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'[EE] Any suggestions for cheap AC power quality mo'
2019\05\03@060302 by Peter Loron

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Hello, all. I have a UPS which after a number of years of faithful
service has started triggering onto battery power and then immediately
back to mains. When this is happening, we do not see the lights flicker
or other devices restart. While I suspect the UPS is toast, I’m trying
to verify that it is at fault and we’re not seeing crummy power quality.

I know there expensive devices from Fluke, etc which can be used to look
at and record such things. Too rich for my blood. Can anyone suggest an
inexpensive way to monitor and record voltage dips at a high enough
resolution that it would reliably catch these quick events? I’ve got a
basic digital oscilloscope, multimeters, etc.

Thanks!

-Pete
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2019\05\03@103303 by Jason White

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If you are a programmer you could easily use the usb/serial/lan/gpib
interface on your oscilloscope/multimeter as an adc. If you are not a
programmer then you would only be able to do it if the manufacturer
provided decent software

If you are willing to build a circuit then I would advise just using an
optoisolator to get a digital on/off corresponding to the mains power (bias
it to trigger only at the very peak of the sine wave). Then look for
missing pulses using your preferred method: microcontroller/555 timer/etc.

On Friday, May 3, 2019, Peter Loron <spam_OUTpeterlTakeThisOuTspamstandingwave.org> wrote:

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2019\05\03@115823 by AB Pearce - UKRI STFC

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I suspect your real problem is the battery in the UPS ... but ...

For mains monitoring, have you had a look at what could be done using the Microchip "smart meter" chips? They have a number of application notes about these, and from memory there are single phase and three phase variants. I suspect that using a DSPic instead of a PIC18 that seems to be the basis of most of the designs I have looked at would allow the design of a mains monitor that would do the most important parts of what an expensive commercial instrument will do.

And fro my $0.02 ... anything called 'smart', from smart meter to smart motorway is the biggest misnomer around, they are anything but 'smart' ...



{Original Message removed}

2019\05\03@131506 by John Coppens

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On Fri, 3 May 2019 06:03:02 -0700
Peter Loron <.....peterlKILLspamspam@spam@standingwave.org> wrote:

> I know there expensive devices from Fluke, etc which can be used to
> look at and record such things. Too rich for my blood. Can anyone
> suggest an inexpensive way to monitor and record voltage dips at a
> high enough resolution that it would reliably catch these quick
> events? I’ve got a

Another solution would be to use a small line transformer, say to a few
volts, then attenuate some more, and feed it to a computer's audio line
input. You can record using any audio program, at a low sample speed
(4000 or 8000 samples/s would do). A megabyte would record 250 seconds
of 'line'... A full day's worth (86400 secs) would occupy 345 MB at
4kHz/s

There's probably some recording soft which could trigger on anomalies.

John

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2019\05\03@133348 by Forrest Christian (List Account) n/a

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Does your oscilloscope have a mask test functionality? If so,  that would
probably work.

Also,  if your ups has a "smart" data port,  often the transfer reason is
logged.

This does sound like a battery failure mode though.   Many upses do a
periodic battery test by switching to battery periodically.  Usually this
is silent but when they start failing the test,  they start making noise.


On Fri, May 3, 2019, 7:15 AM Peter Loron <peterlspamKILLspamstandingwave.org> wrote:

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2019\05\03@173410 by James Cameron

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Here are some of the causes I'm familiar with;

1.  battery near end of life, consuming larger than usual charging
current, therefore very hot, with this heat affecting tolerance of
nearby control circuitry; problem changes with cooling, battery
temperature is easily measured, and correlates with occasional battery
bulging,

2.  lightning damage to the UPS power quality sensing circuitry; it is
being more picky than usual,

3.  actual crummy power; voltage high, voltage low, with thresholds
set too finicky, and someone nearby has a solar grid-tie inverter
which is pushing line voltage up to the regulatory maximum and then
shutting down for the regulated several minutes.  ;-)

An audio input on a computer may help.  Add sufficient filtering, such
as large series resistor and reverse biased blocking LEDs.

http://www.daqarta.com/dw_0all.htm

Or a transformer.

Plenty of safety hazards!

Digital oscilloscope is one such; the probes are earthed, so touching
neutral while anything in a house is drawing current drops a
proportion of that current into the probe shield, and any residual
current device should trip.

On Fri, May 03, 2019 at 06:03:02AM -0700, Peter Loron wrote:
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2019\05\03@195310 by Justin Richards

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I just dont probe mains because of these warnings and those of Dave Jones
"How to blow up you scope" etc which have filled me with fear.

But recently I felt the need while working on a PSU.

I concluded that all should be fine probing the 240v AC input if I set it
to x10 and remove the earth clip on the CRO probe. I figure I don't need
the earth clip as it's already at Ground and therefore close to neutral.

But fear won so I used a fluke handheld meter instead.

Is the conclusion sound? I. e. All things equal, is it safe probing the AC
input side of a PSU as described above?

Justin

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