendor I got the heated bed kit from to get a replacement board.

[gr5 2,173]

Yes I was going to say the same thing. The mosfet. It can fail open or closed in your case it failed short circuit. I'm glad your temp sensor is working though!

[dbotos 5]

Got the new heater board today.  Installed it, started a print, and the red LED on the heater board never shut off above 70 °C (I let it go up to 90 °C before stopping the print).  No toasted MOSFET on the heater board this time.  I'm wondering if the Q1 MOSFET on the main board is stuck...

Edited July 8, 2016 by Guest

[dbotos 5]

With just the Ultimaker sitting on the table (no USB cable plugged in, just power supply), the D1 LED on the heater board comes on immediately upon plugging in the power supply and stays on regardless of the position of the power switch on the Ultimaker.

The main board heated bed output terminals that lead to J4 on the heater board show no voltage.  So, not surprising that disconnecting the cable at J4 did nothing either.  Something is smelling too, but I don't see anything burnt. Wondering if there's a bad batch of heater boards out there or if it's something else.

Edited July 8, 2016 by Guest

[dbotos 5]

No reply from US Ultimaker support today regarding the second bad heater board, so I went high-tech redneck on the heated bed controls tonight. I had an $18 Sommy PID laying around for another project (that I haven't gotten to yet) and decided to press it into service for the heated bed. I built a control setup for it on a foot-long length of pallet slat. Since the heater runs on 24V, I figured I might as well use the nice Mean Well power supply that came with the heated bed upgrade kit. That meant excising the mating connector from the original failed heater board with a ball burr in the Dremel. Five case pins and four +/- pins and they were all the blade style. The connector has a snout on it, so I made the right size hole in a piece of birch plywood and bent a bracket out of pipe hanger strap to keep it from turning or getting pushed out of the hole. Wires are just soldered to the +/- pins on the bottom. I also desoldered the PT100 connector and put some leads on that going to the PID input terminals. Got the PID options set in the menu and then checked output. Looks like the first SSR I picked out of my bag of 10-amp salvaged ones is a dud. Will have to try another one. Also need to form a cover out of plexiglass for the SSR to make sure I don't accidentally put my body or something else across the terminals.

[dbotos 5]

Oops - SSR is an AC-output model. Got a DC-output one on order.

Heard back from US Ultimaker support today. They're going to send another board and a J4 cable. I'm not holding my breath waiting for amazement, but I'll try it when it arrives.

[dbotos 5]

Standalone PID with DC output SSR is alive and working!

US Ultimaker support sent a new main electronics board (version 1.5.7), which I installed and tested before hooking up the standalone PID. Didn't help - the little heated bed board has a mind of it's own and keeps the heated bed on constantly.