Small Bench Top Power Supply

Last crawled date: 4 years, 2 months ago

Small benchtop 3a power supply able to be printed (barely) on a monoprice select mini.
Bill of Materials:
B10K potentiometer
xl2001-5v usb buck converter
dns-vc288 voltmeter / anmeter led display
3a LM2596 buck converter
Male Power Socket with Fuse and Switch 10A 250V 3 Pin IEC320
3a fast blow fuse
spade connectors for power
wire
3mm cap head screws (8) and 3mm hex nuts (6)
clone dell pa9 laptop power supply (outer dimensions of plastic case 50x30x126mm)
High Level Instructions:
I'm not going to provide a full schematic, anyone doing this should have a good working knowledge of electricity, if you don't enlist the help of someone who does.
The 3a buck converter needs to have the onboard pot desoldered and replaced with wires attached to the b10k pot. Only two leads are required the third one on the board isn't connected. Make sure you wire it up so that turning the pot clockwise increases the voltage. The buck converter hangs upside down on the top of the case. When the front and back of the case is assembled, the buck converter is captive, no additional screws required. Note: There are three different versions of this board, they are very similar, but have slightly different dimensions. Get the one pictured if you can otherwise the dimensions must be changed to fit.
The usb charger should be directly connected to DC power, it's not variable power or connected to the meter like the banana plugs. It's just a bonus, it's nice to have a USB charger handy. Two 10-15mm x 3mm screws and the printed usb cover will hold it in place.
Wire up the power outlet with heavy gauge wire and spade plugs. I wired mine so that the switch is only lit when the switch is turned on.
The dsn-vc288 meter should be the very last thing you install, you will need the front space open to install the banana plugs and the pot. Small fingers would help. Installation is not quite a one-way operation, but it's not easy to get it out of the case once inserted. I wired mine up with power coming direct off the dc power supply and power to the banana plugs is monitored. There's a good explanation at the following link, make sure to find the dsn-vc288 section.http://hamguyparts.com/files/Download/Chinese%20DVA.pdf
The banana plugs are the cheapest smallest available on ebay. There are binding posts that look similar, they may fit, but I haven't tested it as I don't have them. To insert the banana plug jacks, you need to take off one plastic surround and push them in. Solder the wires on the tabs, and rotate the tabs outwards and down so that they won't make contact with anything else.
The power adapter I used is a dell pa9 19.5v 4.5a chinese clone. It appears that other clone 19.5v laptop adapters have the same form factor. I measured the outside of the plastic case at 50x30x126mm. The "mickey mouse" plug must be desoldered and the dc wire removed. Line and neutral should go to the power plug switch. Ground goes to the ground tab. Fit is tight in the printed case, but there is a slight bit of wiggle room.
For final assembly, some long 3mm screws would be helpful for inserting the nuts into the appropriately shaped cutouts. Insert the nuts before you put the front and back case together, having that long screw will help to draw the nut in. Once the nuts are in place, assemble the case and fasten the case together with 4 3mm screws.
I suggest printing this in ABS or PETG for temperature resistance, but mine is in PLA. There is no venting on here, I don't know how hot this will get if driven at it's limits, but the power supply never got terribly hot driving my laptop. It wouldn't be too bad to add a small 24v fan if it needs it.
You can print with supports, the only place they should be used is in the banana plug holes. Everything else is designed (at great effort) to print with no supports.
None of these parts should cost much more than $2 each if you are willing to wait for shipping from china. I think I have $10-12 in this in parts (don't ask how long I spent designing it) and the power supply was sitting in my junk box with a broken cord.