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[aprssig] backup pwr systems

Bruce Gordon bgordon at ltronics.com
Mon Dec 11 00:33:56 UTC 2006


Bob,

What you describe is exactly a grid-tie inverter, just not so large as those
used in all house or larger systems.  I have never seen how they protect
themselves and others from the hazards of tying to the grid but I can't
think of a reason that it couldn't be done in a smaller unit.  Might burn up
a little of that "copious free time" however.

Bruce Gordon


----- Original Message -----
From: "Robert Bruninga" <bruninga at usna.edu>
To: "'TAPR APRS Mailing List'" <aprssig at lists.tapr.org>
Sent: Sunday, December 10, 2006 11:06 AM
Subject: RE: [aprssig] backup pwr systems


> What I want, and no-one makes,
>
> Is a 400 watt DC-to-Line synchronous inverter that can back feed
> into my house power to save me a few pennies on the electric
> bill.  It is a whole lot of trouble to configure part of the
> house load to run on DC because then you need a battery, and
> then you have to charge it during the day, when no one is home
> and you don't need any DC, and they run it at night after
> switching over to inverter.  All of this takes work, effort,
> life style changes, and none of it is worth the trouble for just
> a few hundres Watts of excess green power.
>
> But if there was a synchronous 400W inverter with just a line
> cord that you could plug into any outlet in the house and if you
> had up to 400W of free DC power available (wind or solar), then
> just plug this thing in, and it would backfeed your existing
> circuits.
>
> Of course it would be man-safe, and would only provide boost
> current only if there was line voltage alreaady there.  If there
> was no 60 Hz AC, then it would do nothing.
>
> What it WOULD do is reduce my electric bill during the PEAK
> summer rates (time of use metering charges almosst 17 cents per
> KWH duing the summer day).  And it would do this with minimal
> effort, because the total interface is just plugging it in.  And
> I woiuldnt lose the battery charge/discharge inefficiencies nor
> would I be wearing out my batteries every day by cycling for
> this minimal power.
>
> Think of it this way.  There are dozens of stupid little
> "wall-warts" haniging throughout my house that provide a
> constant drain on my electric meter.  The 5W of heat that each
> one is consuming is just not worth re-wiring the house for DC,
> but the total of them adds up to probably a few hundred watts 24
> hours a day.  By injecting my solar power during the midle of
> the day when I get the most, into my mains, it would be like
> paying myself 17 cents for every KWH I put in.
>
> Again, do not confuse this with grid-tie inverters that are
> desigend to run your meter backwards and which require Electric
> Company and all kinds of approvals and all kinds of safety
> issues.  This is just a small device to help "reduce" my
> electric demand.
>
> Anyway, it would be a dun design project for powering my 24/7
> APRS system and any spare power I have.
>
> Bob, WB4APR
>
>
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