SSR defective again - Which method of Thermal Fuse
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@achrn I think that a lot of the cheapo SSRs that people use for bed power switching don't have zero crossing detectors.
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@mrehorstdmd Actually, I've just re-examined the datasheet for what I have used in my most recent build and it specifies that both turn-on and turn-off is at zero crossing. (Panasonic SSRs).
In that case, my graphs are also wrong (but in a differnet way) - it would mean each half-cycle on the mains has an essentially random chance of being found on the output, where the chance is in proportion to the PWM duty cycle.
Agreed that if you use a SSR without zero-crossing switching these behaviours are not relevant.
I run my mains bed SSR at 5Hz (which I think I picked so there were 20 half-waves in each PWM cycle, so my error would be no more than 5%, which seemed close enough). The data sheet doesn't specify a limit on the control frequency, but does note that operate and release times are 'Max. 1/2 cycle of voltage sine wave +1 ms'.
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@achrn I enjoyed your analysis of zero-crossing SSRs and an AC bed heater. Thanks you for that.
This guy is actually talking about a DC bed heater and a DC SSR, so your analysis does not apply to this situation.
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Thank you very much for evry answer. I think first of all I should check the PWM Frequency (Q-Parameter) and change it to 5 Hz as the data sheet says.
I've already ordered a 230V heating bed. So my amps will be much lower. Finally I will install a bimetal switch (130°C) as a thermal fuse to guarantee fire safety...
But I am very thankful for the tip about the PWM Frequency... So far no one could give me an explanation why the SSR got defective.
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Hey, probably shouldn't need to remind anyone, but when implementing high-Voltage wiring, to use extra safe wiring methods. heat-shrink where possible, Insulate all exposed current carrying metals, enclose it if possible, definently fuse it, etc. And be sure to mount the SSR on a heatsink, preferrably finned. In addition to one not desiring to burn-down one's house, it is also unpleasant to electrocute one's pets, children, wife and-or self!! ;-}
Rotsa Ruck!
3mm
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@3mm Also fuse low , if the maximum wattage of your 3d printer is 500 watts remove the 13 amp fuse which will be in the fuse by default and replace with a 3 or 5 amp fuse.
Use a ELCB / RCCB where possible . -
Hi Guys, I've updated my setup- So now I'm running a 230V Heating Bed. I've also added the bimetal switch and finally put my heating parameter (PWM-Frequency) to Q5 (5Hz).
After running autotuning I got this message:
WARNING: Heater behaviour was not consistent during tuning.
Is this a problem? Or is this warning caused by the lower frequency ?
I noticed the the temperatur curve of the heating bed was much more wavey than the old one wich 500Hz, which for me is logical.
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@heinrich-platau Can you post a link to the data sheet for the SSR you are using now?
Since it's an AC SSR, you might be able to run a higher PWM frequency depending on the SSR.
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Here's the data sheet
Seems to be no difference. All SSRs are 5Hz
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@heinrich-platau I see that as well.
I guess I would try those settings and run it up to the temperature you want to print at and see how stable it is.
Or maybe let it cool COMPLETELY to room temperature and tune again?
(I don't have much knowledge of the bed tuning algorithm, I'm sorry to say.)
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@heinrich-platau I had also this message after the first tuning. Try to run the tuning again.
