Introduction: Modular Multiport USB Power Supply

This modular power supply can supply from 9 to 54 USB ports of 5VDC power. Each module provides 9 ports and a total of up to 10 Amps.

It started out as a supply for a Raspberry Pi based Network Training Lab for Hurricane Electric. (Contact me if you are interested in IPv6 Training or consulting or in getting your own training lab).

I made it at TechShop.

A wide variety of input voltages can be accommodated, ranging from 85-265 VAC and from 100-370VDC. AC power can be supplied at any frequency from 47-63 Hz. The supply is engineered to be very tolerant of transients and includes short-circuit protection on the output side. In addition, the modules are protected by an MOV protected by a resistor and all of that is protected by an in-line Fuse sized based on the number of modules. The fuse sizing table on the back of the PCB assumes 230VAC input. For 110, fuse value should be increased by 2 amps for 1-3 modules and by 4 ams for 4-6 modules.

The picture above is of a 2-module supply in a laser cut acrylic case. This Instructable will walk you through building exactly this unit, though the files provided could easily be modified for larger or smaller stacks.

Step 1: Get PCBs Made

The easiest way is to order the boards from OSH Park here:

A set of three boards will cost $78.60 at the time of this writing.

If you prefer to get the boards made elsewhere, feel free to contact author for the Schematic and Board files. Getting the board design from Eagle into your workflow will be entirely your responsibility.

The image above shows the boards from OSH Park. The left side is the front and the right side is the back of the board.

Step 2: Obtain Components and Hardware

  • First you'll need to determine your fuse size. Below, the list shows N. S1/S2 where N is the number of modules, S1 is the rating for 230VAC and S2 is the rating for 110VAC. Fuses should be Slow Blow types, glass or ceramic.
  1. 3A/3A
  2. 4A/5A
  3. 5A/7A
  4. 6A/9A
  5. 7A/11A
  6. 8A/13A

These boards were not engineered to be stacked more than 6 high.

Components per power supply:

Bottom Board Mounting hardware (to case)

  • 5 M3x10mm screws
  • 5 M3x7mm hex male-female standoff

Top Board Mounting Hardware

  • 5 M3 nuts


  • 16 M3x16mm Screws to hold the case together
  • 16 M3 Nuts

Primary Board

  • MOV model V275LA2P (Digikey F3008-ND)
  • IEC320-C14 Power Socket (Digikey Q219-ND)
  • Resistor 1Ω 5W (Digikey 1.0W-5-ND)
  • Fuse Holder 5x20mm (Digikey WK0011-ND)
  • Appropriate Fuse (See fuse sizing above) 5x20mm. (4A 250V SB Digikey 507-1544-ND)
  • 1 M3x10mm screw (Secure inner side of IEC320 to board... Outer side is secured by standoffs)
  • 2 M3x12mm Screws for mounting power connector to case (16mms will be too long)
  • 3 M3 nuts (Mounting IEC320 to Front Panel and inner side of IEC320 to board)
  • M3x35mm* hex male-female standoff... If more than one module in stack (replaces one of the 38mm standoffs used on non-primary modules to accommodate IEC320 Connector)

Components per module:

  • Recom RAC60-05SB Power Module (Digikey 945-1099-ND)
  • 3 3-Port USB Connectors (Digikey 1175-1004-ND)
  • 6-Pin stackable Header connector (If more than one module in stack, mounted on board)
  • Optional 5mm LED in your choice of color (5V Power On indicator)
  • Optional 100-200Ω resistor (tuned to your desired LED brightness at 5V, required if LED used)
  • Optional 2-Pin Header or Right-angle Header connector for 5V Power Out
  • 4 M3x6mm Screws to secure module to board.

Components between each pair of modules in a stack:

  • 3 6-Pin stackable Header connector (Used to extend connector on lower board to meet pins on bottom of upper board in each pair)
  • 5 M3x38mm* hex male-female standoff... except on top of primary module (module with AC connector) where 4 are needed. (1 is replaced with the 35mm standoff mentioned above.)

* Standoffs may not be readily available in lengths specified. A combination of smaller standoffs providing the same board-to-board offset distance (which is what is specified) is all that is required.

I have no connection to Digikey. Digikey part numbers are provided strictly as reference and for convenience. Source parts wherever you like so long as they are compatible with the specified part numbers.

