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A project log for Monoprice Select Mini Electro-Mechanical Upgrades

Endeavoring to build upon the existing fanbase work of this $200-ish printer.

michael-obrienMichael O'Brien 07/28/2016 at 23:170 Comments

There is a bit of tedium involved with the learning curve of 3D printing, apparently. Not a bother, but as such the photorapher portion of what I do has been put on hold while tings are being worked out and the device is setup.

With that said, the burnt out fan MOSFET also took out the pin on the STM32. I've replaced the junction with the equivalent of a 40 ohm resistor so I still have a fan. Need to print out a couple of NEMA 17, 40 mm fan holders because when the Y-axis stepper gets hot and the requested movement is faster than it's capable, it starts skipping down the road. Thankfully this has not affected prints.

After a 3rd full size print, I've successfully created my own copy of this E3D fan duct. It took 4 hours @ 0.1 mm slices & 0.6 mm nozzle because I had to slow the printer down twice. Mostly a function of printing 270˚ rotated so I could observe the fins being printed as this was the feature that had the most difficulty originally. The Gcode generated caused very little time for the fan to rest on these 'wings' and thus they warped from not cooling down. Overall, 4 hrs to print, 4 hours letting my PID variables be tested with the AOD510's instead of AOD484s.

I wasn't too surprised when the nozzle temp bumped when the heater bed's power was adjusted up/down, though it stayed within 1.5 ˚C of the set point. There was an unusual side effect of switching to the AOD510's, the switching frequency increased quite a bit; it now hovers between 300 & 600 Hz. With the same PID parameters, the 'ripple' in the current was about 1/2 of what I had before, though, to be honest, this can be a result of the MOSFET suppression diodes.

Speaking of which, I switched to the AOD510's earlier than expected. I shorted one out when doing the diode testing, PEBCAK, so I replaced one did a small 'burn in' test, and replaced the other. with the [right] side panel off, I only had a chance to feel the hotend 'FET and even after several hours, it never warmed too much to touch, 40-45 ˚C, with ambient temps at 27 ˚C. The fancy new 470 uF, 50 V cap on the other hand was easily +50 ˚C. The stepper drivers' heatsink measured out to 70 ˚C. Active cooling is my next priority.

As an experiment, I dropped in 0603 (US not METRIC) 4.7 uF MLCCs ontothe board where 0.1 uF MLCCs were for decoupling. The noise wasn't significantly affected, but it'd create a 'better' roll off for any noise coming from the thermistors themselves. Since the PID control seems to not be any worse, I'm leaving the caps in place.

Outside of calibrating the extruder for feedrate vs temperature vs nozzle size, 12 V PSU noise and active cooling are my items on the list to solve, currently.

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