PCB Heat bed need a thermistor? Gen7
Posted by Phizinza
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PCB Heat bed need a thermistor? Gen7 August 23, 2012 10:04PM |
Registered: 12 years ago Posts: 160 |
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Re: PCB Heat bed need a thermistor? Gen7 August 24, 2012 10:14AM |
Registered: 11 years ago Posts: 477 |
AFAIK, in order to monitor the bed temperature to allow control of the bed temp, you'll need some form of temperature sensor, so yep.
Mounting? The guys who got me into this have theirs mounted to the underside of the PCB, in the center of the board, and (I think) held in by a strip of Kapton tape. EDIT(4): In fact, the installation guide I got from makerfarm shows it mounted that way (Heatbed MK1 installation guide) Not what I'd call "ideal" mounting, but I suppose it works. I'm inclined to place mine, pre-wired to the cable (carefully before the bed is mounted), in a small pad of thermal transfer grease no bigger than the head of the thermistor, and then sheathed and adhered to the board by some high-temp RTV. Make sure to use enough cable that you can form a relief loop for the wiring to reduce wire fatigue and minimize imparted torque to the bed while the bed is moving back and forth.
Since the bed moves back and forth along the Y-axis, you'll probably want to use flexible, higher gauge wire or to route the signal back to the microcontroller. I have a length of salvaged 24 ga, shielded teflon cable saved for the purpose, but I'd prefer something even smaller for the flex. Since the heated bed operates (depending on the filament type) at up to around 100-110 C (for ABS), or up to slightly above the boiling point of water, 230F, it might be a good idea to use teflon coated wire, as most standard plastic sheathing is meant for consumer temp ranges around what we'd normally see in our daily lives (0-100F). Also, try to avoid running the wiring for the thermistor nearby that of the stepper motor to minimize noise pickup. If you're using shield cable for both, avoid running the shield drain back to the same ground (actual ground, not the board's power supply "ground") to reduce noise further. EDIT (4); To elaborate on what I mean, it would be better practice to use a bit more wire to a multipoint or even a simple star ground than to connect the shields "wherever it's convenient" to save wire)
Type? I bought the same type I'll be using for my hotend to simply the process, although I didn't really think too much on it. 100K-ohm, radial footprint (both leads come out one side) , with a beta of 4066.
Edited 4 time(s). Last edit at 08/24/2012 12:51PM by xiando.
Mounting? The guys who got me into this have theirs mounted to the underside of the PCB, in the center of the board, and (I think) held in by a strip of Kapton tape. EDIT(4): In fact, the installation guide I got from makerfarm shows it mounted that way (Heatbed MK1 installation guide) Not what I'd call "ideal" mounting, but I suppose it works. I'm inclined to place mine, pre-wired to the cable (carefully before the bed is mounted), in a small pad of thermal transfer grease no bigger than the head of the thermistor, and then sheathed and adhered to the board by some high-temp RTV. Make sure to use enough cable that you can form a relief loop for the wiring to reduce wire fatigue and minimize imparted torque to the bed while the bed is moving back and forth.
Since the bed moves back and forth along the Y-axis, you'll probably want to use flexible, higher gauge wire or to route the signal back to the microcontroller. I have a length of salvaged 24 ga, shielded teflon cable saved for the purpose, but I'd prefer something even smaller for the flex. Since the heated bed operates (depending on the filament type) at up to around 100-110 C (for ABS), or up to slightly above the boiling point of water, 230F, it might be a good idea to use teflon coated wire, as most standard plastic sheathing is meant for consumer temp ranges around what we'd normally see in our daily lives (0-100F). Also, try to avoid running the wiring for the thermistor nearby that of the stepper motor to minimize noise pickup. If you're using shield cable for both, avoid running the shield drain back to the same ground (actual ground, not the board's power supply "ground") to reduce noise further. EDIT (4); To elaborate on what I mean, it would be better practice to use a bit more wire to a multipoint or even a simple star ground than to connect the shields "wherever it's convenient" to save wire)
Type? I bought the same type I'll be using for my hotend to simply the process, although I didn't really think too much on it. 100K-ohm, radial footprint (both leads come out one side) , with a beta of 4066.
Edited 4 time(s). Last edit at 08/24/2012 12:51PM by xiando.
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Re: PCB Heat bed need a thermistor? Gen7 August 25, 2012 06:01AM |
Registered: 13 years ago Posts: 7,616 |
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Using gen7 1.3.1 electronics, wiring up my PCB heatbed, wondering if I need thermistor?
It can be done without one. In this case, define a thermistor tpye of TT_NONE in Teacup, uncomment TEMP_NONE, also in config.h and set bed wattage with M140 S1 ... M140 S255.
However, as xiando wrote, you likely want one. Gen7 v1.4.1's wiki page has more instructions oon how to do it, it's the same for v1.3.1: [reprap.org] . Teacup allows to have two different thermistors, which requires two different thermistor tables. See ThermistorTable-single.h vs. ThermistorTable-double.h.
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