Mains Heatpad
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How dangerous is using a mains powered heated? Can it be made safe if not?
This is the pad I got made for my printer but now I'm concerned about dangers of using it powered via mains.
220V 750W from keenovo -
Plenty of people do - me for one. Just take great care to earth everything - especially the frame and fit an rcd plug to the power supply lead. Many people also fit thermal fuses to help protect against fire hazards.
I haven't heard of anyone electrocuting themselves on a 3D printer but some day, I expect to read about someone using one in a bath. Like a guy who recently electrocuted himself by running an extension cable to his bathroom so that he could charge his Iphone while in the bath.
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I'm certainly more careful with mine than with dc beds. If I have to take the bed off my delta to get to the electronics I kill the power in case there is a heater wire uninsulated in the silicone bed. The neutral wire is still energised as the ssr only switches the live wire.
Makes me wonder if a safer version would use two ssrs one for each of the mains cables to the bed. If they made a double pole ssr I'd certainly fit one.
Thermal fuse is a great idea ssrs can fail connected and a 500w bed is going to get very hot left on.
Not all silicone heaters are made equal, obviously, the one I have now had no-name adhesive which peeled off in the middle, this is dangerous as it can create hot spots which increase the resistance in the heater wire locally and can cause the bed to burn out (or burn). I worked around it by having some stiff insulation below to keep the heater pressed onto the aluminium, but have ordered a heater from Keenovo (after having a small one made for another machine) and they are very good quality. I'd order the heater a ways smaller than the aluminium, so it doesn't interfere with the bed mounts, I'm going down from 280mm, on a 300mm aluminium heat spreader to 250mm. The edges might be cooler after its fitted, I will have to see, but I rarely print right at the edge.
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See https://duet3d.com/wiki/Connecting_a_bed_heater#Mains_voltage_AC_bed_heater for some minimum suggested safety precautions.
As DjDemonD says, with any sort of stick-on heater you need to make sure that the weight of the heater does not cause it to detach from the bed plate. On my printer, again the under-bed insulation helps to support the heater weight and press it against the bed plate.
