[ale] sometimes you just need to reboot NOW!

[Michael H. Warfield]

On Thu, 2014-07-31 at 13:51 -0700, Alex Carver 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.

That's just with 3 diodes and resisters for each polarity in a passive
shaping ladder doing the wave shaping.  My point was that it's trivial
to drive the distortion down to the point where you won't be able to
discriminate it.  A 3 diode ladder is junk and I doubt has been used in
any devices made in last 25 years or more.

You've got a higher opinion of the wall power than most of us have, I
suspect.  I use to have a functioning Dranitz (sp?) line disturbance
analyzer (died of old age a decade ago).  You'd be surprised at what
kind of disturbances show up and the power company will just shrug their
shoulders unless it's threatening their equipment or likely to start
fire.

During the early days of ISS (Internet Security Systems) around 1996, we
were in a building off Glenn Ridge and kept having computer problems but
only with certain computers (about 1/3 of all our machines).  I finally
plugged in one of my little Fluke line disturbance detectors (just
LED's, no paper printout like the big Dranitz) and it would light up
like a Christmas on just about 1/3 of the outlets in the office (if you
know something about primary power distribution, you may know where I'm
going with this).

By the time we were done, we had determined that the building was being
feed by "open delta" 3-Phase (two transformers providing all three
phases with one of the phases floating between the other two -
antiquated) AND the building neutral was about 20%-40% varying out of
balance due to some unusual loads on the 4th floor (we were on the 1st
floor).  Building maintenance had to bring in electricians to rebalance
the troubled makers upstairs but we also finally forced the power
company to replace the transformers and provide us with solid 3-phase.

I think it was Mike T was telling me that he has problems with
disturbances every time his neighbors air conditioner kicks on (yes to
all - I need to get back to that line disturbance Raspberry Pi project).

> 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.

Almost none do any more.  Cheap HF switching supplies drove down the BOM
(bill of materials) cost of full sine without the need of a 60Hz
resonant circuit and associated heavy inductors down to the level of
wave shaping square wave inverters, so it just no longer made economic
sense.  Even the cheap junk ones are full sine output any more and
probably have better frequency stability than the line.

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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