A 3d-printable Amiga PSU Enclosure for the Mean Well RT-50B Power Supply
3d-model is created in DesignSpark Mechanical 4.0
For 3d-printing scroll further down!
Cabling is taken from an old dead Amiga 500 PSU. Also the power switch is reused and a couple of power resistors is added to put a dummy load to satisfy the minimum load requirements stated in the datasheet for the Mean Well RT-50B PSU.
Attention: Read the Legal Disclaimer before doing any electrical work yourself.
First strip the two leads on the power switch and attach two terminal blocks. Adjust the cable length and cut the Line lead (brown) and connect to the terminal blocks like in picture. Blue is Neutral (return lead) and green/yellow is GND/Earth. Carefully cut the isolation if needed. Do not cut into the leads themselves.
Now time to fit the Mean Well RT-50B PSU, but first unscrew the front-left screw and use that screw as in picture. Don't screw it all the way down but rather leave some room for the metal chassi to fit in between for a snug fit.
Now secure the PSU with a couple of other suitable screws and then connect and secure the leads.
Plugging the power cord in and turning the power switch on we can verify we got 230V AC input working.
Looking at the datasheet for Mean Well RT-50B we can see that minimum current requirements are specified, this means for the PSU to operate reliably we need to have a minimum current draw just above the minimum threshold on each rail. The Amiga almost exclusively use the +5V rail so no problem there but on -12V and +12V we might need to put dummy loads on.
However, Checking another Mean Well datasheet says differently. Hmm maybe newer versions of the PSU doesn't need it?
Anyway, I will show how to do this dummy load config for those who might need it.
To get the minimum 0.2A on +12V and 0.1 on -12V we can use Power Resistors that will be connected to Common Signal GND. The energy will dissipate as heat so good to place the resistors near a heatsink area and ventilation if possible. I did the case printout in the more heat resistant ABS plastic for this reason. ABS is better in that regard compared to PLA.
Let's calculate Ohm and Wattage to pick suitable resistors. This can easily be done manually or by using a online-calculator like this one: https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html
We see that using a 100 Ohm, 3 watt capable resistor is perfect for the -12V rail dummy load and a 47 Ohm, 5 watt capable resistor is suitable for the 12V.
Applying theory in practice:
Checking the Currents (Amps)...Shows 120mA and 250mA, just as excpected! I put some shrink tube on the resistors legs for safety reasons.
Now let's check voltages:
Switch Off and disconnect power cord from outlet, and wire it up:
- Yellow = GND/Shield/Earth
- White = -12V
- Brown = +12V
- Red = +5V
- Black = 0V/Signal GND
And verify pinout:
Finally put it together.
I printed in ABS-plastic since it feels a lot more safe dealing with power and heat compared to PLA.
Settings: Nozzle 250° C, Bed 120° C, Infill 60%. Printing time: 15 hours!!! with Ender 3-Pro and using the hairspray trick to make the material stick to the polypropylen bed.
I first had a failed print because of wrong temperature and nothing to fixate the ventilation fins with. They came loose and caused problems when "gluing" the parts together.
I went back to DesignSpark Mechanical and made a more printer friendly version of the top part. Fixating the ventilation area together which I later could cut off for design reasons. Now it printed without problem:
In the middle of the print the corners started to come off, I didn't print with a brim which probably would have been better, but the corner creep only improved on the design a little :)
Using a hacksaw and a cutter to trim the design of the vent.
Using similar settings here but printing with a brim to make it stay more flat. 13 hours for this print to finish. I used tape on the brim fringe to make it stick to the bed better.
Although printing with a brim worked better I got some cracks in the body during cooling down. I used some super glue to seal it.
The final result:
