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Heat bed is heating sooo slow

Posted by DOYT 
Heat bed is heating sooo slow
March 03, 2017 03:41PM
I have an MK3 Alu heat bed with EPCOS 100k thermistor and covered with blue tape for adhesion. When I heat it up to 55 60 degree Celsius for PLA it takes a decent time to heat up, about 2:30 minutes (same time hotend is heating up also to 215). But if I want to heat it up to 90-100 degree for ABS, boy...........it take aloooot. Like 7 8 minutes. I have a MEAN WELL SP-320 power supply 12V 25A. My heat bed wiring is different from the one of the hotend so a lack of current should not be a problem. I have 1.5mm wires and they are directly soldered on my motherboard. The problem persist only on heat bead. The thing is that finally reach 90 or 100 degree but the process is so slow after 70 degree above. Is there a way in Marlin to adjust current limitation? I don't even know if something like this exist.
Re: Heat bed is heating sooo slow
March 04, 2017 02:15AM
Make sure that you have MAX_BED_POWER set to 255 (which normally should be, since it is the default).

Other than that, I found that the following measures help speeding up the heating of the heat bed:
  • Put some heat insulation underneath your heatbed, e.g. a layer of cork sheet.
  • When heating up, start with a layer of corrugated cardboard on top of the bed and take it away when getting towards the target temperature.
  • If you can, increase the voltage of your powersupply by 1 or 2 volts. (e.g. increasing from 12V to 13V will give you 17% more heating power.)
Re: Heat bed is heating sooo slow
March 04, 2017 04:55PM
Yeah your advice with increasing the voltage is working, now it heat up both the extruder at 250 and heat bed at 100 in 7 minutes rather than 7:45- 8:00. I can't increase more than 13.6V so..... I'll apply the other advices. Thank you very much.
Re: Heat bed is heating sooo slow
March 06, 2017 08:23AM
Why do I have in Marlin set HEATER_0_MAXTEMP 275 and BED_MAXTEMP 120 and when I want to adjust temperature from my LCD the maximum I can set for Hotend is 260 and for bed is 105?
Re: Heat bed is heating sooo slow
March 06, 2017 10:33AM
I am not an expert on this, but here is how I understand it:

HEATER_0_MAXTEMP and BED_MAXTEMP are the hard limits at which the printing is aborted. So there is a 15 degree "safety zone" between the maximum allowed working temperature and the absolute maximum, which gives some tolerance for overshooting of the temperature regulation.
Re: Heat bed is heating sooo slow
March 06, 2017 12:08PM
Oh........I got it. Make sense....... Sucks thing is that my bed can't keep 100 degree temp. It reach this temp but during the print this value decrease until 92 or so and then I have the message printer halted, please reset. Maybe I shoud place some isolator under that bed. But I don t understand why is behaving like this because prusa or other printers have an empty space under the bed.
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