[ale] sometimes you just need to reboot NOW!

[Jim Kinney]

On Thu, Jul 31, 2014 at 4:51 PM, Alex Carver <agcarver+ale at acarver.net>
wrote:

> On 2014-07-31 13:28, Michael H. Warfield wrote:
> > On Wed, 2014-07-30 at 22:23 -0700, Alex Carver wrote:
> >> On 2014-07-30 11:02, Jim Kinney wrote:
> >>
> >>> The good part is I can justify getting a BeagleBone Black box as an
> upgrade
> >>> to the RasPi :-)
> >>>
> >>> Now if I can do a remote power detection and determine when the room
> power
> >>> is running on battery without actually wiring anything to the units...
> >>>
> >
> >> What kind of UPS are they using?  If it's modified sine wave you could
> >> make a filter that can hunt down the harmonics.  Relatively clean AC
> >> will have low harmonics.  The modified sine will have very dirty
> >> harmonics, enough to pick up and distinguish between the two modes.
> >
> > You might be surprised.  It's been over 20 years since I looked at it
> > but a simple inverter generating a triangular(ish) waveform into a 3
> > break point diode shapper gets close enough to a sine wave that the end
> > result is less than 1% THD without a heavy resonant circuit.  Most
> > modern UPS with high efficiency switching supplies are significantly
> > better than that.
> >
> >> A true sine inverter would be harder to spot.
> >
> > You're going to be really hard pressed.  Modern units might even
> > generate cleaner sine waves out of those switching supplies than what
> > you'll get from the primary power.
> >
> > Regards,
> > Mike
> >
>
> 1% THD is plenty to spot.  The wall power is nominally clean enough to
> be well below 0.1% THD so you've got a 10x factor to play with.  All you
> need to do is spot something near 180 Hz or one of the fractionals
> (3/2f, 5/2f) to give away the source.
>
> It's probably moot anyway.  I just double checked APC's offerings of
> their SmartUPS series and they're all using full sine output.  Only the
> very basic BackUPS series uses mod-sine.
>

These are giant datacenter size monsters the size of 4 racks. They are
running full power conditioning at all times so monitoring the power at my
sockets should show no change between on or off battery.
If I can put a clamp-on ammeter on the power feed for them and read it from
a RasPi, well, problem solved!

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-- 
-- 
James P. Kinney III

Every time you stop a school, you will have to build a jail. What you gain
at one end you lose at the other. It's like feeding a dog on his own tail.
It won't fatten the dog.
- Speech 11/23/1900 Mark Twain


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