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Configs for RailCore Printers
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Correct thermistor values #58

Closed dandancheeseandham closed 5 years ago

dandancheeseandham commented 5 years ago

(as per FB, repeating here for clarity)

@kraegar

Gerard Hudson brought it to my attention that the kit config has an incorrect thermistor value for the e3d thermistor. Everyone, kit or not, should double check their thermistor Beta values. These being wrong can lead to a value for the hotend being reported up to 20c too low. (I had corrected this at one point, but must have somehow copied an old config.g back in over the new one and recreated the earlier mistake.)

The kit config.g has a Beta value for both thermisters of B4240. If your hot end thermistor is an E3D Semitec 104GT2 it should be B4725. The bed thermistor should be B3950.

OK, Here is what I've learned.

1) Bed set at 80°C with old value. My IR thermometer reads 83°C in the middle of the bed. Put in "M305 P0 B3950" in the G-code console - Duet reading changes to 83.1°C - perfect!

2) Hot-end set to 240°C. Can't use IR thermometer for this. Plug "M305 P1 B4725" into the Duet. Temp changes from 240°C to 197°C. I investigate further and end up at https://www.makeralot.com/download/Reprap-Hotend-Thermistor-NTC-3950-100K.pdf and learn that we should probably be using "C7.06e-8" as well. Temp changes from 240°C to 219.7°C , which in the absence of measuring equipment (can anyone chime in here?) will do for now for me.

JohnOCFII commented 5 years ago

My understanding is a thermocouple is really the only way to be sure.

lostapathy commented 5 years ago

Good work - I successfully printed with this. Explains some of their temperature oddities people report around needing higher than normal temps

JohnOCFII commented 5 years ago

Getting around to some testing with my Type K Thermocouple:

With my bed using: M305 P0 T100000 B3950 R4700 and set to 60C, putting the bead of the thermocouple between the top of the bed and the springsteel sheet for 10 minutes yields 54C.

With my hot-end using: M305 P1 T100000 B4388 R4700 and set to 220C, putting the bead of the thermocouple between the silicon sock and the heat-block, with bead between the entry for the heater and the thermistor for 10 minutes yields 187C. I sure don't think my printer is that cool, but I'd guess that difference is based on where I'm doing the reading, so it'll be more the delta of the two settings that I care about.

It looks like I already had corrected my bed thermistor. My hot-end thermistor was different than either the standard old or new configuration. I will change my hot-end to match the new suggested config and test again.

I supposed I should do another PID tune too.