Flaky bed temperature
My Mk2 will not hold the set bed temperature. When printing with ABS and the bed temperature set to 100 the print starts out ok, but after about five minutes the bed temperature starts dropping.
The set point stays the same and the bed LED stays on but the temperature drops to about 80. The print is ruined at this point (warped off the bed) but I let it run to see what would happen. The temperature fluctuates between 80-85 and after some time (not sure exactly how long) it returns to 100. The behavior is not entirely consistent, but I can't get through an ABS print. It seems ok at PLA temperatures.
Below is an image showing that the print is in progress, the bed temperature is set to 100, the actual temperature is 81 (it started out at 100) and the bed LED is on (it was solid, not flickering). Has anyone had a similar experience? Any idea what would cause it? It seems to me that it must be an internal flaw of the bed.
Re: Flaky bed temperature
In an enclosure?
No. There is no enclosure, but also no draft or change in ambient temperature during the print..
Re: Flaky bed temperature
I now see the exact same behavior on my printer - after working perfect for the first 70+ hours.
I mainly prints with PETG and the print start fine, warming up to 85. The set point is changed to 90 on second layer, but the temperature slowly drops to 80 for for the next 5-10min with the bed LED constantly on.
For the next 40min the bed temperature very slowly rises to the set point of 90.
Did you find a solution?
I have checked the bed molex connector and it is ok. (There are some reports of burned connectors in the forum)
Just setting the temperature without printing works fine. The temperature is reached and the LED starts blinking. Have tried temperatures up to 105.
Seems like there is not enough power to drive the printer when printing.
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Re: Flaky bed temperature
Check again your molex connector and also ensure the cable management is precisely according to the manual.
If you did get to temps and suddenly you cannot, then something mush have changed.
Peter
P.S. Worst thing to do is to change anything before you find the problem. If you do need more heat, then you can always increase the voltage from the PSU by 0.5V.
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Flaky bed temperature
I have now checked your suggested possible errors on the printer. The molex connector are securely connected and is cold when warming up the heat bed. The cabling is as described in the manual.
Measuring the voltage on the power supply shows 12.11V unloaded and 11.95V when both bed and hot end is on.
Measuring the voltage on the terminals of the heat bed shows 11.50V when on (0.15V drop from the cabling).
When printing PET the hot bed has no problem warming up to 85/90C before print and on first layer, but at second layer the temperature drops to 80/81, slowly raising to the set point of 90C in the next 60min of printing.
This shows me that it must be the fan turning on to cool the printed part that triggers the drop in temperature. As the part grows higher the the fan moves away from the bed and the temperature can reach the set point.
In the GCode the fan is set to 50% (M106 S127 command) from second layer.
No enclosure, no draft and ambient temperature is steady at 20C.
Properly not a single event leading to this problem - I have just noticed it now.
A solution could be to raise the voltage of the power supply by 1-2V. 1V raise would give approximately 18% higher power (12.5/11.5 ^2).
Anyone knows the voltage limit for Rambo 1.3a board?
Have a look at my models on Printables.com 😉
Re: Flaky bed temperature
Found the answer to my RAMBo 1.3 question at http://reprap.org/wiki/Rambo_v1.3
Heated bed, 12-35V 15A max.
So raising the voltage should not be a problem as long at the current is below 15A. With a current now at approximate 12A the voltage could be raised up to 15V.
Have a look at my models on Printables.com 😉