Dual Power Supply Front End - alt lab supply

An inexpensive alternative to a dual output DC lab supply. Essentially a power supply front-end with voltage adjustment buttons, LCDs for voltage and current readings, banana jacks / binding posts, DC jack, and power switch. Built around two DC-DC buck converter boards; output 0-16.5VDC, 3A peak, 2A continuous (times two boards/channels). I haven't tested the power specs to the max, but I did include mounting for a cooling fan (untested). The total parts cost is about 10 USD. It needs a positive tip power supply under 23VDC not included in that total; laptop chargers are pretty much ideal (~20V, >3 A).

Single Output Version

Thanks for the CAD models:

Banana jacks by Jeroen Lodder
Switch by Milan Samardzija
30mm fan by Phil Maddox

BOM:

Find the tip size of your wall-wart/AC adapter before buying the DC jack. Links for 5.5mm x 2.1mm as well as 5.5mm x 2.5mm are included below. The list includes things I suspect most people already have like screws and an AC adapter. Assuming those are on-hand and the fan isn't installed, I calculated 8.44 USD for parts actually used (items 1 - 4 below). I selected parts with free shipping when possible, but some parts have minimum order quantities above what's needed.

• 1. DC-DC converter board, qty 2
• 1. Banana jacks, link is already qty 2
• 1. Switch
• 1. DC jack, select your tip size
• 1. Optional, fan (30mm, 24V)
• 1. DC DC board screws, M2.5 x 5
• 1. Bottom cover screws, M3 x 5
• 1. Optional, rubber feet
• 1. Wire
• 1. Power supply, 2.5mm positive tip and cable

Assembly Instructions (video is for single, dual is similar):

1. Print the body, bottom cover, and four buttons. Make sure the print bed is smooth because the bottom layer becomes the top of the assembled unit. (The texture of tape or glue may be transferred.) Fan guard regions and buttons may need some filing/pruning and you can cut off the single support rib on the back.

2. Optional: Paint/color the recessed text and the buttons.

3. Install the buttons; drop in, check they move freely and drop all the way down.

4. De-solder/remove the large blue terminal blocks from the DC-DC converter boards. Clean out (wick or sucker) the plated thru-holes. Adding wires to Vin/GND and Vout/GND may make wiring easier later.

5. Install the DC-DC converter boards using M2.5 X 5mm screws (4X). The screw bosses should be effectively self-tapping. Check that the buttons now "pop" when pressed and when released.

6. Install the DC power jack, switch, and banana jacks.

7. Wiring: Use a fairly high-powered iron (GND plane and beefy bananas can suck the heat away before the temp gets high enough to melt the solder).
   + Solder red wires: DC jack+ to switch_in, switch_out to DC-DC boards' Vin [2X], DC-DC boards' Vout to red bananas [2X]. ** Make sure the polarity to Vin is correct! **
   + Solder black wires: DC jack GND to DC-DC boards' GND [by Vin, 2X], DC-DC boards' GND(by Vout) to black bananas [2X].

8. Optional: Install and solder in the fan (black to DC jack GND and red to switch_out), not yet tested. I think the screws are M3 x 16mm in the CAD model. Mind the fan blades and wiring (include internal fan guard?) *** Mind the fan's voltage rating ... they usually have minimum voltages around half the nominal voltage, but max voltages not much over the nominal. So most 24V fans should be okay at 20V, but 12V fans would not be. ***

9. Install the bottom cover with M3x5 flathead screws (6X). They should self-tap into the body.

10. Optional: Apply small adhesive rubber feet (4X).

https://youtu.be/I5ZASDWc5L0
https://youtu.be/0Hl5d5YSglQ