I've asked this question within the Raspberry Pi exchange but they stated that posting the question here might be more useful.
I built a Pi cluster with 6 nodes. This runs off a 90 watt astec atx-93 PSU.
Also attached to the PSU is a 12v fan and a 5v ethernet switch.
However it seems the 5v rail of the PSU is not supplying enough current to power everything.
Only 3 Pis boot properly, the others just keep rebooting. And with the Pi's that do boot, attaching any i/o devices to them send them in a spin.
There're four 5v outputs coming from the PSU. 2 Pi's to each output through the GPIO 5v pin with a fuse to protect incase of a power spike.
The 4th output is used to power the fan which is rated for 12v but I have it at a lower speed at 5v.
There is one 12v rail that has a 5v regulator attached. This is powering the ethernet switch.
If I put a multimeter over the Pi's the voltage is 5.12/5.20 v but the current seems to be around 0.9a to 1a max.
So my question is, is there anyway of getting more current to the devices without having to change to the PSU itself, or is it just that buying a more powerful PSU is the only way forward to get what is needed?
Best Answer
According to the schematic posted on Raspberry PI stack exchange, an on-board 1.1A fuse exists between microUSB and GPIO 5v line. This fuse is not supposed to see current drawn from microUSB to connected USB devices. With your method of supplying 5v power to the PI, this fuse DOES PASS USB device current. It is rather difficult to determine in your complex power scheme (where multiple currents can flow in opposing directions) how much current a particular fuse will see. Fuses act on net current flow. Seems like this fuse is running at its limit, if your current measurements are accurate.
Your power supply is adequate, with Neil_UK's caveats about properly loading its other 12v and/or 3.3v rails.
The PI was meant to be powered through the microUSB - it should be powered from this point, else the on-board fuse may not properly fulfill its function.