Summary Bill of Materials (organized by part rather than placement) ? Quantity indicates variable depending on modules or other changeable characteristics of supply:


  • ? M3x6mm (4 per module)
  • 6 M3x10mm screws
  • 2 M3x12mm screws
  • 16 m3x16mm Screws
  • 24 M3 nuts

  • 5 M3x7mm hex male-female standoff Top Board Mounting Hardware

  • ? M3x35mm* hex male-female standoff... If a module is placed above the primary module (replaces one of the 38mm standoffs used on non-primary modules to accommodate IEC320 Connector)

  • ? M3x38mm* hex male-female standoff... 5 needed between each pair of modules in stack, except on top of primary module (module with AC connector) where 4 are needed. (1 is replaced with the 35mm standoff mentioned above.)

Components (Electronic)

  • 1 MOV model V275LA2P (Digikey F3008-ND)

  • 1 IEC320-C14 Power Socket (Digikey Q219-ND)
  • 1 Resistor 1Ω 5W (Digikey 1.0W-5-ND)
  • 1 Fuse Holder 5x20mm (Digikey WK0011-ND)
  • 1 Appropriate Fuse (See fuse sizing above) 5x20mm. (4A 250V SB Digikey 507-1544-ND)
  • ? Recom RAC60-05SB Power Module (Digikey 945-1099-ND) (1 per module)
  • ? 3-Port USB Connectors (Digikey 1175-1004-ND) (3 per module)
  • ? 6-Pin stackable Header connector (If more than one module in stack) (1 per module + 3 between each pair)
  • ? Optional 5mm LED in your choice of color (5V Power On indicator) (1 per module)
  • ? Optional 20-200Ω resistor (tuned to your desired LED brightness at 5V, required if LED used) (1 per module)
  • ? Optional 2-Pin Header or Right-angle Header connector for 5V Power Out (up to 1 per module)

Step 3: Cut Acrylic Case (Optional Step)

If you're going to make a case for this thing, now is the time to cut the acrylic.

Above, the picture is the 6-pieces of the 2-module case fresh off the laser cutter. The second file is a Corel Draw file which can be used with the laser cutter. Blue lines are intended to be etched. Green lines should be cut all the way through, but all green line cuts should be completed before any red line cuts are made. Red lines should also be cut all the way through. The box is designed to be cut out of 1/4" acrylic. The file is arranged for clarity and ease of manipulation and not the optimal cutting efficiency. Be sure to modify the file as needed to work with your laser cutter. The box shown was cut using an Epilog Helix 60W CO2 laser cutter. The cuts were done using 7% speed, 90% power, and 5000Hz pulse frequency. Etching was done at 100% speed, 40% power, and 5000Hz pulse frequency.

Step 4: Prepare to Build Primary Module

The case shown is designed with the primary module on the bottom. Putting the primary module on the bottom reduces the chances of an accidental contact with high voltage during use if the supply is not installed inside a case. On the other hand, replacing the fuse in a unit with the primary module on the bottom pretty much requires complete disassembly of the stack. Other considerations are that you may well be able to go beyond 6 modules by placing the primary module in the center of the stack, with up to 5 modules on either side of the primary, though this is not recommended. The primary reason for the 6-module limitation (besides the 12Amp potential draw at 110V) is that the amperage across the rather small pins which provide the board-to-board connections also gets rather high. (The AC voltage is passed between the boards by paralleling two header-pins for each trace (Line, Neutral, Ground) on the 6-pin board-to-board header.

The construction of the primary module is nearly identical regardless of where in the stack you place it (though you will need to modify the front panel of the case as well). The only difference is in whether the 6-pin header has its pins trimmed (bottom) or left in tact (top or middle).

For the primary module, you will need to gather the following pieces:

  • 1 PCB
  • 1 Power Connector
  • 1 1Ω 5W Resistor
  • 1 MOV
  • 1 Fuse
  • 1 Fuse Holder
  • 1 LED
  • 1 100-200Ω Resistor
  • 1 Header Connector (Optional)
  • 1 6 pin stackable header
  • 3 3-port USB Connectors
  • 4 M2.5x5mm Screws

Tools useful for this assembly include:

  • Soldering Iron (with solder)
  • Pliers
  • Wire Cutters
  • Screw Driver

Once you have gathered these items, proceed to the next step.

