There are times in a tinkerer’s existence where it is convenient to have the ability to plug in and power a lot of USB devices. Sure, you could use a USB hub but this may not be satisfactory if your devices require a lot of current. A computer may work but is not really a stand alone solution.
[Jeff] and the crew over at Make Lehigh Valley ran into this predicament. They were putting on an Adafruit Trinket class and needed a USB power supply to power all of the Trinkets that were going to be used. As any makerspace would do, they built their own USB Power Station, and the final product is certainly overkill for what they needed (that’s not a bad thing).
An old ATX computer power supply is a logical component to use for this type of project. These power supplies are usually available in abundance and will provide all the amperage any reasonable amount of 5v USB devices can ask for. The 5v output from the ATX power supply was wired to 8 USB jacks. Keeping up with the project’s resourcefulness, those USB jacks were scavenged from a couple of old PCI-slot USB hub panels. Not satisfied with only USB outputs, the guys also wired up some banana jacks so that 3.3, 5 and 12 volts were available for whatever project was being worked on. A 3D printed enclosure keeps everything neat and tidy.
This project used a bunch of recycled parts and solved a problem faced by the group. If you’re interested in using an ATX power supply to make a more bench-top style power supply then check out this build.
If you don’t want to build your own, I highly recommend these as an alternative. Or if you want something a little smaller, or more polished looking (to use in a meeting or somesuch).
http://www.amazon.com/gp/product/B00IBDOB5I
agreed $25 for that 40W model or $18 for 25W. I like that it has a detachable power cable.
why of experience or sheer desperation i dont know why you would make one
I hadn’t seen this before. When I saw this article I was thinking I’d quite like to make the same myself. But after seeing how compact and neat the anker is, I’d rather just buy it!
I recently read about how ATX power supplies have changed drastically over the years. Older computers (pre P4?) drew most of their power for the motherboard and CPU as 5v. The power supplies of the time could provide a hefty 5v, probably enough to power all of those ports adequately.
More modern power supplies are really geared towards the (sometimes multiple) 12v rail(s). Sometimes the 5v rail is severely limited because it’s really not used much anymore.
Then how do components that need 3.3v/5v get their power?
I’ve always seen the +5V rail(s) on a PSU between 20-30A. I don’t think that has ever changed.
+3.3V has always been the same minus AT PSUs, +3.3V was not used on early IBM PC clones.
Drives and peripherals have always gotten 5V from the power supply. Back in the olden days, though, the CPU and PCI/ISA cards also drew from the 5V rail. The original Pentium processor was (if Wikipedia can be trusted) the last Intel processor to run on 5V core voltage, to give an idea of timeframe. As CPUs got faster and transistors got smaller though, the huge power losses from the 5V logic became unbearable and CPU architectures were forced to lower and lower core voltages – nowadays less than 1V is common. Some CPUs draw upwards of 100W, and transporting 100A more than a few inches is far too lossy, so modern motherboards take in (relatively) low current, high voltage 12V and transform it onboard to the 1V or so that the CPU requires. Consequently, the demand on 12V (and thus power supply 12V rail output current) has risen over the last decade while 5V current has remained relatively constant. The same is true of expansion cards – those that have significant power demands (e.g. GPUs) take in 12V and do step-down conversion onboard, while those that do not draw much may take advantage of the power savings and die size reduction of sub-5V operating voltages and run on PCIe’s auxiliary 3.3V rail. 5V is pretty well relegated to USB and drives, and you usually don’t need all that much current for those.
As for 3.3V, it still powers many of the low-level components on the motherboard (chipset and whatnot), and powers the last generation of PCI cards as well as some low-power PCIe cards as mentioned above. That said, of the rails provided by an ATX supply, I suspect that 3.3V is usually the second least utilized – second perhaps to -12V which I think only powers RS232 transceivers nowadays. But industry keeps hinting that 3.3V SSDs are due to become popular any day now, so maybe that’ll change sometime soon.
Not quite.
Here are the specs for one current generation power supply, which is representative of many:
+3.3v: 20A, +5.0v: 20A, +12v: 35.5A, -12v: 0.8A
In case you’re curious, this is from a Corsair CS450M.
As you can see, plenty of current available on the +5v rail.
