Heatbed always below 60!

rodolfo_paulo

Good evening. My main issue at this time, is that after working some time with temperatures no greater than 60ºC., I'm unable to pass this temperature now.
I need to heat the bed at 100ºC, and it is impossible!

This is my config.g, regarding the heaters:
; Heaters
M305 P0 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 0
M143 H0 S130 ; Set temperature limit for heater 0 to 130C
M305 P1 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 1
M143 H1 S290 ; Set temperature limit for heater 1 to 290C
M301 H1 P21.7 I1.50 D78.91

When I carry out a M303 H0, it goes as follows:
21:58:54
Auto tune cancelled because target temperature was not reached
21:38:54
Auto tune phase 1, heater on
21:38:49
M303 H0
Auto tuning heater 0 using target temperature 75.0°C and PWM 1.00 - do not leave printer unattended

I've double checked the wiring, the screws. The power supply is a 12V 33A, the bed is a MK2a, 300x300.
It takes around 15min to get to 60ºC, and then stops...

What can I be missing? Thanks in advance!

A Former User

Its hard to say much without knowing the wattage of the bed, but the 300x300 MK2a refrences I could find suggest around 100W, and that works out to about 0.1w/cm^2 which is very much on the low end of things.

Can you measure the resistance of your bed, or the current flowing through it?

rodolfo_paulo

The resistance seems to be 3.3 omhs, if I measured it correctly!

wilriker

@rodolfo_paulo With 3.3 Ohms resistance and 12V power this would result in a heater with 44W of power. For 300x300mm this is... let's say I am impressed that it reaches 60°C in the first place.

Is your heated bed maybe a 24V or a dual voltage heater and you accidentally connected it in 24V mode? Because when supplying 24V this would result in about 175W of power.

rodolfo_paulo

@wilriker no, it is only 12V.

A Former User

depending on the layout of the bed you may be able to cut some traces and solder some wires to effectively put two halves of the bed in parallell, but the easiest would be to buy a new or ask your vendor for a replacement if that is an option.

rodolfo_paulo

Well, this is solved! I've just cheked with the store, and this is the bed limit!!!
Just got fooled...

Thanks for all the help!