[Beowulf] single power supply for multiple nodes

[Alvin Oga]

On Mon, 28 Jun 2004, Joel Jaeggli wrote:

> at the point where you get a whole rack of nodes off a single 
> powersupply the size of the conductors for some of the voltages get quite 
> large (the 3.3volt and 5volt especially if you need a couple hundred 
> amps)... if you want to go that route you're better off using a very large 
> dc power supply telco style -48volt dc for example and a dc-dc power 
> supply which will be quite compact and relativly efficient. 1kw wouldn't 
> be that huge anyway that's enough for 4-6 dual opteron nodes.

telco style PS is about 5x-10x the regular price of equivalent
consumer/industrial grade power supplies
 
how you power up your motherboard is the trick question of the size of
wires and current capacity you need from the +12v power supply 
	- assumption is each moboard is +12v @3A ... or to be safe, use 5A
	and that'd be trivially provided by the existin 1U, 600W power
	supply

	- 1 power supply for each 10 motherboards
	- 1 power cord instead of 10 ...

	in a rack .. that'd be 100 power cords for 100 power supplies
	vs 10 power supplies used to its typical loads

- the big problem is if that one ps dies, all 5 or 10 systems goes down
  too .. so we're back to 1 ps for each 5 systems which keeps the load
  on the ps at about 25%-50% of its rated +12v capacity
	- all the other 3.3v and -12v and -5v power output is
	just extra heat that is thrown away

	- we use a dc-dc +12v power supply to generate all the atx 
	voltages and currents

- the experiment is how much current is needed for dual opterons in idle
  mode

c ya
alvin