Dead Time Control

edited August 2016 in Extruder & Bed
I have an issue with the heat bed.  It is a 12v so it is connected directly to the RAMPS 1.4 board.  I setup the temperature control for "deadtime control" instead of "Bang Bang".  I was watching the current draw (on my power supply) when it was setup with "bang bang"  and once the extruder kicked on,  the system drew up to 16 amps (ouch).  So I realized I should add some temperature control and selected the easiest to understand.

I have found a thermistor that is really close to measured temperature (set bed temp for 70 C and read about 71 C).  However the temperature never gets to 70 C instead it hovers just under at 68.75 to 69.5 (and holds it there with little to no deviation). That is not an issue except when printing, it never kicks off the extruder heating cycle.  I assume from not reaching the desired temp ?

What can I look at to set the heatbed to act like the extruder and print when close the set temperature? 

Thanks for the help



  • Dead time control is not best for heated bed. Bed has a long cycle and delay making it hard to control anyway. So here PID might be better choice. It could be that you have PWM too low in control range to reach 70°C or the dead time is too long so it stops heating before reaching target temperature. But as said with the long cycle wrong measurements (+/-0.1°c) could also stop heating too early.
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