Spurious heater faults again
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@ctilley79 If you have a reasonably thick bed (which you should have) then having the thermistor at the junction between the heater and the bottom of the bed is the worse place you can put it. When you turn the heater on, the temperature at that junction rises rapidly, so it turns off. Then when the temperature at the junction drops, the heater turns on but soon turns off again. Meanwhile, the temperature at the top of the plate is still cool. This constant one-off cycling plays havoc with the PID tuning and results in excessively long warm up time (for the top of the bed). What I did was drill a small hole in the edge of the bed, as deep as possible and as close to the top surface as possible, and put a thermistor in there. No more probs.....
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@tinchus This doesn't answer your question but using 88% pwm will not limit the power to your heater. It just means that it'll have full power for 88% of the time.
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@deckingman said in Spurious heater faults again:
cycling
I had zero problem for 2 years. The pid tune seems to compensate well enough, until 3.4.2 RC2. Duet provided instructions for using these types of heaters with built in thermistors so I know the less than ideal placement of the thermistor isn't the issue. I do have to heat soak my chamber for a good 30 minutes to allow the heat to transfer to the entire bed. But it worked. Not ideal, but it worked until upgrading to RC2.
Regarding PWM. If I recall, depending on the PWM frequency, it will result in slowing down the heating process via pulsing from high/low 60% of the time.
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@ctilley79 said in Spurious heater faults again:
Regarding PWM. If I recall, depending on the PWM frequency, it will result in slowing down the heating process via pulsing from high/low 60% of the time.
The PWM value is the percentage of time spent "On" vs "Off". So if you used a value of 0.6, then it would indeed spend 60% of the time on (at full power) and 40% of the time off. The PWM frequency is how fast it cycles. So for example if you used a frequency of 100 Hz, that would be one cycle every 10 milliseconds. So within each 10ms period it would be on for 6ms and off for 4 ms.
