3d printer bed heating slowly

[amateur_24]

A 3d printers bed is basically a resistor no? I measured across the power input for the bed, I got 2 ohms. I have overvolted the bed slighty at 12.9v. So it should be drawing closer to 6Amps no? I measured the amperage and it's only drawing 3amps. Could this mean I have damaged the N channel mosfet on the main board? It does otherwise act normal. i.e. When the fet is on I can see 12.9v across the vin for the bed. When the fet is off i get 0 volts across the bed.
I did notice a less 1 micro amp of current flowing when it was off. but thats probably just leakage right?

 

[rjenkinsgb]

What mode is the bed control working in?

(Also, what control board & firmware?)

Such as Reprap firmware can work in either PWM mode, for fast precision control, or thermostat "bang bang" mode, which gives better results with heated beds.

 

[amateur_24]

Sorry I should of made this clear. I accidently shorted out the main board via a paint brush I had on the table. Since then the bed has been heating very slowly. It heats up to around 50 degrees then freezes. I am not sure what set it as.
duet wifi 1.04b
RepRapFirmware for Duet 2 WiFi/Ethernet 2.05 (2019-12-13b1)

; Heaters
M305 P0 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M305 P1 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 1
M143 H1 S280 ; set temperature limit for heater 1 to 280C

 

[rjenkinsgb]

If you are getting the full voltage across the heater when the FET is on, I don't really see how the FET could be faulty.

Could the short have forced the heater to full power for too long and overheated it? It's possible it is going partially open circuit when it gets hot; if there were two parallel elements in it, a fault in one could explain the 3A reading?