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The Small Adjustable DC Voltage Digital 5A Power Supply Project


  • The Small Adjustable DC Voltage Digital 5A Power Supply Project

    By: Mark P.
    Parts Express Line Manager

    It’s inconvenient to lug a big, heavy adjustable 30V 5A DC power supply just to test a 12 VDC amplifier away from your bench. This kit helps shrink the weight and size by using an external AC/DC adapter that you may have laying around the house from an old laptop or portable DVD player. Parts Express Adjustable Step-Down Digital Regulator Board (#320-615) turns that old laptop adapter into a 3 to 19 VDC 4A variable power supply. If you want to increase the DC voltage range I recommend the Parts Express 36 VDC 5A AC Adapter (#120-063) and increase that voltage up to 32 VDC with up to 5A of current output.

    Why This See-Through Enclosure
    The Hammond 1591STBU (#320-725) is the perfect enclose for this project because its translucent blue poly-carbonate lets you see the blue back-lit digital display on the DC step down board without cutting a big rectangle hole. It’s only 7.5" x 4.3" x 2.2", but it has plenty of room to add any extra components to further customize this power supply project. You may add a lighted switch (#060-710), or a fuse holder (#070-612) to add extra protection, even though the step-down board has short circuit protection built-in. You will need to add a resistor if you use a power adapter greater than 12 VDC to prevent burning out the light in the switch.

    Putting the Project Together
    Now let’s build a small 3 to 32 VDC 5A digital power supply. Start by mounting the step-down the board to the lid using
    a standoff kit (#320-3290). Drill four 1/8" holes to match the board mounting holes. Secure four of the 16.25 mm standoffs to the lid using the Phillip screws included in the kit. Secure the board to the standoffs using the remaining 16.25 mm standoffs. Drill a 3/32" hole in the lid directly above each voltage adjustment push button. This enables a standard size test probe to adjust the voltage output up or down, plus adds ventilation to the board. Carefully drill a 7/16" hole in the rear of the box to mount DC power jack (#090-5018). Solder a positive wire to the center post and the negative wire to the long outer terminal. The other end of the wires will hook to + and - in. I recommend 20 or 18 gauge wire (#101-781) to handle the amperage. This power jack accepts 2.5 x 5.5 mm plugs, but if your AC adapter has a different size plug get a DC jack to match it. I chose this jack because the AC adapter (#120-063) I will be using has a 2.5 x 5.5 mm plug. Install the dual binding posts (#091-335) in the front of the box, by drilling two 1/2" holes spaced 3/4" apart on center. Take extra care drilling the larger holes to prevent cracking the ABS box. Use step drill bit set (#365-204), if needed, to gradually make the holes bigger. Solder or wrap the red and the black wire around the corresponding binding post or use crimp-on ring terminals (#095-674). The other end of the wire goes to the positive and negative out terminals on the board. Screw the lid to the box with the four included Phillip screws. Finally, plug in your AC adapter, and you have an adjustable power supply continuous from 3 to 32 VDC up to 5A.

    Small Adjustable DC Voltage Digital 5A Power Supply Project Part # 320-2900
    • Enables you to use existing AC adapters to save cost
    • Much smaller than desktop variable digital power supplies
    • It measures current draw of projects to determine which AC adapter is needed for permanent use

    Project Parts
    Part # Description Qty
    320-615 7A DC 60V Adjustable Step Down Regulator NC Power Supply Module Current Voltage Meter Buck Module 1
    320-725 Hammond 1591STBU Multipurpose Translucent Blue Poly-carbonate Enclosure 4.30" x 3.20" x 1.60" 1
    320-3290 PC Board M3 Standoff Kit with 8 pcs 16mm Stud / 8 pcs 10mm Stud / 4 pcs Phillips Screws 1
    090-5018 2.5mm Metal Panel Mount DC Jack 1
    091-335 Gold Dual Binding Post Banana Jack 1

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