Step 5: Install Power Interface Components in Primary Module

Begin by soldering the components (detailed below) to the PCB. Only the power connector is orientation sensitive and it physically makes sense only in one direction. Follow the layout information on the board. The components should go on the same side of the board with their outlines. The side of the board with the HE logo is where you should apply the solder. Once you have soldered the components in place, trim the leads on the MOV and Resistor.

  1. Install and solder MOV
  2. Install and solder Resistor
  3. Install and solder Fuse Holder
  4. Install fuse in fuse holder
  5. Install and solder Power Connector (Use a good amount of solder for these connections, the pads are large with significant gaps between the pins and the sides of the holes. Be sure to get good coverage.) It may be useful to use a pair of M3 screws and nuts to hold the power connector in place for soldering.

Once you have installed these components, the next steps are identical for all modules. Perform them on the primary module and then repeat for each additional module in the stack.

Step 6: Install 6-Pin Stackable Header Connector, Resistor, LED, and 2-Pin Header

If you are building a single module supply, then all of these are optional. If you are building a multiple-module supply, then you must install the 6-pin stackable header on each module. The rest remain optional. The 2-Pin header is only required if you want to use this additional power connection for a non-USB device. We won't be installing it on these units. The LED and Resistor are optional, but if you intend to use the LED, you must install both the LED and the resistor. They are wired in series and neither does anything without the other. A standard 5mm LED with a nominal voltage around 1.2-2 volts and an expected current draw of 20ma should work well with a 100Ω resistor, but will be very bright. Use of a 200Ω resistor will yield a bit less glare and potentially longer LED life.

In this step, since you can't bent the pins of the header and the header will likely become very hot during soldering, use of hemostats (curved Kelly clamp) to hold the header in place for soldering can be very useful. (see pictures)

  1. Install and solder the 6-pin stackable header connector with the female side up.
  2. Install and solder the resistor
  3. Install and solder the 2-pin header connector. If a right-angle connector is used, install it such that the pins point off the edge of the board, not towards the interior.
  4. Install and solder the LED. The flat side of the LED should line up away from the edge of the board. Polarity is important here and aligning the flat side as described will ensure proper polarity. In case you have trouble identifying the flat edge of the LED package (it can be subtle), the longer lead should go in the exterior hole and the shorter lead should go in the hole farthest from the board edge. Use whatever value will yield your desired level of brightness and LED life for your particular LED given a 5VDC input.

When soldering the 6-pin header, it is useful to first solder one corner pin, then, while maintaining the solder in a liquid state, verify the proper positioning of the header connector, remove the iron, and let the solder solidify before releasing the hold on the header. After this step is completed, solder the opposite corner and again re-check the alignment of the connector in the board. Once proper alignment has been achieved, solder the remaining 4 pins.

When releasing the clamp, be careful not to torque or otherwise stress the connector.

If (and only if) this is the bottom module in a stack, trim the leads of the 6-pin header after soldering.

The pictures do not show installation of the 2-pin header because it is not being used on this module.

FIXME -- Add pictures of LED Installation

Step 7: Install USB Connectors

This step is very straightforward.

Use a good amount of solder on the large tabs as this is the mechanical connection to hold the components in place. Be more judicious in soldering the electrical pins. Also, technically, only the outside pins need to be soldered. Though pads exist and you can safely solder the interior pins, the pads are not connected to any traces, pours, or other pads. By outside, I mean the two rows of 3 electrical pins closest to the mechanical tabs. (See pictures for details. Note that in the pictures, only the outside pins and the mechanical tabs are soldered.

Step 8: Attach RAC60-05SB Module to Board

Begin by positioning the RAC60-05SB pins in the corresponding holes in the board. You will notice that the pins have very different alignments on opposite sides of the RAC60. Pins on the high voltage side are spread farther apart than on the low voltage side. The high voltage side goes with the pins on the same side of the board as the LED and with the two large pins towards the edge farthest from the USB and Power connectors. The low voltage side goes with the pins towards the opposite edge of the board from the LED and with all three pins grouped closer together near the IEC320-C14 Power Socket (or the space where one would be mounted if this is not a primary module).

The easiest way to place the module is to lay it pins-up on the table and position the board (Component side down) over the module, align the pins and carefully lower the board into place. The module is taller than the USB ports or the IEC320 connector, so it will fully support the board without any risk of strain or damage to the other components.

Do be careful to make sure that the fuse holder and the MOV clear the module. If properly installed, they should be close to, but not in contact with the module. The holes are large enough for the module to slide on smoothly, so any resistance should be investigated and resolved by non-forceful means.

