<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Jul 31, 2014 at 4:51 PM, Alex Carver <span dir="ltr"><<a href="mailto:agcarver+ale@acarver.net" target="_blank">agcarver+ale@acarver.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>On 2014-07-31 13:28, Michael H. Warfield wrote:<br>
> On Wed, 2014-07-30 at 22:23 -0700, Alex Carver wrote:<br>
>> On 2014-07-30 11:02, Jim Kinney wrote:<br>
>><br>
>>> The good part is I can justify getting a BeagleBone Black box as an upgrade<br>
>>> to the RasPi :-)<br>
>>><br>
>>> Now if I can do a remote power detection and determine when the room power<br>
>>> is running on battery without actually wiring anything to the units...<br>
>>><br>
><br>
>> What kind of UPS are they using? If it's modified sine wave you could<br>
>> make a filter that can hunt down the harmonics. Relatively clean AC<br>
>> will have low harmonics. The modified sine will have very dirty<br>
>> harmonics, enough to pick up and distinguish between the two modes.<br>
><br>
> You might be surprised. It's been over 20 years since I looked at it<br>
> but a simple inverter generating a triangular(ish) waveform into a 3<br>
> break point diode shapper gets close enough to a sine wave that the end<br>
> result is less than 1% THD without a heavy resonant circuit. Most<br>
> modern UPS with high efficiency switching supplies are significantly<br>
> better than that.<br>
><br>
>> A true sine inverter would be harder to spot.<br>
><br>
> You're going to be really hard pressed. Modern units might even<br>
> generate cleaner sine waves out of those switching supplies than what<br>
> you'll get from the primary power.<br>
><br>
> Regards,<br>
> Mike<br>
><br>
<br>
</div>1% THD is plenty to spot. The wall power is nominally clean enough to<br>
be well below 0.1% THD so you've got a 10x factor to play with. All you<br>
need to do is spot something near 180 Hz or one of the fractionals<br>
(3/2f, 5/2f) to give away the source.<br>
<br>
It's probably moot anyway. I just double checked APC's offerings of<br>
their SmartUPS series and they're all using full sine output. Only the<br>
very basic BackUPS series uses mod-sine.<br></blockquote><div><br></div><div>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.<br>
</div><div>If I can put a clamp-on ammeter on the power feed for them and read it from a RasPi, well, problem solved! <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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</div></div></blockquote></div><br><br clear="all"><br>-- <br><div dir="ltr">-- <br>James P. Kinney III<br><i><i><i><i><br></i></i></i></i>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.<br>
- Speech 11/23/1900 Mark Twain<br><i><i><i><i><br><a href="http://heretothereideas.blogspot.com/" target="_blank">http://heretothereideas.blogspot.com/</a><br></i></i></i></i></div>
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