OK, just grabbed a 200W AT PSU from the Pentium 1 era off my shelf:
+5V @ 4.0-20.0A
+12V @ 1.6-8.0A
-5V @ 0.1-0.5A
-12V @ 0.1-0.5A
I believe the current ranges are because each rail needs a significant load on it in order to regulate the voltage properly. This is why I always thought a hack like this wouldn’t work and why I’ve never used a PC power supply in a project. Have things changed?
Anyway, you can see that there is the same ammount of = power available from both PSUs at 5V, but this power _has_ gone down proportionally to the total Wattage of the PSU in preference to 12V (and the addition of 3.3V).
More info here:
http://www.playtool.com/pages/psunonpc/nonpc.html
I don’t know about proper PSUs, but this guy doesn’t require a load for any of its rails.
It’s pretty sweet if you have a project that needs +5 and +12 rails. and a -12 rail for that matter.
Yeah that’s a nice bit of tech, but you also need a beefy 12V for it to run at full capacity.
Handy though if you don’t want to mess with large heatsinking on linear regulators, and I’d happily trade my box o’ dodgy PC PSUs for one filled with them.
You may be confused and thinking of -5v (negative 5 volts), nothing used it and it was dropped from the ATX specification entirely in 2003. PSU’s typically don’t provide it any more. It used to be pin 20 on the connector, which is now typically not connected.
How well protected are ATX PSUs against short circuits etc.? I really wouldn’t want to accidentally short out the power lines of a 500watt PSU.
My present favourite source for high ampage 12v PSUs are old Xbox 360 PSUs, they give out 5v @ 1A all the time and have a trigger line to turn on the 12v of which the 203watt version outputs @ 16.5A, with short circuit protection to boot.
hate that stupid nonstandard mains input though! nothing a dremel cant fix but I suppose they needed to ensure a beefy enough conductors were used.
A good quality PSU will have all the protection you need. Short circuit protection, over and under voltage protection and over power protection. Can’t say the same for cheapos and old designs. They usually have an op-amp for under and over voltage which kind of works (when shorted, voltages at output rails drop, so it’s shut downs). Only remains the question, does it shut down fast enough that your project doesn’t blow up.
sure they have short circuit – but 20A is still more than enough for a standard USB cable. If there is a short, the USB cable could burn.
Get ATX PSU. Use 12v line to power a couple class d amplifier (such as y148) and some speakers. Use 5v line to power a lot of USB ports. Small and portable unit, take it to a small party, plug speakers to it and let the guests recharge their phones!
12V is a bit low for an amplifier, either it needs an internal boost converter, or you need to add an external one.
I run my portable 2x25W class D off a 6S LiPo (22.2V nominal), or a laptop supply at 19V, or a 24V supply depending on what’s available. 12V won’t give me more than maybe 10-15W output.
That really depends on what voltage level/range the chip specifies. Amplifier power in the normal Class D configurations derives from available amperage, not strictly voltage (yes, going higher in the useable voltage range will yield more power out of the speakers, but it’s still the amperage that’s actually responsible). You’re not going to get very far by overvolting a Class D amp chip, beyond releasing some magic smoke.
Yes of course, but you aren’t really going to find speakers under 4 ohms so choosing a chip with a higher power and higher voltage rating will result in a more realistic output power for a party amp, especially if you are looking to get some bass out of it.
It’s not hard to finish the power supply by cutting or unsoldering the unneeded wires on the inside. Tape comes off, heat shrink can pull off and it’s sloppy practice.
I met these guys – was gonna join last year but it’s a little too far to be driving every day or two. Super nice guys though!
I think the point isn’t “You can go out and buy one” but more “well shit, I can make that at home!” mentality. I’m the same way
I like making stuff too and certainly wouldn’t say this was a waste of time. But the commercial units available (like the anker mentioned above) are so cheap and powerful and portable that I just don’t think it’s worth the time building one other than as a fun project.
Plus I expect it will have problems charging devices like ipads and other apple products which are notably fussy about what power supply they’ll actually run on.
It wasn’t made to charge iProducts so that’s not a problem here.
I think a lot of people are missing the fact that it was made from scrap so it costed nothing but time. I use ATX psu all the time for powering things at 3.3v, 5v or 12v and it works very well as long as your not stupid about it. As far as short circuit protection, all the atx psu I have used have some sort of protection, even the cheap ones, be it that it would have to be a dead short to trigger.