[geeks] Need refs for the clue-impaired on redundant PSUs

[Michael Parson]

On Wed, Sep 07, 2005 at 08:03:45PM -0400, velociraptor wrote:
> Anyone have any good references out there regarding how redundant PSUs
> generally work?  I need something, preferrably from "experts," to give
> to the clue-impaired.
>
> Some *ahem* people (I use this term loosely) are having issues with
> hitting the ceiling on their UPS and incoming power and seem to think
> removing the redundant PSUs on their existing servers will give them
> room to add more servers.

You need an electrician that knows about wiring up datacenters.  Someone
that can show up with an ampmeter and show them current draw.  Any of
the local electrical contractor shops should be able to help you out.

Or, head over to Fry's, or your other suitable electronics store and
pick up a clamping ampmeter and a power cable you can cut up.  Carefully
strip off the outer insulation so you've got the three internal (but
still insulated) wires.  Replace one of the power-cords feeding one of
the redundant power-supplies with this cable.  Clamp the meter around
one (either the black or white) power leads and take a reading.  Remove
the other power-supply (if you can do this hot) and watch what happens.

If the two supplies are splitting the load, then the meter reading
should go up, somewhere around double.  That should be enough of a
demonstration to show what you need to show.  Need something more than
that?  Go to the local university and find an EE and buy him a pizza.

> I disavow all knowledge of the names of the in*duh*viduals
> who think this.
> 
> And, why yes, I have had a couple of interviews lately, why do
> you ask?

*cough*

> If anyone out there has appropriate credentials, I might be able
> to get a 1-2 hour consulting fee...
> 
> I googled, but didn't come up with anything that fit the the
> "Redundant PSUs for Dummies" level I think would be
> necessary.

On one level, I wouldn't expect to find it, but then again, this is a
crazy internet.  All depends on the search terms.  My quick google for
"dual power supply load share" gave some promising looking results.

-- 
Michael Parson
mparson at bl.org