Once the module is positioned in the board, use 4 M3-0.5x6mm screws to secure it in place. Get all 4 screws started before tightening any of them. It is easy to cross-thread screws when starting them. It is very important to avoid this as the threaded inserts in the module cannot be replaced and destroying a $100+ module with a $0.19 screw is not a desired outcome (at least in most assemblies).

After securing the module with screws, solder all of the large pins. Soldering the small pins is optional. None of them are connected. The small (thinner) pins are the pin on either side of the module which is closest to the other components. The larger (thicker) pins are the two on each side which is farthest from the other components and are the ones which actually carry input and output current to/from the supply.

Congratulations... You have now completed a module. Go back to step 6 and repeat to this point for each remaining module before proceeding to the next step.

Step 9: Screws, Standoffs, and Stacking

Now that you have all your modules, the next step will be to stack them and assemble the case. This would be much easier if stackable headers came in the exact correct heights. In the real world, this will require some finesse and may require some judicious (and precise) trimming of stackable headers or some careful application of force to push pins beyond their normal insertion point.

Start with the simplest easiest one. On the primary module, secure an M3x12mm screw through the inner edge of the IEC320 connector and the PCB with a nut on the solder side of the board.

Next, start with the front panel. Using a pair of M3-0.5x12mm screws and a pair of M3 nuts, attach the primary module IEC320 connector to the front panel. Do not tighten yet.

Then, using 5 M3-0.5x10mm screws and 5 7mm M3 standoffs, insert the screws through the bottom side of the case with the threads pointing upward and attach the 7mm M3 standoffs to the screws such that the male threaded part of the standoff points towards the inside of the case. (The standoffs go on the side of the bottom piece with the text engraved on it (inside) and the screw heads go on the blank (outside). Do not tighten the screws yet.

Place the bottom module onto the top of the standoffs and align the standoffs to fit through the appropriate holes in the PCB. Use additional standoffs or nuts to temporarily hold the PCB on the standoffs (snug these down onto the standoffs, but not super tight). If the bottom module is primary, also make sure to line up and interface the fingers where the bottom and front sides of the case meet.

Using a wrench or a pair of pliers to hold each standoff, tighten the screws on the bottom of the case into each standoff. For the one in the very center, it may be necessary to use long-nose pliers or to take the power supply off, preserving its position, tighten it down, then reinstall the power supply and tighten the other standoffs.

Assemble 3 2x3-pin header connectors (stacked one on top of the other) and insert the pins of the bottom one into the corresponding header on the bottom board. The top socket will mate with the pins sticking out of the next board up.

Next, if you haven't already, install 5 38mm standoffs (or, if the bottom module is primary, 4 38mm standoffs and 1 35m standoff) and tighten them down onto the existing standoffs. Again, if you can't get or don't have full-length standoffs, pre-assemble combinations of standoffs with the appropriate total length.

Place the next module on to the stack. The exact technique will depend on whether the front panel is already installed or not. If it is, you will need to tilt the module and line up the top of the USB ports first, then tilt the pins into the connector very carefully, finally aligning the standoffs through the mounting holes in the board. If it is not, the module can be set in vertically, by first aligning the pins into 6-pin socket below and then sliding down onto the standoffs. This operation will require patience and great care to avoid bending pins or damaging components. It is not advisable to loosen the front panel screws from the IEC connector because there is no way to reach the nuts for tightening after installing the upper module.

If the just installed module is primary, install the front panel now.

Repeat the above steps until all modules and are installed and the front panel of the case is secured to the IEC320 connector.

Once the top module is seated, secure it with 5 M3-nuts and optionally 5 M3 star washers.

Step 10: Finishing Up the Case

The bottom and front panels should already be installed on the bottom and primary modules, respectively. The next step is to join them using 2 M3-0.5x16mm screws and nuts. Position the supply such that the nut holding slots (the short axis T slots in the bottom panel closest to the front) can accept the nut without it falling out. Thread an M3-0.5x16mm screw into each nut through the holes in the bottom tabs of the front panel. Carefully align the two panels as you tighten down the screws.

Next, install the right and left panels and secure them to the front panel in a similar manner.

Install the back panel and secure it to the bottom panel and the left and right panels in a similar manner.

Finally, install the top panel and secure it to the front and back panels using 4 M3-0.5x16mm screws and 4 M3 nuts in a similar manner to the other panels.

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