This is a redundant, but not hot-swappable, 12VDC power supply. It has these features:
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Two AC cords. Either cord can lose AC power without disrupting the 12VDC output.
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Five 12VDC output jacks. Any individual jack can supply ~6A maximum but the supply is only capable of providing ~16A maximum across all jacks.
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Remote monitoring. A serial port provides a simple "on/off" status that indicates when one of the two onboard DC supplies loses its AC power or otherwise fails.
It is built on a 1U rack shelf but requires at least 2U because it is slightly taller than 1U. The extra air space is also needed for cooling because the supply has no fans.
Rackmount Automatic Transfer Switches from companies such as APC and CyberPower can be used to provide AC power redundancy for devices with a single AC cord. I wanted redundant power for the single-corded devices in my rack and noticed that they all ran off 12VDC power bricks. Instead of buying an ATS unit and plugging the bricks into it, I built this redundant 12VDC supply to eliminate the bricks. It can be built for less than the cost of most ATS units.
| Part | Qty | Notes |
|---|---|---|
| Meanwell ERDN40-12 12VDC Redundancy Module | 1 | Datasheet |
| Meanwell MSP-200-12 12VDC 16.7A Power Supply | 2 | Datasheet. Selected for built-in protections and no required minimum current. |
| Pinfox 10' 18 AWG 3 Prong Heavy Duty 120V 10A AC Cord | 2 | One AC cord for each MSP-200-12. |
| Raising Electronics 701401004 19" 1U 12" Deep Rack Shelf | 1 | Product Page |
| 10pc M3x6mm Plastic Pan Head Screw | 1 | 10 screws used for mounting the Meanwell units to the shelf. Plastic ensures no possibility of shorting. |
| 10pc M3x25mm Female-Female Steel Standoff | 1 | 4 standoffs used inside the project box to mount it to the shelf and secure the lid |
| 25pc M3x8mm Pan Head Screw Steel Black | 1 | 8 screws used with the 4 project box standoffs (2 screws per standoff) |
| 50pcs M3x6mm Nylon Standoffs with M3x6mm Nylon Screws | 1 | 4 standoffs and 4 screws used to mount PCB inside project box. Plastic ensures no possibility of shorting. Standoffs are epoxied to the project box. |
| Hammond 1591HSBK Project Box | 1 | Datasheet, Bulletin |
| L-Com SDG400XS D-Sub 50pc Jackscrew/Washer/Nut | 1 | Datasheet. 2 jackscrews, 2 lock washers, and 2 hex nuts used to mount DB9 to project box. |
| 5pcs DB9 Female to IDC Panel Mount | 1 | 1 DB9 connector used to make the DB9-to-PCB cable inside the project box. |
| 10pcs 2x5 pin IDC Female | 1 | 1 IDC connector used to make the DB9-to-PCB cable inside the project box. The top of the strain relief must be shaved down a bit to fit in the box. |
| Ribbon Cable 14 conductor 6' long | 1 | Cut down to 10 conductors and 6" long, used to make the DB9-to-PCB cable inside the project box. |
| DB9 Male/Female 5' Cable | 1 | Datasheet. For direct connection between the box and a PC with a DB9 serial port. |
| FTDI-US232R-100 1m USB-Serial Cable | 1 | Datasheet. For connecting to a PC without a DB9 serial port, use this adapter together with the above DB9 cable. |
| Lumex SSI-LXH387GD Panel Mount Green LED | 2 | Datasheet. Mounted on project box to show the "on" status of each power supply. |
| Switchcraft L712ASH 2.5mm Locking Barrel Socket | 5 | Datasheet, Bulletin. Mounted on project box for DC outputs. |
| Switchcraft 761KSH15 2.5mm Locking Barrel Plug | 5 | Datasheet. See bulletin above for electrical info. For building DC cables out to devices. |
| 14 AWG GXL Wire 10' Long | 3 | 1 each: red, green, black. Cut to length for high current DC wiring |
| 1200Pcs Assorted Crimp Terminals | 1 | 21 M4 size ring connectors used with terminal blocks on Meanwell units |
| DC Extension Cable 18 AWG 12VDC 10A 33' Long | 1 | Connectors cut off and discarded; used to make output cables and for wiring inside Project Box |
| 10pc Dupont 2x2 Female Housing | 1 | 1 housing used to make ERDN40 alarm cable |
| 10pc Dupont 2-pin 26AWG Female-Female Jumper Cable | 1 | 2 cables used to make ERDN40 alarm cable |
| Molex KK 22-01-3077 7-pin Housing | 1 | 1 housing used for PCB connector |
| 125pc Rubber Grommet Set | 1 | 1 grommet used around wiring from ERDN40 into project box |
| TICONN 80pc Stainless Steel Hose Clamp Set | 1 | 3 hose clamps used for AC cord strain relief |
| 100pc 1/4" Aluminum Pop Rivet Set | 1 | 3 pop rivets used to secure hose clamps to shelf |
| 6pc Phoenix Contact Cable Tie Mount Base | 1 | 3 bases used for cable management |
| Panduit Cable Tie Assortment | 1 | 3 ties used for cable management |
| 42pc Marine Heat Shrink Tubing | 1 | For insulating cable ends and also cable management |
| Part | Qty | Reference Designators |
|---|---|---|
| ATTINY212-SSF Microcontroller SOIC-8 | 1 | U1 |
| MAX232EID TI RS232 Transceiver SOIC-8 | 1 | U2 |
| ECS-3951M-018-AU-TR Oscillator 1.8432 MHz | 1 | X1 |
| BZX84-A15,215 Zener Diode 15V | 1 | D1 |
| F1206B1R00FSTR Fuse 1206 | 1 | F1 |
| 08055C104J4T2A Capacitor 0.1uF 50V 0805 | 4 | C1, C2, C4, C8 |
| 08053C105K4Z4A Capacitor 1uF 25V 0805 | 4 | C3, C5, C6, C7 |
| CGA4J1X7S1E106K125AC Capacitor 10uF 25V 0805 | 1 | C9 |
| RK73H2ARTTD4702F Resistor 47K 0805 | 2 | R1, R2 |
| ERJ-P06F2000V Resistor 200ohm 0805 | 2 | R3, R4 |
| 22-12-2074 Molex KK 7-pin Right Angle | 1 | J1 |
| IDC 2x5 Header Shrouded Through Hole | 1 | J2 |