Wednesday, August 2, 2017

UMMD 3D Printer Electronics

Major components of the electronics in UMMD are:

In a 3D printer, the extruder requires the most operator input for maintenance and repairs.  The electronics comes in a close second.  Most people building coreXY printers put the electronics in the bottom of the printer, utilizing some of the "dead space" under the bed.  That can be convenient if the printer sits on a table, but UMMD is tall and stands on the floor, just like me.  Putting electronics in the bottom would mean getting down on the floor every time I had to access the electronics.  I also intended to use an LCD control panel to print from SD cards, and LCD panels generally don't work with long cable runs, so the LCD panel has to be kept close to the electronics.

I wanted to keep the electronics easily accessible, and outside of the heated enclosure, and I hate bending over, so I planned to put the electronics on top of the printer from the start.  Most of the electrical connections to the printer have to be made on the XY stage, so keeping the electronics close by keeps cable runs shorter.  The electronics are mounted on the left side of the top of the printer, under a plastic basket used as a protective cover (it's ugly- I'm working on it!).

There are two buck converters in the system.  One provides a source of 12V to power some fans and some of the white LEDs used to light up the printer.  The other is used strictly for powering the UV LEDs.  It would have been less complicated if I didn't have the 12V parts in the system, but it is easier to find 12V LED light bars, and I already had a couple 12V fans, so I used a buck converter.

The other buck converter is used to power the UV LEDs, something not absolutely necessary but aesthetically pleasing when printing fluorescent filament.

You can see more details about the LED lighting in UMMD here.

UMMD has three electrical fuses, one for the main power supply (which probably has its own internal fuse), one for the bed heater circuit, and a spare that is going to be used for an enclosure heater circuit, not yet installed.  Electrical fuses protect against fires caused by wiring or electronic failures.

The bed heater is powered via an SSR that is driven by the controller board.  When SSRs fail, they fail shorted - i.e. on.  The controller normally keeps the bed temperature regulated, but if the controller fails, or the SSR fails, the bed heater could get dangerously hot, and possibly cause a fire.  I added a thermal cutoff (TCO) to the bed plate to protect against that possibility.  It would actually be better to have the TCO mounted on the heater because the heater is attached to the bed plate with adhesive which could let go.  I will probably move the TCO to the heater itself by cementing it with high temperature silicone.  That way if the heater comes off the bed plate, the TCO can still do its job.  Details of the bed and support here.

TCO clamped to the rear edge of the bed plate.

I used a TCO with a operating temperature of 184°C.  That allows the bed to operate normally up to about 160°C (for printing high temperature materials) without opening the TCO.

The rest of the wiring to motors, etc., is standard stuff you can see in the Smoothieboard documentation.

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