DIY: Central powersupply for Raspberry Pi's

One part of my "building a Raspberry Pi - cluster" project was the search for a central powersupply to power the complete cluster. I didn't want to have single wallwart for each Raspi. So i searched the internet, but i couldn't find a ready solution. Hmm, Ok, i'll have to DIY !

These were my conditions for the powersupply:
- it has to be powerful enough to serve 5 to 10 Raspberry Pi's Modell 2.
- it has to be economic, which means that it should have a good efficiency, even if there was a low consumption.
- it has to be cheap: well, i need the money mostly for the Raspis :)
- it should look fancy, because the cluster is sitting on top of my desk.

First the power calculation:
Reliable sources say that i need to provide a maximum of 2 Ampere per Raspi. Ok, this is if everything is connected, including some external USB devices. This means that i need 10-20 Ampere to power the 5-10 Raspis. The voltage is 5 Volt.

The Rapis can handle a +-5% tolerance on their 5 Volts, so this was another restriction.

I found some industrial supply which can handle this. But then i checked the powersupplys of my old computers, which rot in my lab, and saw that they can handle this requirements too, maybe even better and they are for free. One of these old ATX-supplys brought the 5 Volts with 30 Amps. Perfect! Checking the standby consumption was just 16 Watt and the output was 5.24 V which was inside the required tolerance.

How should i connect the Raspis? I choosed the traditional way to power them via the Type-B-micro USB port, to stay compatible to the older Raspi models and hopefully for the next generations to follow.  So the best way would be to use a USB-hub and use short Type-A to Type-B-micro cables. But i wanted the Hub to be also powered over the central supply and to be fixed on the supply. So i searched for a nice 5V USB Hub, which wasn't too expensive and found this one here:

Nice USB-Hub with switches and blue LEDs

So i started to prepare the supply. The best would be if you watch my

Youtube-Video

how i did it.

The result was this black beauty which handles my needs perfectly:

It's an old ATX-powersupply, reduced to only deliver 5V with up to 30 Amps within a voltage tolerance of 5%. The bridged "poweron" connector keeps the supply running, even if there is no consumption. Mounted on the side is a 7 Port-USB-Hub, each port has a small switch an nice blue LED. 

And here you can see it in action. I mounted a small 100Mbit Ethernet-switch, also powered by the supply... sure :)