With the addition of the Raspberry Pi to my rebuilt Up Plus 3D printer I now have three power supplies connected to the machine. The heated bed is using the original 19V power supply that came with the Up, the RAMPS 1.4 and hot-end are using the 12V supply from my old Prusa and the Raspberry Pi is using an old 5V phone charger. This is a lot to connect to start the printer.
I want to simplify things by just using the 19V supply and fit the machine with two step down voltage regulators. I would need one regulator to step the 19V down to 12V and a second to step down again from 12V to 5V. The 5V is easy as the Raspberry Pi Zero W only draws 250mW max so any USB power supply will work. I settled with a dual USB 15W switch mode supply that can handle 6V – 40V input. The larger supply and dual ouput would be handy if I add a WiFi camera later.
The 19V to 12V supply needs to supply the RAMPS 1.4, Arduino, stepper motors and the hotend. I calculated the peak power draw to be 30W (2.5A). I chose a 50W Power Supply Module that included an LCD display that shows the current draw and voltage. The Ebay listing shows that the unit can supply 35W constant without cooling and 50W with the supplied heatsink. I also added a cooling fan.
The first test run had the 12V supply showing peak current draw of under 2.5A so less than 30W but the heatsink was getting too hot to touch even with a fan on it. 10 minutes into the print the printer stopped with the 19V supply shutting down due to short circuit protection. The second MOSFET on the 12V supply had failed short circuit. I contacted the Ebay seller wh didn’t respond to any e-mails. Swindled.
With a doubtful attitude to Ebay sellers I decided to replace the 50W supply with a 200W supply. This new supply doesn’t have a fancy LCD but it shouldn’t burn up during basic use. I kept the cooling fan just to make sure and the power supply is cool during use.
Now with only one power cable this printer is almost looking finished.
So now I have my rebuilt Up Plus 2 3D printer working I need to tidy up the electronics. To do this I downloaded a RAMPS 1.4 case off of Thingiverse and set to printing.
The first problem I had was bed adhesion. The buld plates that came with the printer are similar to a prototyping PCB perf-board with hundreds of tiny holes in it. The PETG filament I am using sticks to the board well enough but all the holes make for a really rough bottom layer. After a little Googling I found that the Up software slicer uses a raft for bed adhesion so I will try that. It took some adjusting to get the first layer height offset correct but it is working.
The next problem was that the prints are warping badly. I had not wired up the bed heater yet as I still needed to change the thermistor. The Ups original 100 ohm thermistor doesn’t work with the RAMPS controller so I replaced it with a 100k ohm thermistor. With the RAMPS power supply set to 13.5V the bed could only reach 65 degrees celsius and even then took 45 minutes to get there. The recommended bed temperature for PETG is 70 degrees so the best I could manage was still 5 degrees too low.
While I had changed the thermistor I didn’t change the heater cartridge in the Ups bed which was designed to work with a 19V power supply. The RAMPS 1.4 has a seperate power input for the heated bed but a look at the schematic shows that the MFR1100 11A PTC resettable fuse is only rated for 16V. A look at how these PTC fuses work and at the datasheet for this particular fuse I see that the critical part is not the voltage but rather the power consumption as the fuses rely on heating of the internal elements for them to work. If more than 16V is applied to the fuse while it is failing then the extra power consumed by the fuse while the internal resistance rises can cause the fuse to fail in a non-resettable way. But since this is what fuses usually do I am willing to risk using the standard PTC fuse at 19V.
I wired up the original Up 19V supply to the 11A input and left the 13.5V supply on the 5A input of the RAMPS and gave it a go. Now it reaches the target 70 degrees in under 15 minutes and has no trouble maintaining that temp.
I had started printing the case for the RAMPS before fixing the bed heater and the case had warped and the print failed when it seperated from the raft 3/4 of the way through. Since it took 14 hours to print as much as I did I didn’t want to start again. I cut the part that printed successfully of the bottom of the model in Cura to finish the print with the bed heater active and then glued the top to my failed print. The pieces don’t quite match due to warping but I now have a momento of how the printer worked before the improvements.