Heavy Lift Electromagnet from Microwave Oven Transformers | 220v Contactor Relay

My fairly large (print volume 450x250x350mm) home-made 3D printer uses a mains-powered heat bed made from a junk-pile sourced electric pancake griddle which I ground down to more or less flat and glued a 24×12″ ceramic floor tile down to its top with high temperature silicone. It has a 10 ohm resistance and I use the original temperature control knob as a safety / sanity interlock against thermal runaway and then it is driven by 120v mains power switched by a 25A solid state relay controlled by the normal RAMPS heatbed output. The mains input runs through a breaker box before going to the 24v power supply for the NEMA23 motors and the ATX power supply for the Arduino, RAMPS, extruders, hotends, and Odroid U3 that make up the rest of the printer.

Although a mains powered heated bed sounds scary for a hobbyist-built 3D printer, there are a number of positives to the design. It would heat up faster, thin down a few parts, and significantly reduce the overall cost of the printer by not requiring another 100 Watts delivered from a 12V power supply. It’s a great idea if it doesn’t burn down the house. Anyone want to help?

Some customers get sticker shock, but I’m not trying to rip you off. You only see the half-hour of work I did in your home, but that’s not the whole story. I spent years training, and now I need to pay my crew (who went out of their way to get to your home), plus deal with marketing and other costs of running a business—and my prices reflect that. Learn 11 more secrets contractors wish homeowners knew.

Unfortunately, by in large, the comments for this article were unnecessarily negative, and downright factually inaccurate.

The run and start capacitors provide the phase shift for starting torque because their capacitances add up when wired in parallel. In fact, both capacitors are wired in series with the start winding and in parallel with the run winding.

Stripping wire with my teeth (my front teeth have a perfect gap at the bottom for it, I could probably specify them in AWG) to fit the socket onto a phone extension cable. While rather stupidly forgetting I’d plugged the damn thing in downstairs. Yowch! Fortunately it wasn’t ringing. As a mistake, it was educational.

I neither would recommend the mains power approach (230V in Europe), the power of 120W is very well to be handled with 24V, even 36V is necessary. This 3D printers are in many cases still some kind of “hacker toy”, often are modifications or experiments done.

Then when you step up a notch to the KV stage the safety rules change because air can now be a conductor.

I don’t know, disassemble an induction heater, use the encased induction coil, feed it with mains, put a metal plate on it, and you got a safe but cumbersome heated bed using mains.

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HDR is a feature that’s easy to over-use, as it can quickly over-flatten the contrast of an image, resulting in a dull, lifeless photo. On the other hand, there are times when nothing else will do. I’ve shot a lot of landscape images over the years where I’ve really wished I had it; situations where there was bright sky and deep shadows, or a bright rockface but also interesting detail I wanted to capture that was in the shade. With an auto-HDR option, I often find myself trying it, but also shooting a normally exposed shot as well. I more often like the normal shot, but sometimes the HDR one is the keeper. (I really wish there were an option to have the camera capture three shots; a normally-exposed one and the the high/low exposure pair it uses to build the HDR image from. It’d be handy to be able to shoot a normal image, with the HDR shot as backup.)

It’s not that simple according to National Electrical Code (NEC) NFPA 70 for several reasons. Here are some additional factors to be considered: