1 Topic by pirvan

  • pirvan
  • pirvan
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  • From: San Francisco
  • Registered: 2013-03-27
  • Posts: 1,797

Topic: MK2 PCB Heater Firmware settings

I just replaced my dead QU-BD heater with a MK2 PCB heater.  The heater didn't include a thermistor, so I found and reused the original SD3 thermistor.  In the firmware I changed the thermistor to type 6 (which is what the original firmware had), instead of 80 (QU-BD).

Now the problem:  I don't have a IR thermometer handy, but I can tell the reported temps are NOT accurate.  The bed feels hotter at 60°C than what the old bed reported at 95°C.  I even lowered it to 45° and did a 3 hour long print and no problems, it held on to the print perfectly.

Doing a PID doesn't make sense, since I don't know what the actual temperature is.  So for the moment I'm using it at 50°C max.  But I'm wondering if there's something I did wrong when I mounted the thermistor.

The setup is:  The PCB is installed on top of the copper platform with VHB tape, which give about 1mm worth of clearance between the platform and the PCB.  The platform has a hole drilled in the middle through which the thermistor pokes through and it goes into the hole of the PCB.  Then there's a sheet of glass on top.  ID did not epoxy or otherwise permanently attach the thermistor to the PCB heater, it's only sitting there in the hole, so I wonder if that is the reason why I see the temperatures I see.

I'm thinking about using some thermal compound (like for CPUs), to pack in the PCB hole around the Thermistor.  Any thoughts on that?

http://www.soliforum.com/misc.php?action=pun_attachment&item=5580

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To print or, 3D print, that is the question...
SD3 printer w/too many mods,  Printrbot Simple Maker Ed.,  FormLabs Form 1+
AnyCubic Photon, Shining 3D EinScan-S & Atlas 3D scanners...
...and too much time on my hands.

2 Reply by pirvan (edited by pirvan 2014-06-17 18:22:07)

  • pirvan
  • pirvan
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  • From: San Francisco
  • Registered: 2013-03-27
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Re: MK2 PCB Heater Firmware settings

I got an IR thermometer from work, and measured the temperature in various places across the print surface.  I also put some flat black stick-on dots on those areas so the glass reflection doesn't affect the readings (as much).

I left the bed heat up for a about 10 minutes  at what the thermistor reads as 65°C, then measured the center, the corners and a couple of spots around the middle.

Center        =  88°
Rear left     =  79°
Rear Right  =  82°
Front left    =  81°
Front Right =  84°
Other         =  85°-89°

So the thermistor readings seem to be off by about 20°C.

FWIW, the PCB bed heats up to temp in about 5 minutes, which is pretty nice.

To print or, 3D print, that is the question...
SD3 printer w/too many mods,  Printrbot Simple Maker Ed.,  FormLabs Form 1+
AnyCubic Photon, Shining 3D EinScan-S & Atlas 3D scanners...
...and too much time on my hands.